Thesis (PhD)--University of South Australia, 1996

The chemistry during regrinding is critical to flotation. It has significant effects on mineral surface properties and can lead to different mineral floatabilities. This research seeks to quantify contributing factors to changes in mineral flotation behavior with grinding and regrinding. The influence of the particle breakage mechanism on mineral floatability is also investigated. In this research, sulphide mineral surface species and hydrophobicity were analyzed by a range of techniques, including X-ray photoelectron spectroscopy (XPS), surface area measurement (BET), ethylene diamine-tetra acid (EDTA) extraction and contact angle measurements. / Thesis (PhD)--University of South Australia, 2010

Thesis (M.Eng.)(Metallurgical)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / Nickel, a valuable base metal, is the predominant product from the Nkomati mine in South Africa. High-grade nickel mineral ores (2%) from the Massive Sulphide Body have been depleted leaving those of low grade (0.3%). The beneficiation of this ore presents a challenge to the minerals processing industry. In response, batch froth flotation tests were used to explore the effects of mixtures of potassium amyl xanthate (PAX) and IPETC (Isopropyl ethyl thionocarbamate) on the grades and recoveries of nickel. In the mixtures, the xanthate accounted for 95.5, 90, 85 and 80 mole% respectively. Generally an increase in the nickel grade and recovery was observed with the mixtures relative to PAX. IPETC gave a significant increase in the cumulative water recovery with a significant decrease in cumulative nickel grade relative to PAX. PAX gave the highest cumulative nickel grade for the singular collector tests (1.9%), while obtaining the lowest cumulative recovery (77%). Out of the collector mixtures, mixtures 85% PAX: 15% IPETC and 90% PAX: 10% IPETC produced the joint highest cumulative grades (1.8%). These mixtures both gave recoveries of 82%. Collector mixture 95.5% PAX: 4.5% IPETC gave the second highest grade (1.7%) and the highest nickel recovery (85%). Although there were differences in the cumulative nickel grades and recoveries there were statistically no significant improvements observed with the use of the mixtures of PAX and IPETC in comparison to the industry mixture (95.5% SIBX: 4.5% IPETC). Tests were performed using the three best performing collector mixtures at molar dosages of 1.3, 0.65 and 0.325mmol/t. The highest cumulative nickel grades were obtained at the lowest collector dosages (at a molar dosage of 0.325mmol/t of 95.5% SIBX: 4.5% IPETC) with collector mixture 95.5% PAX: 4.5% IPETC being the most selective with a nickel grade of 2%. It was also observed that an increase in collector dosage, generally increased the cumulative nickel recovery with collector mixture 95.5% PAX: 4.5% IPETC at a molar dosage of 1.3mmol/t gave the highest cumulative recovery out of the tested mixtures (85%). The study also indicated that an increase in selectivity (i.e. cumulative grade) was at the expense of cumulative recovery. With a decrease in dosage, there was no significant improvement in the cumulative nickel grade and recovery for the tested mixtures compared to the industry mixture. There was however a significant decrease in the water recoveries achieved with PAX and collector mixtures 95.5% PAX: 4.5% IPETC at a molar dosage of 1.3mmolg/t of as well as mixture 90% PAX: 10% IPETC at a molar dosage of 0.65mmol/t.

No description available.

It is generally recognized that the recovery of particles from a flotation pulp is controlled by (i) the flotation rate constant and (ii) the residence time distribution of the particles. In the present work, theoretical and experimental analyses have been carried out to develop methods for predicting these parameters from first principles considerations. In order to predict the flotation rate constant, a bubble-particle interaction model has been developed using a dynamic force balance to determine the trajectory of a particle as it approaches a rising air bubble. The trajectory has been used to determine the probability of bubble-particle attachment, from which the flotation rate constant can be readily obtained. The model is unique in that it simultaneously considers the effects of hydrodynamic and surface forces on the interaction between bubbles and particles. Model predictions have been shown to be in good agreement with results from bubble-particle attachment experiments for narrowly-sized coal and silica samples. In the present work, the residence time distribution of particles in column flotation has been examined by conducting experimental tracer tests. These tests have been performed with two tracer materials to characterize mixing for both the liquid and the solids in a single system. The measured residence time distributions have shown that the assumption of equating liquid and solids residence time distributions is inappropriate, except for very small and low density particles. At larger sizes and higher densities, the correction formula advocated by Dobby and Finch (1985) has been shown to adequately predict the solids residence time. / Master of Science

The interactions of O-isopropyl-N-ethylthionocarbamate (IPETC) and O-isobutyl-N-ethoxycarbonylthionocarbamate (IBECTC) with Cu₂S, CuFeS₂ and FeS₂ have been characterized using thermodynamic calculations, electrochemistry, microflotation tests, contact angle measurements, FTIR, and UV spectroscopy. Pearson’s theory of hard and soft acids and bases (HSAB) has also been applied to these flotation systems, through the use of Drago’s acid-base concept and flow microcalorimetry. The results of the thermodynamic calculations and electrochemical measurements suggest that IPETC and IBECTC adsorption on copper and chalcocite are dependent on potential. This has been verified by contact angle and in-situ spectroelectrochemical measurements. Microflotation tests with these thionocarbamates show that the floatability of Cu₂S and CuFeS₂ is dependent on pH. The floatability of FeS₂ only becomes significant at acidic conditions and high collector additions. Spectroscopic measurements also show that thionocarbamate adsorption is dependent on pH and is most favored on Cu₂S followed by CuFeS₂ and FeS₂. FTIR results indicate that IPETC is adsorbed on Cu°, Cu₂S, and CuFeS₂ through a coordination of the sulfur atom with the surface Cu. IBECTC adsorption on these substrates involves the coordination of Cu with both sulfur and oxygen atoms to form a six-membered chelate ring. Adsorption of these collectors cannot remove or prevent the formation of sulfoxy oxidation products on the FeS₂ surface, unlike the case with the xanthate-pyrite system. This may explain the improved selectivity of IPETC and IBECTC over xanthates. Infrared reflection-absorption spectroscopic studies show that KEX is preferentially adsorbed on Cu° over IPETC and IBECTC. Between IPETC and IBECTC, the latter is more favorably adsorbed than the former. Kinetic studies using UV spectroscopy show that the rate of thionocarbamate adsorption is highest on Cu₂S followed by CuFeS₂ and FeS₂. IBECTC adsorption on each sulfide mineral is relatively faster than IPETC, indicating the higher collecting power of IBECTC. The HSAB concept suggests that the interaction of thionocarbamates (soft bases) with sulfide minerals that are classified as soft acids should be favored. The C/E ratios of Cu₂S and FeS₂ were determined to be 0.86 and 0.52, respectively. This indicates that FeS₂ is a harder acid than Cu₂S, thus providing an explanation for the observed selectivity of both IPETC and IBECTC against FeS₂. / Ph. D.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / The Bushveld igneous complex in northern South Africa has the largest deposit of platinum group elements (PGE) in the world. In trace amounts, these are closely associated with base metal sulphides (BMS). Froth flotation is used to beneficiate these PGE ores. The process constitutes a bulk sulphide recovery. Improvement of recovery of the BMS is required to maximise the recovery of PGEs. The performance of the froth flotation process is largely dependent on the chemical additives used and these chemicals have been extensively studied. Mixtures of collectors are widely used in the flotation of sulphide and platinum group mineral (PGM) ores. A range of performance benefits for the use of mixtures over pure collectors have been observed on many systems. These include improved valuable metal grades and recoveries, lower reagent dosage requirements, improved rates of flotation and enhanced recovery of coarse particles. Improvements observed with mixtures of chemical reagent have been attributed to synergism; defined as the interaction of two or more agents to produce a combined effect greater than the sum of their individual effects. Synergism is highly desired in froth flotation. For this study, mixtures of thiol collectors were used in batch froth flotation tests in an attempt to identify synergism between the different collectors on flotation performance of a typical platinum ore from the Merensky reef. Flotation performance was evaluated in terms of grades and recoveries of copper and nickel, and the rate of metal flotation. Single thiol collectors of xanthate (SIBX), a dithiocarbamate (DTC) and a dithiophosphate (DTP) were evaluated to determine the effect of functional group on flotation performance. SIBX was then used in mixtures with both DTC and DTP at various molar ratios to establish whether synergism occurs between these collectors on this particular platinum ore. Molar ratios of 90:10, 80:20, 70:30 60:40 and 50:50 were considered with SIBX being the major component. Further tests were conducted with the addition of a carboxymethyl cellulose depressant to the collector mixtures.

Trithiocarbonates (TTCs) with less than six carbon atoms per molecule historically have proved to be better bulk sulphide mineral collectors than conventional dithiocarbonates (DTCs). However, high vapor pressures of the short-chain mercaptan decomposition products prevented them from general industrial use. Impala’s commitment in TTC development changed in 2002 when the nC12-trithiocarbonate indicated strong synergism when added to their existing flotation suite. A concerted research effort at the University of Utah followed, and in particular on their surface chemistry. To compliment current research and development at Impala, fundamental work regarding the surface hydrophobicity of pyrrhotite under electrochemically controlled conditions was undertaken at Utah University. Controlled contact angle measurements showed that the surface hydrophobicity of pyrrhotite can be increased by small additions of nC12-trithiocarbonate to SIBX. It was also found that this improvement in the surface hydrophobicity with the SIBX-TTC mixture was more significant at lower oxidation potentials. Work at Utah University further showed that a C12 decomposition product may or may not be present with an adsorbed TTC molecule. External reflectance infrared spectroscopy in the mid infrared region suggested a “crowding” of the collectors at the surface when SIBX and TTC are combined. This was based on an increase in the absorbance of the -CH2- peaks in the mixed collector system. In bench scale flotation tests on PGM bearing samples from the Merensky reef, it was found that a 5 molar percent replacement of SIBX with nC12-trithiocarbonate improved the flotation activity relative to the standard SIBX-DTP mixture. Improvements were in the recoveries of PGMs, copper and nickel. The addition of TTC also increased the flotation rates of both slow and fast floating valuables as is predicted by the Kelsall equation. The optimum mixture for the pilot plant trials was thus a 5 molar percent replacement of the current collector suite with nC12-TTC. Based on the bench flotation results, research was extended to a pilot plant trial. At a depressant dosage of 100g/ton, the PGM concentrate grades from the first rougher cell improved from 120g/ton to 175g/ton when the TTC was introduced. This was achieved without any effect on the recovery from the first cell. This increase in concentrate grade is believed to arise from the nature of both: <ul> <li>The mineral-collector surface state, and</li> <li>The bubble surface interaction.</li> </ul> Overall, the standard SIBX-DTP collector combination and the new SIBX-DTP-TTC collector combination (both at 100g/ton depressant) was also compared to pilot plant tests with SIBX-DTP at high (350g/ton) depressant dosages. The latter suite forms the currents reagent suite at Impala Platinum. When comparing the first two trials, at 100g/ton depressant, the addition of TTC as a ternary collector resulted in a recovery improvement of approximately 2.2% with a simultaneous increase in final concentrate grade from 57g/ton to 73g/ton. The result was a reduction in solids recovery from 5.3% to 4.1%. When comparing the TTC trial to the standard collector suite at high depressant dosages, only a small reduction (3.6% vs. 4.1%) in solids recovery was achieved with a final concentrate grade of 85g/ton. The PGM recoveries were very similar. Based on current Merensky milling rates, depressant and TTC costs, and calculated replacements based on the pilot plant tests, a projected cost saving on chemicals is R9.6 million per annum. Financial impacts on processing, grade and kinetics have not been made. It was also concluded that the detrimental effect of mild steel milling on the flotation activity of SIBX-DTP was diminished with the addition of the long-chain TTC with SIBX and DTP. As part to this research, a preliminary plant trial on UG-2 underground material showed a reduced primary rougher chromite grade as well as a significant increase in PGM concentrate grade for the first two primary rougher cells. This is an important finding, especially for the melting process. In this final study a partial (5 molar percent) replacement of the standard collector used was also made. What was further realised was a significant increase in the final concentrate grade when compared to the standard conditions. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / MEng / unrestricted

Long chain alkyl pyridinium salts have been used as collectors for the flotation of chalcopyrite and copper-activated sphalerite. For the ores tested in this study, these reagents have demonstrated improved selectivity and recovery in comparison to conventional xanthates. The best flotation results, in terms of both grade and recovery, were achieved with cetyl pyridinium chloride (CpCl). A distinct advantage of using CpCl instead of a conventional xanthate, such as sodium isopropyl xanthate (NaIpX), is that the kinetics of flotation are much faster. This may be explained by the reduction in the negative ζ-potential of the sulfide mineral upon adsorption of cetyl pyridinium ions, which, in turn, minimizes the electrostatic component of the disjoining pressure of the wetting film. CpCl has also demonstrated a remarkable selectivity despite the fact that both chalcopyrite and the silicious gangue minerals present in the ore are negatively charged. This may be explained by the premise that cetyl pyridinium ions adsorb more strongly on chalcopyrite than on the gangue. Analysis of the adsorption isotherms established for chalcopyrite and quartz supports this view. Several possible mechanisms have been suggested to explain the 'high affinity' type of adsorption observed in the CpCl-chalcopyrite system. / Master of Science