Arsenic ( As ) -bearing gypsum sludge, one of the biggest As-bearing wastes, has seriously threatened ecological security due to the great mobility and leaching toxicity of As. Unfortunately, most of this sludge was discharged into tailing ponds without treatment. In this paper, a novel co-process of As-bearing gypsum sludge, waste carbon cathode (WCC) and Fe powder for simultaneous separation and solidification of As is proposed via reduction-magnetic separation. In the reduction process, Ca 3 (AsO 4 ) 2 was reduced and then enriched to α-Fe (Fe-As solid solution), and the As solidification ratio reached 90.5%. Meanwhile, NaF in waste carbon cathodes was transformed into CaF 2 and NaCa 2 FSiO 4 . The As and F leached content were only 0.053 mg/L and 3.10 mg/L, when evaluated using the toxicity characteristic leaching procedure. After magnetic separation, α-Fe (magnetic phase) was separated and recovered, and the weight and volume losses of As-bearing waste were 70% and 60%, respectively, compared with the raw material. The As residual content in the non-magnetic phase met the standard of solid waste (As < 0.1 wt%), which acted as a flux during the smelting process, minimizing the environmental risk and realizing resource recycling. Moreover, waste carbon cathodes can be reused as fuel and as a reducing agent, which significantly reduces production costs. This proposed technique reduces hazardous waste, is more effective, and is also more economical.
Tin-bearing middling, a hazardous solid waste produced during beneficiation of tin deposits and tin-bearing tailings, presents a serious environmental pollution risk due to high levels of As. This paper aims to explore an environmentally friendly technology to reduce toxic substances and prepare a high value-added bronze material from tin-bearing middling. The co-process for tin-bearing middling, anthracite , and copper is first proposed at 1073–1123 K. Variables like temperature, amount of added anthracite, and holding time were optimized. Those results showed that 95.56% Sn and 92.79% As were recovered; levels of Fe in the residue reached 73.52 wt%. During roasting, SnO 2 in the tin-bearing middling was initially transformed into SnO(g), then into an Fe–Sn spinel (Fe 3-x Sn x O 4 ) and Ca 2 SnO 4 , and finally a Cu–Sn alloy. Generation of the Fe–Sn spinel came primarily from substitution of Fe 2+ by Sn 2+ , but small amounts of Sn 4+ replaced Fe 3+ in Fe 3 O 4 . Meanwhile, FeAsS and FeAsO 4 were initially transformed into As 4 (g) and then solidified as a Cu–As alloy. Interestingly, the residual As existed as Fe–As alloy, but As leaching levels did not exceed 0.02 mg/L. After initial treatment, the Cu alloy can be prepared for bronze. Meanwhile, subsequent volatilization and solidification of As resulted in a significant reduction of arsenic-bearing waste that minimizes environmental risk.
Zongqiang Zhu,Hongqu Yang,Jie Liu,Yinian Zhu,Shen Tang,Lihao Zhang,Xingxing Wang
Basic ferric sulfate-arsenates [FeSAsOH, Fe(SO 4 ) x (AsO 4 ) y (OH) z ·nH 2 O] were prepared and characterized to study their potential fixation of arsenic in the oxidizing and acidic environment through a dissolution for 330d. The synthetic solids were well-shaped monoclinic prismatic crystals. For the dissolution of the sample FeSAsOH–1 [Fe(SO 4 ) 0.27 (AsO 4 ) 0.73 (OH) 0.27 ·0.26H 2 O] at 25–45°C and initial pH 2, all constituents preferred to be dissolved in the order of AsO 4 3− > SO 4 2− > Fe 3+ in 1–3 h, in the order of SO 4 2− > AsO 4 3− > Fe 3+ from 1–3 h to 12–24 h, and finally in the order of SO 4 2− > Fe 3+ > AsO 4 3− . The released iron, sulfate, and arsenate existed dominantly as Fe 3+ /Fe(OH) 2+ /FeSO 4 + , HSO 4 − /SO 4 2− /FeSO 4 + , and H 3 AsO 4 0 /H 2 AsO 4 − , respectively. The higher initial pHs (6 and 10) could obviously inhibit the release of Fe 3+ from solid into solution, and the solid components were released in the order of SO 4 2− > AsO 4 3− > Fe 3+ . The crystal tops were first dissolved, and the crystal surfaces were gradually smoothed/rounded until all edges and corners disappeared. The dissociations were restricted by the Fe-O(H) breakdown in the FeO 6 octahedra and obstructed by the OH − and AsO 4 tetrahedra outliers; the lowest concentration of the dissolved arsenic was 0.045 mg/L. Based on the dissolution experiment at 25°C and pH 2, the solubility products ( K sp ) for the basic ferric sulfate-arsenate [Fe(SO 4 ) 0.27 (AsO 4 ) 0.73 (OH) 0.27 ·0.26H 2 O], which are equal to the ion activity products (logˍIAP) at equilibrium, were calculated to be -23.04 ± 0.01 with the resulting Gibbs free energies of formation (Δ G f o ) of −914.06 ± 0.03 kJ/mol.
危险品化学品经营许可证（带存储）