Arsenic removal from hydrometallurgical waste sulfuric acid via scorodite formation using siderite (FeCO3)

High concentration of arsenic (As) in waste sulfuric acid (WSA) generated from hydrometallurgical mineral processing must be removed and immobilized for protecting local environments. However, the economical and efficient treatment method for WSA is still lacking. We proposed the precipitation of As in WSA as scorodite by using economical siderite (FeCO3) as an Fe source through a three-step process. Firstly, the WSA is neutralized to pH similar to 1 with Ca(OH)(2) via precipitation of gypsum with low As content (similar to 7.1 x 10(-2) < 1 g/kg As). Secondly, As (III) in the WSA is oxidized to As(V) with H2O2. Thirdly, the produced As(V) is immobilized as scorodite through a mutual cycle composed of siderite dissolution-oxidation by O-2(g) and Fe(III)-As(V) precipitation-crystallization. Slow dissolution-oxidation of siderite produces a low supersaturation of Fe(III), ensuring the continuous Fe (III)-As(V) precipitation as well as scorodite crystallization. Under the optimal condition (pH(initial) = 1.1, Fe/As = 2, Temperature = 95 degrees C, and Time = 10 h), the removal efficiency of As in WSA reached up to 99.99%. The produced solid residue displayed a good stability with leaching As concentration as low as 0.13 mg/L via the TCLP methods due to the formation of different ferric arsenate minerals and the adsorption of As on undissolved siderite and FeOOH minerals. Our findings provide an economical method for safe treatment of As-bearing hydrometallurgical WSA and shed new light on the understanding of As-Fe precipitation in acidic solution.

Automated summary

The high concentration of arsenic in waste sulfuric acid must be removed and immobilized to protect the environment. The proposed method of precipitating arsenic as scorodite using siderite as an iron source is economical and efficient. The three-step process can achieve a high removal efficiency of arsenic from the waste sulfuric acid and produce a stable solid residue.