Removal of arsenic from wastewaters by airlift electrocoagulation. Part 1: Batch reactor experiments

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 1L 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 1000mgL(-1) to 40mgL(-1)-corresponding to a reduction of 96%. At higher initial concentrations (e.g. 5000mgL(-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 100mgL(-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 0.08-0.1mg As/C. The Fe-to-As (mol/mol) ratio, when electrocoagulation was working properly, was in the range of 4-6.