On the basis of analyzing the circular economy development modes of the enterprises,it was figured out that the industrial symbiosis pattern is an effective way to develop circular economy in the enterprises.According to current status of lead-zinc industry,it was pointed that it is necessary to construct industrial symbiosis inside the industry.Then in a case study in a lead-zinc smelting plant,the symbiosis relationship,industry linkage,and economic and environment benefit were analyzed.The result indicated that constructing the industrial symbiosis pattern in the enterprises could raise efficiency of resources utilization,reduce the pollutant discharge and lower the production cost,thus balancing economic benefit and environment protection.Besides,more attention should be paid to the new pollution possibly caused by industrial symbiosis.

Bases on evaluating the ability of sustainable development in regional ecological city construction,take Xianyang City for example,an evaluating index system was introduced.Those indexes are then made dimensionless by the way of averaging procedure and some cost indexes were handled by positive correlation process.Finally,the grey relational grade and grey relational coefficient were calculated by applying grey relational method.From the result,the different levels of ecological city sustainable development can be classified and the primary restriction can also be pointed out.The result of grey relational degree indicates that the sustainable development ability of Xianyang City is going better and better,and there are 10 indexes that have a great gap with the optimized ones.Then according to the results,the faults in Xianyang ecological city construction were pointed out and some countermeasures for realizing the goal of sustainable development drawn up.

The paper presented a case history of attaining the development potential of circular economy for a large integrated lead-zinc plant in Shanxi Province,China.The existing energy and material flows were first reviewed and analyzed based on the circular economy concept;the author then proposed a closed loop industrial chain model consisting of smelting,acid production,electricity generation and precious metal recovery operations.The construction of an industrial chain of circular economy for the lead-zinc plant improved its utilization of material and water resources,reduced energy consumption and manufacturing cost,minimized pollutant discharge,increased economic efficiency,and produced many environmental benefits.