Journal of Environmental Radioactivity 139 (2015) 78e84
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Removal of 226Ra and surfactants solutions
228
Ra from TENORM sludge waste using
M.F. Attallah*, Mostafa M. Hamed, E.M. El Afifi, H.F. Aly Hot Laboratories and Waste Management Center, Atomic Energy Authority of Egypt, PO.13759 Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 July 2014 Received in revised form 14 September 2014 Accepted 15 September 2014 Available online
The feasibility of using surfactants as extracting agent for the removal of radium species from TENORM sludge produced from petroleum industry is evaluated. In this investigation cationic and nonionic surfactants were used as extracting agents for the removal of radium radionuclides from the sludge waste. Two surfactants namely cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX100) were investigated as the extracting agents. Different parameters affecting the removal of both 226Ra and 228Ra by the two surfactants as well as their admixture were studied by the batch technique. These parameters include effect of shaking time, surfactants concentration and temperature as well as the effect of surfactants admixture. It was found that, higher solution temperature improves the removal efficiency of radium species. Combined extraction of nonionic and cationic surfactants produces synergistic effect in removal both 226Ra and 228Ra, where the removals reached 84% and 80% for 226Ra and 228Ra, respectively, were obtained using surfactants admixture. © 2014 Elsevier Ltd. All rights reserved.
Keywords: TENORM sludge Removal of radium Natural radionuclides Surfactants
1. Introduction Radionuclides of natural origin have been found at varying concentrations in soil and water, in food, air and human tissues. All minerals and raw materials in the Earth's crust contain small, but measurable concentrations of natural occurring radioactive materials (NORM). Geochemical properties associated with petroleum formation can result in locally elevated concentrations of 238U and 232 Th within source rocks (Desideri et al., 2006). During the course of oil/water separation in production facilities, these radioactive materials can precipitate onto process equipment and storage tanks. The primary radionuclides of concern in NORM wastes are 226 Ra of the 238U decay series and 228Ra of the 232Th decay series. Other isotopes of concern include isotopes that are produced from the decay of radium radionuclides, such as 222Rn (Desideri et al., 2006; White and Rood, 2001). NORM are present at varying concentrations and can be concentrated or enhanced by different processes associated with the petroleum industry. This “enhanced” NORM, often known as TENORM (Technologically Enhanced Naturally Occurring
* Corresponding author. E-mail addresses: [email protected], [email protected] (M.F. Attallah). http://dx.doi.org/10.1016/j.jenvrad.2014.09.009 0265-931X/© 2014 Elsevier Ltd. All rights reserved.
Radioactive Materials) can be created when industrial activity increases the concentrations of radionuclides or when the material is redistributed as a result of human intervention. TENORM also can be the by-product or waste product of oil, gas and energy production plants (Desideri et al., 2006; OGP Report No. 412, 2008; Baeza et al., 2011). Sludge, drilling mud, and pipe scales are examples of materials that can contain elevated levels of NORM (Desideri et al., 2006; White and Rood, 2001; OGP Report No. 412, 2008; Baeza et al., 2011; Paria and Yuet, 2007). In oil industry, NORM can accumulate in different forms such as scale, sludge and thin films, as shown in Fig. 1 (OGP Report No. 412, 2008). Sometimes, NORM concentrate in the waste streams of oil and gas production operations. Radionuclides were found in many underground formations but are not very soluble in the reservoir fluid. However, the daughter products, radium isotopes, are somewhat soluble as dissolved ions and migrate to the surface (Baeza et al., 2011; Al-Masri and Aba, 2005). Handling, storage, transportation and the use of TENORM contaminated equipment or waste media without controls can lead to the spread of TENORM contamination, resulting in exposure of the public (Desideri et al., 2006; White and Rood, 2001; OGP Report No. 412, 2008; Baeza et al., 2011; Paria and Yuet, 2007; Al-Masri and Aba, 2005). Recently, attention was focused on the environmental and health impacts from the uncontrolled release of TENORM wastes (Desideri et al., 2006; Baeza et al., 2011). Therefore, the treatment of
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84
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2. Experimental 2.1. Surfactant selection
Fig. 1. The origins of NORM, indicating where NORM may accumulate in the recovery process. (OGP Report No. 412, 2008, www.ogp.org.uk. © Copyright 2008, OGP).
Solid phases or soils washing would be more effective when surfactants with a low adsorption capacity to soil or solid phase are used. Two surfactants CTAB and TX100 were used in this study. Cationic surfactant CTAB is usually chosen for surfactant-based remediation procedures because they showed a good solubilizing for many pollutants. TX100 is nonionic surfactant, which has been noted for their unfavorable tendency to sorption to aquifer solids (Ahn et al., 2008; Saichek and Reddy, 2005). Used surfactants are excellent solubilizing agents of many compounds, and their food grade additive status makes them attractive for use in environmentally sensitive areas. Also, they are rapidly biodegradable by soil and/or aquatic microorganisms. These surfactants were used without further purification (Thimmaraju et al., 2003; Lee et al., 2004). 2.2. Reagents
these wastes is of increasing interest since accumulation of large amounts with a significant activity may cause health risks not only to the person directly involved in these activities, but also to the local population (Desideri et al., 2006; Al-Masri and Aba, 2005). The trials towards the treatment of TENORM wastes from different industries are still limited. The commonly used methods include subsurface disposal options, volume reduction, and use of scale and/or sludge inhibitors, recycling, leaching, and extraction process using different solutions (Attallah et al., 2012, 2013; El Afifi et al., 2006, 2009; El Afifi and Awwad, 2005; El Afifi, 2001; Shehata et al., 1999; Smith et al., 2003). Various techniques, including soil bioremediation and soil washing, have been used to treat contaminated areas. Soil washing, a water based process that employs chemical and physical extraction process to remove contaminants from the soil, has recently become a common technique for remediating sites contaminated with different pollutants. Although, soil washing may be the most economical process to clean up contaminants, many contaminants have very low water solubility, and therefore it is necessary to consider the use of surfactants to improve the soil-washing process (Xin et al., 2006; Mulligan et al., 2001; Ahn et al., 2008). Surfactants (surface active agents) are organic chemical wetting, cleaning and disinfecting agents, and they are frequently used in detergents and food products that alter the properties of solution interfaces. They also can be added to washing water to assist in the solubilizing, dispersal and desorption of contaminants (Mulligan et al., 1999). Surfactant enhanced remediation (SER) has been recognized as one of the promising technologies. In SER, surfactants play an important role in solubilizing and the removal of trapped contaminant (Xin et al., 2006; Mulligan et al., 2001). Surfactants can act as an extracting agent for the removal of radionuclides from contaminated soils through either surfactant-aided soil washing or solubilizing them because they could enhance the water solubility and mobility of radionuclides in soil environment and thus increase their removal efficiency. So far in our knowledge, no articles have been published concerning the removal of radium by using surfactants. The present work is focused on the use of selected surfactants for removal of radium isotopes from TENORM sludge waste. The feasibility of using two different types of surfactants (cationic and nonionic) was assessed. To enhance the removal of radium and the factors influencing their behavior at different variables were investigated. These include the type of surfactant, surfactants concentration, shaking time, and temperature as well as surfactants mixture.
Surfactants TX100 and CTAB used as washing agents in the experiments were purchased from Merck. The surfactants were used without further purification. 2.3. Samples collection and preparation TENORM sludge accumulates inside the oil production equipment, e.g. piping, separation heater/treaters, storage tanks and any other equipment where produced water is handled. It occurs when the radium (Ra) coprecipitates with barium, strontium and/or calcium in the form of insoluble sulfate or in the form of slightly more soluble silicates and/or carbonates. In the present study, a limited individual amounts (~1000 g) taken from the sludge piles generated during the periodical maintenance of the oil separator tanks surrounding the oilfield site (Suez gulf region, Egypt). In our laboratory, the collected individual TENORM samples were mixed together and screened in atmospheric air (25e30 C) for 2 weeks. Then, the actual sample was dried under IR lamp for one week till complete dryness and constant weight. The sludge waste was crushed, pulverized and sieved using a programmable sieving vibratory (model: Analyestte, Germany) into two main parts, namely: non-homogeneous and homogeneous waste sludge. Fig. 2 showing the procedure for drying and sieving of the TENORM waste sludge. The total recovery of the sludge waste sieving reached to 99.6%, while the rest 0.4% represented a loss as dust released into atmosphere. The non-homogeneous sludge is discarded due to its coarse particles greater than 2 mm and low sieving recovery of 3.2%. The homogeneous sludge has a particle size less than 2 mm and sieving recovery of 96.4%, therefore it is used for the further treatment investigations. The humidity, total organic matter, clay content and density were determined gravimetrically. 2.4. Spectroscopic measurements 2.4.1. Material characterization TENORM sludge waste was characterized using analytical techniques such as: X-ray fluorescence (XRF), X-ray diffractometer (XRD) and Fourier transform infrared (FT-IR). The elemental analysis of the TENORM sludge waste has been determined by X-ray fluorescence (XRF) using Philips PW-2400 sequential X-ray spectrometer (Japan). The samples were grinded to a fine particle size as possible in a laboratory mill. The resulting powder was pressed into pellets of 40 mm diameter and 5 mm thickness. The main
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rate (c/s) 228Ac at 338.6 and 911 keV. The statistical error associated with counting of the samples during the activity concentration assessment and the treatment evaluation does not exceed 10%. 2.5. Sludge waste treatment
Fig. 2. Drying and preparing of the sludge waste samples produced from the petroleum exploration processes.
mineralogical composition of the waste was determined by X-ray diffractometer (XRD). FTIR spectrum was recorded using Nicolet is spectrometer from Meslo, USA to identify the functional groups using the KBr disc method. In this concern, the sample was thoroughly mixed with KBr as a matrix; the mixture was ground and then pressed with a special press to give a disc of standard diameter. The disk formed was examined in FTIR spectrophotometer in the range from 4000 to 400 cm1. 2.4.2. Gamma spectroscopy The prepared samples for the activity concentration measurements and chemical treatment investigation were done nondestructively using g-ray spectrometry high purity germanium-HPGe (Oxford, TN Nucleus, Oak Ridge, USA), model: ERDS 30 20200, serial no.: 2201. A bias supply of 3400 was applied with a relative efficiency of 30% and a resolution of (FWHM) 2.0 keV at 1.332 MeV for 60 Co. The data acquisition was collected by 8 K multichannel analyzer (MCA) using Genie 2000 Canberra spectrometric software. Sealed standard sources containing 137Cs, 133Ba, and 60Co were used for energy calibration. The non-destructive g-ray measurements were performed using 50 g of the sludge waste (dry weight) to determine the activity concentration of 238U, 226Ra (U-series) and 228 Ra (Th-series) using certified reference materials (CRM) provided by the International Atomic Energy Authority, AQCS, namely: IAEA-312, 313 and 314. Activity concentration of 238U was equivalent to average activity of 234Th at photopeaks of 63 and 92.6 keV. The activity concentration of 226Ra was determined from its photopeak at 186.2 keV. The interference due to contribution of 235U does not taken into account, since the sludge sample contains high level of 226Ra and low level of 238U, in addition the low abundance of 235U (~0.7%) relative to 238U (~99.25%). On the other hand, 228Ra was determined from the average activities of 228Ac at 338.6 and 911 keV assuming the equilibrium conditions between the both radionuclides (parent/daughter). The minimum detection limit of the different radionuclides was 1.4 Bq/kg for 238U (as 234Th), 1.1 Bq/ kg for 226Ra and 0.9 Bq/kg for 228Ra (as 228Ac). On the other hand, for the chemical treatment, 25 g of the sludge waste was used to evaluate removal of radium species. The removal percentage of 226Ra was evaluated directly from its count rate (c/s) at 186.2 keV, whereas 228Ra was indirectly from average of count
Removal of the natural radioactivity due to radium species (226Ra and 228Ra) was investigated based on desorbing, dissolving, suspending the fine particles containing radium species. The experimental procedure was carried out by shaking a known amount of the sludge waste with solideliquid ratio of 1/5 (w/v) for one hour at ambient room temperature (25 ± 1 C), unless otherwise stated. The upper turbid aqueous phase was separated rapidly by decantation. The solid residue phase was left for drying and recounted. Parameters affecting on the radium removal process investigated include effect of shaking time, surfactants concentration and temperature. The effect of possible synergism as a result of surfactant mixture, between TX100 and CTAB at constant concentration of 1% was also investigated. The removal percentage, R%, of the radium isotopes was calculated based on the difference between the net counts of the waste samples before and after treatment with the used solutions as follows:
R% ¼
Ao A 100 Ao
(1)
where A0 is the net count rate (c/s) of the sludge waste samples before treatment and A is the net count rate (c/s) of the sludge wastes samples after treatment. For each surfactant type, two independent treatment and analysis were carried out and the result obtained was an average of the two samples. Moreover, for all radiometric assay each sample was counted three times and the average results was used. The standard deviations calculated in the results section do not exceed ±10%. 3. Results and discussion TENORM waste such as any soil is capable of capturing inorganic and organic compounds in its pore spaces and surface. Depending on the specific physico-chemical properties of rocks and the soil, compounds dissolved in the fluid may be incorporated into the soil matrix. Previous work indicated that most radium isotopes in TENORM produced from oil exploration is associated mainly with clay particles which represent 31% by weight of the TENORM solid waste (Attallah et al., 2012, 2013; El Afifi et al., 2006, 2009; El Afifi and Awwad, 2005; El Afifi, 2001; Shehata et al., 1999). Soil washing typically uses water as the solvent to extract, desorb, and dissolve contaminants. The concept of the treatment in this work is based on the use of suitable surfactant solutions to float these clay particles out of the bulk heavy solid waste matrix. 3.1. Characterization of TENORM sludge waste Table 1 summarizes the main characteristics of the TENORM sludge waste in terms of its mineralogical, chemical and radiological properties (Attallah et al., 2013). The XRD data showed three strong peaks attributed to silicate structure, and some weak peaks due to the minor constituents. XRF data showed that Si, Fe, Al, and alkaline earth elements (Mg, Ca, Sr and Ba) are the major constituents of the waste matrix. g-ray spectra showed peaks characteristic to 238U and 232Th-series and their respective decay daughters (especially 226Ra and 228Ra). The nondestructive g-ray measurements of the sludge waste showed that, the average activity concentration of uranium (238U), 226Ra (U-
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84 Table 1 Mineralogical, chemical and radiological characteristics of the TENORM waste (Attallah et al., 2013). Mineralogical data (XRF and XRD) XRF data
Value (%)
Si Fe Ca Sr Ba
44.1 27.3 13.5 0.9 3.3
± ± ± ± ±
1.9 1.2 0.8 0.1 0.3
XRD analysis Phase composition: Metal-sulfate, carbonate and silicates.
Physico-chemical properties Properties
Value
Humiditya (%) TOMa (%) Clayb (%) Density (g cm3)
0.9 2.4 32.0 0.9
± ± ± ±
0.1 0.1 1.0 0.1
Nuclide (Bq/kg)
Daughters (Bq/kg)
Parent/daughter ratio
238
226
238
Ra (11,960), 222Rn,…210Pb 228 Ac, 228Ra (1750), 224Ra,…208Tl e
silicate, sulfate and carbonate of the major elements and the naturally occurring radionuclides. An FTIR spectrum of TENORM sludge waste was obtained in the range of 4000e400 cm1. The spectrum of sludge displays a number of absorption peaks, indicating the very complex nature of the material under study, as illustrated in Fig. 3. The spectrum displays absorption peaks for a mixture of different petroleum hydrocarbons molecules. Hydrocarbons are molecules that contain hydrogen and carbon and come in various lengths and structures, from straight chains to branching chains to rings such as Paraffins, Aromatics and Napthenes or Cycloalkanes. Other organic compounds contain nitrogen, oxygen, sulfur, and trace amounts of metals in the forms of inorganic salts or organometallic compounds are also present.
3.2. Optimization of chemical treatment using surfactants
Radiological data (g-ray analysis)
U (108) 232 Th (e) 40 K (e)
81
U/226Ra (0.009)
e e
a Humidity and total organic matter (TOM) are determined gravimetrically at 105 and 450 C, respectively. b Clay content was determined by suspension.
series) and 228Ra (Th-series) was 240, 8908 and 933 Bq/kg, respectively (Hilal et al., 2014). It is clear that, the 238U/226Ra ratio is small and equal 0.027. This value indicates that U and 226Ra are far from the secular equilibrium, as a result of the enhancement of 226Ra compared to U in the sludge waste due to the differences in their physicochemical characteristics and the oil exploration conditions. It is known that the natural abundance of 238U and 235U is ~99.25 and ~0.70%, respectively, in addition presence of high activity of 226Ra and low activity of U. Therefore, the influence due to contribution of 235U on the measurement of 226R at photopeak of 186.2 keV can be neglected. The acidification test of the waste using dilute HCl indicated the presence of carbonate salts and evolution of a bad odor of H2S attributed to the inorganic and/or organic-sulfhur contaminants (e.g., sulphides) during oil and gas production. Therefore, the main composition of the waste is a mixed phases containing the hard
To optimize the different parameters affecting the chemical treatments of decontamination of the solid waste under investigations, the following experiments were investigated;
3.2.1. Effect of contact time on dissolution/desorption of radium isotopes In this set of experiments, the effect of contact time on the removal of radium radionuclides (226Ra, 228Ra) from TENORM sludge waste using TX100 and CTAB surfactants was investigated. Kinetics of radium isotopes dissolution/desorption from TENORM sludge are described by plotting the radium species removed from the sludge vs. extraction time. Transport and mass transfers of radium isotopes from the sludge might be a key process responsible for reducing radium from the sludge. To achieve maximum radium species removal, a specific period of time is required. The obtained results are represented in Table 2. It is obvious that the removal efficiency of radium isotopes is increased as the shaking time was increased and reach maximum after 60 min. The highest removal efficiency for 226Ra was obtained using CTAB surfactant, and using TX100 surfactant for 228Ra.However, further increase in the time of experiment leads to decrease of the removal efficiency. Therefore, 60 min shaking time for removal was chosen as optimum time for all further experiments.
Fig. 3. FT-IR spectrum of TENORM sludge waste.
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Table 2 Effect of shaking time on the removal (R,%) of surfactants solutions. Time, min
TX100 solution 226
15 30 60 120 240
Ra (R,%)
16.0 22.0 25.0 15.7 8.2
± ± ± ± ±
1.3 1.5 1.7 1.3 0.8
226
Ra and
228
Ra using 1.0% (w/v)
CTAB solution 228
Ra (R,%)
17.0 20.5 27.0 24.0 18.5
± ± ± ± ±
1.4 1.8 2.1 2.2 1.6
226
Ra (R,%)
20.4 22.7 26.0 23.7 4.2
± ± ± ± ±
1.8 2.0 2.0 2.1 0.4
228
Ra (R,%)
15.0 18.2 22.0 23.7 16.7
± ± ± ± ±
1.3 1.6 1.3 2.0 1.5
3.2.2. Effect of surfactants concentrations on the extraction of radium isotopes Surfactant molecules contain hydrophobic and hydrophilic regions. The combination of hydrophobic and hydrophilic properties in the same molecule gives these species unique solubility properties in water or aqueous media. In dilute aqueous media, surfactants molecules usually exist as monomers. Aggregation of these monomers in different forms called micelles and changes of physical properties of the solution occur at a surfactant concentration known as the critical micelle concentration (CMC). Also, micelle formation enables emulsification, solubilization and dispersion in the aqueous media. These media which contain micelles have been shown to exhibit some interesting features. They are capable of solubilizing many water-insoluble substances within and on the surface of the micelles (Ahn et al., 2008; Mulligan et al., 2001, 1999). Therefore, surfactants concentrations are regarded as an important parameter affecting the removal of radium isotopes from TENORM sludge waste. In order to remove maximum radium isotopes, the concentrations of surfactants (TX100, CTAB) must be chosen carefully. Experiments were carried out to investigate the removals efficiencies by two surfactants at different concentrations (0.25e8%). The results are illustrated in Table 3. The removal of radium species is found to be dependent on the two surfactants concentration. The removal efficiency of radium species for both surfactant solutions increased with increasing surfactant concentration up to 1%. At higher surfactants concentration a slight decrease was observed, as shown in Table 3. The optimum concentrations are found to be 1% for both surfactants solutions. The effective removal of radium species from TENORM sludge can be explained by the increased solubility of radium species in the surfactant micelles. Generally, the change in the concentration of surfactant leads to change in its physical properties such as micelles formation and its solubilization effect for radium species or any contaminant (organic or inorganic species) present in TENORM sludge waste, as shown in Fig. 4 (Mulligan et al., 2001). Therefore, the optimum surfactants concentrations are 1% for this treatment to avoid introduction of excess surfactants into sludge and avoid decrease in the radium removal %. 3.2.3. Effect of temperature The capacity of surfactant aggregation in the aqueous solution is one of the characteristics of surfactants. Micelles are one type of Table 3 Effect of surfactants concentrations on the removal (R,%) of Conc., %
TX100 solution 226
0.25 0.5 1.0 2.0 4.0 8.0
Ra (R,%)
13.5 17.1 25.0 11.9 9.8 9.0
± ± ± ± ± ±
1.4 1.1 1.7 1.1 0.9 0.8
226
Ra and
228
Ra (R,%)
15.0 19.1 27.0 20.5 19.0 13.3
± ± ± ± ± ±
1.3 1.5 2.2 1.9 1.5 1.2
226
Ra (R,%)
12.5 22.7 26.0 24.9 16.9 6.8
± ± ± ± ± ±
0.9 1.7 2.0 1.7 1.4 0.6
aggregation. Several parameters of micellization such as aggregation number and CMC can vary by changing the environmental conditions. Micellization is affected by various factors such as additive, ionic strength and temperature. The effect of temperature on the CMC of cationic and anionic surfactants is not straightforward. It was reported that when the temperature is increased, the CMC first decreases, then undergoes through a minimum, and finally increases. Other authors have observed a similar pattern with nonionic surfactant solutions. On one hand, an increase in temperature can bring a reduction in the hydration of the surfactant hydrophilic group; this is the well-known desolvatation effect. This effect tends to drive the surfactant out of the aqueous solution and thus it favors the formation of micelles, i.e., it decreases the CMC (Crook et al., 1963; Singh et al., 1979). On the other hand, an increase in temperature results in an increasing disorder in the structure of the water phase, in particular the molecules which are located next to the surfactant hydrophobic. The higher the disorder, the less defined the direction of the unfavorable polar/polar contact, and as a consequence the weaker it becomes. Thus the hydrophobic effect which drives the surfactant molecule “tail” out of the water phase is also reduced when temperature is increased, i.e., the CMC is increased (Crook et al., 1963; Schick, 1987). So that temperature of surfactant solutions used for removal of radium species is an important parameter in surfactant aided sludge washing process, and the experiments have been investigated with concentration of 1% TX100 and CTAB at 25e60 C. The results in Table 4 showed that, the removal of radium isotopes is increased with increasing temperature and the removal of radium species reaches a maximum at 60 C using both surfactants solutions. The increase of radium species removal efficiency is due to the properties of surfactants, where an increase in temperature generally results in an increase in the extent of solubility. The cloud point phenomenon occurs when a surfactant above its CMC causes the separation of the original solution into two phases when heated at a characteristic temperature called cloud point temperature. At this temperature, surfactant is no longer soluble in water and solution becomes hazy and cloudy. Above the cloud point, micelles formed from surfactant molecules act as an organic solvent in liquideliquid extraction and the analytes are partitioned between the micelles and aqueous phases (Lee et al., 2004). It has been mentioned that, the cloud point extraction procedure not only effectively
Ra. Table 4 Effect of temperature on the removal of 226Ra and 228Ra using surfactants solutions.
CTAB solution 228
Fig. 4. Schematic diagram of the variation of surface tension, interfacial and contaminant solubility with surfactant concentration. (Mulligan et al., 2001, Copyright © 2001 Elsevier).
228
Ra (R,%)
14.4 20.0 22.0 23.0 14.8 8.8
± ± ± ± ± ±
1.3 2.0 1.3 2.2 1.3 0.9
Temp., C
TX100 solution 226
25 35 45 60
Ra (R,%)
25.0 30.0 53.0 58.6
± ± ± ±
1.7 1.9 1.7 2.1
CTAB solution 228
Ra (R,%)
27.0 39.5 45.3 54.3
± ± ± ±
2.2 2.2 2.0 3.3
226
Ra (R,%)
26.0 28.6 43.5 49.8
± ± ± ±
1.9 2.2 2.7 3.8
228
Ra (R,%)
22.0 35.9 46.2 50.7
± ± ± ±
1.3 2.8 3.4 4.2
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84
solubilization and concentrates pollutants, but also appears to offer a means to further the concentrated surfactant-enhanced wash solutions that have been used in soil treatment process (Abdul and Gibson, 1991). About 25% of the radium species were initially removed from the TENORM sludge by solubilization in surfactants solution (this was prior to temperature alteration). About 55e60% removal was achieved upon the temperature raise to 60 C. 3.2.4. Effect of mixed surfactants The efficiency of the surfactants in removing contaminant from solid phase was also dependent on the hydrophilic/hydrophobic structure of the surfactant molecule and CMC (Mulligan et al., 2001; Stalikas, 2002). Mixtures are usually preferred in commercial applications not only due to the increased expense with pure preparations but also because mixed systems often exhibit enhanced properties through synergism. Synergism in surfactants may be defined as any situation where mixtures of surfactants have superior properties when compared to the properties of any of the single surfactant alone (Lee et al., 2004). There is usually a synergy effect for the CMC of surfactant mixtures (mixture of nonionic and ionic surfactant) (Holmberg et al., 2003). Mixture of TX100 and CTAB surfactants showed synergistic interactions, which can be manifested as enhanced surface properties, spreading and many other phenomena, as shown in Fig. 5. The synergistic behavior of mixed surfactant systems can be exploited to reduce the total amount of surfactant used in a particular application resulting in the reduction of cost (Stalikas, 2002). It was observed that the removal values of radium isotopes of mixed systems of both surfactants are higher than their corresponding values without mixing, which indicate synergistic interaction in mixed CTAB-TX100 as a chemical extraction system. Removal of 84% and 80% for 226Ra and 228Ra, respectively, is obtained using synergistic effect of 1% aqueous solution containing 1:1 of the two surfactants investigated. In other words, mixed micelle formation in aqueous solution can be greater than that of the individual surfactant, and explained by non-ideal solution theory (Lee et al., 2004). 3.3. The mechanism of extractive washing The primary reason to use surfactants is to remove the pollutants in a short time period with less wash water required. Surfactants reduce the free energy of the systems by replacing the bulk
Fig. 5. Effect of synergism surfactant concentration on the removal of radium radionuclides.
83
molecules of higher energy at an interface. They are compounds that promote or increase the wetting, solubilization and emulsification of many types of organic and inorganic contaminants (Ahn et al., 2008; Mulligan et al., 2001, 1999). Two hypotheses have been offered to explain the mechanism behind surfactant enhanced soil washing. First, direct complexation between the surfactant used and solution phase metal effectively removes metal from solution and increases dissolution and desorption according to Le Chatelier's principle. The second is that surfactants can accumulate at the solid/liquid interface and interact with sorbed metals (Huibers and Shah, 1997). Mulligan et al. conclude that interaction of surfactant with the sludge allows direct interaction between the surfactant and the sorbed metal, thereby making it easier to release the sorbed metal (Mulligan et al., 2014, 1999). 4. Conclusion Surfactants are a type that promotes or increase the wetting, solubilization and emulsification of many types of organic and inorganic contaminants. Removal of metal species by surfactant is very interesting, but the research in this area is still quite limited for treatment of radioactive materials. Washing process removes radium radionuclides from TENORM sludge waste by dissolving or suspending them with surfactants solutions. Using washing, aqueous solutions containing the surfactants CTAB removed 22e26% and TX100 removed 25e27% of radium species. Higher solution temperature increases the removal efficiency of radium species due to the special properties of surfactants. Combined extraction of cationic and nonionic surfactants was effective in removal both 226Ra and 228Ra. Experiments indicated that removal efficiency was optimized (80e84%) when a mixture of 1% CTAB and 1% TX100 was employed at ratio 1:1. The theoretical justification for this surfactants solution is based upon two hypotheses, first that surfactant micelles may sequester radium radionuclides which are sorbed to the TENORM sludge waste, and second that the surfactant micelles may increase the concentration of radium radionuclides in the aqueous phase. The developed chemical treatment process would enable to design of an appropriate TENORM sludge washing strategy. References Abdul, A.S., Gibson, T.L., 1991. Laboratory studies of surfactant enhanced washing of polychlorinated biphenyl from sandy material. Environ. Sci. Technol. 25, 665. Ahn, C.K., Kim, Y.M., Woo, S.H., Park, J.M., 2008. Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon. J. Hazard. Mater. 154, 153. Al-Masri, M.S., Aba, A., 2005. Distribution of scales containing NORM in different oilfields equipment. Appl. Radiat. Isot. 63, 457. Attallah, M.F., Awwad, N.S., Aly, H.F., October 2012. Environmental radioactivity of TE-NORM waste produced from petroleum industry in Egypt: review on characterization and treatment. In: Natural Gas e Extraction to End Use. InTech. http://dx.doi.org/10.5772/CHAPTERDOI. Attallah, M.F., El Afifi, E.M., Awwad, N.S., Aly, H.F., 2013. Comparative study on the radioactivity of TENORM in different components of oil separator tanks. Radiochim. Acta 101, 57. Baeza, A., Corbacho, J.A., Guillen, J., Salas, A., Mora, J.C., 2011. Analysis of the different source terms of natural radionuclides in a river affected by NORM (naturally occurring radioactive materials) activities. Chemosphere 83, 933. Crook, E.H., Fordyce, D.B., Trebbi, G.F., 1963. Molecular weight distribution of nonionic surfactants. I. Surface and interfacial tension of normal distribution and homogeneous p,t-octylphenoxyethoxyethanols (OPE'S). J. Phys. Chem. 67, 1987. Desideri, D., Meli, M.A., Feduzi, L., Roselli, C., 2006. The importance of radiochemistry for the characterization of NORM and of environments contaminated by NORM. Int. J. Environ. Anal. Chem. 86, 601. El Afifi, E.M., Awwad, N.S., 2005. Characterization of the TENORM waste associated with oil and natural gas production in Abu Rudies, Egypt. J. Environ. Radioact. 82, 7. El Afifi, E.M., Awwad, N.S., Hilal, M.A., 2009. Sequential chemical treatment of radium species in TENORM waste sludge produced from oil and natural gas production. J. Hazard. Mater. 161, 907.
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El Afifi, E.M., El-Reefy, S.A., Aly, H.F., 2006. Treatment of solid waste containing 226 Ra. Arab. J. Nucl. Sci. Appl. 39, 35. El Afifi, E.M., 2001. Radiochemical Studies Related to Environmental Radioactivities (PhD thesis). Ain Shams University, Cairo, Egypt. Hilal, M.A., Attallah, M.F., Mohamed Gehan, Y., Fayez-Hassan, M., 2014. Evaluation of radiation hazard potential of TENORM waste from oil and natural gas production. J. Environ. Radioact. 136, 121. €nsson, B., Kronberg, B., Lindman, B., 2003. Surfactants and Polymers Holmberg, K., Jo in Aqueous solution, second ed. Wiley, Chichester. Huibers, P.D.T., Shah, D.O., 1997. Langmuir 13, 5762. Lee, D., Chang, H., Cody, R.D., 2004. Synergism effect of mixed surfactant solutions in remediation of soil contaminated with PCE. Geosci. J. 8, 319. Mulligan, C.N., Sharma, S.K., Mudhoo, A., 2014. Biosurfactants: Research Trends and Applications, first ed.. CRC Press. Mulligan, C.N., Yong, R.N., Gibbs, B.F., 1999. Removal of heavy metals from contaminated soil and sediments using the biosurfactant surfactin. J. Soil Contam. 8, 231. Mulligan, C.N., Yong, R.N., Gibbs, B.F., 2001. Surfactant-enhanced remediation of contaminated soil: a review. Eng. Geol. 60, 371. OGP Report No. 412, September 2008. Guidelines for the Management of Naturally Occurring Radioactive Material (NORM) in the Oil & Gas Industry. OGP. www. ogp.org.uk.
Paria, S., Yuet, P.K., 2007. Ind. Eng. Chem. Res. 46, 108. Schick, M.J., 1987. Nonionic Surfactants: Physical Chemistry, second ed. CRC Press. Shehata, F.A., El Afifi, E.M., Aly, H.F., 1999. Fractionation and leaching of naturally occurring radioactive waste produced from oil production. In: Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, Nagoya, Japan, September 26e30, 1999. CD-ROM. Singh, H.N., Swarup, S., Saleem, S.M., 1979. Effect of electrolytes on the micellization of ionic surfactants in n-alkanolewater mixtures. J. Colloid Interf. Sci. 68, 128. Smith, K.P., Arnish, J.J., Williams, G.P., Blunt, D.L., 2003. Environ. Sci. Technol. 37, 2060. Stalikas, C.D., 2002. Trends Anal. Chem. 21, 343. Saichek, R.E., Reddy, K.R., 2005. Electrokinetically enhanced remediation of hydrophobic organic compounds in soils: a review. Crit. Rev. Environ. Sci. Technol. 35, 115. Thimmaraju, R., Bhagyalakshmi, N., Narayan, M.S., Ravishankar, G.A., 2003. Foodgrade chemical and biological agents permeabilize red beet hairy roots, assisting the release of betalaines. Biotechnol. Progr. 19, 1274. White, G.J., Rood, A.S., 2001. Radon emanation from NORM-contaminated pipe scale and soil at petroleum industry sites. J. Environ. Radioact. 54, 401. Xin, K.E., Pei-jun, L.I., Qi-Xing, Z., Yun, Z., Tie-heng, S., 2006. Removal of heavy metals from a contaminated soil using tartaric acid. J. Environ. Sci. 18, 727.
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Removal of 226Ra and surfactants solutions
228
Ra from TENORM sludge waste using
M.F. Attallah*, Mostafa M. Hamed, E.M. El Afifi, H.F. Aly Hot Laboratories and Waste Management Center, Atomic Energy Authority of Egypt, PO.13759 Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 July 2014 Received in revised form 14 September 2014 Accepted 15 September 2014 Available online
The feasibility of using surfactants as extracting agent for the removal of radium species from TENORM sludge produced from petroleum industry is evaluated. In this investigation cationic and nonionic surfactants were used as extracting agents for the removal of radium radionuclides from the sludge waste. Two surfactants namely cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX100) were investigated as the extracting agents. Different parameters affecting the removal of both 226Ra and 228Ra by the two surfactants as well as their admixture were studied by the batch technique. These parameters include effect of shaking time, surfactants concentration and temperature as well as the effect of surfactants admixture. It was found that, higher solution temperature improves the removal efficiency of radium species. Combined extraction of nonionic and cationic surfactants produces synergistic effect in removal both 226Ra and 228Ra, where the removals reached 84% and 80% for 226Ra and 228Ra, respectively, were obtained using surfactants admixture. © 2014 Elsevier Ltd. All rights reserved.
Keywords: TENORM sludge Removal of radium Natural radionuclides Surfactants
1. Introduction Radionuclides of natural origin have been found at varying concentrations in soil and water, in food, air and human tissues. All minerals and raw materials in the Earth's crust contain small, but measurable concentrations of natural occurring radioactive materials (NORM). Geochemical properties associated with petroleum formation can result in locally elevated concentrations of 238U and 232 Th within source rocks (Desideri et al., 2006). During the course of oil/water separation in production facilities, these radioactive materials can precipitate onto process equipment and storage tanks. The primary radionuclides of concern in NORM wastes are 226 Ra of the 238U decay series and 228Ra of the 232Th decay series. Other isotopes of concern include isotopes that are produced from the decay of radium radionuclides, such as 222Rn (Desideri et al., 2006; White and Rood, 2001). NORM are present at varying concentrations and can be concentrated or enhanced by different processes associated with the petroleum industry. This “enhanced” NORM, often known as TENORM (Technologically Enhanced Naturally Occurring
* Corresponding author. E-mail addresses: [email protected], [email protected] (M.F. Attallah). http://dx.doi.org/10.1016/j.jenvrad.2014.09.009 0265-931X/© 2014 Elsevier Ltd. All rights reserved.
Radioactive Materials) can be created when industrial activity increases the concentrations of radionuclides or when the material is redistributed as a result of human intervention. TENORM also can be the by-product or waste product of oil, gas and energy production plants (Desideri et al., 2006; OGP Report No. 412, 2008; Baeza et al., 2011). Sludge, drilling mud, and pipe scales are examples of materials that can contain elevated levels of NORM (Desideri et al., 2006; White and Rood, 2001; OGP Report No. 412, 2008; Baeza et al., 2011; Paria and Yuet, 2007). In oil industry, NORM can accumulate in different forms such as scale, sludge and thin films, as shown in Fig. 1 (OGP Report No. 412, 2008). Sometimes, NORM concentrate in the waste streams of oil and gas production operations. Radionuclides were found in many underground formations but are not very soluble in the reservoir fluid. However, the daughter products, radium isotopes, are somewhat soluble as dissolved ions and migrate to the surface (Baeza et al., 2011; Al-Masri and Aba, 2005). Handling, storage, transportation and the use of TENORM contaminated equipment or waste media without controls can lead to the spread of TENORM contamination, resulting in exposure of the public (Desideri et al., 2006; White and Rood, 2001; OGP Report No. 412, 2008; Baeza et al., 2011; Paria and Yuet, 2007; Al-Masri and Aba, 2005). Recently, attention was focused on the environmental and health impacts from the uncontrolled release of TENORM wastes (Desideri et al., 2006; Baeza et al., 2011). Therefore, the treatment of
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84
79
2. Experimental 2.1. Surfactant selection
Fig. 1. The origins of NORM, indicating where NORM may accumulate in the recovery process. (OGP Report No. 412, 2008, www.ogp.org.uk. © Copyright 2008, OGP).
Solid phases or soils washing would be more effective when surfactants with a low adsorption capacity to soil or solid phase are used. Two surfactants CTAB and TX100 were used in this study. Cationic surfactant CTAB is usually chosen for surfactant-based remediation procedures because they showed a good solubilizing for many pollutants. TX100 is nonionic surfactant, which has been noted for their unfavorable tendency to sorption to aquifer solids (Ahn et al., 2008; Saichek and Reddy, 2005). Used surfactants are excellent solubilizing agents of many compounds, and their food grade additive status makes them attractive for use in environmentally sensitive areas. Also, they are rapidly biodegradable by soil and/or aquatic microorganisms. These surfactants were used without further purification (Thimmaraju et al., 2003; Lee et al., 2004). 2.2. Reagents
these wastes is of increasing interest since accumulation of large amounts with a significant activity may cause health risks not only to the person directly involved in these activities, but also to the local population (Desideri et al., 2006; Al-Masri and Aba, 2005). The trials towards the treatment of TENORM wastes from different industries are still limited. The commonly used methods include subsurface disposal options, volume reduction, and use of scale and/or sludge inhibitors, recycling, leaching, and extraction process using different solutions (Attallah et al., 2012, 2013; El Afifi et al., 2006, 2009; El Afifi and Awwad, 2005; El Afifi, 2001; Shehata et al., 1999; Smith et al., 2003). Various techniques, including soil bioremediation and soil washing, have been used to treat contaminated areas. Soil washing, a water based process that employs chemical and physical extraction process to remove contaminants from the soil, has recently become a common technique for remediating sites contaminated with different pollutants. Although, soil washing may be the most economical process to clean up contaminants, many contaminants have very low water solubility, and therefore it is necessary to consider the use of surfactants to improve the soil-washing process (Xin et al., 2006; Mulligan et al., 2001; Ahn et al., 2008). Surfactants (surface active agents) are organic chemical wetting, cleaning and disinfecting agents, and they are frequently used in detergents and food products that alter the properties of solution interfaces. They also can be added to washing water to assist in the solubilizing, dispersal and desorption of contaminants (Mulligan et al., 1999). Surfactant enhanced remediation (SER) has been recognized as one of the promising technologies. In SER, surfactants play an important role in solubilizing and the removal of trapped contaminant (Xin et al., 2006; Mulligan et al., 2001). Surfactants can act as an extracting agent for the removal of radionuclides from contaminated soils through either surfactant-aided soil washing or solubilizing them because they could enhance the water solubility and mobility of radionuclides in soil environment and thus increase their removal efficiency. So far in our knowledge, no articles have been published concerning the removal of radium by using surfactants. The present work is focused on the use of selected surfactants for removal of radium isotopes from TENORM sludge waste. The feasibility of using two different types of surfactants (cationic and nonionic) was assessed. To enhance the removal of radium and the factors influencing their behavior at different variables were investigated. These include the type of surfactant, surfactants concentration, shaking time, and temperature as well as surfactants mixture.
Surfactants TX100 and CTAB used as washing agents in the experiments were purchased from Merck. The surfactants were used without further purification. 2.3. Samples collection and preparation TENORM sludge accumulates inside the oil production equipment, e.g. piping, separation heater/treaters, storage tanks and any other equipment where produced water is handled. It occurs when the radium (Ra) coprecipitates with barium, strontium and/or calcium in the form of insoluble sulfate or in the form of slightly more soluble silicates and/or carbonates. In the present study, a limited individual amounts (~1000 g) taken from the sludge piles generated during the periodical maintenance of the oil separator tanks surrounding the oilfield site (Suez gulf region, Egypt). In our laboratory, the collected individual TENORM samples were mixed together and screened in atmospheric air (25e30 C) for 2 weeks. Then, the actual sample was dried under IR lamp for one week till complete dryness and constant weight. The sludge waste was crushed, pulverized and sieved using a programmable sieving vibratory (model: Analyestte, Germany) into two main parts, namely: non-homogeneous and homogeneous waste sludge. Fig. 2 showing the procedure for drying and sieving of the TENORM waste sludge. The total recovery of the sludge waste sieving reached to 99.6%, while the rest 0.4% represented a loss as dust released into atmosphere. The non-homogeneous sludge is discarded due to its coarse particles greater than 2 mm and low sieving recovery of 3.2%. The homogeneous sludge has a particle size less than 2 mm and sieving recovery of 96.4%, therefore it is used for the further treatment investigations. The humidity, total organic matter, clay content and density were determined gravimetrically. 2.4. Spectroscopic measurements 2.4.1. Material characterization TENORM sludge waste was characterized using analytical techniques such as: X-ray fluorescence (XRF), X-ray diffractometer (XRD) and Fourier transform infrared (FT-IR). The elemental analysis of the TENORM sludge waste has been determined by X-ray fluorescence (XRF) using Philips PW-2400 sequential X-ray spectrometer (Japan). The samples were grinded to a fine particle size as possible in a laboratory mill. The resulting powder was pressed into pellets of 40 mm diameter and 5 mm thickness. The main
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rate (c/s) 228Ac at 338.6 and 911 keV. The statistical error associated with counting of the samples during the activity concentration assessment and the treatment evaluation does not exceed 10%. 2.5. Sludge waste treatment
Fig. 2. Drying and preparing of the sludge waste samples produced from the petroleum exploration processes.
mineralogical composition of the waste was determined by X-ray diffractometer (XRD). FTIR spectrum was recorded using Nicolet is spectrometer from Meslo, USA to identify the functional groups using the KBr disc method. In this concern, the sample was thoroughly mixed with KBr as a matrix; the mixture was ground and then pressed with a special press to give a disc of standard diameter. The disk formed was examined in FTIR spectrophotometer in the range from 4000 to 400 cm1. 2.4.2. Gamma spectroscopy The prepared samples for the activity concentration measurements and chemical treatment investigation were done nondestructively using g-ray spectrometry high purity germanium-HPGe (Oxford, TN Nucleus, Oak Ridge, USA), model: ERDS 30 20200, serial no.: 2201. A bias supply of 3400 was applied with a relative efficiency of 30% and a resolution of (FWHM) 2.0 keV at 1.332 MeV for 60 Co. The data acquisition was collected by 8 K multichannel analyzer (MCA) using Genie 2000 Canberra spectrometric software. Sealed standard sources containing 137Cs, 133Ba, and 60Co were used for energy calibration. The non-destructive g-ray measurements were performed using 50 g of the sludge waste (dry weight) to determine the activity concentration of 238U, 226Ra (U-series) and 228 Ra (Th-series) using certified reference materials (CRM) provided by the International Atomic Energy Authority, AQCS, namely: IAEA-312, 313 and 314. Activity concentration of 238U was equivalent to average activity of 234Th at photopeaks of 63 and 92.6 keV. The activity concentration of 226Ra was determined from its photopeak at 186.2 keV. The interference due to contribution of 235U does not taken into account, since the sludge sample contains high level of 226Ra and low level of 238U, in addition the low abundance of 235U (~0.7%) relative to 238U (~99.25%). On the other hand, 228Ra was determined from the average activities of 228Ac at 338.6 and 911 keV assuming the equilibrium conditions between the both radionuclides (parent/daughter). The minimum detection limit of the different radionuclides was 1.4 Bq/kg for 238U (as 234Th), 1.1 Bq/ kg for 226Ra and 0.9 Bq/kg for 228Ra (as 228Ac). On the other hand, for the chemical treatment, 25 g of the sludge waste was used to evaluate removal of radium species. The removal percentage of 226Ra was evaluated directly from its count rate (c/s) at 186.2 keV, whereas 228Ra was indirectly from average of count
Removal of the natural radioactivity due to radium species (226Ra and 228Ra) was investigated based on desorbing, dissolving, suspending the fine particles containing radium species. The experimental procedure was carried out by shaking a known amount of the sludge waste with solideliquid ratio of 1/5 (w/v) for one hour at ambient room temperature (25 ± 1 C), unless otherwise stated. The upper turbid aqueous phase was separated rapidly by decantation. The solid residue phase was left for drying and recounted. Parameters affecting on the radium removal process investigated include effect of shaking time, surfactants concentration and temperature. The effect of possible synergism as a result of surfactant mixture, between TX100 and CTAB at constant concentration of 1% was also investigated. The removal percentage, R%, of the radium isotopes was calculated based on the difference between the net counts of the waste samples before and after treatment with the used solutions as follows:
R% ¼
Ao A 100 Ao
(1)
where A0 is the net count rate (c/s) of the sludge waste samples before treatment and A is the net count rate (c/s) of the sludge wastes samples after treatment. For each surfactant type, two independent treatment and analysis were carried out and the result obtained was an average of the two samples. Moreover, for all radiometric assay each sample was counted three times and the average results was used. The standard deviations calculated in the results section do not exceed ±10%. 3. Results and discussion TENORM waste such as any soil is capable of capturing inorganic and organic compounds in its pore spaces and surface. Depending on the specific physico-chemical properties of rocks and the soil, compounds dissolved in the fluid may be incorporated into the soil matrix. Previous work indicated that most radium isotopes in TENORM produced from oil exploration is associated mainly with clay particles which represent 31% by weight of the TENORM solid waste (Attallah et al., 2012, 2013; El Afifi et al., 2006, 2009; El Afifi and Awwad, 2005; El Afifi, 2001; Shehata et al., 1999). Soil washing typically uses water as the solvent to extract, desorb, and dissolve contaminants. The concept of the treatment in this work is based on the use of suitable surfactant solutions to float these clay particles out of the bulk heavy solid waste matrix. 3.1. Characterization of TENORM sludge waste Table 1 summarizes the main characteristics of the TENORM sludge waste in terms of its mineralogical, chemical and radiological properties (Attallah et al., 2013). The XRD data showed three strong peaks attributed to silicate structure, and some weak peaks due to the minor constituents. XRF data showed that Si, Fe, Al, and alkaline earth elements (Mg, Ca, Sr and Ba) are the major constituents of the waste matrix. g-ray spectra showed peaks characteristic to 238U and 232Th-series and their respective decay daughters (especially 226Ra and 228Ra). The nondestructive g-ray measurements of the sludge waste showed that, the average activity concentration of uranium (238U), 226Ra (U-
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84 Table 1 Mineralogical, chemical and radiological characteristics of the TENORM waste (Attallah et al., 2013). Mineralogical data (XRF and XRD) XRF data
Value (%)
Si Fe Ca Sr Ba
44.1 27.3 13.5 0.9 3.3
± ± ± ± ±
1.9 1.2 0.8 0.1 0.3
XRD analysis Phase composition: Metal-sulfate, carbonate and silicates.
Physico-chemical properties Properties
Value
Humiditya (%) TOMa (%) Clayb (%) Density (g cm3)
0.9 2.4 32.0 0.9
± ± ± ±
0.1 0.1 1.0 0.1
Nuclide (Bq/kg)
Daughters (Bq/kg)
Parent/daughter ratio
238
226
238
Ra (11,960), 222Rn,…210Pb 228 Ac, 228Ra (1750), 224Ra,…208Tl e
silicate, sulfate and carbonate of the major elements and the naturally occurring radionuclides. An FTIR spectrum of TENORM sludge waste was obtained in the range of 4000e400 cm1. The spectrum of sludge displays a number of absorption peaks, indicating the very complex nature of the material under study, as illustrated in Fig. 3. The spectrum displays absorption peaks for a mixture of different petroleum hydrocarbons molecules. Hydrocarbons are molecules that contain hydrogen and carbon and come in various lengths and structures, from straight chains to branching chains to rings such as Paraffins, Aromatics and Napthenes or Cycloalkanes. Other organic compounds contain nitrogen, oxygen, sulfur, and trace amounts of metals in the forms of inorganic salts or organometallic compounds are also present.
3.2. Optimization of chemical treatment using surfactants
Radiological data (g-ray analysis)
U (108) 232 Th (e) 40 K (e)
81
U/226Ra (0.009)
e e
a Humidity and total organic matter (TOM) are determined gravimetrically at 105 and 450 C, respectively. b Clay content was determined by suspension.
series) and 228Ra (Th-series) was 240, 8908 and 933 Bq/kg, respectively (Hilal et al., 2014). It is clear that, the 238U/226Ra ratio is small and equal 0.027. This value indicates that U and 226Ra are far from the secular equilibrium, as a result of the enhancement of 226Ra compared to U in the sludge waste due to the differences in their physicochemical characteristics and the oil exploration conditions. It is known that the natural abundance of 238U and 235U is ~99.25 and ~0.70%, respectively, in addition presence of high activity of 226Ra and low activity of U. Therefore, the influence due to contribution of 235U on the measurement of 226R at photopeak of 186.2 keV can be neglected. The acidification test of the waste using dilute HCl indicated the presence of carbonate salts and evolution of a bad odor of H2S attributed to the inorganic and/or organic-sulfhur contaminants (e.g., sulphides) during oil and gas production. Therefore, the main composition of the waste is a mixed phases containing the hard
To optimize the different parameters affecting the chemical treatments of decontamination of the solid waste under investigations, the following experiments were investigated;
3.2.1. Effect of contact time on dissolution/desorption of radium isotopes In this set of experiments, the effect of contact time on the removal of radium radionuclides (226Ra, 228Ra) from TENORM sludge waste using TX100 and CTAB surfactants was investigated. Kinetics of radium isotopes dissolution/desorption from TENORM sludge are described by plotting the radium species removed from the sludge vs. extraction time. Transport and mass transfers of radium isotopes from the sludge might be a key process responsible for reducing radium from the sludge. To achieve maximum radium species removal, a specific period of time is required. The obtained results are represented in Table 2. It is obvious that the removal efficiency of radium isotopes is increased as the shaking time was increased and reach maximum after 60 min. The highest removal efficiency for 226Ra was obtained using CTAB surfactant, and using TX100 surfactant for 228Ra.However, further increase in the time of experiment leads to decrease of the removal efficiency. Therefore, 60 min shaking time for removal was chosen as optimum time for all further experiments.
Fig. 3. FT-IR spectrum of TENORM sludge waste.
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Table 2 Effect of shaking time on the removal (R,%) of surfactants solutions. Time, min
TX100 solution 226
15 30 60 120 240
Ra (R,%)
16.0 22.0 25.0 15.7 8.2
± ± ± ± ±
1.3 1.5 1.7 1.3 0.8
226
Ra and
228
Ra using 1.0% (w/v)
CTAB solution 228
Ra (R,%)
17.0 20.5 27.0 24.0 18.5
± ± ± ± ±
1.4 1.8 2.1 2.2 1.6
226
Ra (R,%)
20.4 22.7 26.0 23.7 4.2
± ± ± ± ±
1.8 2.0 2.0 2.1 0.4
228
Ra (R,%)
15.0 18.2 22.0 23.7 16.7
± ± ± ± ±
1.3 1.6 1.3 2.0 1.5
3.2.2. Effect of surfactants concentrations on the extraction of radium isotopes Surfactant molecules contain hydrophobic and hydrophilic regions. The combination of hydrophobic and hydrophilic properties in the same molecule gives these species unique solubility properties in water or aqueous media. In dilute aqueous media, surfactants molecules usually exist as monomers. Aggregation of these monomers in different forms called micelles and changes of physical properties of the solution occur at a surfactant concentration known as the critical micelle concentration (CMC). Also, micelle formation enables emulsification, solubilization and dispersion in the aqueous media. These media which contain micelles have been shown to exhibit some interesting features. They are capable of solubilizing many water-insoluble substances within and on the surface of the micelles (Ahn et al., 2008; Mulligan et al., 2001, 1999). Therefore, surfactants concentrations are regarded as an important parameter affecting the removal of radium isotopes from TENORM sludge waste. In order to remove maximum radium isotopes, the concentrations of surfactants (TX100, CTAB) must be chosen carefully. Experiments were carried out to investigate the removals efficiencies by two surfactants at different concentrations (0.25e8%). The results are illustrated in Table 3. The removal of radium species is found to be dependent on the two surfactants concentration. The removal efficiency of radium species for both surfactant solutions increased with increasing surfactant concentration up to 1%. At higher surfactants concentration a slight decrease was observed, as shown in Table 3. The optimum concentrations are found to be 1% for both surfactants solutions. The effective removal of radium species from TENORM sludge can be explained by the increased solubility of radium species in the surfactant micelles. Generally, the change in the concentration of surfactant leads to change in its physical properties such as micelles formation and its solubilization effect for radium species or any contaminant (organic or inorganic species) present in TENORM sludge waste, as shown in Fig. 4 (Mulligan et al., 2001). Therefore, the optimum surfactants concentrations are 1% for this treatment to avoid introduction of excess surfactants into sludge and avoid decrease in the radium removal %. 3.2.3. Effect of temperature The capacity of surfactant aggregation in the aqueous solution is one of the characteristics of surfactants. Micelles are one type of Table 3 Effect of surfactants concentrations on the removal (R,%) of Conc., %
TX100 solution 226
0.25 0.5 1.0 2.0 4.0 8.0
Ra (R,%)
13.5 17.1 25.0 11.9 9.8 9.0
± ± ± ± ± ±
1.4 1.1 1.7 1.1 0.9 0.8
226
Ra and
228
Ra (R,%)
15.0 19.1 27.0 20.5 19.0 13.3
± ± ± ± ± ±
1.3 1.5 2.2 1.9 1.5 1.2
226
Ra (R,%)
12.5 22.7 26.0 24.9 16.9 6.8
± ± ± ± ± ±
0.9 1.7 2.0 1.7 1.4 0.6
aggregation. Several parameters of micellization such as aggregation number and CMC can vary by changing the environmental conditions. Micellization is affected by various factors such as additive, ionic strength and temperature. The effect of temperature on the CMC of cationic and anionic surfactants is not straightforward. It was reported that when the temperature is increased, the CMC first decreases, then undergoes through a minimum, and finally increases. Other authors have observed a similar pattern with nonionic surfactant solutions. On one hand, an increase in temperature can bring a reduction in the hydration of the surfactant hydrophilic group; this is the well-known desolvatation effect. This effect tends to drive the surfactant out of the aqueous solution and thus it favors the formation of micelles, i.e., it decreases the CMC (Crook et al., 1963; Singh et al., 1979). On the other hand, an increase in temperature results in an increasing disorder in the structure of the water phase, in particular the molecules which are located next to the surfactant hydrophobic. The higher the disorder, the less defined the direction of the unfavorable polar/polar contact, and as a consequence the weaker it becomes. Thus the hydrophobic effect which drives the surfactant molecule “tail” out of the water phase is also reduced when temperature is increased, i.e., the CMC is increased (Crook et al., 1963; Schick, 1987). So that temperature of surfactant solutions used for removal of radium species is an important parameter in surfactant aided sludge washing process, and the experiments have been investigated with concentration of 1% TX100 and CTAB at 25e60 C. The results in Table 4 showed that, the removal of radium isotopes is increased with increasing temperature and the removal of radium species reaches a maximum at 60 C using both surfactants solutions. The increase of radium species removal efficiency is due to the properties of surfactants, where an increase in temperature generally results in an increase in the extent of solubility. The cloud point phenomenon occurs when a surfactant above its CMC causes the separation of the original solution into two phases when heated at a characteristic temperature called cloud point temperature. At this temperature, surfactant is no longer soluble in water and solution becomes hazy and cloudy. Above the cloud point, micelles formed from surfactant molecules act as an organic solvent in liquideliquid extraction and the analytes are partitioned between the micelles and aqueous phases (Lee et al., 2004). It has been mentioned that, the cloud point extraction procedure not only effectively
Ra. Table 4 Effect of temperature on the removal of 226Ra and 228Ra using surfactants solutions.
CTAB solution 228
Fig. 4. Schematic diagram of the variation of surface tension, interfacial and contaminant solubility with surfactant concentration. (Mulligan et al., 2001, Copyright © 2001 Elsevier).
228
Ra (R,%)
14.4 20.0 22.0 23.0 14.8 8.8
± ± ± ± ± ±
1.3 2.0 1.3 2.2 1.3 0.9
Temp., C
TX100 solution 226
25 35 45 60
Ra (R,%)
25.0 30.0 53.0 58.6
± ± ± ±
1.7 1.9 1.7 2.1
CTAB solution 228
Ra (R,%)
27.0 39.5 45.3 54.3
± ± ± ±
2.2 2.2 2.0 3.3
226
Ra (R,%)
26.0 28.6 43.5 49.8
± ± ± ±
1.9 2.2 2.7 3.8
228
Ra (R,%)
22.0 35.9 46.2 50.7
± ± ± ±
1.3 2.8 3.4 4.2
M.F. Attallah et al. / Journal of Environmental Radioactivity 139 (2015) 78e84
solubilization and concentrates pollutants, but also appears to offer a means to further the concentrated surfactant-enhanced wash solutions that have been used in soil treatment process (Abdul and Gibson, 1991). About 25% of the radium species were initially removed from the TENORM sludge by solubilization in surfactants solution (this was prior to temperature alteration). About 55e60% removal was achieved upon the temperature raise to 60 C. 3.2.4. Effect of mixed surfactants The efficiency of the surfactants in removing contaminant from solid phase was also dependent on the hydrophilic/hydrophobic structure of the surfactant molecule and CMC (Mulligan et al., 2001; Stalikas, 2002). Mixtures are usually preferred in commercial applications not only due to the increased expense with pure preparations but also because mixed systems often exhibit enhanced properties through synergism. Synergism in surfactants may be defined as any situation where mixtures of surfactants have superior properties when compared to the properties of any of the single surfactant alone (Lee et al., 2004). There is usually a synergy effect for the CMC of surfactant mixtures (mixture of nonionic and ionic surfactant) (Holmberg et al., 2003). Mixture of TX100 and CTAB surfactants showed synergistic interactions, which can be manifested as enhanced surface properties, spreading and many other phenomena, as shown in Fig. 5. The synergistic behavior of mixed surfactant systems can be exploited to reduce the total amount of surfactant used in a particular application resulting in the reduction of cost (Stalikas, 2002). It was observed that the removal values of radium isotopes of mixed systems of both surfactants are higher than their corresponding values without mixing, which indicate synergistic interaction in mixed CTAB-TX100 as a chemical extraction system. Removal of 84% and 80% for 226Ra and 228Ra, respectively, is obtained using synergistic effect of 1% aqueous solution containing 1:1 of the two surfactants investigated. In other words, mixed micelle formation in aqueous solution can be greater than that of the individual surfactant, and explained by non-ideal solution theory (Lee et al., 2004). 3.3. The mechanism of extractive washing The primary reason to use surfactants is to remove the pollutants in a short time period with less wash water required. Surfactants reduce the free energy of the systems by replacing the bulk
Fig. 5. Effect of synergism surfactant concentration on the removal of radium radionuclides.
83
molecules of higher energy at an interface. They are compounds that promote or increase the wetting, solubilization and emulsification of many types of organic and inorganic contaminants (Ahn et al., 2008; Mulligan et al., 2001, 1999). Two hypotheses have been offered to explain the mechanism behind surfactant enhanced soil washing. First, direct complexation between the surfactant used and solution phase metal effectively removes metal from solution and increases dissolution and desorption according to Le Chatelier's principle. The second is that surfactants can accumulate at the solid/liquid interface and interact with sorbed metals (Huibers and Shah, 1997). Mulligan et al. conclude that interaction of surfactant with the sludge allows direct interaction between the surfactant and the sorbed metal, thereby making it easier to release the sorbed metal (Mulligan et al., 2014, 1999). 4. Conclusion Surfactants are a type that promotes or increase the wetting, solubilization and emulsification of many types of organic and inorganic contaminants. Removal of metal species by surfactant is very interesting, but the research in this area is still quite limited for treatment of radioactive materials. Washing process removes radium radionuclides from TENORM sludge waste by dissolving or suspending them with surfactants solutions. Using washing, aqueous solutions containing the surfactants CTAB removed 22e26% and TX100 removed 25e27% of radium species. Higher solution temperature increases the removal efficiency of radium species due to the special properties of surfactants. Combined extraction of cationic and nonionic surfactants was effective in removal both 226Ra and 228Ra. Experiments indicated that removal efficiency was optimized (80e84%) when a mixture of 1% CTAB and 1% TX100 was employed at ratio 1:1. The theoretical justification for this surfactants solution is based upon two hypotheses, first that surfactant micelles may sequester radium radionuclides which are sorbed to the TENORM sludge waste, and second that the surfactant micelles may increase the concentration of radium radionuclides in the aqueous phase. The developed chemical treatment process would enable to design of an appropriate TENORM sludge washing strategy. References Abdul, A.S., Gibson, T.L., 1991. Laboratory studies of surfactant enhanced washing of polychlorinated biphenyl from sandy material. Environ. Sci. Technol. 25, 665. Ahn, C.K., Kim, Y.M., Woo, S.H., Park, J.M., 2008. Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon. J. Hazard. Mater. 154, 153. Al-Masri, M.S., Aba, A., 2005. Distribution of scales containing NORM in different oilfields equipment. Appl. Radiat. Isot. 63, 457. Attallah, M.F., Awwad, N.S., Aly, H.F., October 2012. Environmental radioactivity of TE-NORM waste produced from petroleum industry in Egypt: review on characterization and treatment. In: Natural Gas e Extraction to End Use. InTech. http://dx.doi.org/10.5772/CHAPTERDOI. Attallah, M.F., El Afifi, E.M., Awwad, N.S., Aly, H.F., 2013. Comparative study on the radioactivity of TENORM in different components of oil separator tanks. Radiochim. Acta 101, 57. Baeza, A., Corbacho, J.A., Guillen, J., Salas, A., Mora, J.C., 2011. Analysis of the different source terms of natural radionuclides in a river affected by NORM (naturally occurring radioactive materials) activities. Chemosphere 83, 933. Crook, E.H., Fordyce, D.B., Trebbi, G.F., 1963. Molecular weight distribution of nonionic surfactants. I. Surface and interfacial tension of normal distribution and homogeneous p,t-octylphenoxyethoxyethanols (OPE'S). J. Phys. Chem. 67, 1987. Desideri, D., Meli, M.A., Feduzi, L., Roselli, C., 2006. The importance of radiochemistry for the characterization of NORM and of environments contaminated by NORM. Int. J. Environ. Anal. Chem. 86, 601. El Afifi, E.M., Awwad, N.S., 2005. Characterization of the TENORM waste associated with oil and natural gas production in Abu Rudies, Egypt. J. Environ. Radioact. 82, 7. El Afifi, E.M., Awwad, N.S., Hilal, M.A., 2009. Sequential chemical treatment of radium species in TENORM waste sludge produced from oil and natural gas production. J. Hazard. Mater. 161, 907.
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