China Nonferrous Metallurgy

The lime-iron salt process is usually used in the treatment of arsenic-bearing acidic wastewater, and it has the advantages of fewer kinds of reagent to be added, high precipitation efficiency, stable and qualified discharge of wastewater, low running cost, easy operation, etc. In this paper, the reaction mechanism and influence factors of this process are elaborated and summary is made for this process. When the pH value of the reaction liquid is set as 7-8, the oxidizing reaction of Fe²⁺ is high with the best arsenic removal effect; the molar ratio of Fe/As of the reaction liquid is generally 5-10, which is conducive to iron arsenate formation and accelerates flocculation; the partial sediment returning method adopted can play a role of crystal nucleus for the reaction process; in this way, not only the precipitation velocity of the neutralized residue can be raised, but also the reagents can be saved with the volume of neutralized residue reduced. The engineering practice shows that this process can efficiently treat the arsenic-bearing acidic wastewater from copper smelter, the efficiency for removing Cu, Pb, Zn and As can be stably up to 99% or more. In addition, the As in the neutralized residue is in form of pentavalent arsenate and the concentration of toxic leaching is less than 5 mg/L, which can be safely stored in residue pond.