Hazard Study of Sludge from Mining Wastewater Treatment Systems (Tailings), Accumulation of Contaminants and Potential Utilization Proposals

The increase in gold mining activities has led to a substantial rise in tailings generation, which carry distinct physicochemical and microbiological properties. This study aimed to evaluate the hazardous characteristics of mining tailings using the CRETIB (corrosivity, reactivity, explosiveness, toxicity, ignitability, biological-infectious) methodology. The research analyzed concentrations of heavy metals including arsenic, cadmium, copper, chromium, lead, mercury, nickel, and zinc, alongside parameters such as pH, cyanide, hydrogen sulfide, and coliform bacteria. Tailings samples were collected from a mine in Ponce Enriquez, Ecuador, at the surface and at a depth of 2 m across three monitoring campaigns. The results indicate that the tailings do not exhibit hazardous characteristics according to CRETIB criteria. While arsenic, chromium, copper, nickel, zinc, and mercury concentrations showed significant differences between the surface and 2 m depth, accumulating at the bottom of the tailings dam by 30–72%, parameters such as pH, cyanide, and hydrogen sulfide were higher at the surface, likely due to volatilization and precipitation effects. Lead did not show significant differences, but also tended to accumulate at depth. These findings suggest that the tailings could be safely utilized in the production of construction materials such as bricks, geopolymer concrete, and fiber cement, promoting circular economy practices and sustainable development in mining.