EFFECT OF CHEMICAL-AGRONOMIC TREATMENTS ON THE EXTRACTABLE AND FREE CD, CU, PB AND ZN LEVELS SUITABLE FOR REMEDIATING MINE TAILINGS AND POLLUTED SOILS

Mining industry disposes mine tailings and wastes of heavy metals (HM) such as Cd, Cu, Pb, and Zn on common soils. There are several studies related to chemical treatments aimed to reduce danger in these potentially toxic elements (EPTs). Zimapán is a mining district in Hidalgo state, in México, where different dams with a considerable total amount of mine-tailings are located. The aim of this work was to study different agrochemical remediation proposals to manage and remediate mine-tailing dams and heavy metal polluted soils. The proposals were based on the decrease and control of Cu, Cd, Pb and Zn chemical species solubility. Mine tailings and soil samples were collected at El Monte and el Carrizal mines at Zimapán. Four agrochemical treatments were applied to six different mine tailings-soil mixtures considering instrumental inorganic complexing agents like: agricultural lime, gypsum, fertilizer (FERT) and organic matter (MO) as compost. Three different doses were tested, according to the initial metal extractability in: HAcO 0.2N (highest dose), DTPA (medium dose) and H₂O (lowest dose). Bio-toxicity assays were conducted to study the response of a indicator plant HM released from the soil-mine tailings systems with or without treatment measuring the root length. Initial levels of HM in mixtures were below the maximum permitted levels by Mexican laws. The best results were obtained with FERT and OM treatments, extractability of Zn was reduced in a 92% to 93% respectively. Lime and gypsum did not show effectiveness to suppress the extractable quantities of metals. Bio-toxicity studies showed a negative effect on the root plant growth caused by increased HM in the mixture. FERT and OM resulted in positive effects on the root growth, especially at pure tailing systems. FERT and OM can be applied to amend contaminated soils with HM being used to reduce the extractable levels of HM and to promote the development of plants, in phytoremediation and/or phytomining activities.