K.S.E. Forssberg

Mixed collector systems in flotation

The interactions between differently structured surfactant molecules at the solid/liquid and air/liquiid interfaces and their effectiveness for efficient flotation were recognised during the 1950s ...

Surface chemical characterisation of Paenibacillus polymyxa before and after adaptation to sulfide minerals

A heterotroph Paenibacillus polymyxa bacteria is adapted to pyrite, chalcopyrite, galena and sphalerite minerals by repeated subculturing the bacteria in the presence of the mineral until their growth characteristics became similar to the growth in the absence of mineral. The unadapted and adapted bacterial surface have been chemically characterised by zeta-potential, contact angle, adherence to hydrocarbons and FT-IR spectroscopic studies. The surface free energies of bacteria have been calculated by following the equation of state and surface tension component approaches. The aim of the present paper is to understand the changes in surface chemical properties of bacteria during adaptation to sulfide minerals and the projected consequences in bioflotation and bioflocculation processes. The mineral-adapted cells became more hydrophilic as compared to unadapted cells. There are no significant changes in the surface charge of bacteria before and after adaptation, and all the bacteria exhibit an iso-electric point below pH 2.5. The contact angles are observed to be more reliable for hydrophobicity assessment than the adherence to hydrocarbons. The Lifschitz–van der Waals/acid–base approach to calculate surface free energy is found to be relevant for mineral–bacteria interactions. The diffuse reflectance FT-IR absorbance bands for all the bacteria are the same illustrating similar surface chemical composition. However, the intensity of the bands for unadapted and adapted cells is significantly varied and this is due to different amounts of bacterial secretions underlying different growth conditions.

Mechanism of fatty acid adsorption in salt-type mineral flotation

Abstract Our recent studies on the interaction of oleate with salt-type mineral surfaces have been summarized based on adsorption, infrared and zeta-potential measurements. Monolayer coverage in the case of calcite and a bilayer formation in the cases of fluorite, apatite and scheelite, preceding the precipitation of calcium soap has been suggested for the adsorption mechanism of oleate on these minerals. The monolayer coverage is shown to correspond to a condensed state of oleate with a molecular coverage area of 33 A 2 (liquid-crystal state). Depending on the surface potential and its magnitude at basic pH values, oleate is either chemisorbed on the surface calcium or monocoordinated through counter sodium and calcium ions for the monolayer filling.

The solution electrochemistry of sulfide-xanthate- cyanide systems in sulfide mineral flotation

Extensive thermodynamic calculations have been performed for a number of flotation systems of metal sulfide minerals using cyanide as a depressant to investigate the physicochemical principles unde ...

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.

Bio-modulation of galena and sphalerite surfaces using Thiobacillus thiooxidans

The interaction of Thiobacillus thiooxidans (T. thiooxidans) with sphalerite and galena has been investigated through adsorption, electrokinetic, and flotation studies. The amount of T. thiooxidans cells adsorbed onto galena and sphalerite is found to be almost independent of pH. However, a greater amount of cells is adsorbed onto galena compared to sphalerite. The adsorption isotherms of T. thiooxidans onto both galena and sphalerite exhibit Langmuirian behaviour. Electrokinetic measurements reveal that the isoelectric points (iep) of galena and sphalerite are located around pH 2, while that of T. thiooxidans is around pH 3. The isoelectric points of the minerals are shifted to higher pH values after interaction, consequent to bacterial cell attachment, indicating specific adsorption. Additionally, the electrophoretic mobilities are found to become less negative as a function of time after bacterial interaction. Such a trend is also followed in the case of the cells after interaction with the minerals for different time intervals. On a comparative basis, the cells after interaction with sphalerite are less negative vis-a-vis those after interaction with galena. The flotation recovery of sphalerite, beyond 1 h of interaction with T. thiooxidans cells is not affected but galena is totally depressed in the presence of T. thiooxidans cells, in the pH range 5–11. The differential flotation tests on a synthetic mixture of galena and sphalerite reveal that sphalerite can be selectively floated from galena in the presence of T. thiooxidans.

Mineral solution-interface chemistry in minerals engineering

Abstract In the treatment of sulphide ores, the reactions occurring in several processes like wet grinding, flotation, collectorless flotation, leaching/bioleaching and in adsorption mechanisms, for example the interaction of thiol collectors with oxidation-reduction reactions, play a dominant role. To optimize the conditions for metallurgical yield (grinding, flotation, leaching) or to combat a problem (acid mine drainage) understanding of the mechanisms involved in the process is needed. In broad terms this is mineral/solution interface chemistry. These mechanisms are discussed in this paper with emphasis on galvanic interactions.

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.

Beneficiation characteristics of antimony minerals : a review. Part 1

Abstract Antimony has long been reckoned as a strategic metal. It is used today not only in metallic form, e.g. as an alloying element in lead, but also to an increasing extent in the form of Sb2O3 as a flame retardant filler in plastics. The mineral raw material that provides nearly all the worlds supply of antimony is stibnite, Sb2S3. The flotation properties of this mineral are fairly well established. Its crystal structure makes its floatability depend on which surfaces of the mineral are exposed by grinding. Factors of pulp chemistry, however — especially the pH of the pulp — seem to have a more decisive influence on the result of flotation. At about pH 4–5, stibnite floats spontaneously with acceptable recovery, and with collectors it floats very well. Activation with metal salt is needed at neutral pH, while floatability is seriously impaired at pH 10. The beneficiation properties of other antimony minerals have been very little studied. Antimony oxides, pure antimony and jamesonite, Pb4FeSb6S14, are also recovered as values in addition to stibnite. Antimony oxides respond very poorly to flotation with xanthate collectors. The flotation properties of jamesonite are more akin to galena than to stibnite, and this mineral floats best at around natural pH without activation. The high antimony content of some very complex sulphide ores is a problem in beneficiation, giving concentrates heavily contaminated with antimony minerals which, if they cannot be separated, increase the cost of smelting. These impurities can be grouped according to their beneficiation properties: Lead-antimony sulphides jamenosite, Pb4FeSb6S14 boulangerite, Pb5Sb4S11 Lead-antimony-copper sulphide bournonite, CuPbSbS3 Ferrous antimony sulphides gudmundite, FeSbS berthierite, FeSb2S4 The flotation properties of the lead-antimony minerals grow more like those of galena the higher they grade in lead. Bournonite, a fairly common mineral in complex sulphide ores, floats well in process environments where chalcopyrite normally floats; in many cases this makes it impossible to separate from chalcopyrite. Initial studied have indicated that the ferrous antimony minerals have properties resembling those of pyrite and pyrrhotite.

Multivariate statistical analysis of vibration signals from industrial scale ball grinding

Abstract Multivariate statistical modelling based on vibration signal analysis was performed at commercial scale grinding. The source digital signals consist of three channels of mechanical vibrations obtained at the axial, horizontal and vertical directions. The feed rate, power draw, pulp temperature were collected automatically by the control system while samples of the feed material and ground product of the ball mill were manually taken to determine the particle size distributions and pulp densities. Using projection to the latent structure (PLS) and/or principle component regression (PCR), empirical models between grinding parameters of interests and the vibration signals were built based on the training data set collected in two weeks, thus the new grinding parameters could be automatically predicted whenever the vibration signals were known. The modelling results show that both the PCR and PLS model can be used to predict grinding parameters online.