Studies on the flotation of sulphides. I. The effect of Cu(II) ions on the flotation of zinc sulphide

The effect of Cu(II) ions on the froth flotation of ZnS in the absence of any collector has been studied in a Fuerstenau microflotation cell. The flotation of pure synthetic ZnS, in both cubic and hexagonal modifications, can be greatly enhanced by the adsorption of traces of Cu(II) ions. In the case of cubic ZnS, the “activating” effect of Cu(II): (a) involves the stoichiometric replacement of one Zn(II) ion in the lattice by one Cu(II) ion from solution at a rate which is independent of pH (1–5); (b) is noticeable at coverages corresponding to as little as 0.1% of a monolayer, reaches a maximum at coverages of 2–100% of a monolayer, and decreases again at higher coverages; (c) is unaffected by the presence or absence of O₂, by variation of the pH of flotation (6–10), by heating in vacuum at 250°C for two hours or by storing in the dry state for over one year; and (d) does not appear to involve any significant change in surface area or in the state of aggregation of the particles.     

Studies on the flotation of sulphides. III. A manometric study of the uptake of O2 by aqueous suspensions of zinc sulphide particles

A modified Warburg manometer has been used to study the relatively slow uptake of O₂ by particles of pure synthetic ZnS in aqueous suspension at 26°C. When dry ZnS is placed in unbuffered water there is an immediate ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{< 5}\text{s}$) fall in pH (corresponding to the uptake of one HO^? for approximately every 12.5 surface atoms of zinc) and a fairly rapid ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{～ 5}\text{min}$) uptake of O₂ (corresponding to one O₂ for approximately every 20 surface atoms of zinc), followed by a slow steady-state uptake of O₂ (equivalent to one O₂ per approx. 5000 surface atoms of zinc per min). The subsequent addition of Cu(II) ions causes an immediate increase in the rate of O₂-uptake which gradually reverts to the steady-state rate; this provides evidence for a distinct intermediate stage in the formation of Cu(II)-activated ZnS.     

The effect of hydrodynamic conditions on true flotation and entrainment in flotation of a complex sulphide ore

The separation efficiency and selectivity of flotation are directly proportional to recoveries of the mineral species in the feed due to true flotation and entrainment. In this study, effects of the hydrodynamic conditions on true flotation and entrainment were investigated by using a fractional factorial experimental design. A method previously described in the literature was applied to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore. In order to apply the method, the kinetic flotation tests were conducted under various hydrodynamic conditions defined by some physical variables. Some of these tests were conducted in the presence and absence of a collector to evaluate the self-induced floatability. The selectivity index of the mineral species for entrainment was seen to be suitable evaluation of the non-selectivity and efficiency of the entrainment. Furthermore, the results of the size-by-size analysis of the froth products indicated that the presence of the self-induced hydrophobic particles in the feed is as important as the presence of very fine particles for accurate estimation of true flotation and entrainment in flotation of a complex sulphide ore. In addition, the estimated results for entrainment in flotation of the complex sulphide ore can be misleading. Therefore, a new approach would be necessary to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore.     

Electrochemical studies of sulphides,II. Measurement of the galvanic currents in galena and the general mechanism of oxygen reduction and xanthate adsorption on sulphides in relation to flotation

Galvanic currents were measured by short circuiting two half cells; PbS  N₂ (g)  KNO₃ | KNO₃  O₂ (g) or H₂O₂  PbS, and then after adding xanthate to the l.h.s. cell. Such addition of xanthate resulted in a 10 fold (with O₂ in the r.h.s. cell) and 100 fold (with H₂O₂ in r.h.s. cell) increase in the short circuit and steady state currents and also lead to bubble attachment on galena in the l.h.s. cell, in nitrogen atmosphere. The results indicated a heterogeneous, two site electrochemical mechanism for the reduction of oxygen and oxidative adsorption of xanthate on galena.     

Electrochemical studies of sulphides,I. The electrocatalytic activity of galena,pyrite and cobalt sulphide for oxygen reduction in relation to xanthate adsorption and flotation

The electrocatalytic activity of galena, pyrite and Co₃S₄ for oxygen reduction has been studied by potentiostatic methods. Open circuit potentials of the sulphide electrodes have also been measured as a function of pH in nitrogen, air and oxygen atmospheres and also in the presence of H₂O₂ and ethyl xanthate. The adsorption of xanthate on sulphides was followed by observing bubble attachment to the electrodes.The catalytic activity for oxygen (or H₂O₂) reduction (the cathodic currents), the electrode potentials and the xanthate adsorption as shown by bubble attachment within certain pH limits, all varied as $\text{Co}{}_3\text{S}{}_4\text{> pyrite (≈ PbS in H}{}_2\text{O}{}_2\text{) ? PbS}$ indicating considerable dependence of the redox processes in flotation on the d - electron character of the sulphides.In the absence of oxygen, xanthate is probably bonded to the water structure of the surface through hydrogen-bonding, thus keeping the surface hydrophilic. Such adsorption reduces the electrode potential and inhibits oxygen reduction.     

Sulphidizing reactions in the flotation of oxidized copper minerals,II. Role of the adsorption and oxidation of sodium sulphide in the flotation of chrysocolla and malachite

The rate of consumption of sulphide in the sulphidizing reactions of malachite and chrysocolla has been measured. The oxidation of sulphide ions at the surface of sulphidized chrysocolla was shown to take place. The influence of thiosulphate anions on the xanthate flotation of sulphidized malachite and chrysocolla was investigated and it was shown to depress the flotation of chrysocolla strongly.The result suggest, that the presence of thiosulphate as a product of simultaneous oxidation can be one of the reasons for the more difficult flotation of sulphidized chrysocolla.     

Galvanic interaction between grinding media and arsenopyrite and its effect on flotation: Part II. Effect of grinding on flotation

Arsenopyrite floatability was correlated with the galvanic current, calculated from polarization curves measured during grinding, as well as the amount of oxidized iron, measured by EDTA extraction, in the mill discharge. The adverse influence of galvanic interaction during grinding on arsenopyrite floatability was quantified.     

The effect of thermal treatment on the flotation of chrysocolla

Flotation studies using a Hallimond tube have been carried out on purified samples of chrysocolla. The results confirm that by heating the sample to 550°C, flotation of the sulphidized sample with amyl xanthate is considerably improved. Flotation with sodium dodecyl sulphate is also considerably higher. The recovery with cationic collectors is not modified by the thermal treatment.Electrophoretic mobility measurements and flotation studies using benzene instead of air for the collection of the particles suggest that the increase in flotation after thermal treatment is a consequence of (1) an increase in the solubility of copper ions and their adsorption on to the surface of the particles, and (2) an increase of the intrinsic hydrophobicity of the particles due to condensation of some of the free silanol groups on their surface.     

Pressure Solution of Sulphides in Some Massive Sulphide Zinc—lead Deposits of Western Canada：Its Significance in Mobilization of Ore—forming Materials

Pressure solution is a common phenomenon in massive sulphide zinc-lead deposits of western Canada and may have been an important factor leading to the mobilization of ore-forming materials during diagenesis, deformation and metamorphism of sedimentary ores.The control of ductile shear zones over gold mineralization could be explained in view of pressure solution of gold-bearing miner-als under shearing stress and the tesultant mobilization of this metal.     

Supergene alteration of sulphides,I. A chemical model based on massive nickel sulphide deposits at Kambalda,Western Australia

An electrochemical model for the weathering of massive sulphide deposits that have undergone conditions similar to those affecting the Kambalda nickel deposits is presented. Galvanic corrosion due to aeration of the top of the ore body near the water table results in a deep anodic reaction whereby primary sulphides undergo an oxidative transition to sulphur-rich violarite—pyrite ore and also a shallow oxidative anodic reaction where the violarite—pyrite ore is oxidised to sulphate and gossanous oxides. Electrons are conducted through the ore from the anodes to the cathode where dissolved oxygen radicals are reduced and the corrosion cells are completed by ionic transport through the groundwaters to the anodic regions that can be some 200 m deep in the case of deep weathering processes. The kinetics of the weathering are described in terms of resistance to the flow of corrosion currents in the electrochemical cells. The effect on the model of physical perturbations such as rising and falling water table, faulting, etc. is discussed.     

Activation of zinc sulphide with CuII,CdII and PbII: II. Activation in neutral and weakly alkaline media

The results of a study of the activation of zinc sulphide by the heavy metal ions Cu^II, Cd^II and Pb^II are reported here. Metal-ion uptake follows a logarithmic dependence on time, depending on the particular metal ion and pH region. In some cases there is no well-defined rate equation. A mechanism for the activation process is proposed and related to activation in weakly acidic media.     

A laboratory study of the influence of sodium sulphide and oxygen on the collectorless flotation of chalcopyrite

The flotability of chalcopyrite in the absence of conventional collectors and its dependence on the oxidation-reduction state of the system has been determined in batch flotation tests on high-grade mineral both alone and mixed with quartz. It has been concluded that chalcopyrite is not floatable in reducing conditions either in the presence or absence of sodium sulphide but becomes floatable when oxygen is made available. No evidence was found to suggest that chalcopyrite ground in the near absence of oxygen is highly floatable.     

The use of a new modifier,Kr6D,in differential sulphide flotation

The suitability of a new reagent, Kr6D, as a depressant for galena and sphalerite in a differential sulphide flotation stage has been tested. Small-scale laboratory flotation tests on pure sulphide minerals indicated that the reagent is capable of depressing both galena and sphalerite when used in small doses. At higher concentrations, chalcopyrite is also depressed. Single-stage batch-scale flotation tests have been carried out on bulk sulphide concentrates containing the three sulphide minerals. Kr6D has been compared with starch as a depressant both in the presence and in the absence of sulphur dioxide. In each case the new modifier has been shown to be more effective. When using sodium dichromate as a differential depressant in similar tests, it has been shown that the quantity necessary to achieve selectivity between chalcopyrite and galena may be considerably reduced if small quantities of Kr6D are added.     

The flotation of gersdorffite in sulphide nickel systems — A single mineral study

The flotation response of gersdorffite has been determined in a series of batch flotation tests in which a sulphide sample containing about 76% gersdorffite was floated from mixtures with quartz.Using xanthate as collector, the arsenide floated strongly at pH 9, irrespective of whether lime, sodium hydroxide or sodium carbonate was used as pH modifier. When the pH was raised further to 10 or more using lime, the flotability decreased sharply.Changing the pulp potential at pH 9 also strongly affected the flotation response. Above about − 230 mV SHE, the mineral floated strongly, but below this potential it was essentially non-flotable. As far as it was tested (up to + 400 mV SHE), no upper limiting potential was found.Adding cyanide to the grinding mill brought about only a weak depressant effect on subsequent gersdorffite flotation at both pH 9 and 10. However, adding the same amount of cyanide to the flotation cell produced a strong depressant effect at the same pH values. At both pH 9 and pH 10, a threshold cyanide addition existed below which gersdorffite floated strongly, and above which it did not. For the conditions used in this study, this addition equates to about 100 g/t at pH 9 and about 80 g/t at pH 10. A hypothesis for the depression effect is presented which is consistent with both the available flotation data and a series of diagnostic analyses of grinding and flotation pulps completed during the test work.     

The effect of air flow rate on the kinetics of flotation. Part 3: Selectivity

The flotation rate from the slurry to the froth of a strongly hydrophobic galena and weakly conditioned chalcopyrite were determined in a batch experimental flotation cell, as a function of air flow rate (AFR). The selectivity of the transfer from the slurry to the froth was found to be highest at intermediate AFR, and lowest at very low or very high AFR. The flotation rate of a strongly conditioned magnetite-galena mixture was investigated in the same cell as a function of AFR and froth thickness (FT). The rate constant which characterizes the transfer rate from the froth over the cell lip was found to be identical for both minerals within experimental errors.     

The effect of dextrin on surface properties and the flotation of molybdenite

The effect of dextrin on molybdenite surface properties has been investigated experimentally through measurements of zeta potentials, adsorption densities, contact angles, Hallimond tube flotation and oil flotation response. These studies indicate that the adsorption of dextrin on molybdenite occurs through physical interaction with the surface, possibly due to hydrophobic bonding. The hydrophobic bonding mechanism is in accord with the magnitude of the adsorption free energy, which was estimated to be—5.4 kcal per mole of dextrin monomers. Dextrin was found to be a very effective depressant for the air flotation of molybdenite in the absence of a collector, whereas it does not effectively depress molybdenite in an oil flotation process using iso-octane. This has been discussed qualitatively from the contributions of electrical double layer repulsion, van der Waals' attraction, and hydration effects.     

Formation and recognition of alkyl xanthyl thiosulphates in sulphide ore flotation liquors

Alkyl xanthyl thiosulphates (R.OCSS.S₂O₃^?) (RXT^?) are formed in solution by mild oxidation (e.g. by I₂) of solutions containing both xanthate and thiosulphate. They can also be formed by reaction of Cu²⁺ with xanthate and thiosulphate, reaction of dixanthogen with thiosulphate, and by reaction of xanthate with tetrathionate; these last three reactions can occur in flotation pulps in slightly acid or alkaline solutions (pH 5–10).Alkyl xanthyl thiosulphates are stable in acid and neutral solution; the solutions have a UV absorption maximum at 289 nm. In strongly alkaline solution (pH 12) RXT^? decomposes within a few minutes to yield a xanthate (mostly) plus a little perxanthate. At pH 10 this decomposition to xanthate takes about 48 h. At pH 7–9 RXT^? is relatively stable. RXT^? is not extracted from aqueous solution with common solvents (chloroform, iso-octane, cyclohexane, or ether). It forms a water-insoluble adduct with cetyltrimethyl-ammonium bromide (CTAB); this adduct can be extracted into chloroform, and the extract has a UV absorption maximum at 296 nm.RXT^? was found in solutions from the gangue-sulphide flotation section at Renison Ltd, the zinc flotation circuit and the copper flotation circuit at Mount Isa Mines Ltd, and the lead flotation section of The Zinc Corporation Ltd. The presence of RXT^? in operating flotation plants has various practical and theoretical implications.     

Supergene alteration of sulphides,II. A chemical study of the Kambalda nickel deposits

An electrochemical study of nickel sulphide ore from three Kambalda shoots shows that the various parameters measured correlate both with depth and the degree of alteration of the ore. Eh and pH, respectively, vary from about ?0.3 V (SHE) and 8–9 for the deeper primary ore to about +0.3 V (SHE) and 5–6 for the shallower weathered ore. Leaching and simulation experiments as well as resistivity measurements all give results that support the hypothesis that galvanic corrosion resulting from differential aeration is the major mechanism in weathering of the ore. The release of iron from the ore to solution, and its subsequent hydrolysis, could exert a major influence on the pH, as indicated by the reaction: Fe²⁺ + 3H₂O → Fe(OH)₃ + 3H⁺ + e^?. The redox potential of the original mineral assemblage also plays an important role in pH control. Exploration and metallurgical consequences are discussed.     

The effect of bubble size on the rate of flotation of fine particles

Flotation experiments have been carried out in a cell in which bubbles of known size could be generated independently of the turbulence levels, which could be controlled by varying the impeller speed. The mean bubble size ranged from 75 μm to 655 μm.Results are reported for the flotation rates of fine particles, less than 50 μm diameter. The materials floated were polystyrene latex particles, quartz and zircon. These were chosen to give a wide range of specific gravity.It was found that the flotation rate was very strongly affected by the bubble size, there being an increase of up to one hundred-fold when the bubble size was reduced from 655 μm to 75 μm. Effects of particle density and impeller speed are also reported.