Collaborative Research: Thermodynamic Properties of Solutions Generated by Acid Rock Drainage: Fe2O3-SO3-H2O systems

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

0230323 Kettler The oxidation of metal sulfide minerals can generate solutions that have pH values as low as -3.6 and contain less than 190 g H2O per liter of solution. Such acid rock drainage can be generated in any locality where sulfides are exposed to the weathering process, including mine workings and wastes, exposed coastal sediments, and exposures of ancient marine sedimentary rocks. These solutions have a high environmental impact that is estimated to be in the billions of dollars in North America alone. Acid rock drainage has also generated large ore deposits, makes possible the economic recovery of copper and other metals from disseminated mineralization, and hosts some unusual microbial communities. The ability to model the chemistry of these systems accurately would aid greatly in efforts to remediate environmentally sensitive sites, improve the recovery of metals by hydrometallurgic processes, and better understand the processes that control diurnal and seasonal variations in the chemistry of acid rock drainage. Such detailed modeling is currently impossible for many systems: activity coefficients are lacking for strongly acidic ferric sulfate brines as are some basic equilibrium constants needed to model the aqueous and mineral species effectively. This project will take three steps to remove some of those obstacles. 1)Osmotic coefficients of ferric sulfate and mixed ferric-ferrous sulfate brines will be measured. The data will be modeled to retrieve interaction parameters necessary to calculate activity coefficients using the specific ion interaction model. 2)The association constants for ferric sulfate complexes will be measured using a mercury/mercurous sulfate concentration cell. These association constants will be necessary to complete the activity modeling. 3)The solubility of jarosite will be measured over a range of temperatures and ionic strength and in different ionic media. This research will improve significantly the ability to accurately model natural acid-sulfate waters.