A novel arsenic immobilization strategy via a two-step process: Arsenic concentration from dilute solution using schwertmannite and immobilization in Ca–Fe–AsO4 compounds

Park, Ilhwan; Ryota, Takashino; Yuto, Takeuchi; Tabelin, Carlito Baltazar; Phengsaart, Theerayut; Jeon, Sanghee; Ito, Mayumi; Hiroyoshi, Naoki

A novel arsenic immobilization strategy via a two-step process: Arsenic concentration from dilute solution using schwertmannite and immobilization in Ca–Fe–AsO4 compounds

2021

Acid mine drainage (AMD) with toxic arsenic (As) is commonly generated from the tailings storage facilities (TSFs) of sulfide mines due to the presence of As-bearing sulfide minerals (e.g., arsenopyrite, realgar, orpiment, etc.). To suppress As contamination to the nearby environments, As immobilization by Ca–Fe–AsO₄ compounds is considered one of the most promising techniques; however, this technique is only applicable when As concentration is high enough (>1 g/L). To immobilize As from wastewater with low As concentration (~10 mg/L), this study investigated a two-step process consisting of concentration of dilute As solution by sorption/desorption using schwertmannite (Fe₈O₈(OH)₈–₂ₓ(SO₄)ₓ; where (1 ≤ x ≤ 1.75)) and formation of Ca–Fe–AsO₄ compounds. Arsenic sorption tests indicated that As(V) was well adsorbed onto schwertmannite at pH 3 (Qₘₐₓ = 116.3 mg/g), but its sorption was limited at pH 13 (Qₘₐₓ = 16.1 mg/g). A dilute As solution (~11.2 mg/L As) could be concentrated by sorption with large volume of dilute As solution at pH 3 followed by desorption with small volume of eluent of which pH was 13. The formation of Ca–Fe–AsO₄ compounds from As concentrate solution (2 g/L As(V)) was strongly affected by temperature and pH. At low temperature (25–50 °C), amorphous ferric arsenate was formed, while at high temperature (95 °C), yukonite (Ca₂Fe₃–₅(AsO₄)₃(OH)₄–₁₀·xH₂O; where x = 2–11) and johnbaumite (Ca₅(AsO₄)₃OH) were formed at pH 8 and 12, respectively. Among the synthesized products, johnbaumite showed strongest As retention ability even under acidic (pH < 2) and alkaline (pH > 9) conditions.

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