Evidence for arsenic-driven redox chemistry in a wetland system: a field voltammetric study

Abstract

Environmental context.The speciation of the toxic element arsenic directly controls its environmental mobility and toxicity. The current study took place on site in an historic mine processing environment that is extremely arsenic-rich and comparatively sulfur-deficient. When arsenic is one of the major chemical components, redox state and pH of the chemical system are closely linked to arsenic speciation. Abstract.This study investigates the chemistry of the AsIII–AsV redox couple in association with As-rich processing residues (up to 40 wt%) from a historic gold mine in New Zealand. The site provides a unique natural laboratory of a sulfide-free chemical system driven by arsenolite dissolution. Field based cathodic stripping voltammetry, which circumvents post-sampling preservation issues, was successfully applied to analyse the AsIII to the microgram level. The AsIII–AsV redox couple, in particular the oxidation of AsIII, was found to have a noticeable influence on system pH and EH. The As redox pair itself is controlled by a range of processes, which were identified for the varying aqueous environments present on the studied site.