New Xochiquetzalli Method for Sulfide Ion Determination in Aqueous Media--Application to Tailings Analysis

摘要

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/ CCl_4) 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.