Routine determination of inorganic arsenic speciation in precipitates from acid mine drainage using orthophosphoric acid extraction followed by HPLC-ICP-MS

Abstract

A simple chemical extraction method is proposed for the routine determination of the proportions of As(III) and As(V) species in iron-rich precipitates originating from acid mine drainage (AMD). The procedure consists of orthophosphoric acid (1 M) extraction and subsequent analysis of As(III) and As(V) concentrations in the extract by HPLC-ICP-MS. The proposed method was validated on a series of synthetic As(III)/As(V)-schwertmannite samples and of AMD samples exhibiting various mineralogical compositions, total As concentration, As/Fe and As(III)/ΣAs ratios as determined by X-Ray Diffraction (XRD), total digestion-ICP-MS and synchrotron-based X-ray Absorption Near Edge Structure spectroscopy (XANES), respectively. High arsenic extraction efficiency (99 ± 10% of total As) was achieved with orthophosphoric acid since As-bearing iron phases that form in AMD are poorly crystalline. As(III) and As(V) proportions determined using the chemical extraction method followed by HPLC-ICP-MS analysis well matched the arsenic redox data obtained from the As K-edge XANES spectra analysis, showing the possibility to routinely measure the As oxidation state in AMD precipitates using this new simple extraction method.