Preparation of an Aluminum and Iron‐Based Coagulant From Fly Ash for Industrial Wastewater Treatment

Abstract

Fly ash was investigated to produce a composite coagulant containing aluminum (Al) and iron (Fe) salts through the calcination and leaching processes. The extraction of Al and Fe oxides from fly ash demonstrated similar results for HCl and H2SO4 leaching. Besides, the calcination pretreatment of fly ash (without any additive) was found to be less effective in extraction. However, the conversion efficiencies of Al and Fe were affected greatly by calcination pretreatment with addition of Na2CO3, and leaching conditions of ratio of solution to fly ash (L/S) and H+ concentration. The maximum concentrations of Al and Fe solubilized from fly ash were 0.21 and 0.04 mol/L, respectively, which were attained by calcination pretreatment using an optimal mass ratio (ca. 1:16.7) of Na2CO3 to fly ash at 805°C. These concentrations correspond to conversion efficiencies of 31.2% for Fe and 18.3% for Al in the fly ash. The slurry was filtrated to obtain a solution containing Al‐ and Fe‐sulfates and silicates. The Al/Fe/Si mole ratio indicated the feasibility of further production of inorganic polymer coagulant. The produced coagulant was determined to be effective for treating soybean wastewater and dairy wastewater in terms of COD and SS removal.