《Table 1Differences between WPPC and traditional pollution-control methods.》

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《基于高效清洁生产的全过程污染控制（WPPC）——中国钨行业典型案例研究》

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As shown in Fig.3，the whole process，from raw materials to product/intermediate product，can be divided into four steps:conversion，separation/purification，product preparation，and waste treatment.By mapping the energy and material distribution/flow in each step，the consumption details can be identified for each step of the process.The comprehensive cost is then determined using Eq.（1）.During conversion，extraction of the target metals from the corresponding mineral/waste material occurs；this process may include several operation steps based on the process design.In separation/purification，impurities are removed from the target materials.If hydrometallurgical leaching is applied to process the raw materials，solvent extraction or ion exchange could be used in this step.If smelting of the raw materials is applied，purification should be conducted based on high-temperature refining or electrochemical refining.After purification，the product preparation varies depending on the form of the product.The waste treatment step requires significant attention in order to lower the environmental impacts of current primary metal production.The cost can fluctuate significantly in this step，even in the same area，depending on the regulations and management efficiency[25].The cost indicator of a specific step such as leaching/smelting，CE，can be calculated by summarizing the cost（including materials and energy）of all the steps in the section.The difference in the cost indicator provides a guideline for evaluating the significance of the process optimization of a specific step，where a decrease in value indicates an improvement in the efficient utilization of materials and energy.