Abstract

BURILLO, Juan Carlos; CARDONA, Antonio; CASTRO-LARRAGOITIA, Javier  and  MONTES, Isidro. Determination and hydrogeochemical modeling of mining leachates in San Luis Potosí, Mexico. Bol. Soc. Geol. Mex [online]. 2017, vol.69, n.3, pp.637-654. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2017v69n3a7.

A Hydrogeochemical modelling approach was used to understand differences between mine leachates and aqueous extracts of stream sediments and sulfide mine residues from the historical mine district of San Luis Potosí. In Both solutions, leachates and aqueous extracts, Al, Ca, Fe, SO4 and Zn species predominate. Concentration of these species was higher in mine residue extracts than stream sediment extracts. Residues present two types of conditions: free without protection and semi-confined. The concentration of aqueous species from extracts of mine residues exposed to the weather was higher than semi-confined ones. XRD mineralogical characterization indicates the presence of jarosites in aqueous extracts and leachates. Configuration of reaction path reaction as a titration model shows dissolution-precipitation of minerals: gibbsite Al (OH)3, gypsum (CaSO4.2H2O), galena (PbSO4), alunite KAl3 (OH) (SO ) and melanterite FeSO :7H O occurring, as a function of the quantity of calcite reacted and pH. In general, Fe exists as Fe2+ and S as SO 2-The use of a mix model, mine leachate (pH < 3) vs rain water solution, originated a near neutral pH solution. Evaporation of leachates produced metallic sulfates, gypsum and melanterite, which were founded in mine residues XRD analysis too. Water evolves from HCO3 -Ca to SO 2--Ca type, probably due to common ion effect. Moreover, the most contaminated water extracts come from mine residues, which correspond to leachates spatially, reflecting the limited capacity of stream sediments to retain metals. This paper shows the importance of complement mine residue characterization, based on current environmental standards in Mexico, in order to propose best basis remediation plans.

Keywords : mine leachates; San Luis Potosi; mine residue characterization; hydrogeochemical modeling.