Abstract
This study investigates the chemistry of the As-III-As-V 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 As-III to the microgram level. The As-III-As-V redox couple, in particular the oxidation of As-III, was found to have a noticeable influence on system pH and E-H. 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.