Arsenic immobilization from high-As sulfide copper ores through high-pressure leaching with ferric and sodium chloride media

The processing of high-impurity ores has become increasingly common in recent years. Enargite (Cu 3 AsS 4 ) is an important source of copper, but it is notorious for its high arsenic content, posing serious environmental concerns. This study explores the potential of a high-pressure leaching system for treating high-arsenic-containing copper ores. The leaching behavior of enargite was studied to elucidate the role of ferric sulfate and NaCl in enhancing the dissolution of enargite and the fixation of As in the residue. Under optimized leaching conditions of 160 °C, 1.0 MPa, 0.1 mol/L Fe 2 (SO 4 ) 3 , and 0.34 mol/L NaCl, excellent copper extractions (97 %) and immobilization of arsenic (98 %) was achieved. The Fe/As ratio in the feed significantly influenced arsenic removal minerals, with lower ratios of less than 1 favoring scorodite precipitation, while higher ratios (Fe/As > 1) promoted arsenic removal through sorption and co-precipitation with natrojarosite. Sodium chloride addition enhanced natrojarosite precipitation, reducing the total dissolved iron in the leachate. Arsenic attenuation onto jarosite was found to be difficult to form in the absence of NaCl and was more effective with mixed minerals (enargite, chalcopyrite, and pyrite) as opposed to only enargite. A relationship was established between Fe and free acidity in the leachate when NaCl was used, with a correlation coefficient of 0.992. Additionally, a correlation coefficient of 0.921 was obtained between final Fe and As concentrations in the leachate suggesting that As tenors can be managed by controlling free acidity. Evaluation of the environmental stability of the leach residue using the TCLP test showed an As leachability of 5.84 mg/L. • High-pressure leaching yielded 97 % Cu extractions and fixed 98 % As as scorodite. • The role of added Na + and Cl - ions in the leaching process was revealed. • High pyrite content can act as a major oxidant and catalyst for enargite leaching. • The relationship between As, Fe, and free acidity in the leachate was established. • Environmental stability of leach residues for As elution was conducted.