David Milton Lewis

The effective separation of ore is based on two fundamental processes: liberation and separability. Liberation involves the reduction of size, yielding smaller particles with enhanced compositional homogeneity. Understanding liberation requires an understanding of rock breakage, as it impacts mineral liberation and helps identify ores suitable for pre-concentration. Non-random breakage, influenced by textural and mineral properties, introduces heterogeneity in mineral distribution across size fractions. Physical attributes, including ore and gangue mineralogy and texture, influence fractionation tendencies during breakage. Notably, the presence of mineralization in veins substantially assists early-stage liberation in mineral processing. The aim of this study is to develop a methodology that allows the prediction of natural fractionation tendencies based on geological, mineralogical, and textural data using Discrete Element Method (DEM) modeling. DEM simulations provide insights into granular material behavior, capturing phenomena such as crack initiation and propagation. The use of DEM, particularly with models such as the Flat Joint Model (FJM), enhances our understanding of rock damage mechanisms. In this paper, DEM is used to predict preferential grade by size deportment, and a numerical model is developed to reflect grade distributions across size fractions. A fragmentation analysis is conducted after rock breakage simulations using DEM to analyze the fragment sizes and grades and calculate the Response Rankings of synthetic specimens.

An individual trace metal present in a soil at its ecological screening value or investigation level (trigger/threshold) is expected to cause phytotoxicity. However, phytotoxicity may be induced by a mixture of multiple metals, each present at a concentration lower than the corresponding investigation level. To investigate the accumulative impact of metals present below their individual investigation levels, three successive phytotoxicity trials were conducted in a greenhouse using the triticale plant CrackerJack (Triticosecale rimpaui), a cereal crop, in a sandy acidic soil treated jointly with Cd, Cu, and Zn at various rates. Seed germination and seedling growth were monitored. The metal rates in the first two trials were either too toxic or nontoxic. In the third trial, it was found that the mixture of Cd, Cu, and Zn at rates of 2.5, 97.5, and 188 mg kg⁻¹, respectively, did not affect seed germination, but caused a slight reduction in plant growth. Although metal concentrations used were lower than the Australian Ecological Investigation Level (Urban) for Cd, Cu, and Zn, which are 3.0, 100, and 200 mg kg⁻¹, respectively, the reduction occurred due to synergy. It was concluded that, to enhance the usefulness of environmental investigation limits, the synergistic effects of multiple metals present at levels slightly below the established limits must be considered.

Bactericidal proteins from the Moringa oleifera seed are reported to be suitable alternatives to conventional methods of bacterial reduction in water. In this study the cationic bactericidal M. oleifera proteins were isolated by attachment onto the surface of silicon dioxide. This functionalised SiO₂(ƒ-SiO₂) was then exposed to Escherichia coli and Micrococcus luteus to examine whether the ƒ-SiO₂ could be used to inactivate the bacteria. The effect of the non-ionic surfactant dodecyl glucoside on the attachment of these bacteria to the ƒ-SiO₂ was examined with the aim of developing a method of reusable bacterial inactivation. The primary result of this study was that the E. coli could be readily separated from the ƒ-SiO₂, allowing the ƒ-SiO₂ to be used for further bacterial inactivation. The regeneration of the ƒ-SiO₂ was demonstrated using fluorescence microscopy on bacterial cells stained with propidium iodide, and zeta potential measurements. Future applications of this work include a reusable method of removing bacteria from contaminated water.

Moringa oleifera seeds are well known for their ability to cause flocculation in turbid water and facilitate bacterial inhibition. These effects are due to the cationic polypeptide MO_2.1, which affects the surface charge of suspended particles and causes lysis of bacterial cells. However, the attachment of bacteria to MO_2.1 prevents further bacterial attachment, reducing the effectiveness of the seeds. This research investigated the effect of surfactants on functionality and reuse of Moringa seeds to develop a sustainable water treatment technique. The seed extracts (MO_2.1) were used with a functionalised sand system, and the sands were exposed to commercially available (ionic and non-ionic) surfactants, dodecyl glucoside and sodium dodecyl sulfate. Artificially polluted water contaminated with Escherichia coli was used to evaluate the efficiency of the system. The non-ionic surfactant was found to be effective at separating E. coli from the functionalised sand without the detachment of the MO_2.1 and subsequent loss of the system efficiency. This was successfully repeated four times. The results demonstrated a sustainable, reusable technique to inhibit bacterial contamination in water.