Heap leaching of black schist

Abstract

Bioleaching is proven technology for recovering metals. In its simplest form it has been used for copper recovery from low-grade materials since the 1500s in Spain. At present, approximately 20% of the world's annual copper production is recovered by bioleaching (Anonymous 2002). The heap leaching of low-grade sulfidic ores is the widest application of mining biotechnology (for a review, see Brierley and Brierley 2001). A typical solution from heap leaching has a low pH and not more than a few grams per liter of valuable base metals. In addition, the solution can have small amounts of rare and precious metals. Simplicity, low-cost and applicability to low-value ores are the main benefits of biohydrometallurgy. Bioleaching has the potential to be used for obtaining metals from mineral resources that have not been accessible by conventional mining (for reviews, see Bosecker 1997; Brandl 2001; Brierley and Brierley 2001; Hsu and Harrison 1995). The understanding of the number and kind of biocatalysts in bioleaching environments has advanced from the days when Acidithiobacillus ferrooxidans and At. thiooxidans were the only microorganisms considered (for reviews, see Johnson 1998; Hallberg and Johnson 2001; Rawlings 2002).