TY - JOUR

T1 - Alkali Extraction of Arsenic from Groundwater Treatment Sludge

T2 - An Essential Initial Step for Arsenic Recovery

AU - Wang, Kaifeng

AU - Holm, Peter E.

AU - van Genuchten, Case M.

N1 - Funding Information: This work was supported by a Start-up Grant from GeoCenter Denmark and by a Project1 Grant (Thematic Research for the Green Transition) from the Independent Research Fund Denmark (project no. 1127-00207B). Kajsa Sigfridsson Clauss and Susan Nehzati at MAX IV are thanked for support during XAS data collection. We acknowledge MAX IV Laboratory for time on the Balder beamline under Proposal 20221096. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III, and we would like to thank Edmund Welter for assistance in using the P.65 beamline.

PY - 2024

Y1 - 2024

N2 - Arsenic (As)-bearing Fe(III) precipitate groundwater treatment sludge has traditionally been viewed by the water sector as a disposal issue rather than a resource opportunity, partly due to assumptions of the low value of As. However, As has now been classified as a Critical Raw Material (CRM) in many regions, providing new incentives to recover As and other useful components of the sludge, such as phosphate (P) and the reactive hydrous ferric oxide (HFO) sorbent. Here, we investigate alkali extraction to separate As from a variety of field and synthetic As-bearing HFO sludges, which is a critical first step to enable sludge upcycling. We found that As extraction was most effective using NaOH, with the As extraction efficiency increasing up to >99% with increasing NaOH concentrations (0.01, 0.1, and 1 M). Extraction with Na2CO3 and Ca(OH)2 was ineffective (<5%). Extraction time (hour, day, week) played a secondary role in As release but tended to be important at lower NaOH concentrations. Little difference in As extraction efficiency was observed for several key variables, including sludge aging time (50 days) and cosorbed oxyanions (e.g., Si, P). However, the presence of ∼10 mass% calcite decreased As release from field and synthetic sludges considerably (<70% As extracted). Concomitant with As release, alkali extraction promoted crystallization of poorly ordered HFO and decreased particle specific surface area, with structural modifications increasing with NaOH concentration and extraction time. Taken together, these results provide essential information to inform and optimize the design of resource recovery methods for As-bearing treatment sludge.

AB - Arsenic (As)-bearing Fe(III) precipitate groundwater treatment sludge has traditionally been viewed by the water sector as a disposal issue rather than a resource opportunity, partly due to assumptions of the low value of As. However, As has now been classified as a Critical Raw Material (CRM) in many regions, providing new incentives to recover As and other useful components of the sludge, such as phosphate (P) and the reactive hydrous ferric oxide (HFO) sorbent. Here, we investigate alkali extraction to separate As from a variety of field and synthetic As-bearing HFO sludges, which is a critical first step to enable sludge upcycling. We found that As extraction was most effective using NaOH, with the As extraction efficiency increasing up to >99% with increasing NaOH concentrations (0.01, 0.1, and 1 M). Extraction with Na2CO3 and Ca(OH)2 was ineffective (<5%). Extraction time (hour, day, week) played a secondary role in As release but tended to be important at lower NaOH concentrations. Little difference in As extraction efficiency was observed for several key variables, including sludge aging time (50 days) and cosorbed oxyanions (e.g., Si, P). However, the presence of ∼10 mass% calcite decreased As release from field and synthetic sludges considerably (<70% As extracted). Concomitant with As release, alkali extraction promoted crystallization of poorly ordered HFO and decreased particle specific surface area, with structural modifications increasing with NaOH concentration and extraction time. Taken together, these results provide essential information to inform and optimize the design of resource recovery methods for As-bearing treatment sludge.

KW - Arsenic recovery

KW - Critical raw materials

KW - Synchrotron X-ray characterization

KW - Waste management

KW - Waste upcycling

KW - Water treatment residuals

KW - Arsenic recovery

KW - Critical raw materials

KW - Synchrotron X-ray characterization

KW - Waste management

KW - Waste upcycling

KW - Water treatment residuals

U2 - 10.1021/acs.est.4c00939

DO - 10.1021/acs.est.4c00939

M3 - Journal article

C2 - 38857431

AN - SCOPUS:85196141473

VL - 58

SP - 11175

EP - 11184

JO - Environmental Science &amp; Technology

JF - Environmental Science &amp; Technology

SN - 0013-936X

IS - 25

ER -