Abstract:The alkaline leaching of arsenic (As₂O₃) by Na₂S, together with its precipitation by Fe₂(SO₄)₃ was studied. Response surface methodology based on central composite design was employed to quantify and qualify the effect of pertinent factors and to develop statistical models for optimization purposes. Based on the obtained results, 89% of arsenic is removed from the dust under following optimum predicted conditions: Na₂S concentration of 100 g/L and solid to liquid ratio of 0.163 g/mL at 80 °C. It is found that solid to liquid ratio and Na₂S concentration are the significant factors influencing the leaching process. In the precipitation process, more than 99.93% of arsenic from the leaching solution is removed in the form of amorphous ferric arsenate, at pH 4.8 when Fe³⁺ to arsenic and H₂O₂ to arsenic molar ratios are set at 5:1 and 4:1, respectively. Also, Fe³⁺ to arsenic ratio and pH are the most significant factors, and the interaction between these terms is significant.

Key words: flue dust; arsenic; response surface methodology; alkaline leaching; precipitation