Experimental study on prevention of acid mine drainage by silica coating of pyrite waste rocks with amorphous silica solution |
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| Authors: | Masahiko Bessho Takaaki Wajima Takuro Ida Takashi Nishiyama |
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| Institution: | (1) Department of Energy Science and Technology, Faculty of Energy Science, Graduate School of Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan;(2) Department of Materials-Process Engineering and Applied Chemistry for Environments, Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata, Gakuen-machi, Akita 010-8502, Japan;(3) Emeritus professor of Kyoto University, Kyoto, Japan; |
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| Abstract: | Acid mine drainage (AMD) is a widespread environmental problem associated with working and abandoned mining operations. It
results from the microbial oxidation of pyrite in the presence of water and air, affording an acidic solution that contains
toxic metal ions. Pyrite microencapsulation, utilizing silica coating, is a novel approach for controlling AMD that has been
shown to be very effective in controlling pyrite oxidation. The roles of the solution pH and silica concentration in the formation
mechanism for the AMD-preventing coating were investigated. A silica coating can be formed from silica solution at pH 7, at
which the amount of Fe eluted from pyrite into the solution is small. No coating was formed at other pH values, and the amounts
of eluted Fe were larger than at pH 7, especially at pH 11. The silica coating forms from 2,500 to 5,000 mg/L silica solutions,
but not from 0 or 1,000 mg/L silica solutions. The coating formation rate was slower in the 2,500 mg/L silica solution than
in the 5,000 mg/L silica solution. The formation of silica coating on pyrite surfaces depends on three main steps: formation
of Fe(OH)3 on the surface of pyrite, reaction between Fe(OH)3 and silicate in the solution on the pyrite surface, and growth of the silica layer on the first layer of silica. The best
pH condition to enable these steps was around 7, and the silica coating formation rate can be controlled by the concentration
of silica. |
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