Thermodynamics of Arsenic in FeOx-CaO-SiO 2 Slags
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INTRODUCTION
LOW levels of toxic elements such as arsenic, antimony, bismuth, cadmium, mercury, selenium, and tellurium commonly are found in base metal ores. Clean, coarsely grained ore bodies are becoming depleted with the ore bodies of the future becoming more complex, finer grained, and containing increasing amounts of toxic elements. Worldwide, the industry mines and processes hundreds of millions of tons of base metal ores each year; thus, the accumulated mass of minor elements introduced into the biosphere is large and one could expect a significant environmental impact to result. The current knowledge of the levels of the minor elements mined and brought into the biosphere each year is limited and insufficient for accounting purposes. However, research at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) is aimed at gathering the required data for developing predictive models to account for the dispersion of minor elements in various solid, liquid, and gaseous streams. The present study provides a component of the work carried out to enable the development of predictive tools for studying the deportment of minor and trace elements between different phases during the processing of base metal ores. The accurate accounting of arsenic in copper smelting processes is a challenging task, and mathematical tools
often are sought to assist in bridging gaps in data and accounting for uncertainties resulting for nonrepresentative sampling and characterization of inhomogeneous samples from the commercial processes. Predictive models also are necessary to assist the industry in understanding the effects that process variables have on the deportment of minor elements such as arsenic between phases. This understanding can be used to develop alternative practices for controlling the deportment of minor elements between different product streams and for the safe storage/disposal of such toxic elements. The thermodynamics of arsenic (As), such as its equilibrium distribution between slag and copper, its oxidation state in the slag, and its activity coefficient in the various slags, have been the subject of a numerous studies[1–9] over the last 30 years. A summary of the experimental conditions and partial results from these publications are provided in Table I with some key findings being summarized subsequently. Nagmori et al.[1] measured the distribution of As between the liquid copper alloys and the iron silicate slags at oxygen potentials (PO2 ) in the range of 10–11 to 10–6 atm at 1473 K (1200 C). They proposed the following equilibrium: v AS þ O2 ¼ AsOv 2
½1
for which the equilibrium constant is expressed as follows: CHUNLIN CHEN, Senior Research Scientist, and SHARIF JAHANSHAHI, Theme Leader - Sustainable Processing, are with CSIRO Minerals Down Under National Research Flagship, Clayton South, VIC 3169, Australia. Contact e-mail: [email protected] Manuscript submitted July 1, 2009. Article published online September 9, 2010. 1166—VOLUME 41B, DECEMBER 2010
cAs Ov ðXAs Ov Þ ½nT cAs Ov ðwt pct
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