Limonite as a source of solid iron in the crystallization of scorodite aiming at arsenic removal from smelting wastewater

Abstract

Removal of arsenic from aqueous solution in the form of scorodite is one of the promising processes for the disposal of arsenic-containing wastewater. While it suffers from the strict reaction conditions including high Fe/As molar ratio, narrow pH range, and low Fe/As supersaturation when the liquid iron sources of Fe2+/Fe3+ are used as the iron sources. We proposed to use limonite as an in situ solid iron source to promote scorodite crystallization via heterogeneous nucleation for the effective removal of arsenic from high-arsenic smelting wastewater. Under the condition of 90 °C, limonite dosage at an Fe/As molar ratio of 4 and pH of 1.5, 99.6% of arsenic in the smelting wastewater (As 10300 mg/L and sulphuric acid 72500 mg/L) was precipitated in the form of well-crystallized and environmentally stable scorodite with a particle size around 4.6 μm. Limonite acts as an in situ iron donator and seeds, allowing a low iron supersaturation in the solution during the arsenic precipitation and transformation into scorodite. Moreover, the residual arsenic concentration in the filtrate obtained from the abovementioned scorodite synthesis could be further lowered to 0.1 μg/L using fresh limonite in virtue of its high arsenic adsorbability. The proposed process shows a great potential for the arsenic removal from smelting wastewater, which will advance the large-scale disposal of arsenic-bearing wastewater and provide an important insight into the application of solid iron source for scorodite synthesis and arsenic fixation.