EARTH

[3913-23-07] Effect of complicated arsenic calcium residue pretreatment on the stabilization of arsenic

○Jiangchi Fei¹, Jingjing Ma¹, Xiaobo Min¹, Liyuan Chai¹, Yanjie Liang¹ (1. Central South University)

Chairman: Carlito Tabelin （Hokkaido University）

Keywords:Calcium arsenic residue, Leaching, Stabilization, BCR sequential extraction, Toxicity characteristic leaching procedure (TCLP)

Complicated arsenic calcium residue (CACR), produced after the lime neutralization of arsenic-containing wastewater, typically has high content of arsenic in the form of complex calcium arsenic compounds which pose serious arsenic pollution risk. The pretreatments of CACR before cement curing is benificial for the traditional stabilization/solidification procedure. In this study, the unstable calcium arsenic compounds in the CACR were firstly removed using leaching treatment, then adding crystallization agent to promote the stable transformation of the remaining calcium arsenic compounds. Results of the leaching process demonstrated that the cumulative content of arsenic leaching increased with the decreasing particle sizes of CACR, as well as the decrease of pH values. The crystallization process declined the arsenic concentration to 4.38 mg/L. The SEM and XRD patterns proved that leaching-crystallization process transformed the phase of Ca₄(OH)₂(AsO₄)₂·4H₂O into Ca₅(AsO₄)₃OH, while the latter is more stable in the environment. Therefore, the leaching-crystallization process is of great significance for the effective control of the long-term stability of arsenic residue.