Regeneration of Foam Electrodes Used for for the Removal of Mercury from Aqueous Solutions

Abstract

Mercury is a heavy metal of great environmental concern. It possesses great environmental mobility and is highly toxic for both humans and wildlife. An electrochemical mercury decontamination technique that uses Pt-Hg alloy formation to collect mercury from aqueous sources has been developed and shows great promise and many advantages over existing techniques. The goal of this thesis is to study the regenerative capacity of platinum-coated foam electrodes used in this technique over decontamination cycles. Regeneration in this case refers to the re-release of mercury in the form of Hg-ions via the oxidation of Pt-Hg alloy. Using a three-electrode set-up in batch experiments, mercury was removed from 0.5 M sulphuric acid with a mercury concentration of 1000 ppb using a platinum-coated stainless steel foam. Mercury was also removed from contaminated concentrated sulphuric acid from a zinc smelter using a platinum-coated RVC foam. Unfortunately, complete regeneration was not achieved in any experiment, typically releasing less than half of the collected mercury. This partial regeneration is likely due to suboptimal experimental conditions. Despite this, the stability of the foams was demonstrated over multiple formations/regenerations. The problems identified also highlight possible ways forward for future research on the studied mercury decontamination technique. Decontamination with the RVC foam in concentrated sulphuric acid managed to reach mercury levels below the industry standard for high purity, something that has not been presented in previously published research.