Masahiko Bessho

Publications (2)1.06 Total impact

• Article: Experimental study on prevention of acid mine drainage by silica coating of pyrite waste rocks with amorphous silica solution

  Masahiko Bessho, Takaaki Wajima, Takuro Ida, Takashi Nishiyama
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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 5,000mg/L silica solutions, but not from 0 or 1,000mg/L silica solutions. The coating formation rate was slower in the 2,500mg/L silica solution than in the 5,000mg/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. KeywordsAcid mine drainage–Pyrite–Silica–Precipitation–pH
  Environmental earth sciences 05/2012; 64(2):311-318. · 1.06 Impact Factor
• Article: High-Grade Silica Refined from Diatomaceous Earth for Solar-Grade Silicon Production

  Masahiko Bessho, Yasuhiro Fukunaka, Hiromu Kusuda, Takashi Nishiyama
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  ABSTRACT: A refining processing of high-purity silica from biogenic diatomaceous earth is newly proposed to exploit the steady and stable resource to the solar-power generation industry. The specimens collected from various representative diatomaceous earth deposits, including both marine and freshwater origin, were chemically analyzed. Trace element distribution in diatomaceous earth was influenced by the biotope habitat of diatoms, when compared to that in quartz of igneous origin. Al, K, and Fe were mainly terrestrially derived, while Si and B were from diatom shells. B content in diatomaceous earth specimens from lacustrine sources was less than that in marine origin. Diatomaceous earth was then dissolved into caustic alkaline solution. With a decreasing pH value, amorphous silica precipitated with impurities. Al and Fe were concentrated in silica precipitated in the pH range of 12.5−10.5, while B was more soluble than silica at pH less than 9. Silica can be precipitated in the pH range of 10.5−9.0, followed by acid leaching to reduce Al and Fe content. A simple chemical operation consisting of extraction, precipitation, and acid leaching has been proposed. Repetition of chemical processing 3 times provides more than 5 N silica from diatomaceous earth samples from freshwater-source rocks.
  08/2009;