Removal of Arsenic from Wastewaters by Airlift Electrocoagulation. Part 1: Batch Reactor Experiments

Abstract

Arsenic removal from wastewater is a key problem for copper smelters. This work shows results of electrocoagulation in aqueous solutions containing arsenic in a newly designed and constructed 1 L batch airlift reactor. Iron electrodes were used in the cell. The airlift electrocoagulation reactor allowed simultaneously a) anodic Fe2+ production, b) Fe2+ to Fe3+ oxidation by air or oxygen, and c) precipitate/coagulate formation due to the turbulent conditions in the cell. A series of electrocoagulation experiments were carried out in the batch airlift reactor. The variables were: initial As(V) concentration, use of either a pure oxygen or an air flow, and electric current density. The results showed that the airlift electrocoagulation process could reduce an initial As concentration from 1000 mg L−1 to 40 mg L−1–corresponding to a reduction of 96%. At higher initial concentrations (e.g. 5000 mg L−1 As) the oxidation of Fe2+ to Fe3+ seems to be rate determining. Oxidation with compressed oxygen was clearly more efficient than air at high initial As concentration. Arsenate removal from a solution with initially 100 mg L−1 was efficient with both air and oxygen addition–more than 98% of As precipitated. When the electrocoagulation process was working efficiently, the arsenic removal rate in the cell was found to be around 0.08–0.1 mg As/C. The Fe‐to‐As (mol/mol) ratio, when electrocoagulation was working properly, was in the range of 4–6.