Binary modelling the milling of UG2 ore

Platinum group elements (PGE) are mineral resources that serve as strategic economic drivers for the Republic of South Africa. Most of the known to date remaining reserves of PGM’s in South Africa are found in the UG2 chromite 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 interlocked texture between chromite and the valuable minerals predisposes the PGM ores to an inefficient froth flotation and thereby leads to drastic problems at the smelters. Entrainment of fine chromite is a major problem, so the reduction of fine chromite content in the UG2 ore prior to flotation is therefore crucial. The Council for Mineral Technology (Mintek) has been aiming at improving the secondary ball milling of the Platinum Group Ores by optimisation of the ball milling parameters from the perspective of a preferential grinding of the non-chromite component in the UG2 ore. To this end, we looked at determining which one amongst speed, liner profile and ball size better controls the energy consumed. Moreover, this work sought at determining which combination of the above variables maximises the reduction of the chromite sliming of UG2 ores. Prior to the experimental work, preliminary evaluations of the load behaviour and power draw under different milling conditions were performed by use of the Discrete Element Modelling (DEM). The DEM was also used to assess the distributions of tumbling mill’s impact energy dissipated between balls and between balls and mill shell. The ability of the Discrete Element Modelling (DEM) to match selected experimental scenarios was appraised as well. The actual ball milling test results indicated that variables, such as mill liner profile and ball size affect the milling efficiency and the size distribution of the products whereas, the mill rotational speed had little to no effect. Use of 45° lifters and small balls enhanced the grinding efficiency. These results agreed fairly well with the DEM simulation predictions. A model describing the chromite content within the UG2 ore sample as a function of density and particle size was also developed. The model was found to be reliable in the range of data tested and proved to be a strong function of the ore sample density. The particle size was less relevant but nevertheless important. The UG2 ore was then assumed to be constituted of a binary mixture: chromite and nonchromite components. The kinetics study was then conducted for each individual component, from the feed sizes: -600+425, -425+300, -300+212, -212+150 μm. With regard to the Selection Function (Si), when comparing the characteristic a values (slope of Si with respect to particle size), faster breakage was obtained for the chromite component, followed by UG2 ore and the non chromite component. The cumulative breakage distribution function (Bi,j) values obtained for these two components were different in terms of the fineness factor γ. The value of γ was smaller for the chromite component, indicating that the higher relative amounts of progeny fines were produced from the breakage, while the value of γ was large for the non-chromite component, indicating that less relative amounts of fines were produced. Finally, a matrix model transformation of a binary UG2 ore was developed for a basic closed ball mill-hydrocyclone circuit. The model described satisfactorily the grinding behaviour of the chromite and non-chromite separately. This model is useful for showing effects of the milling of a binary ore on the ball mill circuit output

Plugging mechanisms and plugging reduction techniques in heap leaching operations: a review.

Abstract: Plugging of pore spaces is the most significant contributor to ponding, decrease in the mineral resource recoveries and stability problems in heap leaching operations as ore permeability is reduced. Consequently, the identification of different plugging mechanisms is very important for optimisation of heap leaching processes. This paper reviews various pore spaces plugging mechanisms, including ore heap compaction, migration of fine particles, presence of large fractions of clays in ores, agglomerate destruction under acid effect and dissolution-precipitation processes. Proactive plugging reduction techniques including ore placement, ore agglomeration, heap aeration and lixiviant application techniques are also explained as means to prevent pore spaces plugging during heap leaching operations. The findings of this paper can be useful in guiding laboratory and industrial heap leaching operations.Abstract: Plugging of pore spaces is the most significant contributor to ponding, decrease in the mineral resource recoveries and stability problems in heap leaching operations as ore permeability is reduced. Consequently, the identification of different plugging mechanisms is very important for optimisation of heap leaching processes. This paper reviews various pore spaces plugging mechanisms, including ore heap compaction, migration of fine particles, presence of large fractions of clays in ores, agglomerate destruction under acid effect and dissolution-precipitation processes. Proactive plugging reduction techniques including ore placement, ore agglomeration, heap aeration and lixiviant application techniques are also explained as means to prevent pore spaces plugging during heap leaching operations. The findings of this paper can be useful in guiding laboratory and industrial heap leaching operations

Structural equation modelling the leaching of oxidised copper-cobalt ore in HCl aqueous solution

Abstract: Structural Equation Modelling (SEM) is now widely used to explore the joint performance of factors affecting a process and to quantify the effect of each factor in the presence of the others. In this research work, SEM analysis was conducted to develop Structural Equation Models that well predict the leaching behaviour of Cu, Co, Ni and Fe in HCl aqueous solution of an oxidised copper-cobalt ore. A comprehensive set of experimental batch leaching tests was executed to study the effect of operating variables (pH, time, temperature and stirring speed) on the relative leaching yields of Cu, Co, Ni and Fe during the leaching of an oxidised copper-cobalt ore sample in an HCl aqueous solution. The gangue acid consumption was also measured to aid in understanding the behaviour of the gangue. The experimental results obtained were statistically analysed and modelled using the SEM procedure. The Structural Equation Models obtained showed that Cu and Co leaching yields had a strong positive dependence on both the leaching time and leaching temperature, while Fe leaching yield had a moderate dependence on the leaching temperature, stirring speed and the covariate Z (Z = stirring_speed*pH). On the contrary, Ni leaching yield had a strong negative dependence on both the stirring speed and the covariate Z. The Structural Equation Models agreed fairly with the experimental results obtained upon leaching. This is a clear indication that the models can be used to predict the leaching yields given a set of leaching parameters

Plugging mechanisms and plugging reduction techniques in heap leaching operations: a review.

Abstract: Plugging of pore spaces is the most significant contributor to ponding, decrease in the mineral resource recoveries and stability problems in heap leaching operations as ore permeability is reduced. Consequently, the identification of different plugging mechanisms is very important for optimisation of heap leaching processes. This paper reviews various pore spaces plugging mechanisms, including ore heap compaction, migration of fine particles, presence of large fractions of clays in ores, agglomerate destruction under acid effect and dissolution-precipitation processes. Proactive plugging reduction techniques including ore placement, ore agglomeration, heap aeration and lixiviant application techniques are also explained as means to prevent pore spaces plugging during heap leaching operations. The findings of this paper can be useful in guiding laboratory and industrial heap leaching operations

Binary modelling the milling of UG2 ore using a matrix approach

The study reports a binary matrix modelling and simulation studies to improve the performance of the secondary grinding circuit of UG2 ores. The model developed was intended to help searching for optimal operating conditions of the secondary milling circuit so that the platinum group element (PGE) recovery is increased while reducing Cr2O3 entrainment in the subsequent flotation stage. A series of laboratory batch-scale tests was carried out in order to estimate the milling kinetics parameters of the chromite and non-chromite components. Finally, two alternatives circuit configurations for a better performance were evaluated using simulations. The optimal design consisted of a conventional ball mill in closed circuit with a hydrocyclone to separate the milling product into lights (non-chromite-rich) and heavies (chromite-rich) fractions followed by a vibrating screen to de-slime the cyclone underflow before it is returned to the mill for further grinding

Clarification and solvent extraction studies of a high talc containing copper aqueous solution

Effects of different flocculants on the clarification of a copper aqueous solution destined for solvent extraction were investigated. The test work was conducted on the pregnant leaching solution (PLS) of a high talc containing copper ore that had a high propensity of bearing a large amount of suspended solids. The clarification test work was conducted using three commercial high molecular anionic polyacrylamide polymer flocculants: rheomax® DR 1050, brontë 103, and senfloc® 2660. Solvent extraction tests were done using 30% (v/v) LIX 984N at pH 1.8. The parameters of clarification and solvent extraction were the flocculant dosage (0, 58.14, 116.28, 232.56 and 348.84 g/t) and the ratio O/A (1/5, 1/2, 2/3, 1/1, 3/2, 2/1, and 5/1), respectively. The analysis results of the PLS showed it contained 2000 ppm of solids in suspension. The optimal conditions for clarification and solvent extraction were a dosage of 116.28 g/t and an O/A of 1.5, respectively. Under optimal conditions, the residual total suspended solids (TSS) in the clarified solutions were 1196 ppm, 954 ppm, and 928 ppm; the phases disengagement time (PDT) for organic continuous dispersion were 70 s, 80 s and 60 s; the percent TSS entrained in the organic phase were 26.76%, 28.93% and 25.32%; copper recoveries were 97.63%, 98.98% and 95.13%, with rheomax® DR 1050, brontë 103 and senfloc® 2660, respectively. Keywords: Copper, Talc, Leaching, Pregnant leaching solution, Clarification, Flocculants, Solvent extractio

Removal of Fe and Mn from polluted water sources in Lesotho using modified clays

This paper reports the use of unfunctionalized and phenylalanine functionalized clays as an alternative cost effective, environmental friendly and efficient sorbent for the removal of Mn and Fe from polluted drinking water sources in Lesotho. The Mn and Fe metals were adsorbed on two different clays (clay Aa black clay and clay Ba yellow clay) collected from Ha-Teko in Maseru (clay A) and Phoqoane in Mafeteng district (clay B). Comprehensive batch test studies were performed to assess the effect of pH, stirring time and initial concentration of Mn and Fe. The adsorption of the metals was greater at higher pH and equilibrium was reached at pH 8 after 30 min of stirring. The phenylalanine functionalized clays displayed improved adsorption efficiency of up 100% (Fe adsorption using clay A in 30 min) while the unfunctionalized clays gave relatively low adsorption of up to 70% (Fe and Mn adsorption using clay A). The clays, which are present in abundance in Lesotho, can be effectively used for the removal of Fe and Mn from drinking water sources