Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The equilibrium between free, conducting ions and associated, nonconducting species was examined for solutions of electrolytes in sulfur dioxide experimentally and theoretically and in several other nonaqueous solvents theoretically. New values of equilibrium constants for this process were obtained by a suitable analysis of equivalent conductance data measured as a function of concentration at constant temperature; limiting equivalent conductances were also obtained. The equilibrium was studied at several temperatures and the enthalpy and entropy changes for the equilibrium process were obtained from the temperature dependence of the free energy change. The results are summarized in Table 1. [TRUNCATED] / 2999-01-01

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The effects of sulfur dispersing agents (SDAs) in the oxygen pressure leaching of nickel concentrate at medium temperature were investigated. Liquid sulfur-aqueous solution interfacial tensions and liquid sulfur-sulfide mineral contact angles were measured at 140ºC, 690 kPa overpressure by nitrogen, and 1.0 mol/L NiSO₄. The effects of SDAs including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid were evaluated by the calculation of the work of adhesion in the liquid sulfur-sulfide mineral-aqueous solution systems. It was found that the sulfide mineral surface is sulfophobic at pH from 4.1 to 4.5 due to the hydrolysis of nickel (II) ions to nickel hydroxide and the deposition of nickel hydroxide on the mineral surface. These findings apply to four different sulfide mineral systems, including pentlandite, nickeliferous pyrrhotite, pyrrhotite, and chalcopyrite. Lignosulfonate, Quebracho, and humic acid were found to significantly reduce the work of adhesion indicating they should be effective SDAs. OPD is ineffective in changing the work of adhesion of sulfur on the mineral sulfides indicating that it is not a good candidate for sulfur dispersion. The adsorption behavior of SDAs, including lignosulfonate, Quebracho, OPD, and humic acid on elemental sulfur and on nickel sulfide concentrate was investigated. Lignosulfonate, Quebracho, and humic acid were characterized by their infrared spectra. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) in the absence or presence of SDAs. The adsorption of lignosulfonate on molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was investigated at ambient temperature. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was found to be monolayer adsorption, which was fitted to the Langmuir adsorption isotherm. Electrostatic interaction and ion-binding are the possible mechanisms for the adsorption of lignosulfonate and humic acid on the nickel concentrate. Quebracho is adsorbed on the nickel concentrate through hydroxyl and sulfonate groups. OPD cannot adsorb on the molten sulfur surface. OPD undergoes chemical change in aqueous solution in the presence of ferric at ambient temperature. Oxygen pressure leaching experiments were performed at 140 or 150ºC under 690 kPa oxygen overpressure. The particle size of the nickel concentrate was found to be an important factor in leaching. During the leaching of nickel concentrate with P₈₀ of 48 µm, the SDAs were believed to be fully degraded before nickel was fully extracted. At most 66% nickel was extracted in the presence of 20 kg/t OPD. Fine grinding (P₈₀ of 10 µm) was sufficient for 99% nickel recovery at low pulp density while at high pulp density, the nickel extraction increased from 95% to 99% with addition of SDAs. Based on the leaching results on a nickel concentrate sample (-44 µm), OPD had the effect of increasing the nickel extraction to about 99%, followed by Quebracho (83%), lignosulfonate (72%), and humic acid (61%). It is suggested that the oxidation product of OPD is effective in solving the sulfur wetting problem in leaching. 97% nickel was recovered in the presence of 5 g/L chloride ion. Chloride ion has an effect to enhance the performance of lignosulfonate under leaching conditions.

The effects of sulfur dispersing agents (SDAs) in the oxygen pressure leaching of nickel concentrate at medium temperature were investigated. Liquid sulfur-aqueous solution interfacial tensions and liquid sulfur-sulfide mineral contact angles were measured at 140ºC, 690 kPa overpressure by nitrogen, and 1.0 mol/L NiSO₄. The effects of SDAs including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid were evaluated by the calculation of the work of adhesion in the liquid sulfur-sulfide mineral-aqueous solution systems. It was found that the sulfide mineral surface is sulfophobic at pH from 4.1 to 4.5 due to the hydrolysis of nickel (II) ions to nickel hydroxide and the deposition of nickel hydroxide on the mineral surface. These findings apply to four different sulfide mineral systems, including pentlandite, nickeliferous pyrrhotite, pyrrhotite, and chalcopyrite. Lignosulfonate, Quebracho, and humic acid were found to significantly reduce the work of adhesion indicating they should be effective SDAs. OPD is ineffective in changing the work of adhesion of sulfur on the mineral sulfides indicating that it is not a good candidate for sulfur dispersion. The adsorption behavior of SDAs, including lignosulfonate, Quebracho, OPD, and humic acid on elemental sulfur and on nickel sulfide concentrate was investigated. Lignosulfonate, Quebracho, and humic acid were characterized by their infrared spectra. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) in the absence or presence of SDAs. The adsorption of lignosulfonate on molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was investigated at ambient temperature. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was found to be monolayer adsorption, which was fitted to the Langmuir adsorption isotherm. Electrostatic interaction and ion-binding are the possible mechanisms for the adsorption of lignosulfonate and humic acid on the nickel concentrate. Quebracho is adsorbed on the nickel concentrate through hydroxyl and sulfonate groups. OPD cannot adsorb on the molten sulfur surface. OPD undergoes chemical change in aqueous solution in the presence of ferric at ambient temperature. Oxygen pressure leaching experiments were performed at 140 or 150ºC under 690 kPa oxygen overpressure. The particle size of the nickel concentrate was found to be an important factor in leaching. During the leaching of nickel concentrate with P₈₀ of 48 µm, the SDAs were believed to be fully degraded before nickel was fully extracted. At most 66% nickel was extracted in the presence of 20 kg/t OPD. Fine grinding (P₈₀ of 10 µm) was sufficient for 99% nickel recovery at low pulp density while at high pulp density, the nickel extraction increased from 95% to 99% with addition of SDAs. Based on the leaching results on a nickel concentrate sample (-44 µm), OPD had the effect of increasing the nickel extraction to about 99%, followed by Quebracho (83%), lignosulfonate (72%), and humic acid (61%). It is suggested that the oxidation product of OPD is effective in solving the sulfur wetting problem in leaching. 97% nickel was recovered in the presence of 5 g/L chloride ion. Chloride ion has an effect to enhance the performance of lignosulfonate under leaching conditions.

The effects of sulfur dispersing agents (SDAs) in the oxygen pressure leaching of nickel concentrate at medium temperature were investigated. Liquid sulfur-aqueous solution interfacial tensions and liquid sulfur-sulfide mineral contact angles were measured at 140ºC, 690 kPa overpressure by nitrogen, and 1.0 mol/L NiSO₄. The effects of SDAs including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid were evaluated by the calculation of the work of adhesion in the liquid sulfur-sulfide mineral-aqueous solution systems. It was found that the sulfide mineral surface is sulfophobic at pH from 4.1 to 4.5 due to the hydrolysis of nickel (II) ions to nickel hydroxide and the deposition of nickel hydroxide on the mineral surface. These findings apply to four different sulfide mineral systems, including pentlandite, nickeliferous pyrrhotite, pyrrhotite, and chalcopyrite. Lignosulfonate, Quebracho, and humic acid were found to significantly reduce the work of adhesion indicating they should be effective SDAs. OPD is ineffective in changing the work of adhesion of sulfur on the mineral sulfides indicating that it is not a good candidate for sulfur dispersion. The adsorption behavior of SDAs, including lignosulfonate, Quebracho, OPD, and humic acid on elemental sulfur and on nickel sulfide concentrate was investigated. Lignosulfonate, Quebracho, and humic acid were characterized by their infrared spectra. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) in the absence or presence of SDAs. The adsorption of lignosulfonate on molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was investigated at ambient temperature. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was found to be monolayer adsorption, which was fitted to the Langmuir adsorption isotherm. Electrostatic interaction and ion-binding are the possible mechanisms for the adsorption of lignosulfonate and humic acid on the nickel concentrate. Quebracho is adsorbed on the nickel concentrate through hydroxyl and sulfonate groups. OPD cannot adsorb on the molten sulfur surface. OPD undergoes chemical change in aqueous solution in the presence of ferric at ambient temperature. Oxygen pressure leaching experiments were performed at 140 or 150ºC under 690 kPa oxygen overpressure. The particle size of the nickel concentrate was found to be an important factor in leaching. During the leaching of nickel concentrate with P₈₀ of 48 µm, the SDAs were believed to be fully degraded before nickel was fully extracted. At most 66% nickel was extracted in the presence of 20 kg/t OPD. Fine grinding (P₈₀ of 10 µm) was sufficient for 99% nickel recovery at low pulp density while at high pulp density, the nickel extraction increased from 95% to 99% with addition of SDAs. Based on the leaching results on a nickel concentrate sample (-44 µm), OPD had the effect of increasing the nickel extraction to about 99%, followed by Quebracho (83%), lignosulfonate (72%), and humic acid (61%). It is suggested that the oxidation product of OPD is effective in solving the sulfur wetting problem in leaching. 97% nickel was recovered in the presence of 5 g/L chloride ion. Chloride ion has an effect to enhance the performance of lignosulfonate under leaching conditions. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate