A comprehensive assessment of gold leaching wastewater through pollution and water quality indices. Case study: Small scale extraction facilities in the department of Caldas—Colombia

Abstract

This study introduced a comprehensive methodology (the Six-Indices method for Water Pollution Assessment) to evaluate the quality of gold leaching effluents. Sampling was conducted for 14 months in small-scale gold mining facilities in the department of Caldas, Colombia. 23 physicochemical parameters were selected based on environmental regulations, standards of use for agricultural purposes and WHO recommendations. They covered general characteristics of effluents and critical inputs of the leaching process. 15 (pH, COD, TSS, CN−, Cl−, SO42−, S2−, Cd, Zn, Cu, Cr, Fe, Ni, Ag, and Pb) of them exceeded permissible limits. Multivariate statistical analysis (Person's correlation and hierarchical clustering analysis) and six Wastewater Quality Indices (WWQIs: Arithmetic Weighted Water Quality Index, WAWQI, Synthetic Pollution Index, SPI, Index of Water Pollution, WPI, Comprehensive Pollution Index, CPI, Heavy Metal Pollution Index, HPI, and Degree of Pollution, Cd) were used to comprehensively assess the effluent contamination. Key pollutant interactions (hydrocarbons & fats and oils, Zn & CN−, Cu & Cl−, as well as CN− & COD & SO42−) were revealed guiding targeted mitigation strategies. CN− and heavy metals were the main pollutants, posing serious environmental risks due to their high levels. The calculated HPI value was above the critical level of 100, indicating that the artisanal gold leaching operations in the studied area could be hazardous to human health. This study provides a starting point for developing effective and sustainable strategies to manage wastewater in mining regions in Colombia and other areas with similar mining practices.