Evaluation of the extractive gold process: open-pit mining through exergy analysis

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.