2649 The manufacturing of wear materials generates GHG emissions and must be accounted for in the LCA. At this stage, data on these materials are required: the wear rate (i.e., how fast they deteriorate, in g/kWh of mill operation), as well as the EF for producing the wear material (in kg CO2e/kg of material). The wear rates of the mill liners and grinding media were collected as primary data. To obtain the EF (secondary data), the liner and ball mill materials must be known. These are made of chromium-molybdenum (CrMo) steel, but since Ecoinvent does not provide an EF for CrMo, the EF for low-alloyed steel (2.123 kg CO₂e/kg) is used as proxy60. Ecoinvent’s system boundary covers steel production only up to the point of cast steel, so additional processing is required to form the final liners and balls into the specific shape/size/specifications. Therefore, the EF for ‘forged steel’ (1.252 kg CO₂e/kg) is added to account for the forging process. Assuming 1 tonne of steel yields 1 tonne of low-alloyed steel, the total estimated EF for CrMo steel is 3.375 kg CO₂e/kg [(2.123 + 1.252) kg CO₂e/kg]. To further investigate the accuracy of the wear materials’ environmental impact, the following can be considered: (1) Location of production, (2) Recycling of wear parts, and (3) Replacement of broken parts. The production location of wear materials significantly affects the EF. For steel, the manufacturing country can lead to discrepancies of up to 270% [14]. If materials are produced in a different country from where they are used, transport emissions must also be considered, further increasing the total impact. Although Metso operates across 8 global market regions [15], precise knowledge of the manufacturing or forging location would enable more accurate EF selection. In this study, though, global averages were used. Recycling may also influence the results. Metso currently recycles some liners; however, detailed data on recycling volumes were not available. To include recycling in the LCA, information would be required on quantities recycled, the locations, transport distances / modes, and the energy and resource requirements of the recycling process itself. This would allow a more complete assessment of environmental impacts and the potential to expand recycling practices. Recycling was not considered in this review. The replacement of broken parts was not included due to a lack of equipment-specific data. This could affect results and should be considered in future LCAs. Processing plants often have approximate replacement frequencies for components such as flotation rotors and stators, blowers, filter cloths, and membranes. To assess the impact, data on material type, EFs, and component weight would be required. Reagents: The reagents used in the copper processing plant include collectors, frothers, activators, pH regulators, and flocculants. The manufacturing of these materials is responsible for GHG emissions and must be accounted for. At this stage of the LCA, obtaining the data of these materials is required: the consumption rate (i.e., how much reagent is consumed per tonne of processed material, in g/t), as well as the EF for producing the reagent (in kg CO2e/kg of reagent). The reagent consumption rates were collected as primary data. The EFs were obtained as secondary data from Ecoinvent and are provided in the table below. Table 3 – EFs of reagents used in copper concentrator Reagent Specific name Emission factor (kg CO2e/kg reagent) Collector Xanthate (AERO MX-5141) 3.0140 Frother Foaming agent (MIBC) 2.5809 Activator Xanthate (butyl potassium xanthate) 3.0140 Regulator CaO (lime) 1.2476 Flocculant Polyacrylamide (Magnafloc) 3.9994 All required data / information were collected during the LCI stage and are summarised in Table 4. 60 As suggested by Metso experts
RkJQdWJsaXNoZXIy MTM0Mzk2