Investigation of the effect of mineralogy as rate-limiting factors in large particle leaching

Although heap leaching is by now well established in the mining industry, the process remains limited by low recoveries with different rate-limiting factors that are not clearly understood. In this study, three large particle size classes (+19/-25, +9.5/-16, +4.75/-5 mm) were prepared from a sphalerite ore by two different methods of comminution (HPGR and cone crusher). The particles were then packed into leach reactors that were operated continuously for eleven months with well-mixed internal circulation of the leach solution. Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where although sphalerite grains are accessible to the solution, they remain unreacted. X-ray tomography and QEMSCAN® analysis of the selected samples before, during and after leaching, showed increased leaching of sphalerite grains associated with pyrite due to galvanic interactions. Mineral chemistry (Fe, Mn content of sphalerite) and jarosite precipitation were also investigated as factors influencing sphalerite leaching

Flotation of coal and sulphur from South African ultrafine colliery wastes

Flotation of coal and sulphur from a typical South African ultrafine colliery waste has been achieved in laboratory-scale batch flotation tests, using dodecane, kerosene, and oleic acid as coal collectors, and xanthates to float the sulphide minerals (with the aid of dextrin as a coal depressant). The use of oleic acid as collector, in conjunction with MIBC frother, produced a coal yield of 56 per cent (much more than was obtained with dodecane or kerosene) at an ash content of 18 per cent, from a feed ash of 34.4 per cent; and a low- sulphur tailings. Sulphide flotation using potassium xanthate (PAX) recovered 26.3 per cent of the total sulphur in the concentrate. Staged addition of xanthate increased the total sulphur recovery to 42.1 per cent and reduced the sulphur content of the tailing further

Modelling of froth transportation in industrial flotation cells: Part I. Development of froth transportation models for attached particles

Modelling of froth transportation, as part of modelling of froth recovery, provides a scale-up procedure for flotation cell design. It can also assist in improving control of flotation operation. Mathematical models of froth velocity on the surface and froth residence time distribution in a cylindrical tank flotation cell are proposed, based on mass balance principle of the air entering the froth. The models take into account factors such as cell size, concentrate launder configuration, use of a froth crowder, cell operating conditions including froth height and air rate, and bubble bursting on the surface. (C) 2004 Elsevier Ltd. All rights reserved

The rate variable batch test (RVBT) - A research method of characterising ore floatability

As part of the AMIRA P9 project, a methodology has been developed by which a comprehensive flotation model can be built from survey data around an existing plant, combined with laboratory batch flotation tests carried out on samples of a number of the circuit streams. The output of the model, in terms of ore floatability, is a discrete number of floatability classes for each mineral of interest, each with its own first order rate constant, and each comprising a certain mass fraction of the feed. Currently, this methodology must be applied to an operating plant during ore treatment. The ambit of the modelling methodology would be greatly extended if the floatability of an ore could be characterised before it is processed in a flotation plant. Developing a laboratory procedure to predict the fl oatability parameters will allow for better planning and forecasting of the fl otation performance of a given ore. The Rate Variable Batch Test (RVBT) method is such a procedure, and is the subject of this paper. The RVBT method involves floating a number of identical samples of an ore in a laboratory batch cell at different input air fl ow rates. It was developed and tested at three porphyry copper ore mine sites in conjunction with surveys of the operating plants to enable the floatability parameters obtained from the RVBT procedure to be compared with those derived from the current best practice method. The results indicated that the models developed from the RVBT data were able to represent the experimental data well and the derived kinetic parameters were statistically reliable; even though these parameters were not identical to those derived from the operating plant models. Nevertheless, a sensitivity analysis showed that the model predictions (mass, recovery, grade) were not overly sensitive to changes in the derived input parameters, i.e., for the same ore, the RVBT parameters predicted final grades and recoveries comparable to those predicted from a model developed using the current method

A Technique to Study the Adsorption of Oily Collectors onto Coal and Gangue Minerals

A technique has been developed to study the adsorption of paraffinic i.e. alkane (or other hydrocarbon oil) collectors onto coal and gangue mineral surfaces under dynamic conditions. The oily collector is present as the dispersed phase of a dilute oil-in-water dispersion. Solid particles are added to this dispersion and agitated to give a system analagous to that found in flotation cells prior to aeration, i.e. during conditioning. The technique enables study of the overall or apparent kinetics involved in the collision and effective adsorption of collector droplets onto coal or mineral particles. Results obtained show that adsorption is very rapid and tenacious, even under turbulent conditions. The hydrocarbon collectors are selective. Adsorption onto gangue (undesirable minerals) is limited and decreasing adsorption is evident as coal fractions become increasingly dense, i.e. as their gangue (ash) content increases. Commercial kerosene (Shellsol K) behaved in a similar way to the pure alkane collector with similar boiling point (dodecane)

The significance of internal recycle in froth flotation

Significant research effort in froth flotation modelling has been directed towards decoupling the pulp and froth zone contributions to overall recovery. This paper examines the material flows in and around a flotation cell when floatability was changed by varying collector addition rate. Highly controlled experiments were conducted in a continuously operated pilot scale flotation rig in which all stream flows could be measured with high precision. A Bubble Load analyser was used to measure the internal fl ows of material between the pulp and froth zones. The work was carried out in the lead circuit of a silver-lead-zinc mine, on a reagent-free stream to which collector could be added. Totally contrary to expectation, the fl ow of galena entering the froth phase attached to bubbles was found to decrease with increasing collector addition rate. This was a result of the froth becoming more stable with increasing collector addition rate. Higher froth stability meant that more galena exited in the concentrate, and less dropped back into the pulp to be re-attached to bubbles, resulting in a low Bubble Load. At low collector addition rates, the froth was less stable, and there was a large amount of galena recirculating between the pulp and froth, resulting in very high Bubble Loads. This has provided a valuable insight into the significance of the internal recirculating fl ow of hydrophobic material between the pulp and froth zones. In this system, the fl ow returning via dropback from the froth essentially dictates the observed Bubble Load in the pulp. This has important implications for flotation modelling, in that the pulp and froth zones – far from being decoupled – are highly interdependent via the fl ow of attached/detached material between them. Thus mechanistic models of the pulp and froth zones must be developed together in order to provide meaningful results. The current definition of floatability, as the response of mineral particles to pulp phase phenomena only, is insufficient to capture this interdependence

Studies on impeller type, impeller speed and air flow rate in an industrial scale flotation cell - Part 1: Effect on bubble size distribution

Bubble size distributions were measured at different locations in a 2.8 m portable industrial scale sub-aeration flotation cell, treating zinc cleaner feed in the Hellyer Concentrator in Tasmania, Australia. The cell was fitted in turn with four different impeller-stator systems, and operated over a range of air flow rates and impeller speeds. The mean bubble size was found to increase with increase in air flow rate at different locations in the cell, for all four impellers, and to decrease with increase in impeller speed. The mean bubble size was largest close to the impeller shaft and smallest at the impeller discharge point, for all the impellers. The shape of the bubble size distribution also changed with location in the cell. The "global mean" bubble size calculated by simple arithmetic average of the values at six locations in the cell coincided remarkably well with the mean bubble size measured halfway between the impeller shaft and the side of the cell, at the top of the pulp. In general, the impellers produced "global mean" values of 1.0 mm or less at the manufacturer's recommended impeller speed

An evaluation of different models of water recovery in flotation

Water recovery is one of the key parameters in flotation modelling for the purposes of plant design and process control, as it determines the circulating flow and residence time in the individual process units in the plant and has a significant effect on entrainment and froth recovery. This paper reviews some of the water recovery models available in the literature, including both empirical and fundamental models. The selected models are tested using the data obtained from the experimental work conducted in an Outokumpu 3 m(3) tank cell at the Xstrata Mt Isa copper concentrator. It is found that all the models fit the experimental data reasonably well for a given flotation system. However, the empirical models are either unable to distinguish the effect of different cell operating conditions or required to determine the empirical model parameters to be derived in an existing flotation system. The model developed by [Neethling, SJ., Lee, H.T., Cilliers, J.J., 2003, Simple relationships for predicting the recovery of liquid from flowing foams and froths. Minerals Engineering 16, 1123-1130] is based on fundamental understanding of the froth structure and transfer of the water in the froth. It describes the water recovery as a function of the cell operating conditions and the froth properties which can all be determined on-line. Hence, the fundamental model can be used for process control purposes in practice. By incorporating additional models to relate the air recovery and surface bubble size directly to the cell operating conditions, the fundamental model can also be used for prediction purposes. (C) 2005 Elsevier Ltd. All rights reserved