B.A. Wills

Chromite- mineralogy and processing

Abstract Chromite is an important strategic mineral. In this paper, its deposition, mineralogical properties, and beneficiation are briefly reviewed.

The shaking table concentrator — The influence of operating conditions and table parameters on mineral separation — The development of a mathematical model for normal operating conditions

Abstract The effects of several variables on the performance of a shaking table have been investigated on a laboratory-scale Wilfley table using a synthetic mixture to represent a typical industrial metallic ore. The following main conclusions can be drawn from the study: 1. (i) Feed pulp density should be kept below 35% solids. 2. (ii) A minimum level of wash-water is required to effect separation. 3. (iii) There is an optimum deck inclination for any given material. 4. (iv) Increasing a particular density and size fraction of the feed, causes a corresponding increase in the band width of this material at its discharge point. A modified logistic function was used as a regression model to predict the cumulative distribution curves of the species. The general form of the equation is: y i = Tanh 2 (x i a 3 ) [1.0+exp(−[a 1 +a 2 {x i −1.0}])] where yi=cumulative % of a species xi=crossbed length The physical significance of the model coefficients is described. The development of secondary equations to relate the model coefficients to particle size and density is also outlined. The limitations of the model are examined and the areas requiring further work are highlighted.

Extraction and recovery of silver from low-grade liquors using microalgae

Abstract The silver-binding properties of two strains of the alga Chlorella vulgaris (211/11b and 211/12) have been investigated. Rapid Ag + uptake from an aqueous solution has been proven. The relative affinity of the strains based on varying silver concentrations has been measured. Over a silver concentration range of 10 mg/l to 200 mg/l strain 211/11b had the greater affinity for the Ag + ion, reaching a maximum loading of 56.7 mg/g of algae when contacted with 200 mg/l AgNO 3 solution. The binding of the Ag + ion is largely pH-independent when present in a low concentration but pH-dependent when present in a high concentration. When contacted with a simulated photoprocessing effluent, over 80% of the silver can be removed by strain 11b. Froth flotation can be an efficient technique in the removal of silver-bound Chlorella vulgaris from a reaction solution with efficiencies of recovery attaining 97.5% for Ag + bound strain 211/11b and 89% for silver thiosulphate-bound strain 211/11b. The flocculant aluminium sulphate was usually required for most efficient flotation; however when floating the algae from the growth medium the presence of Al 3+ ions actually inhibited flotation. All the flotation experiments were carried out in a Hallimond tube using the amine collector ARMAC-T. The optimum concentration for this collector was 0.4 g/l. Owing to the algas high sorbtive capacity for the silver thiosulphate complex at low concentrations, retrieval systems based on Chlorella vulgaris would be best applied for final cleansing of effluents from existing silver recovery systems.

Some observations on the fracture and liberation of mineral assemblies

Abstract Comminution is one of the most intensively researched areas of the minerals industry. Much effort has been spent in attempting to reduce the high operating costs, but relatively little in developing practical methods to promote enhanced liberation of the minerals from each other. This paper considers the need to research more deeply the mechanisms of the breakage processes in current comminution machines, particularly the promotion of intergranular fracture. In order to do this control of crack propagation, and the nature and role of grain boundaries, are areas deserving most attention.

Review of methods of improving mineral liberation

Abstract Most of the important developments in comminution have been aimed at reducing its high operating costs. However, the most important role of comminution in the minerals industry is not merely to reduce particle size, but to liberate minerals from each other. Conventional methods liberate relatively inefficiently, due to the indiscriminate nature of the breakage process. Inadequate mineral liberation in itself leads to higher operating costs, as finer grinding has to be performed to achieve an adequate degree of liberation, and this can lead to the generation of ultra-fine slimes particles, which may be lost in the downstream process. This paper reviews the methods that have been researched in order to enhance mineral liberation by directing comminution energy to grain boundaries in order to promote intergranular rather than transgranular fracture.

Technical note Enhancement of cassiterite liberation by high pressure roller comminution

Abstract Samples of ore from South Crofty tin mine, Cornwall, were ground by rod mill and by high-pressure roller press. Heavy liquid analyses of the products suggest that mineral liberation may be enhanced by the use of the roller press.

Optimisation of thermally assisted liberation of a tin ore with the aid of computer simulation

Abstract A model developed for the simulation of the effect of grind size on gravity circuits has been applied to a sample of Cornish tin ore in an attempt to assess the viability of thermal pretreatment as an economic method of enhancing metallurgical performance.

Shear flocculation — A review

Abstract Shear flocculation is the process where hydrophobic ultrafine particles with high surface charge are aggregated under high shear conditions. It makes use of the energy of hydrophobic association that takes place when the hydrocarbon chains of the collector, adsorbed on the surface of the particles, come in contact. A shear field of sufficient magnitude to overcome the energy barrier separating the particles is necessary to bring them together for hydrophobic association. A review of the mechanism of shear flocculation and its potential for treating mineral ultrafines is presented in this paper.

Selective aggregation of ultrafine hematite and quartz under high shear conditions with conventional flotation collectors

Abstract Recovery of ultrafine minerals, of less than 10 microns in size, remains one of the most difficult problems faced by the minerals engineer. Shear flocculation is one technique that can be applied to minerals in this size range. The technique involves aggregating mineral particles, made hydrophobic with flotation collectors, under high shear conditions. The work presented considers the use of primary aliphatic amines and sodium oleate for the selective aggregation of hematite and quartz. Sodium oleate was shown to offer potential for selective aggregation of hematite whereas the amines tested could not provide the desired selectivity. Factors that affect the size of the aggregates formed were investigated. Collector concentration and pH were found to be the most important with each system tested.

The development of minerals engineering in the 20th century

Abstract Minerals engineering, and particularly mineral processing, has developed during this century from a relatively crude process operation performed by the mining engineer to a serious professional discipline in its own right, involving utilisation of engineering, physical, chemical, and increasingly biological principles. This paper shows how minerals engineering, particularly base metal mineral processing, has had to adapt to lower ore grades and the increasingly refractory nature of mined ores, as well as to periods of deep recession within the industry.