Abstract

CORRALES-PEREZ, Daniel  and  ROMERO, Francisco Martín. Hazard assessment of mine tailings in Nicaragua and Mexico and alternatives for remediation. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.3, pp.427-446. ISSN 1405-3322.

A geochemical study was carried out in order to assess the hazards posed by tailings from various mining areas in Nicaragua (El Limon, La Libertad and Bonanza) and Mexico (Taxco). The "tailings from Nicaragua" showed the lowest concentrations (mg/kg) of potentially toxic elements such as Pb (9 - 871), As (16 - 35), Ba (97 - 263), Zn (50 - 1060), Cu (50 - 125). On the other hand, Corrales-Pérez y Romero the "tailings from Mexico" showed higher concentrations (mg/kg) of potentially toxic elements such as Pb (3049 - 5248), As (1176 - 2746), Ba (334 - 619), Zn (474 - 5559), Cu (97 - 204). Likewise, these tailings reported relatively low concentrations (mg/kg) of other potentially toxic elements such as Ag (41 - 70), Ni (114 - 133) and Cd (16 - 50), that were not present in the tailings from Nicaragua. Another difference between the studied tailings is Fe content, which is greater (Fe = 7.0 % - 15.9 %) in the tailings of México than in tailings from Nicaragua (Fe = 0.8 % - 3.4 %). Our results indicate that the tailings from Mexico are dangerous because they generate acid mine drainage. This can be proved by leachate acidity (pH = 2.2 - 2.5). Besides, these leachates show high concentration6. Agradecimientoss of sulfates (SO₄²- = 3509 - 12249 mg/L) as well as potentially toxic dissolved elements (mg/L) such as As (0.7 - 1.3), Cd (2.8 - 12.3), Cu (6.1 - 23.7), Fe (459.3 - 1505.0) and Zn (334.5 - 1262.5). In contrast, the tailings from Nicaragua are not dangerous since they do not generate acid drainage. This can be confirmed by the leachates' basic character (pH = 8.0 - 8.8), low sulfate concentrations (SO₄²- = 2.8-265.6 mg/L) and absence of potentially toxic dissolved elements. In order to suggest alternatives to reduce the hazards posed by the tailings from Mexico, the efficiency of different rock types outcropping in the area was evaluated in terms of their capabilities of neutralizing pH and controlling potentially toxic dissolved elements in the acidic drainage that may be generated from these wastes during the rainy season. Results of batch leaching tests indicate that rocks significantly increase the pH (up to 6.1 - 7.0) in the treated leachate due to the dissolution of calcite, dolomite and, possibly, muscovite. The neutralization of acid leachate promotes the removal of sulfates that precipitate like gypsumand remove metal ions due to the formation of the corresponding metal oxyhydroxides. Furthermore, As removal is inferred to be due to its retention, via sorption processes, on the surfaces of the Fe-oxyhydroxides that precipitate during the treatment. The removal of heavy metals such as Zn and Cd was partial (43 % - 92 % for Zn and 28 - 100% for Cd). However, hydrogeochemical modeling suggests that removal of these elements would be efficient if pH or Eh are slightly increased during treatment.

Keywords : tailings; Nicaragua; Mexico; hazard; acid mine drainage treatment.