Substance flow analysis of production process: a case study of a lead smelting process

The metabolism of a production process can be researched by identifying all the material or substances that flow into or out of the production system. Effective methods for tracing the material and substance destinations and quantities in a system could determine the metabolism efficiency and the pathways through which pollutants are generated and emitted-very useful information for the resource and environmental management of a factory, particularly for pollution prevention and control. In this study, substance flow analysis (SFA), an analytical tool, was applied in a lead production system. To apply SFA in the lead smelting process, the framework for applying SFA in a typical lead smelting system was outlined, and a substance flow chart model of a single process and the entire system were developed. Lead was selected as the objective substance, and all lead-containing material flows were sampled and tested. The lead substance balance account of each process and the entire system were established based on producing one ton of final product: lead ingot. The unsuspected losses of the system were viewed as a kind of virtual substance flow. Several indicators-such as process rejection rate, process waste circulation rate, resource efficiency-were set up to evaluate the metabolism efficiency of the system. The result shows that the lead resource efficiency of the investigated production process was 81.28% and the total resource efficiency was 85.02%. Furthermore, to produce one ton of lead ingot, 0.0466 t of the solid waste generated was reused in other systems instead of being discharged into the environment. While 0.0062-0.0641 t lead was discharged or emitted into the environment, taking into consideration of unsuspected losses. Pollutant prevention and control could benefit both resource utilization and environmental protection for the lead smelting production. Some recommendations for improving emission control and pollution prevention for a lead smelting factory are put forward in the conclusions of this study.