Papers by Author: R.E. Rivera-Santillán

Abstract: Mining activities have deleterious impacts on the environment, such as the formation of acid mine drainage (AMD), which occurs by the action of acidophilic bacteria in tailing deposits, generating diverse types of pollution. Hence it is important to examine the potential of mining waste material to produce acid solutions. Currently, the determination of the net potential of neutralization considers the criteria of the Enviromental Protection Agency of the United States. It was concluded from experiments carried out with diverse samples from Mexico that the tailing samples studied have a high capacity of autoneutralization; although the drainage waters from the tailings and the aqueous extracts from tailing samples react acidic. It is obvious that this method of determination of the neutralization potential and the criteria accepted at the moment do not reflect the reality of the problem. The sulfide analysis in aqueous solution consists of an indirect titration of the excess iodine in two phases (water/ CCl4) with a thiosulfate solution using starch as indicator. Since the iodine is insoluble in water, the equivalent point can be uncertain because part of the iodine can be retained by the starch. Thus, the XOCHIQUETZALLI method for the sulfide ion titration, has been developed. It covers the chemical aspects of the titration procedure, such as the suitable reagents and the maximum permissible concentrations, based on the law of Lambert and Beer. This titration procedure was successfully applied to determine dissolved sulfides extracted from tailing samples.

Abstract: The exploitation of mineral deposits generates large amounts of wastes such as fine size particles, known as tailings. Mine wastes are characterized by the presence of pyrite, pyrrotite, galene, sphalerite, chalcopyrite and arsenopyrite. One of the most important environmental problems derived from the treatment and disposition of mining tailings is acid mine drainage (AMD) which results from the oxidation of the sulfurous minerals contained in these tailings. The acid generated is produced by a series of complex chemical reactions; the production rate is controlled by leaching microorganisms, which are present mining processes. In this work the bioleaching kinetics of heavy metals such as Cu, Fe, Zn, Cd, Pb, Ni and As, from a Tizapa tailing sample in presence of mesophilic and moderately thermophilic bacteria were studied and compared. The microorganisms used in this work were previously adapted to the tailing sample by the conventional method of successive steps. The percentage of dissolution of heavy metals at 45°C was smaller than at 35°C and the value of parameters such as redox potential and bacterial growth increased with temperature. Bioleaching studies were compared with the corresponding control systems.