S.R. Grano

Control of grinding conditions in the flotation of chalcopyrite and its separation from pyrite

Abstract A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on chalcopyrite flotation and chalcopyrite separation from pyrite. The mechanism of galvanic interaction between minerals and grinding media was investigated by ethylene diamine-tetra acetic acid disodium salt (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) measurements. Chalcopyrite flotation was strongly dependent on both iron oxidation species and metal deficiency on the chalcopyrite surface. Iron oxidation species from grinding media played a dominant role in depressing chalcopyrite flotation, while metal deficiency from chalcopyrite oxidation improved chalcopyrite flotation. Therefore, chromium grinding medium produced a higher chalcopyrite recovery than mild steel grinding medium while gas purging during grinding had little effect on chalcopyrite flotation. Chalcopyrite separation from pyrite was affected by the activation of pyrite flotation by copper species dissolved from chalcopyrite. Grinding media had a large effect on the reduction of copper(II) to copper(I) on the pyrite surface. The reducing grinding condition generated by mild steel medium favoured formation of copper(I) sulphide phase, which resulted in high pyrite activation. Thus, chromium medium produced better chalcopyrite selectivity against pyrite than the mild steel medium.

Control of grinding conditions in the flotation of galena and its separation from pyrite

Abstract A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on galena flotation and galena separation from pyrite. The various reactions occurring on the mineral surface were investigated by a range of techniques, including OH − addition to maintain the grinding pH, ethlenediamine tetra acetic acid disodium salt (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and Time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements. Galena flotation and galena separation from pyrite were strongly dependent on the metal oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, while lead oxidation species activated pyrite but had little effect on galena. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation to be controlled. Aeration during grinding interfered with oxygen reduction occurring on the mineral acting as the cathode, as a result of galvanic interaction, and influenced the flotation of that cathodic mineral. Oxygen purging during grinding depressed galena flotation in single mineral experiments but increased galena selectivity against pyrite.

Surface Analytical Studies of Oxidation and Collector Adsorption in Sulfide Mineral Flotation

The physical and chemical forms of sulfide mineral surfaces are reviewed. The initial surfaces and oxidation products have been studied by Scanning Auger Microscopy (SAM), X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Changes to surface speciation as a function of time, pH, Eh and collector adsorption, related to mineral flotation, have been followed with these techniques. Oxidation products are formed in different processes, namely: metal_de ficient sulfides, polysulfides and sulfur; oxidized fine sulfide particles; colloidal hydroxide particles and flocs; continuous surface layers (e.g. hydroxide, oxyhydroxide, oxide species) of varying depth; sulfate and carbonate species; isolated, patchwise and face-specific oxide, hydroxide and hydroxycarbonate development. The actions of collector molecules (e.g. xanthates, dithiophosphinates) have been identified in several modes, namely: adsorption to specific surface sites; colloidal precipitation from solution; detachment of small sulfide particles from larger particle surfaces; detachment of small oxide/hydroxide particles; removal of adsorbed and amorphous oxidized surface layers; inhibition of oxidation; disaggregation of larger particles; and patchwise or face-specific coverage. The different modes of oxidation and collector action are exemplified using case studies from the literature and recent research.

Recovery mechanisms for pentlandite and MgO-bearing gangue minerals in nickel ores from Western Australia

Abstract The flotation behaviour of a Western Australian nickel ore was characterised by size-by-size flotation rate tests to extract rate constant information. The aim was to identify the effect of surface interactions on the flotation of the nickel sulphide mineral, pentlandite, with magnesium-silicate bearing minerals (predominantly serpentines). Flotation tests were carried out using collector (amyl xanthate), both with and without the other standard reagents for this ore. In this study the latter were carboxy-methyl cellulose (CMC) and soda ash. The addition of soda ash and CMC was shown to improve pentlandite flotation rate and recovery. Soda ash addition was found to be essential for improving flotation performance, as without it nickel recovery was unacceptably low. It is proposed that carbonate ions, derived from soda ash addition, enhance dispersion in the pulp and that CMC may assist removal of adhering slime particles from pentlandite surfaces. Drawing on the literature in this area, a number of mechanisms are proposed to explain the observed flotation behaviour of gangue magnesium-silicate bearing minerals.

Influence of electrochemical environment on the flotation behaviour of Mt. Isa copper and lead-zinc ore

Abstract The flotation of a copper and a lead-zinc sulphide ore from Mt. Isa has been studied in the absence and presence of specific collectors and depressants over a range of grinding and flotation Eh conditions. The surface composition of the products of flotation has been determined by X-ray photoelectron spectroscopy. It is shown that a substantial proportion of the iron sulphide minerals is naturally floatable as a result of a surface coating of graphitic carbon formed during ore genesis. In addition, an overlayer of ferric hydroxides and carbonates reduces the exposure of the sulphide minerals at the surface to low levels. Both chalcopyrite and galena exhibit only moderate collectorless flotation properties. Flotation of both ores with collector show a strong dependency on Eh. The collector selectively removes the ferric hydroxides and carbonates from the surface of the chalcopyrite. Significant collector-induced flotation of the iron sulphide minerals occurred which was largely reduced by the addition of cyanide. Grinding in an oxidising environment reduced selectivity due to increased flotation of the iron sulphide minerals. The influence of the ferric hydroxide and carbonate layers on selective flotation is discussed. It is argued that the addition of complexing depressants during grinding in a reducing environment enhances selectivity by minimising mineral interactions. Implications for flotation practice are considered.

Surface modifications in the chalcopyrite-sulphite ion system. I. collectorless flotation, XPS and dissolution study

Abstract The effect of sulphite on the collectorless flotation of chalcopyrite has been studied, while the mechanism of interaction between sulphite and chalcopyrite surfaces has been investigated by X-ray photoelectron spectroscopic (XPS) and dissolution kinetic studies. The effect of sulphite on the collectorless flotation of chalcopyrite strongly depends on the state of the chalcopyrite surface prior to sulphite conditioning. In the case of a chalcopyrite surface which was only moderately oxidised, exhibiting significant collectorless flotation, sulphite strongly depressed its flotation. This was attributed to the decomposition of a sulphur-rich surface phase by adsorbed sulphite. However, in the case of chalcopyrite which had significant surface concentration of adsorbed iron oxyhydroxide, for which the collectorless flotation was low, sulphite increased chalcopyrite collectorless flotation. This was attributed to the removal of the interfering iron oxyhydroxide and concomitant exposure of the sulphur-rich sub-layer. A mechanism involving reduction of adsorbed ferric oxyhydroxide to more soluble ferrous species is proposed to explain this behaviour.

Investigating fine galena recovery problems in the lead circuit of mount isa mines lead/zinc concentrator. Part 1 : Grinding media effects

A plant survey was carried out on the lead secondary rougher and scavenger banks of the Lead/Zinc Concentrator of Mount Isa Mines Limited. Sizing analysis of the survey samples demonstrated that a major limiting factor to overall lead recovery in this section of the plant was the diminished recovery of the fine galena in the minus 5 microns particle size fraction. Batch flotation experiments were carried out on a plant sample of lead secondary rougher feed and a sample of rod mill feed ore. Mineral recovery-size data for these tests showed similar fine galena flotation behaviour to that observed in the plant. Increased collector addition did not improve either the maximum recovery or the flotation rate constant of the fine galena but did reduce the selectivity of galena against sphalerite. Changing of the grinding media used for the ore sample from a high carbon steel to a high chromium alloy steel resulted in a significant increase in the maximum recovery and flotation rate constant of the fine galena. EDTA (ethylene diaminetetraacetic) extractable iron measured for the high carbon steel media were similar in magnitude to those measured within the plant and were higher than those measured for the high chromium alloy steel media. The increased surface concentration of hydrophilic layers of oxidised iron species on the fine galena was a likely reason for their diminished flotation behaviour both in the laboratory and in the plant.

The effect of high intensity conditioning on the flotation of a nickel ore. Part 1: Size-by-size analysis

Abstract High Intensity Conditioning improved pentlandite flotation from a nickel ore. Specifically, High Intensity Conditioning increased the flotation rate of pentlandite contained in the 8 to 75 μm particle size range. There was also a significant increase in the maximum recovery of pentlandite over the same particle size range. By contrast, the rate and maximum recovery of pentlandite contained in particles less than 8 μm were not significantly increased by High Intensity Conditioning. Desliming was affected by hydrocycloning to remove particles less than 8 μm in size from the ground ore. Desliming caused similar changes in the size-by-size flotation behaviour of pentlandite as High Intensity Conditioning. Mechanisms of High Intensity Conditioning are discussed in terms of the particle size dependent flotation behaviour of pentlandite.

Surface modifications in the chalcopyrite-sulphite ion system, II. Dithiophosphate collector adsorption study

Abstract The effect of sulphite and ferric species on the collector-induced flotation of chalcopyrite has been studied, while the effect of these species on the rate of dicresyl dithiophosphate (DCDTP) adsorption has been monitored in situ using UV spectroscopy. Chalcopyrite, which had been previously conditioned with Fe(III) species, exhibited decreased affinity for DCDTP adsorption. Under these conditions, the flotation rate and recovery of chalcopyrite was reduced. The extent of flotation depression by iron oxyhydroxide depended on pH, conditioning gas, and the presence of adsorbed collector on chalcopyrite. Prior interaction of the chalcopyrite surface with sulphite significantly increased both the adsorption rate as well as the surface coverage of DCDTP on chalcopyrite. Sulphite removes adsorbed iron oxyhydroxide, present due to its specific introduction or oxidation of chalcopyrite, from the chalcopyrite surface and promotes the formation of an iron-deficient chalcopyrite. The rate of DCDTP adsorption onto chalcopyrite was increased due to both removal of iron oxyhydroxide previously existing on the chalcopyrite surface and the formation of an iron-deficient chalcopyrite. Under these conditions, the flotation rate and recovery of chalcopyrite was increased. Reasons why the surface modified chalcopyrite exhibited enhanced DCDTP adsorption are discussed.

The effect of high intensity conditioning on the flotation of a nickel ore, part 2: Mechanisms

Abstract It has been found that High Intensity Conditioning (HIC) significantly increases the flotation rate of pentlandite from a nickel ore. A systematic investigation of slime surface coatings and the effect of HIC on surface cleaning of the nickel ore was carried out using Scanning Electron Microscopy (SEM), Image Analysis, X-ray Diffraction (XRD), and a sieving technique. The sieving technique was established to semi-quantitatively determine the state of slime (