Treatment of steel industry wastewater by Poly-Aluminum-Ferric-Silicate coagulant prepared from coal gasification ash

Abstract

The coal gasification industry generates a large amount of coal gasification ash (CGA) which can contaminate environment by seeping harmful substances into both soil and water. In this study, CGA was used for the preparation of Poly-Aluminum-Ferric-Silicate coagulant (PAFSiC) to treat steel industry wastewater, and the effects of acid leaching, alkaline leaching, and copolymerization stages were investigated. Our results indicated that the dissolution rates of iron and aluminum from CGA were 53.49% and 55.43%, respectively, under leaching temperature at 95 °C, time at 1.4 h, and concentration of HCl at 5.1 mol/L. The dissolution rate of silicon from the residue of CGA leaching by HCl was 41.44% under leaching temperature at 75 °C, time at 0.5 h, and concentration of NaOH at 5 mol/L. The PAFSiC prepared under (Fe+Al)/Si molar ratio at 4.3 indicated the best coagulation performance, and its removal rates for turbidity, color, and chemical oxygen demand (COD) from steel industry wastewater were 93.69%, 36.47%, and 62.66%, respectively. Compared to commercial polysilicate aluminum ferric (PSAF), PAFSiC increased removal rates of for turbidity, color, and COD by 28.67%, 18.21%, and 7.38%, respectively. The coagulation efficiency of PAFSiC was influenced by pH; a removal rate of color of 54.43% was recorded from the steel industry wastewater using PAFSiC prepared at pH of 2. PAFSiC synthesized from CGA under (Fe+Al)/Si molar ratio at 4.3 exhibited a branching amorphous structure with spatial stereoscopic sense, resulting in higher capacity to bind with and remove contaminates. Our results underline the potent performance of PAFSiC as a viable solution to alleviate pollution from the steel industry.