The decomposition behavior of several mining reagents (i.e., xanthate, dithiocarbamate, dithiophosphate and dithiophosphinate) used widely in mineral processing operations was studied. Decomposition has been reported to generate toxic compounds such as CS₂ (carbon disulfide) and COS (carbonyl sulfide), causing severe concerns to SHE (safety, health and environment). With the global trend of becoming sustainable/green and the increasingly strict regulations, the mining industry is facing an unprecedented pressure to handle the problematic reagents that can lead to the adverse impacts. Unfortunately, the interests of the prior research are biased on the performance of the reagents to optimize the efficiency and lower the cost, while the examination of the decomposition behavior is almost neglected. Under the circumstance of poor endeavor found in the prior investigations, the knowledge gap awaits to be filled in a systematic and integrated manner to recommend countermeasures for those problematic reagents. It can be seen from those fragmented studies collected from literature that only a limited understanding of thermal or aqueous decomposition behavior is achieved. It is far from sufficient for industrial guidance of mitigation. One key reason is the lack of robust methods to investigate decomposition under various conditions that are interesting to the mining companies (e.g., the flotation conditions). Consequently, the method development has always been considered of the utmost importance upon the start of this work to align with our overall goal of understanding the decomposition behavior under the various conditions. Three methods under a consistent strategy were designed to examine the decomposition under three conditions from Simple (in aqueous solutions alone), to Complex (in ore pulp under flotation conditions), to Specific (in solution containing metal ions). These three conditions were chosen based on the general interests from several prominent mining companies (Vale, Barrick, Freeport McMoRan and Newmont) to understand the decomposition mechanism and kinetics. The Simple is to serve as control for all other conditions. Besides, most of the prior studies in the literature are only conducted for the Simple condition. Therefore, the Simple is to resolve all discrepancies and conflicts, and provide a relatively comprehensive summary of the decomposition under the control condition. The Complex puts decomposition in a new environment that has never been explored before: the ore pulp under the simulated batch flotation conditions. Conclusions drawn from this part provide the most practical guidance for industrial mitigation. The Specific goes after the Complex to thoroughly understand the effect of a specific factor on decomposition. The decomposition responding to the variation of a certain factor is followed within a closed system with the compositional changes measured in all phases. The integrated analysis enables the correlation of the decomposition behavior to its original causes, which are the interactions of the reagent with other components in the system. Through the systematic investigation of decomposition of various reagents under various conditions, it is concluded that decomposition depends heavily on those parallel or sequential interactions that occur along with the decomposition reaction. For example, the decomposition reaction of xanthate throughout our entire study is regarded as ROCS₂⁻→CS₂. When xanthate forms xanthic acid, monothiocarbanate or dixanthogen with the change of pH, its breakup into CS₂ is altered. When xanthate interacts with Cu²⁺ forming Cu₂X₂, decomposition is depressed, but with Fe³⁺ forming FeX₃ decomposition is promoted. The CS₂ generated from decomposition could interact with OH- to form CS₃²⁻ or dissolve in solution or adsorb on minerals, leading to the decrease of CS₂ detected. The bonding properties between the –CS₂ moiety and other atoms or radicals in the molecule affect the stability of the reagents and the subsequent decomposition. The necessity to include a list of the side-interactions as complete as possible is key to understand and predict the decomposition behavior. With experimental efforts taken to develop methodologies to measure the decomposition under various conditions, the attempt to model the decomposition behavior is also initiated in this work. Based on the conclusions from experimental results, major components determining the output of the final decomposition products are identified. Unsurprisingly, the decomposition reaction together with its parallel and sequential interactions is critical. Simulation using Matlab to assess the decomposition of a simplified system containing SIBX and Cu²⁺ ions has achieved preliminary success by matching well with the experimental measurements. This establishes the groundwork for furthering the simulation of more complex systems and model development. Reagents decompose differently, although they might be applied to function similarly during an operation. As flotation collectors used for sulfide ore beneficiation, dithiocarbamate and xanthate possess some similarities in the decomposition in terms of generating CS₂. Their decomposition also decreases with the chain length. On the other hand, the decomposition of dithiophosphate and dithiophosphinate are different as the breakup of the molecule is mainly at their alkyl chain to generate moieties such as olefins. Compared to the studies carried out to understand the performance of the reagents when being used, research on decomposition requires more attention. Therefore, derivative work can be conducted based on results achieved in this work. For example, it is useful to further examine how reagents decompose after adsorbing on the mineral surfaces. It complements the knowledge to thoroughly understand decomposition at different spots within a complex system. The chemical fate studies of mining reagents with respect to the understanding the decomposition open up the window of developing methodologies to examine adverse behaviors. The experimental setups are applicable to simulate various conditions under which the reagent is being used and generating the adverse impacts. The strategy of analyzing decomposition within a complex system as shown in this study also provides insight into systematically investigating the other types of adverse behaviors.

A 20 litre experimental batch and continuous test rig and 5 litre batch and 50 litre continuous test rigs for stirred ball milling were built at the University of Natal and Mintek respectively. All the mills featured a grinding vessel with a central shaft equipped with pins and a torque measurement system. A washed chrome sand from the Bushveld Igneous Complex was used for the grinding experiments. Particle size analysis of products was performed using standard sieves and a Malvern Particle Sizer. Batch tests were run in the 20 litre stirred ball mill to achieve efficient grinding conditions. The effects of grinding conditions such as pulp density, media size, media density and shaft rotation speed and mill design parameters such as ball load, pin spacing and pin diameter on product size, power consumption and media wear were studied. It has been shown that the median size of the product can be calculated by the Charles' Energy-Size Equation. The stirred ball mill has been found to be more energy efficient than the tumbling ball mill. An energy reduction of 50% was possible for a product size of 6 microns when the stirred ball mill was employed instead of the tumbling ball mill. The energy input per ton of grinding media in the stirred ball mill could be 10 times higher than for the tumbling ball mill. Although during coarse grinds the media wear was higher in the stirred ball mill than in the tumbling mill, it became less so as grinding proceeded and for a product median size of 4.8 microns it was the same. Using a 5 litre batch mill, an experimental programme was designed to study the comminution characteristics of the stirred mill. A factorial design was prepared with the following parameters, which influence grinding in the stirred ball mill: pulp density, pin tip velocity and ball density and size. The energy required for grinding the chromite sand in the stirred ball mill was determined by the use of Charles' Equation. The findings were in agreement with the results predicted by this equation. It was shown that the Rosin-Rammler size distribution equation was a suitable procedure for presenting and comparing grinding data obtained from the stirred ball mill. The factors that had the greatest effect on grindability were, in order of importance: ball size, pin tip velocity and ball density. Interactions between grinding parameters were negligible. results implied that accurate predictions can be made to determine the grinding conditions required to achieve a desired product specification. An attempt was made to study the grinding kinetics the chromite are using the mass population·balance model. Grinding tests were performed with two mono size fractions ·53+38 and -38+25 microns and natural feed ·100 microns using various pin tip velocities, ball densities and within the normal stirred ball milling operating range. relationship between the ball diameter and the particle was explained by the "angle of nip" theory which applied for roller crushers. It was shown that the particle giving the maximum breakage rate was directly proportional to the ball diameter. Estimated grinding kinetic parameters from monosize provided a good basis for predictions of natural feed. However, the breakage rate obtained from monosize tests appeared to be lower than those from the natural feed It was found that if the selection and breakage functions were determined by monosize tests, it was possible to modify selection function parameters by back-calculation which gave the best fit to the natural feed size. A good correlation was obtained between the experimental and product distributions using a population-balance model. The links between the empirical model combining Charles' and Rosin-Rammler equations and the first-order batch grinding equation were also shown. The stirred ball mills were operated in batch and continuous mode. The median size of the products from the batch stirred ball mill experiments closely matched those of the continuous grinding experiments under similar grinding conditions. Using a salt solution as a tracer material, an attempt was made to estimate the residence time distribution based on a simplified analysis of the motion of the water in tile mill. The current scale-up methods for the stirred ball mill are discussed. A torque model was developed for given shaft geometry and ball relating the power rements of the stirred ball mill to the following prime design and operating parameters : mill diameter, mill height, pin tip velocity and effective density of the mill load. The basic assumptions underlying the model were that the mill content behaved as a fluidised bed, consequently a P effg h type model for the pressure was applied throughout the grinding media bed the effective charge velocity was proportional to the pin tip velocity. It was found that pin spacing, pin diameter and ball diameter significantly affected the mill torque. A semi-empirical torque model was derived to include these parameters. The relationships formulated from these models were shown to be in excellent agreement with experimental results. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

Production of platinum and associated metals is a major source of revenue for South Africa. Significant losses occur in the concentrating stage (10 to 15 per cent) and this research is focused on optimising platinum flotation. Research begins by conducting laboratory batch flotation tests. However, subsequent pilot-plant tests often produce different results. It is believed these differences arise from the artificial nature of laboratory techniques. This project was focused on improving flotation techniques in the laboratory. The largest source of platinum in South Africa is the UG2 reef and two samples of this ore were used for testing: ‘good’ and ‘bad’ ore. These had different characteristics with regards to the recovery of PGMs and the presence of talc. The latter is an unwanted floatable mineral, which must be depressed to prevent excessive recovery. The conventional laboratory test procedure makes use of batch tests in various sizes of flotation cells. The procedure was made more realistic, by using four stages of flotation, rather than just two, to mimic a typical platinum flotation plant. The use of four stages made it possible to separate the fast-floating and slow-floating stages and to control froth conditions accordingly. Attention was also given to the fact that in laboratory tests, water is often added to the ‘cleaner’ stage of flotation, to make up the level. Experiments showed that this dilution, which does not take place in practice, had a significant impact on overall efficiency. A method of measuring frother concentration was developed and used to determine the realistic level of frother in cleaning tests. Tests at these levels of frother concentration showed that significant improvements could be made to plant performance, by making use of a thickener to reduce the frother concentration in the cleaning stages. The improved test procedure was used on both good and bad ores, and the effect of regrinding was also tested. A combined solids recovery of 2 % over both cleaners was targeted for all test work. At this recovery, the regrinding of the bad ore increased the PGM recovery from 67 to 76 per cent at the cost of an additional 8 g/t depressant. An investigation of the effect of frother concentration in the cleaning stage, using good ore, demonstrated that that rejection of chromite could be improved significantly by reducing frother concentration. The tests mimicked the use of a thickener to separate some of the water with a high concentration of frother. Tests conducted on the good ore showed that use of two thickeners, as opposed to none, reduced the Cr2O3 content of the final concentrate from 4.2 to 3.2 per cent for the equivalent concentrate mass and PGM recovery. The depressant requirement was also reduced from 67 to 55 g/t. These tests provided insight on how to improve performance on a platinum flotation plant, particularly when floating the bad ore.

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Thesis (PhD) -- University of Western Sdyney, 2001. / "A thesis presented in accordance with the regulations governing the award of the degree of Doctor of Philosophy, University of Western Sydney" "November 2001" Bibliography: leaves 249 - 254.

Thesis--University of Missouri, School of Mines and Metallurgy, 1903. / R.T. Rolufs determined to be Roluf Theodore Rolufs from "Thirty-Third Annual Catalogue of the School of Miens and Metallurgy." The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed Nov. 3, 2008).

Thesis (M.Sc.(Applied Science-Metallurgy))--University of Pretoria, 2008. / Abstract in English. Includes bibliographical references (leaves 136-145).

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1929. / Figures 2-5 and Tables 1-5 are missing from text document. The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed October 1, 2009)

Thesis (Ph.D.(Electronic Engineering))--University of Pretoria, 2009. / Summaries in Afrikaans and English. Includes bibliographical references.