THE SPECIATION OF ARSENIC IN IRON OXIDES IN MINE WASTES FROM THE GIANT GOLD MINE, N.W.T.: APPLICATION OF SYNCHROTRON MICRO-XRD AND MICRO-XANES AT THE GRAIN SCALE

Abstract

Understanding the solid-phase speciation of arsenic in soils and sediments is important in evaluations of the potential mobility of arsenic and of its bio-availability in the environment. This is especially true in mine-infl uenced environments, where arsenic commonly is present at concentrations two and three orders of magnitude above quality criteria for soils and sediments. Arsenicbearing particulates dispersed through hydraulic transport or aerosol emissions can represent a persistent source of contamination in sediments and soils adjacent to past mining and metallurgical operations. The stability and mobility of arsenic associated with these phases depend on the chemical form and oxidation state of the arsenic and the interaction with post-depositional geochemical conditions. The Giant mine in Yellowknife, Northwest Territories, roasted arsenic-bearing gold ore from 1949 to 1999. The roasting process decomposed arsenic-bearing sulfi des (pyrite and arsenopyrite) to produce a calcine containing fi ne (generally <50 � m) arsenic-bearing iron oxides. We have applied synchrotron As K-edge micro X-ray Absorption Near-Edge Structure