Numerical Modelling of the Effectiveness of Sealants in Retarding Acid Mine Drainage from Mine Waste Rock

Abstract

An extensive study was carried out to determine the effectiveness of various sealants in retarding or preventing the production of acid mine drainage (AMD) from mine waste rock and reactive tailings. In addition to cementitious compounds, the sealants included polymer and organic based solutions. Coated and uncoated (control) samples of mine waste rock and tailings were placed in large leaching columns and the leachate solutions were regularly analyzed for parameters such as pH level, redox potential (Eh), conductivity, sulphate and the dissolved heavy metals, Fe, Ni, and Cu. Concurrent with the laboratory tests, samples were exposed to weathering effects for seven months, which included one complete winter season.Mathematical models were fitted to moving averages of the measured data to establish the relationships between pH and Eh, and conductivity and sulphate concentrations which are necessary for indicating AMD production or lack thereof. These models also enabled the estimation of the terminal pH and Eh values. The results indicate that uncoated samples produce significant AMD and that the polymer and organic based solutions were more effective in retarding AMD than the cementitious coatings. Resume-On a mene une etude poussee afin de determiner l'efficacite de divers produits d'etancheite a retarder ou prevenir la generation d'ecoulement acide de mine (EAM) provenant des rejets rocheux de mine et des residues reactifs. En plus de composes a base de ciment, les produits d'etancheite incluaient des solutions a base de polymere et de materiau organique. On a place des echantillons recouverts et nonrecouverts (controle) de rejets rocheux de mine et de residus dans de grandes colonnes de lessivage. On a analyse regulierement divers parametres des solutions de lessivage, tels que Ie niveau de pH, Ie potential redox (Eh), la conductivite, Ie sulfate et les metaux lourds dissous, Fe, Ni et Cu. En parallele avec les essais de laboratoire, on a expose des echantillons aux effets de desagregation par les intemperies pendant sept mois, parmi lesquels une saison hivernale complete. On a ajuste des modeles mathematiques aux moyennes changeantes des donnees mesurees afin d'etablir les relations entre Ie pH et Ie Eh et entre la conductivite et la concentration de sulfate, necessaires a la detection d'EAM. Ces modeles ont aussi permis l'evaluation des valeurs terminales de pH et de Eh. Les resultats indiquent que les echantillons non-recouverts produisent un EAM important et que les solutions a base de polymere et de materiau organique etaient plus effectives a retarder l'EAM que les revetements a base de ciment.

Aplicación de residuos de combustión del carbón para el autosellado de balsas mineras productoras de drenaje ácido de mina

“…Existen otros ensayos encaminados a prevenir o retardar la producción de AMD. Así, Farah et al (1997) propusieron la aplicación de aislantes fabricados con cemento o resinas naturales sobre residuos mineros dispuestos en enormes pilas expuestas a condiciones de meteorización naturales. Ambos tipos de aislantes forman una capa cuya principal función es la de proteger a los residuos de su oxidación, y por tanto, retardar la generación de AMD.…”

“…A second remediation option is the physical treatment, which consists in the application of synthetic sealants on the tailings to prevent oxygen ingress and water infiltration (e.g. Farah et al, 1997;Romano et al, 2003). These cover systems minimize waste oxidation and, hence, AMD generation.…”