In-situ oxidative arsenic precipitation as scorodite during carbon catalyzed enargite leaching process

This study explores the in-situ precipitation of scorodite (FeAsO₄.2H₂O) during the atmospheric enargite leaching in acid chloride media. The temperature, oxygen sparging rate and the different fractions of the catalyst and ferric ions were the effective parameters on the scorodite precipitation process. Crystalline scorodite was precipitated out of the leach solution in the absence of seed at temperatures above 80 °C where the ratio of both AF5 to concentrate and activated carbon (AC) to concentrate were 1:1. The minimal dosage of ferric ions to form the scorodite residue was 5 g/L. Seed addition facilitated the scorodite precipitation process where the primary scorodite particles precipitated after 6 h of enargite leaching. Via this process it was shown that the residual concertation of arsenic in the pregnant leach solution can be reduced as low as 50 mg/L. A series of the toxicity characteristic leaching procedure (TCLP) tests on the generated scorodite exhibited a low arsenic release ranging from 0.2 to 0.7 mg/L, showing an acceptable stability of the scorodite in the residue.