Refinement of low-grade clay by microbial removal of sulfur and iron compounds using Thiobacillus ferrooxidans

• Published in: Journal of fermentation and bioengineering 1995, Vol.80 (1), p.46-52
• Main Authors: Ryu, Hee Wook, Cho, Kyeoung Suk, Chang, Yong Keun, Kim, Sang Done, Mori, Tadahiro
• Format: Article
• Language: English
• Subjects: Biohydrometallurgy. Microbial leaching; Biological and medical sciences; Biotechnology; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; low-grade clay; microbial refinement; Thiobacillus ferrooxidans
• ISSN: 0922-338X
• DOI: 10.1016/0922-338X(95)98175-K

The refinement of low-grade clay, of which impurities are mainly sulfur and iron compounds, is required because of the recent shortage of high-grade clay for manufacturing of structural ceramics. The major impurity compound contained in the low-grade clay we treated was identified as pyrite by X-ray powder diffraction and inductively coupled plasma analyses. The well-formed crystals of pyrite had a framboidal form of 1 μm–20 μm diameter. The microbial removal of pyrite from the low-grade clay was investigated by using a sulfur and iron-oxidizing bacterium, Thiobacillus ferrooxidans. About 82–90% of the pyrite was removed in 5–12 d for pulp densities up to 70% (w/v). The removal rate of pyrite ranged from 270 to 914 mg-pyritic sulfur/ l·d depending upon clay pulp density. The rate of pyrite removal (r) could be expressed as a function of pyritic sulfur concentration (S): r (mg-pyritic sulfur/ l·h) = 1.96 × 10 −2 S (mg-pyritic sulfur/ l). The logarithm of the amount of oxidized pyrite per unit volume and the final pH in the reaction medium were found to have a linear relationship which could be expressed as pH = 2.43–0.55 log [FeS 2 (mM)]. With the refined clay no red color due to the presence of pyrite was developed after firing, and its whiteness was similar to that of a high-grade clay.