Physico-Chemical Characteristics of Spodumene Concentrate and Its Thermal Transformations

Spodumene concentrate from the Pilbara region in Western Australia was characterized by X-ray diffraction (XRD), Scanning Electron Microscope Energy Dispersive Spectroscopy (SEM-EDS) and Mineral Liberation Analysis (MLA) to identify and quantify major minerals in the concentrate. Particle diameters ranged from 10 to 200 microns and the degree of liberation of major minerals was found to be more than 90%. The thermal behavior of spodumene and the concentration of its polymorphs were studied by heat treatments in the range of 900 to 1050 °C. All three polymorphs of the mineral (α, γ and β) were identified. Full transformation of the α-phase was achieved at 975 °C and 1000 °C after 240 and 60 min treatments, respectively. SEM images of thermally treated concentrate revealed fracturing of spodumene grains, producing minor cracks initially which became more prominent with increasing temperature. Material disintegration, melting and agglomeration with gangue minerals were also observed at higher temperatures. The metastable γ-phase achieved a peak concentration of 23% after 120 min at 975 °C. We suggest 1050 °C to be the threshold temperature for the process where even a short residence time causes appreciable transformation, however, 1000 °C may be the ideal temperature for processing the concentrate due to the degree of material disintegration and α-phase transformation observed. The application of a first-order kinetic model yields kinetic parameters which fit the experimental data well. The resultant apparent activation energies of 655 and 731 kJ mol−1 obtained for α- and γ-decay, respectively, confirm the strong temperature dependence for the spodumene polymorph transformations.

A new mathematical model for copper concentrate combustion in flash smelting furnaces

A novel mathematical model for combustion of a single copper concentrate particle is presented. The model includes particle volatilization, fragmentation, smelting, and combustion phenomena. This model has been incorporated into a general computational fluid dynamics code to calculate flow field and particle trajectories needed to simulate the smelting process in flash furnaces. In this model, Lagrangian approach was used to handle solid particles and droplets of liquid fuel charged, while Eulerian framework was used to handle the gas phase flow field. The results show that the effect of particle fragmentation was remarkable in flash smelting process as compared with experimental data and should be considered in combustion modeling. Moreover, the flash smelting process simulation results show that the reaction shaft design should be optimized based on a combination of furnace dimension and type of concentrate burners.

Comparison of Cyanide and Chloride-Hypochlorite Leaching of a Ball Milled Refractory Gold Concentrate with Ultra-Fine Particles

In this research, cyanide and chloride–hypochlorite leaching of gold from a pyritic concentrate (particle size: −75+53 µm, gold content: 27.15 g/t) were compared. It was shown that only 13.6 % of gold was extracted after 24 h leaching by cyanide, as compared to 37.2 % after 8 h by chloride–hypochlorite. Effect of ultra–fine milling of the concentrate on the leaching was investigated using a high–energy planetary ball mill at different milling times. It was found that the leaching rate of gold by both leachants could be substantially enhanced after the milling of the particles to sub–micron dimensions. This was attributed to the increase of specific surface area and the accumulation of energy in the pyrite particles. After 480 min milling (air atmosphere, 300 rpm, sample/ball:1/20), 96.1 % of gold was extracted by 24 h cyanide leaching, while 100 % extraction could be achieved after only 45 min milling and 30 min chloride–hypochlorite leaching. This was attributed to the oxidation of pyrite by the hypochlorite oxidant and the complete liberation of gold encapsulated in the pyrite particles.

Preparation and Characterization of Surface Modification of Sphalerite Concentrate with Sodium Lignosulfonate

In order to prevent sphalerite particles from coming together in leaching solution, and to reduce the loss of organic solvent, the surface modification of sphalerite concentrate with sodium lignosulfonate was investigated. The modified sphalerite concentrate particles were characterized by dispersion experiments, determination of adsorption rate of oil, determination of contact angle, FT-IR spectra and X-ray photoelectron spectra. The results showed that the modified sphalerite concentrate particles exhibited good dispersibility in water. The sedimentation volume reduced from 0.85 ml•g-1 to 0.61 ml•g-1. The adsorption rate of oil reduced from 0.15 ml•g-1 to 0.06 ml•g-1. The contact angle between sphalerite concentrate particles and water changed from 86.9˚ before modification to 32.7˚ after modification with sodium lignosulfonate. The checking results of FT-IR and XPS spectra indicated that some modification regents were coated on the particle surface. The modifier combined to sphalerite concentrate particle surface through the chemical bond, resulting in the comprehensive stability action of static and steric effect.