Resumo

ROMERO, Francisco Martín; ARMIENTA, María Aurora; GUTIERREZ, Margarita Eugenia  e  VILLASENOR, Guadalupe. Geological and climatic factors determining hazard and environmental impact of mine tailings. Rev. Int. Contam. Ambient [online]. 2008, vol.24, n.2, pp.43-54. ISSN 0188-4999.

A comparative geochemical study was conducted within oxidized tailings in mining regions of Nacozari-Sonora (Cu-sulfide of porphyry copper deposits), Santa Bárbara-Chihuahua (Pb-Zn-Cu hydrothermal veins), Zimapán-Hidalgo (Pb-Zn-Ag skarn) and Taxco-Guerrero (Pb-Zn-Cu hydrothermal veins). These mining wastes were studied in order to evaluate the capacity of acid drainage generation and to evaluate the importance of geological and climatic factors in their potential hazard and environmental impact. Consequent with the main mineralogy of the exploited ore bodies, the Nacozari's tailings contain low total concentrations of As (8.9 mg kg^-1), Pb (< 20 mg kg^-1) and Zn (91 mg kg^-1) and high total concentrations of Cu (535 mg kg^-1) and Fe (6.9 %); whereas tailings from Santa Bárbara are characterized by the high total concentrations of As (1140 mg kg^-1), Pb (6669 mg kg^-1), Zn (12531 mg kg^-1) and Cu (851 mg kg^-1). However, the lowest concentration of Fe (3.4 %) was measured in the Santa Bárbara's tailings. In tailings from Zimapán were determined the highest total concentrations of As (12735 mg kg^-1) and Fe (16.5 %), and high total concentrations of Pb (2034 mg kg^-1), Zn (2982 mg kg^-1) and Cu (600 mg.kg^-1). Finally, total concentrations of potentially toxic elements (PTE) in tailings from Taxco are 585 mg kg^-1 As, 1479 mg kg^-1 Pb, 460 mg kg^-1 Zn, 72 mg kg^-1 Cu and 9.4 % Fe. The high total Fe concentrations in tailings from Nacozari, Zimapán and Taxco indicate the relative abundance of Fe-sulfides, mainly pyrite. Oxidation of pyrite and insufficiency of acid-neutralizing minerals have produced low pH values in tailing leachates: pH_Zimapán = 2.6, pH_Taxco = 2.8 and pH_Nacozari = 3.0. Acidic leachates of Nacozari's tailings contain high concentration of dissolved SO₄^2-, Fe, Cu and Zn. The acidic leachates of tailings from Zimapán and Taxco additionally contain dissolved As and Pb. These results indicate that in Zimapán and Taxco there is a greater environmental risk because the acidic leachates that contain high concentrations of PTE drain to streams of the surroundings and although they do not affect the quality of waters, cause the accumulation of PTE in sediments. Chemical and mineralogical results of tailing from Santa Bárbara indicate the abundance of calcite and low pyrite content in these tailings. The pH values of leachates from Santa Bárbara's tailings are slightly above neutral (pH = 8.4) and are characterized by the lowest concentrations of dissolved PTE, which indicates that the acid-neutralizing capacity of the tailings has been sufficient to consume the acidity generated by sulphide oxidation. The results of this study allow to conclude that the mineralogy of the exploited ore bodies is the main factor that influences the acid drainage generation from the studied tailings impoundment, and climatic factors are determining in the processes that cause the dispersion of these mine waste and its leachates to the surroundings.

Palavras-chave : mine tailings; acid drainage; geological and climatic factors.