China Nonferrous Metallurgy

The smelting waste acid contains a large amount of arsenic. Currently, the conventional approach to arsenic removal involves the use of a sulfide-lime neutralization method for iron salts. However, this method is associated with high costs, environmental concerns, and a substantial burden on the system. The primary cause of these issues is the high solubility of the sulfide agent in the waste acid, which hinders its effectiveness in arsenic removal. This paper presents a slow-release arsenic removal technique using zinc sulfide (ZnS). The study is based on E-pH analysis of the test conditions, ZnS arsenic removal kinetics, and in-depth characterization of the reaction products to explore the ZnS arsenic removal mechanism. The main conclusions are as follows: In the As-S-H2O system, when the pH value is less than 2, arsenic ions are found to be in the stable existence region of As2S3. The most effective process conditions for arsenic removal by ZnS retardant are determined to be a S/As substance amount ratio of 7.5, a reaction temperature of 80℃, and a reaction time of 240 minutes. Under these conditions, the arsenic removal rate reaches 98.42%, and the arsenic content in the waste acid is reduced from 1017mg/L to 16.04mg/L. The reaction rate of ZnS in removing arsenic from waste acid follows a mixed diffusion model, with an apparent activation energy of 28.29kJ/mol. ZnS is a spherical particle with a rough surface and a large specific surface area, and arsenic in the waste acid adheres to the surface of ZnS in the form of As2S3 precipitation after the reaction. This process takes advantage of the dissolution characteristics of zinc sulfide, slowly releasing S2- to remove arsenic from the waste acid. It avoids the introduction of sodium ions, reduces the burden on the system, and lowers environmental risks, effectively removing arsenic from the waste acid. This provides a new approach for the treatment of waste acid.