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M.Tech. (Extraction Metallurgy) / Please refer to full text to view abstract

An electrochemical study was carried out on various electrodes of sphalerite, pyrite, pyrrhotite, chalcopyrite and galena in deoxygenated and air-saturated solutions at different concentrations of potassium ethyl xanthate (KEtX), i.e. 0 M, 10⁻⁵ M, 3 x 10⁻⁵M, 10⁻⁴ M, 3 x 10⁻⁴ M, 10⁻⁴M, 10⁻³ M and pH (1 to 12) at 25°C ± 1°C. The effect of galvanic contact between various sulphides and metallic iron on various electrochemical characteristics of the galvanic couple was also investigated. Following a pseudo Nernst relationship, the rest potentials of various electrode systems became more negative with the higher concentration of KEtX. The electrochemical series of the sulphide minerals investigated, in potassium ethyl xanthate solution, in the order of their nobility, were sphalerite, pyrite, pyrrhotite, chalcopyrite and galena. All sulphide-xanthate-air systems displayed more noble rest potentials than the redox potential of potassium ethyl xanthate at natural pH; however, the rest potentials of most sulphides except for sphalerite became more negative than the redox potential of potassium ethyl xanthate at a pH of 9. Solution purging with air caused the rest potentials of all sulphides investigated to shift in the noble direction because of the oxygen reduction. Various sulphide-iron galvanic couples acquired mixed potentials which lay between the rest potentials of sulphides and iron. The exact value of the mixed potential of the particular electrode system was varied depending on the relative surface area of the two electrodes in galvanic contact. The experimental potential-pH diagrams were constructed for the minerals and metallic iron in the solutions of 0 M and 10~5 M of potassium ethyl xanthate. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

本論文示範了兩款過渡金屬硫化物量子點 (二硫化銀銦量子點與硫化錳量子點) 在量子點敏化太陽能電池上作為光敏化劑的應用，這也是它們在量子點敏化太陽能電池上的初次應用。 / 二硫化銀銦量子點的合成採用了一鍋合成法，合成的量子點隨後透過3-巰基丙酸連接到二氧化鈦的表面。研究發現，當量子點溶液的濃度處於較低水平的時候，量子點在二氧化鈦的吸附量會較高。另外，從不同研究小組在量子點吸附行為的報告中，觀察到量子點的吸附行為決定於實驗條件，如量子點的大小和表面活劑，納米二氧化鈦多孔膜的孔隙度和量子點的溶劑。實驗中，最高性能的二硫化銀銦量子點敏化太陽能電池的短路電流為0.49 mA/cm²，開路電壓為0.245 V，填充因子為38.26 %，光電轉換效率為0.046 %。 / 透過連續離子層沉積反應法，硫化錳量子點生長並組裝到二氧化鈦的表面上。能譜測量顯示，錳跟硫的比率在不是1:1。這現象懷疑是源於錳(2+)的小離子半徑，對錳(2+)和硫(2-)之間的化學反應產生了不良的影響，導致吸附了的錳(2+)沒有反應過來。通過優化連續離子層沉積反應法週期的數量，最高性能的硫化錳量子點敏化太陽能電池的短路電流為0.65 mA/cm²，開路電壓為0.30 V，填充因子為48.21 %，光電轉換效率為0.095 %。 / QD-SSCs sensitized with novel transition metal sulfides have been demonstrated. Both AgInS₂ QD-SSC and MnS QD-SSC presented in this thesis are new and are the first demonstrated works in the research field. / AgInS₂ QDs was synthesized by one-pot hot colloidal synthesis approach. The as-synthesized QDs were attached to the TiO₂ surface through 3-mercaptopropionic acid. Optimization process on QDs adsorption was done, and it has been observed that the amount of QDs adsorbed is higher when the concentration of the QDs solution is at low level. The variations in the behaviors in QDs adsorption between works from different research groups are considered to originate from experimental conditions such as the sizes and surfactants of QDs, porosities in the TiO₂ matrix, and the solvent for QDs dispersion. The optimized AgInS₂ QD-SSC attained a short-circuit current of 0.49 mA/cm², an open-circuit voltage of 0.245 V, a fill factor of 38.26 % and a power conversion efficiency of 0.046 %. IPCE measurements confirm the successful sensitization from AgInS₂ QDs, indicating the energetically favourable electron injection from AgInS₂ QDs to TiO₂. / By adopting the SILAR technique, MnS QDs was in-situ grown and deposited on the TiO₂ surface. EDX measurements indicated that the Mn/S ratio in the TiO₂/MnS film is not 1:1. The reason is suspected to originate from the small ionic radius of Mn²⁺ that promoted an adverse effect on the reaction between Mn²⁺ and S²₋. It is proposed that a portion of the adsorbed Mn²⁺ did not react with the S²₋., resulting an excess concentration of Mn²⁺ in the film. By optimizing the number of SILAR cycles, MnS QD-SSC was optimized to exhibit a short-circuit current of 0.65 mA/cm², an open-circuit volatge of 0.30 V, a fill factor of 48.21 % and a power conversion efficiency of 0.095 %. IPCE measurements confirm the sensitization is originated from MnS QDs, which consequently reveal an energetically favourable electron injection from the MnS QDs to TiO₂. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Cheng, Kai Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Solar cells --- p.2 / Chapter 1.2.1 --- Developments --- p.2 / Chapter 1.2.2 --- Nanostructured solar cells --- p.4 / Chapter 1.2.2.1 --- Bilayer organic solar cells --- p.4 / Chapter 1.2.2.2 --- Bulk heterojunction organic solar cells --- p.5 / Chapter 1.2.2.3 --- Organic-inorganic hybrid solar cells --- p.7 / Chapter 1.2.2.4 --- Dye-sensitized solar cells --- p.8 / Chapter 1.2.2.5 --- Quantum dot-sensitized solar cells --- p.11 / Chapter 1.2.3 --- Characterization of solar cells --- p.11 / References --- p.14 / Chapter Chapter 2 --- Quantum dot-sensitized solar cells --- p.18 / Chapter 2.1 --- Quantum dots --- p.18 / Chapter 2.1.1 --- Quantum confinement --- p.18 / Chapter 2.1.2 --- Multiple exciton generation --- p.20 / Chapter 2.2 --- Quantum dot-sensitized solar cell --- p.22 / Chapter 2.2.1 --- Principles --- p.22 / Chapter 2.2.2 --- Assembly of oxide/quantum dot film --- p.25 / Chapter 2.2.3 --- Light harvesting and electron injection --- p.29 / Chapter 2.2.4 --- Titanium dioxide as electron acceptor --- p.33 / Chapter 2.2.5 --- Redox process of electrolyte --- p.37 / Chapter 2.2.6 --- Counter electrode materials --- p.39 / References --- p.41 / Chapter Chapter 3 --- Experimental Details --- p.45 / Chapter 3.1 --- Materials --- p.45 / Chapter 3.2 --- Preparation of the TiO₂ mesoporous film --- p.46 / Chapter 3.3 --- Synthesis of AgInS₂ quantum dots --- p.47 / Chapter 3.4 --- Preparation of the TiO₂/QDs film --- p.47 / Chapter 3.5 --- Configuration of the QD-sensitized solar cell --- p.49 / Chapter 3.6 --- Characterization and Photoelectrochemical Measurements --- p.51 / References --- p.52 / Chapter Chapter 4 --- Experimental Results --- p.53 / Chapter 4.1 --- AgInS₂ QD-sensitized solar cell --- p.54 / Chapter 4.1.1 --- Characterization of AgInS₂ QDs --- p.54 / Chapter 4.1.2 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.56 / Chapter 4.1.3 --- Photoelectrochemical measurements of the AgInS₂ QD-SSC --- p.60 / Chapter 4.2 --- MnS QD-sensitized solar cell --- p.64 / Chapter 4.2.1 --- Characterization of MnS QDs --- p.64 / Chapter 4.2.2 --- Photoelectrochemical measurements of the MnS QD-SSC --- p.69 / References --- p.74 / Chapter Chapter 5 --- Discussions and Conclusions --- p.75 / Chapter 5.1 --- Discussions --- p.76 / Chapter 5.1.1 --- AgInS₂ QD-SSC --- p.76 / Chapter 5.1.1.1 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.76 / Chapter 5.1.1.2 --- Electron injection --- p.80 / Chapter 5.1.1.3 --- Problems encountered and future directions --- p.83 / Chapter 5.1.2 --- MnS QD-SSC --- p.84 / Chapter 5.1.2.1 --- Growth of MnS QDs on the TiO₂ surface --- p.85 / Chapter 5.1.2.2 --- Effects of SILAR cycles on MnS QD-SSC --- p.86 / Chapter 5.1.2.3 --- Problems encountered and future directions --- p.88 / Chapter 5.1.3 --- AgInS₂ QD-SSC versus MnS QD-SSC --- p.89 / Chapter 5.2 --- Conclusions --- p.91 / References --- p.94

The high temperature, high pressure electrochemical behavior of A516 Gr. 70 carbon steel in aqueous alkaline sulfide solutions was studied by means of polarization tests and cyclic volt-ammetry. The effects of variation of temperature (90-150°C), sulfide concentration (0-3 m), scan rate (1-50 mV/s) and scan range, and the effects of stirring and polarization at the switching potentials between scans were investigated. Passivation was consistent with formation of a protective Fe₂O₃ film. An understanding of the electrochemical behavior of iron in the alkaline sulfide solutions was facilitated by the construction of E-pH diagrams for S-H₂0 and Fe-S-H₂O systems at 25, 100 and 150°C. Sulfide, S²-, currently considered to be stable only at extremely high pH, was excluded from the E-pH diagrams. Reference electrodes, compatible with sulfide solution, were designed for use with an autoclave. The response of the Ag/Ag₂S electrode (SSSE) to variation of temperature, sulfide and hydroxide concentration, and chloride addition was studied. Liquid junction potential and thermal liquid junction potential corrections were applied. The SSSE was not reliably predictable thermodynamically, but was stable and was proven effective in the polarization study. The electrochemical potentials of inert metal reference electrodes, Hg and Pt, were found to be consistent with the mixed potential between polysulfide Sײ⁻, and thiosulfate, S₂O₃²⁻. The Tafel slopes from anodic polarization curves of Pt in alkaline sulfide solutions were consistent with oxidation of HS⁻ to S₂0₃²⁻ at the mixed potential. At more noble potentials, oxidation to polysulfide occurred. Reaction path mechanisms were proposed. Understanding of sulfide oxidation aided in interpretation of the electrochemical behavior of steel in the alkaline sulfide solutions. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

This investigation has been carried out for the purpose of determining the effect of solid particle size distribution on the roasting and leaching of a complex sulfide ore. The effect of pulp density in the leaching process has also been studied. The oxidizing roast of the combined sulfide concentrates, prepared by bulk sulfide flotation and tabling, was conducted with a fluidized-bed kiln. The calcines were leached by dilute sulfuric acid in an autoclave. The following conclusions have been reached: 1. In the fluidized-bed roasting, the solid particles within the size range of minus 35 to plus 150-mesh would have a higher overflow rate from the fluidized bed. This inference might be effective only when the roasting is conducted under the conditions performed in this investigation. 2. In the process combining fluidized-bed roasting and dilute sulfuric acid leaching, the effect of solid particle size is significant. The solid particles within the size range of minus 65 to plus 150-mesh have the highest iron recovery, the highest copper and zinc extraction rates and the lowest sulfur content of leach residue. 3. In dilute sulfuric acid leaching there is no significant effect of pulp density within the range tested in this investigation. The general trends are: iron recovery decreases as the pulp density decreases, extraction rates of copper and zinc decrease as pulp density increases, and there is little pulp density effect on the sulfur content of leach residue. / Master of Science

This investigation deals with the application of high pressure and high-temperature leaching techniques to separate out zinc and copper from the iron constituents of a calcined sulfide ore. An important variable in this study proved to be the concentration of the leaching reagent -- sulfuric acid. The leaching temperature was varied within a range of 250°F to 550°F., and 8 cubic centimeters to 20 cubic centimeters of sulfuric acid in 2000 cubic centimeters of distilled water was employed as the leaching agent concentration. The major equipment utilized for roasting was the fluidized bed and an autoclave for leaching. After the physical and chemical treatments of roasting and leaching of the calcine, the resulting constituents were studied by means of quantitative chemical analysis. Numerical theories were used to correlate the points obtained into continuous functions of the leaching temperature, concentration of sulfuric acid and the recovery percentage. From these curves, it is concluded that the recovery of the impurities in the calcine is proportional to the leaching temperature and the concentration of the leaching agent. However, under certain circumstances, the leaching action causes loss of iron in the calcine, and the minimizing of the loss in leaching is also studied. / Master of Science

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