Optimization of Bioscorodite Crystallization for Treatment of As(III)-Bearing Wastewaters

Abstract:

Arsenic (As) is a major impurity contaminated in metal refinery wastewaters. To immobilize As ions, we have previously reported microbial scorodite (FeAsO₄·2H₂O) crystallization using the thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In order to extend the applicable range of As (III)-bearing metal refinery wastewaters (especially for dilute As (III) concentrations of 250–1500 ppm), this study investigated the effect of several factors possibly affecting the bioscorodite crystallization efficiency; (i) [Fe (II)]_ini/[As (III)]_ini molar ratio at different target As (III) concentrations, (ii) initial pH, and (iii) seed scorodite with different morphologies. The [Fe (II)]_ini/[As (III)]_ini molar ratio strongly affected the bioscorodite crystallization efficiency at each target As (III) concentration. Whilst the [Fe (II)]_ini/[As (III)]_ini molar ratio of 1.4 was most effective at 500–1500 ppm As (III), the optimal molar ratios for treating more dilute concentrations (< 500 ppm) were shown to be relatively higher. However, further increasing the [Fe (II)]_ini/[As (III)]_ini molar ratio resulted in formation of unwanted potassium jarosite (KFe₃(OH)₆(SO₄)₂) together with scorodite. Lowering the initial pH from 1.5 to 1.2 resulted in earlier scorodite nucleation, but lesser overall As immobilization. Feeding chemical-and bio-scorodite seed crystals differently affected the reaction speed and the stability of newly-precipitated bioscorodite. The TCLP test indicated that scorodite formed on bioscorodite seeds is more stable than that formed on chemically-synthesized scorodite seeds.

• Periodical: Solid State Phenomena (Volume 262)
• Pages: 555-558
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.262.555
• Online since: August 2017
• Authors: Masahito Tanaka, Tsuyoshi Hirajima, Keiko Sasaki, Naoko Okibe*
• Keywords: Acidianus brierleyi, Acidophiles, As(III)-Oxidation, Fe(II)-Oxidation, Scorodite

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