Acid‐bacterial and ferric sulfate leaching of pyrite single crystals

Abstract

Pyrite single-crystal cubes were cut, polished. and x-rayed to produce orientations of (100), (110), (111), and (112). These crystallographically developed surfaces then were prepared to expose an area of 1 cm(2), and the remainder of the crystal was coated with an acid-resistant silicone cement. Crystals with representative orientations then were leached in ferric sulfate solutions adjusted to a pH of 2.3 with H(2)SO(4) containing up to 6 x 10(3) ppm of Fe(3+) at 30 and 55 degrees C. Leaching was also conducted in acid-bacterial lixiviants containing Thiobacillus ferrooxidans at 30 degrees C and a thermophilic microorganism at 55 degrees C. Surface corrosion and pitting associated with pyrite leaching were examined by scanning electron microscopy. Pyrite leaching in ferric sulfate solutions was observed to be different when compared to acid-bacterial leaching. Ferric sulfate leaching required nearly 2 x 10(3) ppm of Fe(3+) at 30 degrees C while acid-bacterial leaching at 30 degrees C occurred without additions of Fe(3+), and values of Fe(3+) never exceeded 10(2) ppm. Because of precipitate formation, an accurate assessment of the role of crystallographic orientation on the leaching of pyrite is difficult.

The biological and chemical leaching of an auriferous pyrite/arsenopyrite flotation concentrate: A microscopic examination

“…The pitting reflected the mineral structure and was regular. This agrees with the observations on pyrite by Bennett and Tributsch (1978) and Keller and Murr (1982).…”

“…The effect of crystal structure on leaching has been reported by other workers (Duncan and Drummond 1973;Tributsch 1976;Bennett and Tributsch 1978;Southwood and Southwood 1986). However, although Hiltunen et al (1981) and Keller and Murr (1982) found no proof of it when bacterially leaching pyrite. The latter authors also noted that crystallographic orientation had no effect.…”

“…This confirms other observations that the bacteria attach only to energyyielding minerals, although their numbers are not always high. Coatings of various types have also been reported (Pinches 1975;Polkin et al 1975;Lundgren and Silver 1980;Hiltunen et al 1981 ;Keller and Murr 1982;Deny and Whittemore 1983). In this study it was noted that when the jarositic coating was removed from the particles by hydrochloric acid wash, the bacteria were also removed.…”

“…Total mineral dissolution may even be possible. Tarnishing, pits, grooves, holes, and jagged edges have all been observed on several types of minerals (Duncan and Drummond 1973;Bennett and Tributsch 1978;Keller and Murr 1982;Southwood and Southwood 1986).…”

Iron Pyrite Oxidation by Thiobacillus Ferrooxidans: Sulfur Intermediates, Soluble End Products, and Changes in Biomass†

“…+ 6H+. (13) The insoluble nature of pyrite and the attachment formed between the cells and the substrate make conventional enumeration techniques such as direct cell counts and viable cell counts inadequate as biomass measurements. One technique that seems to be adaptable to this system is the determination of protein after separation of suspended solids and bulk solution.…”