Precipitation of arsenic as Na3AsS4 from Cu3AsS4–NaHS–NaOH leach solutions

This study investigates the feasibility of a precipitation process for the removal of arsenic from highly alkaline enargite leaching solutions in the Cu3AsS4–NaHS–NaOH system and regeneration of the leaching reagents. The main objective was to reduce elemental sulfur and subsequently oxidize arsenite (As (III)) to arsenate (As (V)) for the formation and precipitation of Na3AsS4. First, solutions with over 35 g/L As were prepared with either arsenic trisulfide (As2S3) or enargite (Cu3AsS4) in the NaHS–NaOH system. These solutions were conditioned at 90 °C followed by addition of elemental sulfur and fast cooling to 30 °C for precipitate formation. The effect of elemental sulfur addition (sulfur/arsenic ratio), NaHS and NaOH concentrations and times for conditioning and precipitation were evaluated, as well as the recirculation of the mother liquor containing arsenic with leach reagents. sults showed that conditioning solution with high arsenic concentration at 90 °C in NaHS (100–250 g/L) and NaOH (50–100 g/L), and sulfur addition at 1/2 wt of arsenic in solution for 1–2 h followed by fast cooling to 30 °C and conditioning for 3–5 h reduced arsenic concentration in solution by over 60%. Characterization by XRD showed Na3AsS4 as the dominant phase. Starting solutions prepared from As2S3 and Cu3AsS4 produced similar results. The recirculation of process filtrates for re-use in enargite leaching continued to give reproducible leaching results.