MINERALOGICAL STUDY OF BASE-METAL TAILINGS WITH VARIOUS SULFIDE CONTENTS, OXIDIZED IN LABORATORY COLUMNS AND FIELD LYSIMETERS

Oxidation of a flotation-derived, low-sulfide tailings containing appr oximately 0.4 wt.% S was compared with simultaneously oxidized tailing s containing 1.0 wt.% S and 2.5 wt.% S to assess their acid generating characteristics. Each tailings type was exposed to oxidation for thre e years in laboratory columns and in lysimeter pits in the field. In t hese tailings the sulfide mineral of principal concern with respect to acid generation is pyrrhotite (Fe1-xS). In past studies the alteratio n of pyrrhotite has been characterized by initial replacement with mar casite (FeS2) and ferric iron sulfates, which are followed by developm ent of ferric oxyhydroxides such as goethite and lepidocrocite. Macros copic characterization of the tailings shows varying and progressive d egrees of oxidation correlative with the three different sulfur conten ts. As expected, the tailings with the lowest sulfur content are the l east oxidized, and those with the highest sulfur content have reacted the most. The column tests, which represent accelerated reaction condi tions relative to those for the lysimeter pits, show much higher degre es of oxidation, and a markedly more distinct boundary between the oxi dized and unoxidized zones; as well, differences among the three taili ngs types are more pronounced.