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Results and Discussion Copper cathode. Operational WF for copper cathode contributed 97% of the total WF, whereas the supply chain WF only accounted for the remaining 3%. The largest component of the operational WFs was the blue WF associated with evaporation in the heap and surrounding storage ponds (73%) in which evaporation in heap contributed the highest portion in comparison with the evaporation in the surrounding ponds. It was largely due to the vast area in heap leach pad. WF in neutralisation and SX-EW amounted to the remaining 18% and 9 % respectively (Fig. 1). Figure 1. Operational Blue WF for Cu cathode Figure 2. Supply chain Blue WF for Cu cathode Figure 3. Operational Blue WF for Cu conentrate Four different pollutants – Cu, Zn, CN and As were analysed to determine the operational grey water footprint. Within the scope of the assessment, copper was the critical pollutant from the Zijinshan mine. The operational grey WF accounted for 12% of the total operational WF with the remaining 82% for operational blue WF. Although process effluent was treated before discharge and the copper concentration met the national discharge limit, it still contributed to the grey water footprint. It is due to the fact that some of the surface water capacity to assimilate the pollutants has been consumed.
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ie., the waste assimilation capacity of the receiving water body is diminishing. In the overhead operational blue WF, dust suppression accounted for 94%, while water consumption by employees contributed only the remaining 6%. All ingredients from the supply chain were locally sourced. The largest consumption was lime which was used for effluent treatment and it contributed to 51% of the supply chain water footprint, followed by diesel consumption in trucks for ore transportation 22% (Fig. 2). Copper concentrate. In the operational WF components, each processing circuit contributed similar proportion with crushing and grinding (25%), milling and flotation (38%) and evaporation from tailings dam (37%) from 2013 data (Fig. 3). Copper concentrate had a zero grey water footprint because there was no water discharge into the freshwater bodies. Operational overhead blue WF was similar to copper cathode production with dust suppression accounted to 91% and water consumption by employees contributed 9% (2013 data). Sustainability assessment. The WF sustainability assessment addresses both process water efficiency and WF sustainability in the water basin focusing on blue water scarcity and water pollution level. Base on the Ting Jiang River run off data collected from 1996-2005, together with available global data of Han Jiang basin, the blue water availability and scarcity of the Ting Jiang basin was analyzed. Result shows that there was no water scarcity of this river basin for any month of a year on average. Ting Jiang basin where the process water footprint component located was not identified as a blue water scarcity hot spot. Research literature, government reports and news showed that water pollution of Ting Jiang basin was of high environmental and social concern. Therefore, this basin was seen as a water pollution hotspot. The WF sustainability assessment identifies in copper cathode production, the water footprint was largely due to evaporation in the heapleaching process and the inefficient effluent treatment in neutralization circuit; whereas in copper concentrate production, the WF was mainly attributed to the excessive washing and rinsing in the flotation circuits and evaporation in the tailings dam. Conclusions This assessment has helped the company better understand the water footprint of the two chosen products, both in direct operations and in their supply chain. The essence of the WF assessment is the consideration of the timing and location of the associated resources, information on when, where and how water is used and its type, and the sustainability of the water consumption and pollution, and ultimately a formulation of response strategies to reduce impact on the environment. Assessment of the two copper products shows that blue WF lied predominately in the direct operations rather than the supply chain. Response strategies will focus towards reducing evaporation in heap leach pad and storage ponds for copper cathode production. For copper concentrate, reduction of water usage in cleaning and rinsing and more recycling will further improve water efficiency. At present, water footprint database for agricultural products and processes are more readily available. However, a comparable database for industrial products is still lacking. This WF assessment for industrial operations highlights a great importance to fill such data gap. Importantly, the WFA has shown the largest components and locations of water consumption and potential impact on local watersheds, highlighting the need to engage more directly with suppliers, governments, other stakeholders and communities on responsible water stewardship. Acknowledgement The WF Network is acknowledged for giving valuable technical advice to this study. The authors are grateful to individuals from the mine site for providing data and Zijin Mining Group Company for financial support to facilitate this work. References.
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