Double-pathway arsenic removal and immobilization from high arsenic-bearing wastewater by using nature pyrite as in situ Fe and S donator

Abstract

Nonferrous smelting wastewaters containing high levels of arsenic and sulfuric acid threaten human health and ecological environments due to insufficient disposal technologies and/or possible leakages during transportation to long-term storage facilities. Chemical precipitation is one important route for arsenic removal and immobilization via the formation of arsenic-stabilized minerals. In this study, we propose a new strategy for the treatment of wastewaters containing high levels of arsenic using pyrite as an in situ S and Fe source to prepare environmentally friendly scorodite and As2S3 precipitates. Dissolved pyrite release (S-II) and Fe (II) ions in highly acidic wastewater, both of which drive arsenic precipitation. Sulfide ions readily react with As(III) to generate the stable As2S3 while Fe(II)/As(III) were oxidized to Fe(III)/As(V) by H2O2. The reaction between Fe(III) and As(V) took place on the pyrite surface as a nucleation site to form amorphous ferric arsenate that ultimately transformed into crystalline scorodite. Sulfide ions were oxidized to H2SO4 that further promoted pyrite dissolution. Up to 99.4% of arsenic was successfully removed from copper smelting wastewaters with an initial arsenic concentration of 11200 mg/L. The concentration of leached As from the As-bearing precipitate was 1.78 mg/L under optimized conditions, which were: a 1.4 FeS2/As molar ratio, an initial solution pH of 2, an H2O2/As molar ratio of 1%, a reaction temperature of 90 °C, and a reaction time of 12 h. In summary, a prospective process successfully shows arsenic removal and immobilization from smelting wastewater, and further demonstrates the potential for the efficient and affordable disposal of wastewater.