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Waste - Nexa | 2017 Annual Report

Material Issue

Note 16: The values were changed due to a adjustment in the total waste generated at the El Porvenir unit. GRI 102-48, 103-1, 103-2, 103-3

In recent years, we have been working on research and development of technologies to reduce waste generation, or to enable its reinsertion into production chains. Our best result was obtained in the Zero Waste Project at the Morro Agudo mine, whose production process change resulted in the elimination of tailing generation, in exchange for the generation of agricultural products, responsible for 5% of unit’s revenues in 2017. A more recent example was the use of the slag generated in the Waelz furnace at Juiz de Fora as a raw material for cement production. These results are in line with the strategic plan, whose commitment in 2015 was to reduce the volume of mineral and metallurgical waste generated and/ or sent to landfills by 50%.

Other actions that resulted in reduced consumption of natural resources and costs, as well as a lower level of environmental impacts associated with waste disposal, were: adding a flotation cell for the separation of silver and lead present in the ore at the mine in Vazante.

In 2017, our operations generated a total of 16.8 million tonnes of mineral and metallurgical wastes, 33% non-hazardous and 67% hazardous — a 7% overall reduction compared to 2016’s result (18.1 million tonnes).

Mineral-Metal and Industrial Wastes (thousand tonnes) GRI 306-2 and MM3

Dam Management

For the management of tailings dams, which is one of the main risks associated with mining activities, we apply the International Commission on Large Dams’ guidelines. Currently, we use three waste disposal methods in our operations: dams, for which we employ coating techniques, leak monitoring systems; dry stacking, continuous surveying and management (Nexa has 39 dams, 18 in Brazil and 21 in Peru); or mine backfill, filling the spaces from which the minerals were withdrawn.

Some operations may combine one or more layout methods. At the Atacocha, Cerro Lindo and El Porvenir units in Peru, we adopted the backfill method, whereby 38% of the tailings is returned to the Pasco Complex mines and 48.7% to the Cerro Lindo mine. In Cerro Lindo, the waste not used as backfill is filtered, separating water and solids. The water is recirculated and the waste is sent to specific deposition piles. This same model is being considered in new projects in Brazil (Aripuanã and Caçapava do Sul). In 2017, we obtained the environmental license for the dry-tail disposal project at the Vazante mine. Implementation should begin in 2018 and be completed by 2020.

For the management of these dams, we have an efficient system in place that focuses on security, optimization and stability with continuous rather than the twice-ayear monitoring actions required by law. Dam management is one of the topics included in our business risk management processes and regularly discussed at executive meetings, where reports are presented on the stability of these structures.

We also rely on the work of an independent consulting firm (Geoconsultoria) to jointly monitor and measure the performance of key control indicators, in addition to discussing actions for each of the 39 dams.