Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 277-298). Also available via the Internet.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1929. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed Oct. 6, 2009). Includes bibliographical references (p. 18).

Thesis (M.S.)--Virginia Polytechnic Institute, 1934. / Abstract. Includes bibliographical references (leaves 145-149). Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

[No abstract submitted] / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The changes in the adsorption characteristics of potassium ethyl xanthate (KEtX) on galena (PbS) and marmatite [(Zn,Fe)S] due to illumination have been investigated. Studies by others have indicated that: (1) the amount of surfactant adsorbed by a semiconductor depends on its n-type or p-type character, (2) copper activation of sphalerite (ZnS) is required for flotation, (3) sphalerite is a semiconductor with an energy gap of 3.6 eV whereas galena is a semiconductor with an energy gap of 0.3 7 eV. The amount of xanthate adsorbed from aqueous solution on galena and marmatite was found to depend on both the intensity and photon energy (0.5 to 3.5 eV) of the incident light. In the galena system, increasing the light photon energy above the energy gap value increased adsorption of xanthate. The amount of xanthate adsorbed by the p-type galena was three times the amount adsorbed by the n-type galena. This suggested that the reaction may involve the transfer of an electron from the adsorbate to the adsorbent. The effect of the presence of an oxide film on the surfaces of galenas was also investigated and appeared to be less significant than the type of charge carrier originally dominant in the mineral. When copper-activated marmatite was illuminated by light with photon energies lower than the intrinsic gap (3.6 eV), adsorption of xanthate was less than when the mineral was kept in darkness. Similar "photodesorption" effects have been reported in the literature. These were explained by excitation of electrons from traps to the conduction band and subsequent recombination with holes in the valence band. Fewer charge carriers would then have been available to participate in the adsorption reactions. Flotation experiments agreed with the adsorption results above. Flotation recovery of activated marmatite dropped ca. 10% when the mineral was illuminated with a high intensity of 0.6 eV photons as compared to the recovery in daylight. A model that takes into account the surface concentration of electrons and the type and concentration of impurities is discussed. The activity and selectivity of surface reactions are explained in terms of the electrochemical potential, i.e. the Fermi energy level, the actual position and/or displacement of which is affected by the impurities present. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

In the course of the experimental work conducted it was found that when galena was treated with chromate salts or dichromate salts in an aqueous solution, lead chromate identified by infrared spectroscopy was the main species adsorbed on the galena surface. The formation of chromium hydroxide or chromium oxide was not observed. Thermodynamic considerations of the Pb-Cr-S-H₂0 bulk system indicate the very stable character of lead chromate as shown in the potential-pH diagram constructed in this study. It is also seen that no stable domain of lead dichromate exists. The adsorption rate as well as adsorption amount of dichromate at the pseudo-equilibrium condition increases with the decrease in pH value. This phenomenon supports the fact experienced in galena flotation that a dichromate salt is a much more efficient depressant than is an equivalent chromate salt. The desorption of xanthate from galena surfaces covered with more than a monolayer thickness of xanthate was found to be possible by adding chromate salt to the system, whereas chromate desorption from galena surfaces due to xanthate addition was not observed. It was found that under comparable conditions xanthate adsorbed on lead chromate surfaces oxidized to dixanthogen much more readily than xanthate adsorbed on galena surfaces. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Electrochemical methods and small scale flotation tests were used to study the effects of sulphur dioxide and potassium amyl xanthate on the floatabilities of pentlandite, chalcopyrite and nickeliferous pyrrhotite, at pH 5.5. Mixed potentials of all three mineral systems were positive to the dixanthogen/xanthate redox couple, even in the presence of aqueous SO₂. Thus the existence of dixanthogen is thermodynamically favoured in all these systems. The tests also indicated that adsorption of xanthate by: (i) chalcopyrite is enhanced by SO₂; (ii) pentlandite is impaired by SO₂; (iii) pyrrhotite is unaffected by SO₂; Anodic polarization curves, determined on mineral electrodes, suggested that, in xanthated systems, the collector (probably dixanthogen) forms a film on the electrodes. This film inhibits the continued electron transfer reactions on the surface. The protective character of the film is higher for chalcopyrite (increased by SO₂), than for pentlandite (decreased by SO₂), than for pyrrhotite (unaffected by SO₂). Cathodic polarization curves indicated that the cathodic process, on pentlandite and pyrrhotite electrodes, is controlled by oxygen reduction. The reduction of oxidized species on the surface is suggested as the controlling mechanism on chalcopyrite electrodes. Small scale flotation tests showed that the presence of SO₂ increases an already very high,recovery of chalcopyrite; decreases a high recovery of pentlandite, and decreases further a very low recovery of pyrrhotite. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

This dissertation involves a study of the collector-depressant equilibria of the flotation system potassium ethyl xanthate-potassium cyanide-molybdenite, based upon mineral-air bubble contact measurements made by a modified captive bubble technique. The Cook theory of single site free acid adsorption is used to interpret the data. The standard free energies of adsorption of ethyl xanthic acid and hydrocyanic acid on molybdenite are calculated.

A dissertation submitted to the faculty of Engineering and the Built Environment University of Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering January, 2019 / The prevalence and treatment of low grade, finely disseminated iron ore has resulted in the production of primary and secondary slimes that constitute potential resources. Slimes processing is hindered by the particle size limits of current process equipment and this dissertation explores the potential of coupling selective flocculation with magnetic and gravity separation to improve separation efficiencies. Base case tests (without selective flocculation) were conducted on the SLon-100 (laboratory scale pulsating Wet High Intensity Magnetic Separator) and the laboratory scale Reflux Classifier (RC). The base case tests were conducted to determine the optimal intensity for the SLon-100 and a semi-batch test was done on the RC to determine the effect of increasing water fluidisation rates on the response variables namely Fe concentrate grade, Fe concentrate recovery and separation efficiency. Thereafter selective flocculation conditions were optimised by coupling the process with magnetic separation in order to determine the effect of the operating variables on the response variables mentioned above. A Box-Behnken design was utilised and the ANOVA models developed for the significant response variables were used to optimise the selective flocculation process by simultaneously maximising the response variables whilst minimising the three factors (sodium oleate, paraffin dosage and conditioning time). The optimised selective flocculation conditions were then coupled with the RC in order to compare magnetic and gravity separation with and without selective flocculation. The optimised selective flocculation conditions (1 kg/ton sodium silicate; pH 10; 500g/t sodium oleate; 1431.1g/t paraffin and 4.6 min conditioning time) coupled with magnetic separation showed improved metallurgical performance when compared to the base case test. Selective flocculation coupled with magnetic separation improved the magnetic product Fe grade from 52.28±0.38% to 59.21±0.42% Fe whilst simultaneously improving the separation efficiency from 40±1.46% to 56.8±2.0% and maintaining the Fe concentrate recovery within the 95% confidence limits (69.9% to 72.1%). These results were achieved under laboratory and ideal conditions and may differ from industrial scale results. Inconclusive results were achieved with selective flocculation coupled with the RC and additional testwork is recommended / MT 2019