Innovative Technology for Secondary Fly Ash Full Resource Utilization: Industrial Testing and Life Cycle Assessment Research

Abstract

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