Coal Fly Ash Solidification by Calcination Products of CaCO3–Al(OH)3 Mixtures Accompanied by Prevention of Oxoanion Leaching

CaCO3-Al(OH)(3) mixtures with different mixing ratios were calcined at different temperatures in the range of 1073-1473 K. To solidify the coal fly ash, it was mixed with the calcination product and water, and allowed to stand under saturated steam at 348 K for 3 d. The compressive strength of the solidified product using the calcination product was measured and compared with those of alumina and Portland cements. The calcination conditions and solidification conditions were examined to optimize the compressive strength of the solidified products. The calcination product reacted with fly ash to form crystalline Ca3Al2(SiO4)(OH)(8), thus contributing to the high compressive strength of the solidified product. The leaching behavior of fly ash artificially contaminated with CrO42-, B(OH)(4)(-), AsO43-, and SeO42-, and solidified with the calcination product was examined. The solidified product formed from the calcination product prevented the leaching of all four oxoanions more effectively than the solidified products formed from other cements. The higher compressive strength of the solidified product facilitated this lower oxoanion leaching concentration from the solid.