Bertil Pålsson

Statistical interpretation of flotation kinetics for a complex sulphide ore

Kinetic flotation models were applied to data from tests with reactive gases (hydrogen and sulphur dioxide) on a complex sulphide ore. The models were evaluated by statistical techniques, after non-linear regression on the model parameters. It is found that a first order model with rectangular distribution of floatability fits the test data very well. Statistical tests on copper, silver and lead kinetic data show that reactive gases have a greater influence on silver mineral flotation compared to copper-lead minerals. Sulphur dioxide generally gives higher ultimate silver recoveries than sodium bisulphite, and the magnitudes depend on the interactions between the modifiers and theflotation gases (5% H2 N2 and air). Correlation analysis suggests that silver flotation is probably determined by the floatability of a separate mineral such as tetrahedrite. Multivariate analysis on pulp chemistry data reveals that the pulp pH is the most significant variable among the pulp chemistry data, provided the grinding is iron free. The pH effect is attributed to the addition of sulphur dioxide. After autogenous or non-reducing grinding, the naturally-occurring variations in redox levels are too small to influence the flotation results, despite the tests being made with a complex sulphide ore.

Flotation of a complex sulphide ore II. Influence of grinding environments on Cu/Fe sulphide selectivity and pulp chemistry

Abstract A fine-grained complex sulphide ore with high pyrite and pyrrhotite content was used to test for the influence of grinding media and pre-treatment with oxygen-deficient gases on the flotation selectivity between copper and iron sulphides. The tests followed a statistical design with two major levels of grinding environments, four levels of pre-conditioning, and three levels of flotation gas type. Additionally, an air-sparged mild steel mill was used to test the influence of the oxygen content in grinding on Cu Fe sulphide separation. It is found that the grinding environment is the most dominant variable influencing the flotation results. Strong interactions exist between mild steel grinding, pre-conditioning, and the type of flotation gas. Test results shows that air-sparged mild steel grinding gives no advantage in Cu Fe sulphide selectivity compared with ordinary mild steel grinding. The best selectivity is achieved after mild steel grinding and a combination of low-oxygen pre-conditioning and air flotation. Pulp chemistry data treated with multivariate statistical analysis show that the mild steel grinding, through some form of galvanic interaction, causes enhanced oxidation of the mineral surfaces, releasing more sulphur species into the pulp liquid. For mild steel grinding, the amount of oxygen in the flotation step and in pre-conditioning is most important, and the aeration during grinding plays a lesser role. Theoretical calculations suggest that the hydrophobic entity responsible for chalcopyrite flotation is a surface precipitate similar to the stoichiometric copper-collector compound. The dimer cannot influence the flotation results since it is not stable in the potential range investigated.

Flotation of a complex sulphide ore I. : Cu/Zn selectivity control by adjusting pulp potential with different gases

Abstract To investigate the possibility of using gases with varying oxygen activity and their influence on copper-zinc selectivity, flotation tests were done in a mechanical laboratory cell on a fine-grained complex sulphide ore with high pyrite and pyrrhotite content. The pulp environment was modified by changing the grinding media and by using different gases in the pre-conditioning a flotation steps. A statistical design with two levels of grinding media, four levels of pre-conditioning, and three levels of flotation gas type, was used. It is found that the grinding environment is the most dominant variable influencing the flotation results. Strong interactions exist between the pre-conditioning type and the flotation gas for mild steel grinding. Such interactions, and even the direct influence of pre-conditioning and flotation gas type, are statistically insignificant for stainless steel grinding, which often gave good copper flotation. The Cu Zn selectivity shows a strong dependence on the pre-conditioning type and flotation gases for mild steel grinding, but not for stainless steel grinding. The best Cu Zn selectivity happens for the combination of 5% oxygen pre-conditioning and air flotation after mild steel grinding. It seems that galvanic reactions after or during the mild steel grinding facilitate surface oxidation of sulphides. A mechanism similar to ferric leaching is proposed. As expected, it was observed that the oxidising or reducing environment in the pulp, as measured by the pulp potential, has a strong influence on the flotation results.

Computer-assisted calculations of thermodynamic equilibria in the galena-ethyl xanthate system

Abstract Calculations show that thermodynamic data can be used to construct pulp chemistry models that satisfactorily describe events in mineral pulps. The introduction of kinetic restrictions, derived from pulp chemistry analysis of full-scale flotation processes, will additionally enhance the models. For the galena-ethyl xanthate system the following results are obtained: (1) the pulp carbonate content is the factor which has the greatest influence on the nature of the surface of the galena/lead mineral in flotation systems; (2) the theoretically calculated upper precipitation limit of Pb(EtX) 2 (s) is in good agreement with published data; and (3) Pb(OH)EtX(s) can be formed in carbonate-deficient environments, in a bigger area than Pb(EtX) 2 (s), where flotation has been observed while overdosing xanthate. Furthermore, introducing the hypothesis that the surface compound-Pb-EtX is the contact point for the stronger hydrophobizing reagents, the surface compound may be a sort of ternary surface complex.

Ore characterisation for––and simulation of––primary autogenous grinding

Abstract In this work, the purpose was to study the impact of variations in feed ore properties on the performance of a primary autogenous grinding circuit by ore characterisation and simulation. Samples were selected to represent various points in the production system; ore faces with different drillability, grinding circuit feed, mill charges and waste rock. The investigation was carried out at the LKAB Kiruna mine in northern Sweden. The result clearly shows that self-breakage occurs ahead of the mill since the ore hardness, or resistance to breakage, increase with the distance from the mining face. Ore from a location, which by the mine is characterised as “hard to drill”, has the lowest resistance to breakage, and the surrounding rock is clearly harder than the magnetite ore. Validation of a simulation model for the primary autogenous grinding circuit reveals that the differences between simulated and experimental data are small. Therefore, the model is used to simulate the influence of variations in feed ore characteristics on the circuit performance. The simulations show that the net throughput from the circuit at a coarse–hard feed will be ≈10% higher compared to a situation when the feed is fine–soft. Moreover, a fine and soft feed results in a coarser particle size distribution of the mill discharge, compared to a coarse and hard material. However, it is the amount of coarse material in the feed, which is the most influential factor.

Computer-assisted calculations of thermodynamic equilibria in sphalerite-xanthate systems

Abstract Sphalerite flotation is analyzed on the basis that it occurs in a pulp chemistry environment, where the dominant variables are the electron activity (pe), and the hydrogen ion activity (pH). The literature indicates that sphalerite can be floated with long-chained xanthates in neutral pulps, and that hydroxoxanthates of Zn and Fe(III) are possible intermediate steps in the flotation process. Theoretical computations indicate the following properties: (1) the pulp carbonate content is the factor having the strongest influence on the nature of the surface of sphalerite/zinc minerals in flotation systems; (2) ethyl xanthate and zinc will not form any solid compounds; (3) the theoretically calculated precipitation area of zinc isopropyl xanthate coincides with pH-areas known for enhanced zinc flotation; (4) Zn(OH)iPX(s) and Zn(OH)AX(s) can be formed under conditions similar to those encountered in flotation; (5) Zn-ethyl xanthate complexes will not contribute significantly to the mobilization of Zn into solution, but might likewise cause a high, environmentally disquieting, content of metal-organic compounds in concentrator effluents; (6) Fe(III)-hydroxoxanthates, but not Fe(II)xanthates, can be formed under the conditions studied. Computational results obtained so far indicate that the contents, i.e. the metallic content of the solution, are controlled by the formation of solid bulk compounds such as hydrozincite, while the formation of simpler surface compounds (surface complexes) is controlled by conditions on the mineral surface. One way to take this into account would be to include an extra fluid phase, which will model the mineral/solution boundary layer.

Robust estimation of particle velocity profiles in high concentration magnetite suspensions

In the mining industry magnetite particles are transported in aqueous suspension through different stages of the process. In some stages it is of interest to monitor both the concentration and part ...

Towards the measurement of local particle mass fractions in magnetite suspensions

In the mining industry, magnetite particles are transported in suspensions with water through different stages of the process. In some of these stages, it is of interest to monitor both the concentration and particle velocity over a cross-section of the flow. High particle concentration makes development of flow measurement techniques challenging. An additional challenge is that the flow is often accessible from one side only, which further limits the selection of applicable techniques. Previous work by the authors focused on using pulse-echo ultrasound for flow velocity profile estimation. In this paper the same setup is used to simultaneously study local variations in solids concentration. Ultrasound pulses are transmitted into the suspension, and the resulting backscatter is recorded. The statistics of the backscatter depend on solids concentration, particle size distribution, particle density, etc. We demonstrate how a short-time (windowed) Power Spectral Density (PSD) estimate can be used to obtain qualitative information about local solids concentration variations. For demonstration, a magnetite suspension carrying up to 7.5 vol% particles (29 wt%, mean particle size 34 μm) is pumped through a closed rectangular channel. When the pump is stopped, pulse-echo ultrasound (with a center frequency of 2.25 or 3.5 MHz) is used to monitor the sedimentation process. Nine snapshots of the process are included. These show a time lapse of the sedimentation, with 5 s between each image. It is clear that the short-time PSD is a good indicator of local mass fraction variations.

Redox control in a pilot flotation column

Abstract Results from pilot-column flotation tests on a lead-zinc ore show that it is possible to control the redox potential of the column pulp by varying the oxygen activity of the flotation gas fed to the spargers. As a result, the process changes so that the fine zinc minerals are more actively floating in an oxidising environment, at the same time xanthate and frother consumptions increase. The placement of electrodes in the column does change the redox potential readings but only as a result of a change in the oxygen concentration of the pulp. However, the values from a Glassy-Carbon (GC) electrode are consistently lower than those from a Pt foil electrode at the same location. Actual positions of operating points as measured by GCelectrodes fall within the theoretical area for precipitation of lead xanthate.

Computer-assisted calculations of chemical equilibria with relevance to the chromate depression of galena

Abstract The computation of theoretical chemical equilibria, to simulate the conditions in the copper-lead separation bank of a flotation plant, is performed. The calculations, and results reported in the literature, indicate that chromate to a large extent acts as a redox controlling reagent in the pulp. If the action of dichromate/chromate essentially is that of an oxidant, then there ought to be cheaper and environmentally safer alternatives.