Cellulose is the most abundant and the most resistant and stable natural organic compound on earth. Enzyme hydrolysis is difficult because of its insolubility and heterogeneity. Some (anaerobic) microorganisms have overcome this by having a multienzyme system called the cellulosome. The aims of the study were to isolate a mesophilic Clostridium sp. from a biosulphidogenic bioreactor, to purify the cellulosome from this culture, to determine the cellulase and endoglucanase activities using Avicel and carboxymethylcellulose (CMC) as substrates and the dinitrosalicyclic (DNS) method. The organism was identified using 16S rDNA sequence analysis. The sequence obtained indicated that a strain of Clostridium beijerinckii was isolated. The cellulosome was purified from the putative C. beijerinckii sLM01 host culture using affinity chromatography purification and affinity digestion purification procedures. The cellulosomal and non-cellulosomal fractions of C. beijerinckii sLM01 were separated successfully, but the majority of the endoglucanase activity was lost during the Sepharose 4B chromatography step. These cellulosomal and non-cellulosomal fractions were characterised with regards to their pH and temperature optima and effector sensitivity. Increased additions of sulphide activated the cellulase activity of the cellulosomal and non-cellulosomal fractions up to 700 %, while increased additions of sulphate either increased the activity slightly or inhibited it dramatically, depending on the cellulosomal and non-cellulosomal fractions. Increased additions of cellobiose, glucose and acetate inhibited the cellulase and endoglucanase activities. pH optima of 5.0 and 7.5 were observed for cellulases and 5.0 for endoglucanases of the cellulosomal fraction. The noncellulosomal fraction exhibited a pH optimum of 7.5 for both cellulase and endoglucanase activities. Both fractions and enzymes exhibited a temperature optimum of 30 °C. The fundamental knowledge gained from the characterisation was applied to anaerobic digestion, where the effect of sulphide on the rate-limiting step was determined. Sulphide activated cellulase and endoglucanase activities and increased the % chemical oxygen demand (COD) removal rate. Levels of volatile fatty acids (VFAs) were higher in the bioreactor containing sulphide, substrate and C. beijerinckii. Sulphide therefore accelerated the rate-limiting step of anaerobic digestion.

A study of the Lauth's Violet absorptiometry method for the analysis of sodium sulphide was carried out. The order of adding the reactants in the development of the color, the use of three different methods of titration for standardizing the solutions used for determining the calibration factor, and the effects of varying the concentrations of the reagents were all investigated. In the formation of Lauth's Violet from sodium sulphide, addition of reactants in the order base electrolyte, sodium sulphide, and p-phenylenediamine was shown to be best. The arsenious oxide method of titration was selected for determining the concentration of sodium sulphide in standard solutions used for calibration. If the reagents: base electrolyte containing ferric chloride, and p-phenylenediamine, were used at the concentrations of 0.16% and 5% by weight, respectively, the calibration factor remained constant up to concentrations 16 grams per litre of sodium sulphide. The applicability of the Lambert-Beer law and the effect of sodium thiosulphate on the absorptiometry method also were studied in detail. The oxidation of sodium sulphide was studied under atmospheric pressure at various temperatures by use of two different apparatuses. From the measurements of the amounts of oxygen absorbed, the oxidation of sodium sulphide probably gives disulphide, thiosulphate, sulphite and sulphate. The stoichiometry corresponds to thiosulphate being the main product of this reaction. The rate of absorption of oxygen with simultaneous, oxidation of sodium sulphide was observed to decrease, with increasing temperature from 25° to 45°C Nevertheless, the maximum absorption rate was found at 55°C, and the absorption rate decreases again with temperature at least to 85°C. The reaction orders for the oxidation of sodium sulphide depend upon temperature, being second order at 25°C, order of 1.5 at 35° and 45°C., and first order from 55° to 85°C. The reaction order with respect to oxygen is first order, irrespective of temperature. The maximum rate of oxidation also occurs at 55°C. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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

The oxygen pressure leaching of pyrite has been studied in sulfuric and perchloric acid using an oxygen-18 tracer technique. The results are consistent with an entirely electrochemical mechanism. The leaching potential of a pyrite pulp has been measured as 0.699V SHET*(110°C, 1M H2S04, 176 psi 02) and potentiostatic experiments at that potential have yielded the same reaction product ratios as observed in oxygen pressure leaching. The ratio of sulfate to elemental sulfur produced during pyrite leaching has been found to be a function of the leaching mixed potential. The yield of sulfate is increased with increasing potential until all the mineral sulfur is converted to the sulfate form at potentials above 1.0V. A mechanistic model of pyrite leaching has been advanced, which includes the electrochemical formation of a protective sulfur film as its basis. The theory has been supported by polarization studies in combination with Eh-pH diagrams. Chalcopyrite leaching has been studied using the same 0¹⁸ technique. Again the results are consistent with an electrochemical mechanism. The ratio of the sulfate to elemental sulfur in the reaction products has been observed to increase with higher oxygen pressures. The mixed potential of leaching is also increased at higher pressure indicating that the same type of mechanism observed in the pyrite work is operational for chalcopyrite. Molybdenite leaching has also been discussed in terms of the electrochemical model derived for pyrite with good results, and the mechanism therefore appears to have applications in many, if not most, sulfide systems. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This dissertation presents the results of a collector - depressant equilibria study of the flotation systems potassium n-amyl xanthate - sodium cyanide - molybdenite and ethyl zanthate sodium sulfide - molybdenite and the study of conditions necessary for the selective flotation of covellite, tetra-hedrite, bornite, chalcopyrite, molybdenite, marcasite and pyrite in the system ethyl xanthate and sodium cyanide; the conditions necessary for the selective flotation of pyrite, covellite, bornite, galena, chalcopyrite, active sphalerite, and molybdenite in the system potassium ethyl xanthate and sodium sulfide; the conditions necessary for the selective flotation of molybdenite and pyrite in the system of potassium n-amyl xanthate and sodium cyanide; the condition necessary for the flotation of molybdenite and galena in the system potassium n-amyl xanthate and sodium sulfide.

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