Innovative\nTechnology for Secondary Fly Ash Full Resource\nUtilization: Industrial Testing and Life Cycle Assessment Research

The application of incineration fly ash (IFA) sintering\ntechnology\nhas brought a large amount of secondary fly ash (SFA) rich in heavy\nmetals and chlorides, and its treatment has attracted much attention.\nA unique three-step treatment technology involving acid washing, heavy\nmetal precipitation, and chloride evaporation has recently been developed\nto achieve complete resource utilization of SFA. The industrial test\nresults showed that the optimum liquid/solid (L/S) ratio and Ca(OH)<sub>2</sub> amount added were 2:1 and 30%, respectively, in the acid\nwashing step. In the heavy metal precipitation step, the use of a\nsolid NaOH precipitant at pH 10 was optimal for the removal of heavy\nmetals. For chloride evaporation, the average consumption of steam\nand electricity for each tonne of filtrate was 0.4 t and 16.5 kw·h,\nrespectively. Furthermore, the environmental impact of the three steps\nwas evaluated separately through the life cycle assessment (LCA) method\nbased on the industrial test results. The results indicated that the\nacid washing stage had the greatest environmental impact on the whole\nprocess. Finally, considering that the IFA sintering ceramics plant\nhas a large amount of available deacidification waste solution and\nwaste heat flue gas, the potential for improving the environmental\nand economic performance of the overall process through technological\ninnovation was analyzed using LCA and the life cycle costing (LCC)\nmethod. The LCA results showed that the optimization scenario with\ntwo innovative units performed better in terms of environmental sustainability,\ndecreasing the global warming impact by 29.5% compared to the normal\nscenario. The LCC results demonstrated that the optimization scenario\nwith an LCC value of −8.15 USD/t was more economically efficient\nthan the normal scenario with that of 4.27 USD/t.