91
selection, preparation and access to the exploitation zone continues through the
clearing and stripping by suction dredgers. This process converts vegetation cover
to bare soil by cutting and removing the superficial horizons of the soil (UNDP 2016).
Mineral beneficiation activities occur simultaneously with the beginning of operations. Mineral excavation (consisting of the excavation of sand, gravel, clay, and
the mineral of interest) is carried out by dipper dredger (dredging line step), which
extracts the ore from the alluvial deposits. This is followed by an analysis of the
gold physical beneficiation by size classification (mechanical screening) and gravimetric concentration using hydraulic jigs and sluice boxes. As a result of the first
stages of this process, a waste line (typically a sterile material such as gravel or
sand) is produced. Additionally, a second wet process flow, which is rich in gold and
mixed with sands, ferrous metals, and other impurities, continues down the process
line in order to increase the concentration and purification of gold (flotation stage).
The 11% of ore (dry basis) enters along a continuous stage in both the beneficiation
line and the separation stage, where 99% of the process stream moisture is chemically
removed for further concentration. This process is carried out with the objective of
recovering 4% of the gold not recovered in the flotation stage. These gold-rich flows
(wet basis), which are produced in the flotation and chemical separation process,
continue in the drying line, and simultaneously the gold is separated from the
ferrous minerals which correspond to about 3% of the gold-rich flow line. The gold
obtained from these concentrates is then melted and casted. Assuming no losses in
the smelting and casting process; 3103 ton/year is melted, which amounts to
approximately 155 ingots with a 900 millesimal fineness.
Tailings generated in both the filtration-separation and chemical separation
stages are submitted to a Waste Tailings Treatment Plant (WTTP), where 99% of the
water used in the beneficiary process is recovered and reused in this same process,
together with the water obtained from dewatering the tailings pond. Ferrous metal
is then stored for future economical uses, as a coproduct of the process.
7.3 Methodology
7.3.1 Life Cycle Assessment
Life cycle assessment (LCA) is an environmental approach that considers both natural resource consumption and pollutant emissions throughout a product or activities’ entire life cycle (Blengini et al. 2012). The methodology is standardized by
ISO 14040 (ISO 1998) and made up of four stages: goal and scope definition, inventory analysis, impact assessment, and interpretation. For the first stage, the research’s
motivation is to determine the selection of impact categories and characterization
methods while defining the system boundaries and the functional unit. The second
step, inventory analysis, involves collating all relevant data including resource
inputs, products, and emissions. Impacts are then quantified through characteriza7 SDG 6 Clean Water and Sanitation
selection, preparation and access to the exploitation zone continues through the
clearing and stripping by suction dredgers. This process converts vegetation cover
to bare soil by cutting and removing the superficial horizons of the soil (UNDP 2016).
Mineral beneficiation activities occur simultaneously with the beginning of operations. Mineral excavation (consisting of the excavation of sand, gravel, clay, and
the mineral of interest) is carried out by dipper dredger (dredging line step), which
extracts the ore from the alluvial deposits. This is followed by an analysis of the
gold physical beneficiation by size classification (mechanical screening) and gravimetric concentration using hydraulic jigs and sluice boxes. As a result of the first
stages of this process, a waste line (typically a sterile material such as gravel or
sand) is produced. Additionally, a second wet process flow, which is rich in gold and
mixed with sands, ferrous metals, and other impurities, continues down the process
line in order to increase the concentration and purification of gold (flotation stage).
The 11% of ore (dry basis) enters along a continuous stage in both the beneficiation
line and the separation stage, where 99% of the process stream moisture is chemically
removed for further concentration. This process is carried out with the objective of
recovering 4% of the gold not recovered in the flotation stage. These gold-rich flows
(wet basis), which are produced in the flotation and chemical separation process,
continue in the drying line, and simultaneously the gold is separated from the
ferrous minerals which correspond to about 3% of the gold-rich flow line. The gold
obtained from these concentrates is then melted and casted. Assuming no losses in
the smelting and casting process; 3103 ton/year is melted, which amounts to
approximately 155 ingots with a 900 millesimal fineness.
Tailings generated in both the filtration-separation and chemical separation
stages are submitted to a Waste Tailings Treatment Plant (WTTP), where 99% of the
water used in the beneficiary process is recovered and reused in this same process,
together with the water obtained from dewatering the tailings pond. Ferrous metal
is then stored for future economical uses, as a coproduct of the process.
7.3 Methodology
7.3.1 Life Cycle Assessment
Life cycle assessment (LCA) is an environmental approach that considers both natural resource consumption and pollutant emissions throughout a product or activities’ entire life cycle (Blengini et al. 2012). The methodology is standardized by
ISO 14040 (ISO 1998) and made up of four stages: goal and scope definition, inventory analysis, impact assessment, and interpretation. For the first stage, the research’s
motivation is to determine the selection of impact categories and characterization
methods while defining the system boundaries and the functional unit. The second
step, inventory analysis, involves collating all relevant data including resource
inputs, products, and emissions. Impacts are then quantified through characteriza7 SDG 6 Clean Water and Sanitation