Chlorine-free emission disposal of spent acid etchant in a three-compartment ceramic membrane reactor

Electrochemical technologies for the on-site treatment of spent acid etchant have received great attention due their ease of operation and economic benefits. On the other hand, a large amount of Cl₂ is generated during the electrolysis process, which leads to potential environmental risks. In the present work, a novel three-compartment ceramic membrane flow reactor, including a cathode chamber, an anode chamber, and a gas absorption chamber was developed. The three chambers were divided by an Al₂O₃ ceramic membrane and a breathable hydrophobic anode diffusion electrode (ADE). The Cl₂ evolution onset potential of the ADE was increased to 1.19 V from 1.05 V of the graphite felt, effectively inhibiting the chlorine evolution reaction (CER). The anode-generated Cl₂ diffused into the gas absorption chamber through the ADE and was eventually consumed by the H₂O₂ adsorbent. Cu could be recovered without emitting chlorine due to the special structure of reactor. The current efficiency of copper precipitation and cathode reduction from Cu²⁺ to Cu⁺ reached 97.7% at a working current of 150 mA. These results indicated that the novel membrane reactor had high potential for application in the copper recovery industry.