Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 23-26). Also available via the Internet.

The intake of lead into the human body has become an area of major concern because high levels of lead are harmful and can cause physiological damage, especially in children. It has been suggested that adding NaSiO₃might control Pb²⁺ contamination of drinking water supplies (c.g., Thresh 1922). PbSiO₃ (am), the white, gelatinous precipitate formed by mixing Na₂SiO₃ solutions with Pb²⁺ bearing solutions, dissolves at pH<7 by the reaction: PbSiO₃ + H₂O + 2H⁺ = Pb²⁺ + H₄SiO₄ Measurements of the solubility of PbSiO₃ show that the K_eq for this reaction is 7.41x10⁵ and the ΔG_f° (PbSiO₃ (am)) is 1061.81 kJ mol⁻¹. This high value of K means that extreme amounts of a Na₂SiO₃ additive are required in a water supply system to reduce the Pb²⁺ concentration to the EPA MCL action level of 15 ppb. Furthermore, the high pH values that result from NaSiO₃ water treatments lead to the formation of lead hydroxycarbonate (hydrocerussite) because this carbonate phase is more stable in the pH range of natural waters (pH 5-8) than lead silicate. / Master of Science

The present thesis gives a summary of results obtained through theoretical and experimental studies of systems with relevance to copper smelting and converting. Many chemical elements are involved in the copper production pro­cesses and a detailed experimental study would be very time- consuming and expensive. A complicating fact is also the corrosivity of the liquid phases towards container material. A powerful alternative is equilibrium calculations, in which models for the liquid phases as well as reliable basic thermodynamic data are needed. In the present thesis, a generalized structure based model for liquid silicates was developed and used in assessments of the sys­tems PbO-SiO2, Fe-O-SiO2, CuO0.5-SÌO2 and Cu-Fe-O-SiO2. In the model, the non-ideal silicate melt is treated as an ideal solu­tion but containing a few complexes. The PbO-Si02 melt could be described by introducing the complexes Pb3Si207, Pb4Si4010 and Pb13Si12O37 in addition to the components PbO and Pb2Si04. The species considered in the Fe-O-SiO2 melt were FeO, FeO1.5, Fe2Si04, Fe3Si207, Fe3Si6O15 and in the CUO0.5-SiO2 melt CuO0.5 ana CU4SiO4. Trie calculated phase diagrams, the activities of me­tal oxides and the oxygen partial pressures were all in good agreement with the published data. Two of the papers in this thesis concern the determination of Gibbs free energies for Cu2S(s,l) and Ca2Fe2O5(s) through emf measurements utilizing a solid electrolyte. Activities and termi­nal solubilities in the solid solution [Fet,Ca]0 were also deter­mined. The results obtained from the quantitative equilibrium calcula­tions for conventional copper smelting and converting were used to outline the overall reactions taking place and the outcome of changes in process parameters. Comparison with observed values, however, showed that the copper and magnetite contents in slag were calculated too low. These discrepancies could be completely explained by using a non-equilibrium approach in which the con­verter was assumed to consist of several segments with concentra­tion gradients between the segments. / digitalisering@umu.se