Remediation of metal-contaminated mine tailings by the application of organic and mineral amendments

Tailings are generally characterized by severe physicochemical conditions that limit the establishment of vegetation. The present study aimed to select suitable combinations of organo-mineral amendments to improve the physicochemical, biochemical, and biological properties of spolic technosols, highly contaminated with metals. Several substrates were prepared by mixing mine tailings (MT) of an abandoned mining area with non-contaminated agricultural soil (anthrosol), green waste compost, lime, and rock phosphate at different rates: S1 — 50% of MT + 50% of agricultural soil; S2 — S1 + 3% of lime (CaCO3); S3 — S1 + 6% of rock phosphate; S4 — S1 + 10% of compost; S5 — S1 + 10% of compost + 3% of lime; S6 — S1 + 10% of compost + 6% of rock phosphate. Untreated MT and agricultural soil were analyzed immediately, and 8 months after incorporating the amendments. Heterotrophic microorganisms were not recovered from untreated MT due to the highly acidic pH and available metal concentrations. However, the addition of organo-mineral amendments ameliorated the tailings’ characteristics by increasing pH, conductivity, total organic carbon, and available P levels. Moreover, after 8 months, heterotrophic microorganisms were recovered from those substrates and dehydrogenase activity was enhanced. The incorporation of agricultural soil and green waste compost mixed either with lime (S5) or rock phosphate (S6) was the most effective treatment. Both S5 and S6 mixtures successfully reduced the environmental risk posed by tailings, suggesting the potential use of these amendments for the remediation of pyrite mines.