Ralph J. Holmes

Bioflotation and bioflocculation review: microorganisms relevant for mineral beneficiation

Abstract In a world of diminishing resources, current research efforts are often directed to extending the life of existing resources and developing technology to treat resources deemed uneconomic. To this end, biotechnology has been explored as a potential low cost, environmentally benign alternative to many of the current mineral processing techniques. Microorganisms and their metabolites have been successfully applied in the leaching of metals from medium and low grade sulphide minerals for many years. Recent fundamental studies have shown that selected bacteria may also assist in the beneficiation of these minerals through bioflotation and bioflocculation. The current published research demonstrates that several bacteria and their excreted proteins and polysaccharides have a significant effect on the surface chemical properties of some minerals. As such, the bacterial cells and their metabolites can be utilised as flotation collectors and modifiers enabling selective separation. To date, these studies have primarily focused on the sulphide minerals; however, there is considerable scope to expand this research for the beneficiation of oxide minerals such as those contained in iron ores. This paper provides a comprehensive review of current research on the use of microorganisms for mineral beneficiation and the potential use of genetically modified bacteria and, further, discusses the applicability of bioflotation and bioflocculation for the beneficiation of Australian iron ores.

A simplified variogram method for determining the estimation error variance in sampling from a continuous stream

Abstract The underlying theory for determining the estimation error variance of the mean of samples taken from a moving stream is reviewed. Situations where standard formulae will give incorrect results are identified and appropriate corrections given for those situations. On the basis of this theory, a simplified method, using only results for a linear variogram, is proposed. The proposed method is shown to work correctly for multistage sampling and also when the variogram itself is varying. Examples are given of the application of the method to determination of the estimation error variance and to the design of sampling schemes.

Bulk Analysis Using Nuclear Techniques

Abstract A number of bulk analysis techniques developed particularly for the mining industry by the CSIRO Division of Mineral Physics are reviewed. With these techniques, analyses are obtained directly from 3–30 kg samples without further sample preparation, or from material located on conveyor belts. Because penetrating neutron and γ-radiation is used, measurements are obtained from a large volume of sample, which ensures that the analyses are representative of the bulk. γ-Ray techniques have been used to determine the grade of 25 kg samples of iron ore and to detect shale on conveyor belts. The bulk analyser for iron ore measures the backscattered gamma rays from a 60Co γ-ray source, and an accuracy of 0.35% Fe can be obtained. The on-stream shale detector distinguishes shale from high-grade iron ore by means of the greater natural γ-ray activity of the shale. A thermal-neutron irradiation technique (called SIROSA, for CSIRO On-Stream Analysis) that uses a 252Cf neutron source has been developed for the simultaneous determination of iron and aluminium (expressed as Al2O3) in iron ore on a conveyor belt. Although the speed of the conveyor has no direct effect on the iron measurements, it must not exceed about 3 m/min if good accuracy for alumina is required. Consequently, an auxiliary conveyor belt is required to avoid interference with normal ore processing. Dynamic trials have demonstrated that accuracies of 0.6% Fe and 0.1% Al2O3 can be obtained. Other applications of thermal-neutron activation analysis include the determination of alumina in 10–20 kg samples of bauxite and coal with accuracies of 0.5 and 0.2% Al2O3 respectively, and the determination of manganese and alumina in manganese ores. Fast-neutron activation analysis using 241Am-Be neutron sources has also been adapted to bulk analysis. Successful applications include the determination of silicon (expressed as SiO2) in iron ores with an accuracy of 0.15% SiO2, and the simultaneous determination of alumina and silica in bauxites with accuracies of 0.7% Al2O3 and 0.3% SiO2. A combination of fast- and thermal-neutron activation has been applied to the determination of soil in shredded sugar cane with an accuracy of 0.1% soil.

A Comparative study on a vertical stirred mill agitator design for fine grinding

Comminution is an energy intensive process. A small change in efficiency can lead to substantial benefits in an overall economy of the process plant. This study focused on the comparison of vertical stirred mill agitator designs. A double helical screw agitator was designed for this purpose. A series of stirred mill experiments were performed with two types of agitator designs a standard pin type and CSIRO’s designed double helical screw stirrers. The effects of operating parameters such as grinding time, stirrer speed, and pulp density on grinding performance was investigated using a magnetite concentrate. Grinding performance was analyzed by considering the product fineness and the energy consumption. The test results show that the grinding time and stirrer speed played a significant role; however, the pulp density had little impact on grinding performance in both cases of agitator designs. The 80% passing target product size of 38 μm was obtained with double helical screw agitator in 20 min of grinding with an expend of 10.53 kWh/t specific energy, whereas, the target product size of 38 μm was achieved with the pin type stirrer at the rate of 21.73 kWh/t. It is evident that grinding in a vertical stirred mill with a double helical screw is more efficient than that using a pin type stirrer in terms of the product size distribution and the specific energy consumption. It is concluded that the double helical screw design provides better energy efficiency compared to the pin type stirrer design. The models were developed for the responses P80 and Ecs. Both models show high regression coefficients thus ensuring a satisfactory of models with experimental data. The model equations developed were then optimized using a quadratic programming to minimize the P80 size at minimum specific energy.

Importance of textural information in mathematical modelling of iron ore fines sintering performance

ABSTRACT Predicting the sintering performance of iron ore fines and the possibility of targeted optimisation of specific sinter properties are very important for the iron ore industry and related research organisations. A comprehensive database of pilot-scale sintering experimental results was established and empirical modelling conducted to predict values for sintering performance parameters such as Tumble Index, low temperature Reduction Disintegration Index and productivity. Together with other variables, the models developed include the abundances of several different ore textures which were combined into different textural factors corresponding to different sinter properties. Coefficients for the variables within specific regression equations can provide a better understanding of the effect of the variables on the corresponding sintering performance. The modelling results were also used to predict the sintering performance of tested mixtures that were not part of the database used to establish the models, so all models were thus verified on an independent set of data.

Iron ore processing

Creating steel from low-grade iron ore requires a long process of mining, crushing, separating, concentrating, mixing, pelletizing, and shipping. The process of mining low-grade iron ore, or taconite, requires massive resources. Heavy industrial mining equipment, expansive mines, and a skilled labor pool are all required. The equipment used includes diamond-bit rotary drills, hydraulic shovels and loaders, water wagons, production trucks and heavy-duty conveyors.