Arsenic speciation and mobility in mine wastes from a copper–arsenic mine in Devon, UK: a SEM, XAS, sequential chemical extraction study

Abstract

The nature of As speciation is a determining factor for As mobility in mine wastes. In this study, scanning electron microscopy (SEM), X-ray absorption spectroscopy and sequential chemical extraction methods were used for the environmental, mineralogical and genetic characterisation of mine spoil and calciner wastes from Devon Great Consols Mine, an abandoned copper-arsenic mine in Devon, UK. The geochemical control of As-bearing phases on dissolved As during leaching was investigated.Arsenic is mainly present as As(V) co-precipitated or adsorbed with, or on, iron oxyhydroxides. The water extracts from the mine spoil and calciner wastes indicated a generally low dissolution of As, especially in sandy tailings (As water soluble 0.0004% of total As content). Thermodynamic calculations did not identify a major As phase controlling the composition of the water leachates, which suggests a process of desorption of iron oxyhydroxide-bound As as the source of As in the solution. A relative higher As mobility (As water soluble 3.7% of total As content) was found in the waste material with an alkaline pH in the vicinity of the ore crusher. Available thermodynamic data supported by SEM evidence and chemical extraction data suggest that calcium-arsenate phases such as weillite (CaHAsO 4 ) and calcium-copper arsenates together with scorodite (FeAsO 4 Á2H 2 O) and iron oxyhydroxides may all contribute to the higher As content in the alkaline waste leachates. The results indicate the importance of considering the nature of As in mine waste management. IntroductionEngland has a legacy of metalliferous mining possibly extending back to Roman times. A knowledge of the evolution of mine wastes and dispersion patterns is required to reduce concern in respect of the health hazard Trace Metals and other Contaminants in the Environment, Volume 9, 431-460