ARSENIC CONTROL IN THE METALLURGICAL INDUSTRY
CIM Vancouver 2002
Patricio A Riveros, John E Dutrizac,
Arsenic is frequently found in close association with base and precious metals and, as a result, the co-extraction of arsenic from mineral deposits during metallurgical activities is inevitable. The fate of the co-extracted arsenic depends on the metallurgical process. In pyrometallurgical operations arsenic volatilizes and is collected in electrostatic precipitators or wet gas scrubbers. These arsenic-rich dusts are usually recycled within smelting operations to force the dissolution of arsenic into the slag, but the relatively low solubility of arsenic compounds in conventional silica-based slags limits the total amounts of arsenic that can be disposed in this manner. In many cases, the arsenic-rich dusts are stockpiled, which poses long-term problems. In many hydrometallugical circuits, arsenic is precipitated from solution, usually as ferric arsenate compounds. This practice generates large volumes of ferric oxyhydroxide and gypsum sludges of somewhat uncertain long-term stability. High-temperature high-pressure oxidation, as in the processing of refractory gold ores, promotes the formation of insoluble scorodite (FeAsO4.2H2O) and/or related compounds, but other leaching processes produce soluble arsenic compounds. Mill tailings usually contain residual arsenic-bearing sulphides, and these compounds may dissolve as a result of acid mine drainage, algal activity or mineralogical transformations. Increasing environmental awareness is leading to more stringent regulations for the use and the disposal of arsenic compounds. Within this framework, the current arsenic disposal methods used by the industry are reviewed and the factors that influence the long-term stability of the disposed arsenic compounds are discussed; these include the disposal site environment, the particle size and crystallinity of the precipitate, the presence of complexing agents, and the effects of bacterial activity.
Arsenic, Waste, ferrihydrite, disposal, Metallurgy, scorodite