No abstract

Thermodynamic methods, such as exergy analysis allow the assessment of environmental load (environmental impacts), by calculating the entropy generated or exergy destroyed due to the use of renewable and non-renewable resources along the entire production chain. In this research, exergy analysis will be approached as an extension of LCA to ExLCA (Exergy Life Cycle Assessment), as complementary tools, for sustainability assessment of two gold mining systems in Colombia: open-pit and alluvial mining. It is quantified exergy life cycle efficiencies; Cumulative Energy/ Exergy Demand, by distinguishing between renewable and non-renewable resources used in the process. The energy contained in renewable and non-renewable resources, interpreted as a measure of its utility potential, and which inefficient use generates waste streams with an exergy content that may be a measure of its potential to cause environmental damage. For open-pit mining 53% of exergy consumed comes from fossil energy, and 26% of energetic use of water, while in alluvial mining, 94% of exergy flow comes from water as a resource used within process activities. In order to reduce the environmental impact associated with gold generation life cycle described in this study, four strategies should be implemented; 1) Increasing efficiency, by reducing the exergy required in tails and extraction stages in open-pit mining process and, casting and molding stage in alluvial mining process, where large exergy supplies are required. 2) Increasing efficiency through the reduction of exergy emissions and residues in casting and molding stage in alluvial mining, and stripping stage in open-pit mining. 3) Using external exergy resources, such as renewable resources from nature (solar, wind, hydraulic). 4) Applying the concept of circular economy, which implies the reduction in consumption of resources.

Colombia is a major flower exporter of a wide variety of species, among which the chrysanthemum plays a major role due to its exporting volume and profitability on the international market. This study examines the major environmental impacts of the chrysanthemum supply chain through a life cycle assessment (LCA). One kg of stems export quality was used as the functional unit (FU). The study examines cut-flowers systems from raw material extraction to final product commercialization for two markets (London and Miami) and analyzes two agroecosystems: one certified system and one uncertified system. The transport phase to London resulted in more significant environmental impacts than the transport phase to Miami, and climate change (GWP100) category was significant in both cities, generating values of 9.10E+00 and 2.51E+00 kg CO2-eq*FU for London and Miami, respectively. Furthermore, when exclusively considering pre-export phases, the uncertified system was found to have a greater impact than the certified system with respect to fertilizer use (certified 1,448E-02 kg*FU, uncertified 2.23E-01 kg*FU) and pesticide use (certified 1.24 E-04 kg*FU, uncertified 2.24E-03 kg*FU). With respect to the crop management, eutrophication (EP) and acidification (AP) processes imposed the greatest level of environmental impact. Strategies that would significantly reduce the environmental impact of this supply chain are considered, including the use of shipping and a 50% reduction in fertilizer use.

Purpose Gold mining has historically and significantly contributed to the Colombian economy. Gold extraction in Colombia is mainly done through two techniques: open-pit and alluvial mining. In this study, the environmental impacts of both these mining systems were analyzed using the life cycle assessment (LCA) framework, including identification of the system components that contribute most to impacts. Methods Inventory data were obtained for two medium-scale mines in Colombia, one representing the open-pit method and the other the alluvial method. Environmental impacts were classified and characterized by mid-point impact categories and further aggregated into end-point indicators through the ReCiPe (v. 1.11) methodology, which uses a hierarchist perspective. Results Results for end-point indicators show that the open-pit mining presents higher values in the human health damage category, influenced primarily by tailings and by the excavation process. For the alluvial mining, the overall impacts were an order of magnitude lower, with ecosystem quality as the most significant contributor due to the stripping of soil and vegetation. In the case of mid-point indicators, freshwater and marine ecotoxicity contribute the most to open-pit mining, while for alluvial mining, metal depletion and natural land transformation contribute the most. Climate change is also a significant impact category for alluvial and open-pit mining. Conclusions The is a substantial difference in environmental impacts between the two mining systems: the quantified total environmental impact was 1.0 × 10 04 points for the open-pit mine and 2.4 × 10 03 points for the alluvial mine. Since these mines represent specific Colombian operational conditions, this conclusion cannot be confidently extended to other operational contexts. For example, results in other cases may depend on the local geological features and natural environment conditions. Knowing the critical mining supply chain stages for environmental performance will allow the decision-makers to provide the tools for more sustainable extraction and production.

The Colombian mining sector is characterized by the production of coal, nickel, emeralds, gold, and construction materials. It is considered by the National Development Plan of Colombia 2018e2022 as an economic agent that boosts development in the region and one that requires the strengthening of its policies and environmental liability. Therefore, this paper aims to show the importance of implementing methodologies based on the logic of nature (exergy) that objectively indicate the environmental impact of an extractive gold activity, such as open-pit gold mining. The extractive activity or process to be studied consists of the following stages: topsoil removal by using machinery and explosives to create craters and to access the mineral present in the subsoil; the physical transformation of the extracted material through crushing, grinding, gravimetric separation, flotation, leaching, adsorption, elution, and electrodeposition, along with smelting and casting to obtain gold and silver ingots. Thus, this paper analyzes the exergy performance of each unit process of the open-pit extractive process. The obtained results are used in a sensitivity analysis, which determines the system efficiency, by assuming the increase of gold in the extracted material in the exploitation stage, by using the same supplies and input of the current process. In other cases, the open-pit mining process is analyzed by changing its technologies in the mining process and assuming that this change reduces the inlet ore to 60%, by discarding 40% of material without gold and by reducing supply consumption by 25%. By improving the system efficiency, the exergy destroyed is reduced and the emissions to the environment diminish. Therefore, this method may be implemented as a basic guideline when it comes to decision-making processes in the planning of the extractive processes by integrating the environmental component with gold production.