Removal and stabilization of arsenic from anode slime by forming crystal scorodite

Abstract

A process was proposed for removing and stabilizing arsenic (As) from anode slime. The anode slime with high arsenic concentration was pretreated by circular alkaline leaching process. Then, the arsenic in the leaching solution can be further precipitated as a form of scorodite crystalline (FeAsO4·2H2O). In the precipitating arsenic reaction, in which ferrous ions were oxidized by air gas, the effects of acidity (pH), reaction temperature, air flow rate, initial concentration of arsenic and initial molar ratio of Fe(II) to As(V) on arsenic precipitation were investigated. The results showed that sufficiently stable crystal scorodite could be achieved under the condition of initial arsenic concentration of 10 g/L, pH 3.0–4.0, Fe/As molar ratio of 1.5, the temperature of 80–95 °C, and the air flow rate higher than 120 L/h. Under the optimal condition, more than 78% of arsenic could be precipitated as a form of scorodite crystalline. The As leaching concentration of the precipitates was less than 2.0 mg/L and the precipitates may be considered to be safe for disposal.