Removal of arsenic from smelting wastewater using Fe3O4 as an in situ Fe source: the effect of pre-dissolution and the evolution process of scorodite

Abstract

Arsenic (As) pollution is a serious worldwide problem that requires urgent attention, as this heavy metal poses a serious threat to both human and environmental health. Here, Fe₃O₄ was used as an in situ Fe source removal agent to study the effect of pre-dissolution time on arsenic removal by Fe₃O₄. Fe₃O₄ is uniquely well suited for the treatment of industrial wastewater due to its structural characteristics. Assays were conducted at a Fe/As molar ratio of 3 : 1, and these components were pre-dissolved at 23 °C for 2 h to establish the optimal initial conditions for Fe-mediated arsenic removal at a high temperature. The adsorption capacity of arsenic in the pre-dissolution stage was 143.99 mg g⁻¹. After adjusting the pH value to 2.5 and allowing the Fe and As to react at 90 °C for 24 h, 99.1% of the As was precipitated from the wastewater with an initial arsenic concentration of 8276.1 mg L⁻¹. The leaching of this As-bearing precipitate was as low as 0.3 mg L⁻¹. As a solid iron source, Fe₃O₄ provides a large number of nuclear sites for arsenic precipitation in the pre-dissolution stage and the high-temperature synthesis stage. At the same time, the supersaturation of the system was regulated by controlling the reaction and dissolution characteristics. Upon further characterization, the removal of As by Fe₃O₄ in the pre-dissolution process was attributed to a combination of physical adsorption and chemical precipitation.