South African Journal of Chemical Engineering - Volume 16, Issue 1, January 2011

Extraction of platinum group elements (PGE) is a major source of revenue in South Africa and the reserves represent about 75 per cent of world reserves. Most of the remaining PGE reserves are located in the UG-2 chromitite layer of the Bushveld Igneous Complex. Platinum concentrators experience significant losses of valuable PGE in their secondary milling circuits due to insufficient liberation of platinum-bearing particles. The chromium oxide (Cr2O3) content in UG-2 concentrates is typically 3%, which results in severe operational problems in the downstream smelting process. This paper follows up from the work done in 2010 which indicated that spiral concentrators could be incorporated into the secondary milling circuit design for UG-2 platinum concentrators for separate grinding of platinum-bearing silicate particles and chromite-rich particles.

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A detailed mineralogical analysis was conducted on a plant audit sample from the secondary rougher tailings (SRT) stream for comparison with the laboratory test work to assess the degree of potential losses of PGEs experienced with the conventional milling circuit.The effect of the size-by-assay analyses of the laboratory milled products and flotation tailings for a low grade UG-2 ore sample from the hydrocyclone (densifier) underflow were compared to the standard process. The effects on the recovery of PGEs, and the entrainment of Cr2O3 were measured in combined batch rougher flotation tests. Mineralogical evaluations of the SRT plant sample showed losses of about 37% of the PGEs in that stream to the coarse fractions (+75 µm). The chromite entrainment was significantly reduced (>30%) with a 3.6% increase in the PGE recovery. This paper confirms the benefit of separate ball milling in the secondary milling circuit for a chromite-rich (>50%) UG-2 platinum ore.

Phytosterols are important chemicals due to their applications as health products and as nutritional supplements. An important source of phytosterols is the waste tall oil soap from the Kraft process in pulp and paper production. Extraction of phytosterols therefore has two objectives: recovery of a valuable chemical and waste beneficiation. The effect of pH of tall oil soap on the extraction of phytosterols was conducted in laboratory tests before application in a counter-current, Vibrating Plate Extractor (VPE). A decrease of pH from 12 to 7 of the tall oil soap solution increased the content of phytosterols in the extracted phase. The extraction efficiency increased by 17-39%. Permanent emulsions were formed at a pH of 8, which should thus be avoided as an operating condition. Lastly, operating below a pH of 6 is not recommended due to the liberation of fatty and resin acids that contaminate the phytosterols in the extract.

Liquid-liquid extraction is the separation of the constituents of a liquid solution by contact with another insoluble. The reciprocating column (RPC) and vibrating plate column (VPE) are two types of mechanically aided columns. This paper aims at developing appropriate correlations for the prediction of NTU/HETS and the mass transfer coefficient, kox for the VPE based on the agitation level of the plates (af - the product of frequency and amplitude of the plate motion), the plate spacing and the flow rates which will allow for the simplification in the design of this type of column. The system chosen was the acetone-toluene-water system (standard test system - EFCE) with the acetone in toluene forming the feed that is dispersed in the column as it moved upward while the water moved as a continuous phase down the column. Experiments were conducted to evaluate the hydrodynamics of the droplets moving up the column and to evaluate the mass transfer that occurs (in order to evaluate NTU, HTU and kox) while varying the agitation levels and spacing of the plates in the column. Successful correlations were developed using some of the experimental data and these correlations were verified with additional data.

The air dense medium fluidized bed separator which has been developed for the dry beneficiation of coal and recognized as a low cost and high efficiency process. In some cases the efficient beneficiation process are not found to be very effective for the Indian coals due to their typical washability characteristics. So a systematic study has been carried out to verify the suitability of this process by considering three different Indian coals of different characteristics. The results show that this separation process is quite efficient for the beneficiation of coal in the size range of -50+25 mm with Ep values in the range of 0.037-0.055. However, lower separation efficiency for finer coal of -13+4.75 mm size indicates towards the non-suitability of the process. Based on this study, the air dense medium separation process was established to be a possible alternative to the conventional wet beneficiation method for processing coarser size Indian coals.

Fugitive emission of dust is common in various chemical, mining and metallurgical process industries and causes severe health problem of the workers in the plant. To control such huge emission generally bag filter system is suitable when temperature is not more than 150 °C. The performance of bag filter depends on the characteristics of dust and its nature of particle settling velocity. In this work an attempt have been made to investigate the effect of particle size distribution and capture velocity of particle on the removal efficiency of the file dusts by using bag filter system. It has been observed that by marinating a capture velocity much higher than terminal settling velocity of the particle resulted in enhanced collection efficiency of the particles and thus minimizes the fugitive emission, which meets the stringent regulations of environmental pollution.