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.     

The flotation of chrysocolla by mercaptan

Laboratory experiments have demonstrated that chrysocolla and malachite can be floated with a mercaptan as collector. In contrast, even when used in large quantities, the higher xanthate homologs (hexyl, dodecyl) will float malachite but not chrysocolla. The flotation of chrysocolla with mercaptan is readily accomplished in a pristine system, but in the presence of finely ground gangue particles, additions of the mercaptan to the grinding mill gave superior recoveries to those achieved when the mercaptan is added to the flotation cell. A model for the attachment of the mercaptan to the chrysocolla surface is proposed which involves the reaction of molecular mercaptan with the copper sites. This results in the formation of copper mercaptide at the surface and the splitting off of a molecule of water. By extension, this model should describe the reaction of mercaptan with any base metal oxide or sulfide mineral where the metal mercaptide is relatively insoluble.     

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.     

Effect of collector, pH and ionic strength on the cationic flotation of kaolinite

The effect of amine collector type, pH, and ionic strength on the flotation behaviour of kaolinite was investigated in a series of laboratory batch flotation tests. In distilled water, ether diamine, a strong collector for silica, does not induce any flotation or only very weak flotation of kaolinite over a wide pH range from pH 3 to pH 10.5. Ether monoamine causes strong flotation of kaolinite in distilled water, especially in acidic solutions, but high dosages of the collector are required. Such observations are in contrast to the flotation behaviour of oxide minerals such as silica for which ether diamine shows stronger collecting power than ether monoamine. The pH dependence of kaolinite flotation is also opposite to that of oxides, with lower flotation recovery obtained at higher pH. In contrast to oxides, the flotation recovery of kaolinite increases with ionic strength. It was demonstrated that the enhanced flotation of kaolinite in NaCl solutions cannot be attributed to the frothing ability of NaCl or the intercalation of kaolinite by alkylamines. It is proposed that the screened zeta potential of kaolinite particles in a high ionic strength environment causes random aggregation of kaolinite particles exposing hydrophobic (001) silica plane in the presence of ether amines.     

Oxidation-Reduction effects in the flotation of chalcocite and cuprite

A laboratory study of the batch flotation of chalcocite from chalcocite-quartz mixtures and of cuprite from cuprite-quartz mixtures with potassium ethyl xanthate as collector has shown that the oxidation-reduction state of the flotation pulp can have a pronounced influence on mineral floatabilities. At pH 11 chalcocite floated over a relatively narrow Eh range of about 300 mV; pH had no influence on the potential of the lower flotation boundary in reducing conditions but had a significant effect on the potential of the upper boundary in oxidizing conditions. Below this upper limit, the floatability was reversible with respect to Eh. Provided the Eh was in correct region chalcocite could be floated in the absence of measurable concentrations of dissolved oxygen.Cuprite displayed a high level of floatability with ethyl xanthate for which, by contrast with chalcocite, no flotation limit in reducing conditions was found; over a small range of potentials close to zero, its behaviour was strongly pH dependent.An attempt to account for the floatabilities of chalcocite and cuprite in terms of the formation of cuprous ethyl xanthate on their surfaces did not lead to correlations with the observed behaviour in reducing conditions but provided a rough correlation with the upper flotation potential limit. It is believed that more detailed and properly controlled comparative flotation studies of the chalcocite-xanthate and cuprite-xanthate systems could help to resolve some of the uncertainties associated with the effects of Eh, pH and oxygen concentration in sulphide mineral flotation.     

The stabilizing effect of Na2S on the collector coating of chrysocolla

The heterogeneous reaction between natural and sulphidized chrysocolla and potassium amyl xanthate in solution is investigated.It is found that, together with the consumption of large amounts of xanthate, particles composed of the reaction products are spontaneously released from the surface of chrysocolla giving rise to a colloidal dispersion. In principle the mechamism is related to the peptizing effect of the excess xanthate ions that are found when Cu²⁺ and X^? ions are made to react in a homogeneous phase.In sulphidized chrysocolla this phenomenon is markedly reduced, showing that Na₂S has a stabilizing effect on the collector coating.Flotation experiments performed with aqueous amyl dixanthogen emulsions show that stable adhesion occurs only on properly sulphidized chrysocolla. It is believed that the mechanism controlling adhesion in this case is similar to that which determines the stability of the collector layer.     

5-alkylsalicylaldoximes as collectors in flotation of sphalerite,smithsonite and dolomite in a Hallimond tube

Flotation tests for sphalerite, smithsonite and dolomite were carried out in a Hallimond tube at various pH values and two concentrations of collector.Adsorption of 5-alkylsalicylaldoximes on the surface of minerals was examined and isotherms for 5-butylsalicylaldoxime plotted.It was shown that sorption intensity of 5-alkylsalicylaldoximes on the surface of minerals decreased in the order: smithsonite, sphalerite and dolomite.Relationship between length of aliphatic chain and collecting activity of 5-alkylsalicylaldoximes was investigated in microflotation tests in a Hallimond tube.5-Propylsalicylaldoxime proved to have the best selectivity in flotation for the range of parameters studied, taking the difference in flotation rates of smithsonite and dolomite as a criterion.It was found that modifications of pH value resulted in changes in both adsorption and flotation.     

Aspects of the mineralogy and hydrometallurgy of chrysocolla,with special reference to the Cuajone,Peru, ores

Chrysocolla in the Cuajone ores appears to be microcrystalline and to exhibit a fibrous structure.Sulphuric acid leaching of the chrysocolla is facilitated by a microcracked surface structure. A marked surface structural change is evidenced as hydrogen ions replace the copper. The end result is a noncontinuous surface layer of silica from which the copper has been essentially completely removed.The results of this study provide confirmatory evidence for the structure and hydrometallurgy of chrysocolla.     

Electrokinetic properties and flotation behaviour of apatite and calcite in the presence of sodium oleate and sodium metasilicate

Calcite is generally associated with apatite minerals in phosphate deposits. To explore the possibility of separating these minerals by a soap flotation technique, their electrokinetic properties and flotation behaviour were studied in the presence of sodium oleate.Microelectrophoresis data indicate oleate adsorption on these minerals, and from Hallimond-tube flotation tests it has been noted that in a controlled pH environment and for a certain sodium oleate concentration range, separation of these minerals is possible.The study of apatite/calcite-sodium metasilicate-sodium oleate systems indicates the preferential adsorption of silicate at the calcite surface. This suggests the potential use of sodium metasilicate as the modifying agent for the separation of apatite from calcite by depressing calcite when using sodium oleate as collector.     

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.     

Hallimond tube flotation of scheelite and calcite with amines

Hallimond tube flotation experiments have been carried out on the two calcium minerals scheelite and calcite using dodecylammonium chloride as collector. The main variables studied were the calcium ion concentration and the pH.In the case of scheelite, addition of calcium chloride markedly lowered the flotation recovery. Recovery was also lowered when the pH was reduced below about 10. Since it is known that the zeta potential of scheelite is almost independent of pH this confirms that co-adsorption of un-ionized amine is necessary for good flotation. Other un-ionized long-chain molecules can replace the amine; thus it was shown that excellent flotation can be obtained event at about pH 7 by adding dodecanol together with dodecylammonium chloride. With the completely ionic trimethyldodecylammonium chloride recoveries were poor and were independent of pH.In the case of calcite, calcium chloride had no immediate effect on flotation recovery, but at low collector concentrations marked depression occurred after many hours standing in the presence of calcium ions. The effect of pH on flotation of calcite was anomalous and there appear to be two pH regions in which recoveries are high.The results are discussed and attention is drawn to the need for more thorough studies of the calcium carbonate/water interface.     

Effects of pretreatment and aging on chromite flotation

Anionic and cationic flotation of a Stillwater Complex chromite was studied as a function of pH and various pretreatments of the mineral. Aging the ground mineral in air markedly decreased anionic (sodium dodecylsulfate) flotation below pH3 and enhanced it above pH 4–5. Such aging increased cationic (dodecylammonium chloride) flotation in the basic pH region. Mildly preheating the mineral enhanced anionic flotation. Increased conditioning time in collector solution decreased anionic flotation. Strongly acid pretreating the mineral caused it to behave like a simple charged oxide toward both anionic and cationic flotation. These phenomena appear to be related to the effect of aging on the amounts of Fe(II) and Fe(III), of Cr(III) and Cr(VI) and of Mg(II) on the mineral's surface.     

Interaction of thionocarbamate and thiourea collectors with sulphide minerals: a flotation and adsorption study

The ability of O-isopropyl-N-ethyl thionocarbamate (IPETC), O-isobutyl-N-ethoxycarbonyl thionocarbamate (IBECTC) and butyl ethoxycarbonyl thiourea (BECTU) collectors to increase the flotation of the sulphide minerals, chalcopyrite, galena and pyrite, has been studied. For each collector, the flotation characteristics of these minerals, flotation rate constant and flotation recovery maximum, have been calculated from the flotation data and compared as a function of pH and collector concentration. Overall, the flotation performance of these collectors is stronger for chalcopyrite than for galena and pyrite. Flotation increases with collector concentration and decreasing pH values. For chalcopyrite, the collector performances of BECTU are slightly better than those of IPETC but far superior to those of IBECTC, especially at high pH values or at low collector concentrations. The flotation performance of these collectors has been shown to be in good agreement with the amount of collector adsorbed at the mineral surface. The affinity of BECTU for the various minerals has been calculated using a multilayer adsorption model.     

Effect of surface oxide/hydroxide products on the collectorless flotation of copper-activated sphalerite

The change in collectorless flotation of sphalerite with pH and Cu(II) concentration was correlated with the type and proportion of species present on the sphalerite surface. The solution and surface species were determined using a combination of analytical techniques including zeta potential measurement and X-ray photoelectron spectroscopy. An optimum copper concentration for maximum sphalerite flotation was identified, beyond which flotation decreased. This decrease in flotation coincided with the precipitation of copper hydroxide in neutral to mildly alkaline pH conditions. The hydrophobic polysulfide and hydrophilic copper hydroxide species were the main surface species influencing sphalerite flotation.     

Flotation and depression control of arsenopyrite through pH and pulp redox potential using xanthate as the collector

The role of pH and pulp redox potential (E_H) to control the flotation and depression of arsenopyrite has been investigated through studies on microflotation of arsenopyrite crystals and batch flotation of an arsenopyritic ore using isopropyl xanthate as collector. The transition between flotation and depression of arsenopyrite is established by the reversible potential of the xanthate/dixanthogen couple. Adsorption of arsenate ions on ferric hydroxide has been studied through electrokinetics to delineate mechanisms involved in the depression of arsenopyrite using oxidants. Chemical binding between arsenate species and ferric hydroxide sites on arsenopyrite is suggested as the mechanism responsible for depression of arsenopyrite. E_H conditions are given for the flotation and depression of arsenopyite at various pH values for the arsenopyritic ore.     

The anomalous behavior of kaolinite flotation with dodecyl amine collector as explained from crystal structure considerations

The electrokinetics and flotation behavior of kaolinite have been investigated through flotation experiments, zeta potential measurements, and FTIR spectral analysis. These results have been explained based on crystal structure considerations and quantum mechanical calculations. It has been shown that the PZC of kaolinite is at pH 4.2. Kaolinite exhibits good floatability in weakly acidic solution with dodecyl amine (DDA) collector. The negative zeta potential of kaolinite increases with an increase in pH, and hence the adsorption of DDA on kaolinite increases. However, the flotation of kaolinite decreases with an increase in pH and an increase in DDA adsorption. This anomalous flotation behavior is rationalized based on crystal structure considerations and particle aggregation phenomena. It is considered that the silica (001) and the alumina (001¯) basal planes of kaolinite are negatively charged. From quantum chemistry calculations, the interaction between DDA and the (001) plane was found to be stronger than at the (001¯) alumina plane due to the difference in the structure at the (001) and (001¯) planes. The self-aggregation between (001¯) faces and the edge planes and the adsorption of DDA at the silica (001) plane make the kaolinite aggregates hydrophobic, and good floatability is achieved in acidic solution. In alkaline solution, the kaolinite particles are dispersed. In the presence of DDA, hydrophobic aggregation appears to occur in alkaline solution between the (001) planes due to adsorbed DDA, and thus the hydrophilic (001¯) faces are exposed and flotation is not achieved.     

The Role of Flotation Reagents in the Reverse Flotation of Carbonate-Containing Iron Ores

The Influence of pulp pH, dispersants and auxiliary collectors on reverse flotation of carbonate-containing iron ores were explored. Interactions between iron ores and quartz were theoretically analyzed by flotation solution chemistry and DLVO theory. The results indicated that the iron concentrate grade improved sharply when pH increased from 11.0 to 12.0, but changed unobviously when pH was larger than 12.0, which was related to solution chemistry of siderite and interactions among particles. Sodium tripolyphosphate was an effective dispersant and sodium dodecyl sulfate was an effective auxiliary collector of KS-III. Both recovery and grade enhanced by the action of sodium dodecyl sulfate or sodium tripolyphosphate when pH was 12.0.     

Effect of oxidation potential and zinc sulphate on the separation of chalcopyrite from pyrite

The effects of oxidation potential (Eh) and zinc sulphate on the separation of chalcopyrite from pyrite were investigated at pH 9.0. The flotation recovery of these minerals is Eh dependent with maximum separation obtained at 275 mV SHE. Zinc sulphate addition improved this mineral separation at an Eh value of 275 mV by selectively depressing pyrite flotation. A different result was obtained at lower Eh values where zinc sulphate addition improved chalcopyrite flotation but had no or little effect on pyrite flotation. These opposite effects of zinc sulphate on mineral flotation were reconciled by examining the surface species of these minerals. The selective depression of pyrite flotation by zinc sulphate was also confirmed in the flotation of two copper ores.     

Characterization and pore structure analysis of a copper ore containing chrysocolla

The physical and chemical characteristics of a chrysocolla-bearing copper ore have been investigated with special emphasis on elucidation of its pore structure through gas adsorption techniques. The effect of such variables as particle size and outgassing temperature on the pore structure and size distribution has been investigated in detail. The results obtained show that the chrysocolla is a microporous solid and that its microporous nature can be considerably altered by heat treatment around 550°C. A possible reason for the so-called “thermal activation of chrysocolla” has been postulated.     

An electrochemical investigation of pyrite flotation and depression

The oxidation of ethyl xanthate on pyrite electrodes, and the influence of the flotation depressants hydroxide, cyanide, and sulphide, have been investigated using cyclic voltammetry. A layer of a hydrated iron oxide has been identified on pyrite surfaces. Xanthate does not interact with this layer but is oxidized to dixanthogen at positive potentials. An increase in pH results in an increase in the background current due to oxidation of the mineral, and at pH=11 this reaction becomes faster than xanthate oxidation. Cyanide interacts with the electrode to form a surface species which inhibits xanthate oxidation. Sulphide gives rise to an anodic wave preceding the wave due to xanthate oxidation. The flotation and depression of pyrite are interpreted in terms of mixed-potential mechanisms.