Accepted Manuscript Title: Mechanisms of mercury removal by biochars produced from different feedstocks determined using X-ray absorption spectroscopy Author: Peng Liu Carol J. Ptacek David W. Blowes Richard C. Landis PII: DOI: Reference:
S0304-3894(16)30007-3 http://dx.doi.org/doi:10.1016/j.jhazmat.2016.01.007 HAZMAT 17359
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
14-10-2015 17-12-2015 5-1-2016
Please cite this article as: Peng Liu, Carol J.Ptacek, David W.Blowes, Richard C.Landis, Mechanisms of mercury removal by biochars produced from different feedstocks determined using X-ray absorption spectroscopy, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.01.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mechanisms of Mercury Removal by Biochars Produced from Different Feedstocks Determined using X-ray Absorption Spectroscopy Peng Liua, Carol J. Ptaceka* [email protected], David W. Blowesa, Richard C. Landisb a
Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada N2L 3G1 b E. I. du Pont de Nemours and Company, 974 Centre Road, Wilmington, DE 19805 * Corresponding author at: Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada N2L 3G1. Tel: +01 (519) 888 4567, ext. 32230.
1
Highlights
Dissolved Hg decreases by >90% with high-T biochars (600 and 700 oC)
Elevated SO42- (up to 1000 mg L-1) is released from manure-derived biochar
XRF results indicate Hg is distributed heterogeneously throughout biochar particles
S XANES indicates presence of reduced and oxidized S species in biochar
Hg EXAFS indicate Hg is bound to S atoms in biochar particle when S content is high
2
Abstract Thirty-six biochars produced from distinct feedstocks at different temperatures were evaluated for their potential to remove mercury (Hg) from aqueous solution at environmentally relevant concentrations. Concentrations of total Hg (THg) decreased by >90% in batch systems containing biochars produced at 600 and 700 °C and by 40-90% for biochars produced at 300 °C. Elevated concentrations of SO42- (up to 1000 mg L-1) were observed in solutions mixed with manure-based biochars. Sulfur X-ray absorption near edge structure (XANES) analyses indicated the presence of both reduced and oxidized S species in both unwashed and washed biochars. Sulfur XANES spectra obtained from biochars with adsorbed Hg were similar to those of washed biochars. Micro-X-ray fluorescence mapping results indicate that Hg was heterogeneously distributed across biochar particles. Extended X-ray absorption fine structure modeling indicates Hg was bound to S in biochars with high S content and to O and Cl in biochars with low S content. The predominant mechanisms of Hg removal are likely the formation of chemical bonds between Hg and various functional groups on the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications for stabilization of Hg in surface water, groundwater, soils, and sediments.
Keywords: Mercury; biochar; black carbon; sulfur; X-ray absorption spectroscopy
3
1. Introduction Large volumes of solid-phase reactive materials are required in treatment systems to control the release of metals and other contaminants to the environment. For example, construction of permeable reactive barriers [1, 2], containerized treatment systems [3, 4], and alternative treatment wetlands [5-7] all require use of large volumes of adsorbents, reductants, or other treatment materials. Biochar and other carbonaceous materials are widely used as treatment materials to remove a range of metals (e.g., As, Cd, Cr, Cu, Ni, Pb, Zn) and organic contaminants from aqueous solutions [8-13]. Biochar has also been evaluated with respect to Hg stabilization [1416]. The majority of Hg removal studies have focused on the determination of sorption isotherms, kinetic rate constants, or factors influencing sorption. Most of the studies have been conducted in experimental systems with relatively high initial Hg concentrations (5-2000 mg L-1) [16-19], which is typical of industrial wastewater but much higher than commonly observed in the environment. Additional studies have been conducted for Hg removal at environmental concentrations [20-24]. For example, Klasson et al. [23] and Hollerman et al. [22] reported that Hg concentrations decreased from 1 µg L-1 to
S0304-3894(16)30007-3 http://dx.doi.org/doi:10.1016/j.jhazmat.2016.01.007 HAZMAT 17359
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
14-10-2015 17-12-2015 5-1-2016
Please cite this article as: Peng Liu, Carol J.Ptacek, David W.Blowes, Richard C.Landis, Mechanisms of mercury removal by biochars produced from different feedstocks determined using X-ray absorption spectroscopy, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.01.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mechanisms of Mercury Removal by Biochars Produced from Different Feedstocks Determined using X-ray Absorption Spectroscopy Peng Liua, Carol J. Ptaceka* [email protected], David W. Blowesa, Richard C. Landisb a
Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada N2L 3G1 b E. I. du Pont de Nemours and Company, 974 Centre Road, Wilmington, DE 19805 * Corresponding author at: Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada N2L 3G1. Tel: +01 (519) 888 4567, ext. 32230.
1
Highlights
Dissolved Hg decreases by >90% with high-T biochars (600 and 700 oC)
Elevated SO42- (up to 1000 mg L-1) is released from manure-derived biochar
XRF results indicate Hg is distributed heterogeneously throughout biochar particles
S XANES indicates presence of reduced and oxidized S species in biochar
Hg EXAFS indicate Hg is bound to S atoms in biochar particle when S content is high
2
Abstract Thirty-six biochars produced from distinct feedstocks at different temperatures were evaluated for their potential to remove mercury (Hg) from aqueous solution at environmentally relevant concentrations. Concentrations of total Hg (THg) decreased by >90% in batch systems containing biochars produced at 600 and 700 °C and by 40-90% for biochars produced at 300 °C. Elevated concentrations of SO42- (up to 1000 mg L-1) were observed in solutions mixed with manure-based biochars. Sulfur X-ray absorption near edge structure (XANES) analyses indicated the presence of both reduced and oxidized S species in both unwashed and washed biochars. Sulfur XANES spectra obtained from biochars with adsorbed Hg were similar to those of washed biochars. Micro-X-ray fluorescence mapping results indicate that Hg was heterogeneously distributed across biochar particles. Extended X-ray absorption fine structure modeling indicates Hg was bound to S in biochars with high S content and to O and Cl in biochars with low S content. The predominant mechanisms of Hg removal are likely the formation of chemical bonds between Hg and various functional groups on the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications for stabilization of Hg in surface water, groundwater, soils, and sediments.
Keywords: Mercury; biochar; black carbon; sulfur; X-ray absorption spectroscopy
3
1. Introduction Large volumes of solid-phase reactive materials are required in treatment systems to control the release of metals and other contaminants to the environment. For example, construction of permeable reactive barriers [1, 2], containerized treatment systems [3, 4], and alternative treatment wetlands [5-7] all require use of large volumes of adsorbents, reductants, or other treatment materials. Biochar and other carbonaceous materials are widely used as treatment materials to remove a range of metals (e.g., As, Cd, Cr, Cu, Ni, Pb, Zn) and organic contaminants from aqueous solutions [8-13]. Biochar has also been evaluated with respect to Hg stabilization [1416]. The majority of Hg removal studies have focused on the determination of sorption isotherms, kinetic rate constants, or factors influencing sorption. Most of the studies have been conducted in experimental systems with relatively high initial Hg concentrations (5-2000 mg L-1) [16-19], which is typical of industrial wastewater but much higher than commonly observed in the environment. Additional studies have been conducted for Hg removal at environmental concentrations [20-24]. For example, Klasson et al. [23] and Hollerman et al. [22] reported that Hg concentrations decreased from 1 µg L-1 to
