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.     

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.     

Depression of galena by slime gangue in an agitated pulp

The effect of gangue on mineral behaviour in a miniature batch version of an industrial flotation machine was examined. The flotation systems consisted of a sulphide, galena, with a specific collector, potassium ethyl xanthate, and a particular non-sulphide gangue in each case. Three gangue minerals were selected: corundum, fluorite and quartz. Flotation experiments were augmented with spectrophotometric adsorption and zeta potential measurements. Based on this data, the validity and significance of the slime-coating hypothesis in the context of the environment characteristic of industrial flotation processes were assessed.     

On the cathodic reaction coupled with the oxidation of xanthates at the pyrite/aqueous solution interface

The adsorption of ethyl, propyl and butyl xanthates on pyrite has been studied through electrokinetics, batch adsorption tests, and quantification of Fe²⁺ ions in solution. Adsorption isotherms for the three alkyl xanthates indicate that their adsorption to dixanthogen produces Fe²⁺ ions in solution and decreases the pyrite zeta potential negatively. It seems that the oxidation reaction of xanthates to dixanthogen on pyrite is coupled with the reduction reaction of surface-ferric hydroxide to ferrous ions, leading to the dissolution of hydrophilic ferric hydroxide and growth of hydrophobic dixanthogen on the surface of pyrite. Flotation of pyrite is presented as a function of pH using various ethyl xanthate concentrations. The floatability results are explained in terms of the surface coverage relationship between ferric hydroxide and dixanthogen, which is pH dependent.     

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.     

Interactions between sulphide minerals and xanthates,I. The formation of monothiocarbonate at galena and pyrite surfaces

The rate of decomposition of potassium ethyl monothiocarbonate has been determined at pH values between 5 and 10, and its molar absorptivity at 221 nm determined to be 1.24 · 10⁴mol/cm.A novel apparatus for use in the study of reactions between sulphide minerals, oxygen and thiol reagents has been developed, and applied to the reactions of potassium ethyl xanthate with galena and pyrite. It has been shown that both minerals react with ethyl xanthate in the presence of oxygen or oxidation products to form soluble as well as adsorbed xanthate derivatives. The soluble derivative has been identified to be ethyl monothiocarbonate. The adsorbed xanthate at a galena surface, unlike that at a pyrite surface, is gradually converted to a soluble monothiocarbonate under the action of dissolved oxygen. The effect of variables such as pH, the initial xanthate and oxygen concentrations, and the initial state of oxidation of the mineral on the formation of monothiocarbonate has been studied. It is tentatively proposed that an intermediate adsorbed mixed xanthate-hydroxide species is involved in the formation of monothiocarbonate at both galena and pyrite surfaces.The significance of the formation of monothiocarbonate to flotation practice is discussed briefly. The formation of monothiocarbonate represents a wastage of reagent, and could lead to a decrease in flotability of xanthated galena with time of exposure to aerated solutions.     

Adsorption of xanthate and starch on synthetic graphite

In the processing of sulphide ores containing graphite, starch is occasionally employed for depressing graphite while xanthate is used as a sulphide collector. In such a system the adsorption of starch by graphite is also influenced by xanthate. In the present investigation the adsorption of xanthate and starch at various values of pH and adsorbate concentrations have been carried out. The results show that xanthate is hardly adsorbed in the xanthate-N₂ system, but in the presence of oxygen it is catalytically oxidised to dixanthogen which adsorbs on graphite. Xanthate and starch are partly adsorbed at the same or adjoining sites of graphite with starch being adsorbed faster than xanthate. The ability of starch to depress graphite is reduced in the xanthate-starch system.     

Polymer-stabilized emulsions and fine-particle recovery,II. The chalcopyrite-quartz system

The interaction between fine, generally ?2 μm chalcopyrite and polymer-stabilized oil droplets has been studied as a function of pH and weight percent solids in the pH range from 5 to 12. Oil droplets stabilized by partially esterified polymethacrylic acid and cellulose xanthate have been used as collectors. Chalcopyrite may be efficiently separated from fine quartz gangue at pH 11, using cellulose xanthate stabilized emulsions. Good recovery and grade may be obtained at pH 11 up to pulp densities of at least 5.1 wt.%. At other pH values, selectivity is poor due to Cu¹¹ species from chalcopyrite activating the quartz surface.     

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.     

Decomposition of alkyl dixanthogens in aqueous solutions

Alkyl dixanthogens, (ROCSS)₂, decompose in aqueous solution in the presence of nucleophiles in many ways.It is proposed here that in alkaline solution the principal methods of decomposition of ethyl dixanthogen are by simultaneous attack of OH^? ions on the sulphur-sulphur bond to give products which include xanthate ion (ROCSS^?) and peroxide (H₂O₂) and on the carbon-sulphur bond to give products which include monothiocarbonate ion (ROSCO^?), sulphide ion (S^2?), and sulphur (S⁰). Above pH 12 reaction is complete in a few minutes, and more monothiocarbonate than xanthate is formed. At pH 9 the reaction takes over 20 h and more xanthate than monothiocarbonate is formed.The primary products react further to give various ions which depend in part on the pH of the system. In alkaline solution some of the xanthate and peroxide react to give perxanthate (ROCSSO^?). In acid solution both xanthate and monothiocarbonate decompose rapidly; CS₂ is formed from xanthate and OCS from monothiocarbonate.In the presence of other nucleophiles at pH 9.2, dissolved dixanthogen decomposes much more quickly than with OH^? alone, and other reactions occur. With thiosulphate a higher proportion of xanthate is formed together with some xanthyl thiosulphate and monothiocarbonate but no perxanthate. With sulphite (in the absence of oxygen) or cyanide the products include xanthate and monothiocarbonate but no perxanthate. With sulphite in the presence of oxygen, perxanthate is also formed.Suspensions of dixanthogens react slowly but in a similar fashion to dissolved dixanthogens.Longer-chain dixanthogens are much less soluble than ethyl dixanthogen but, in general, react in a similar way. Higher temperatures increase the rate of decomposition by OH^?.This work has various implications in operating plants.     

Flotation of galena. Influence of grain size,of pulp deoxygenation,and of cleaning with ammonium acetate

The flotation of < 10, 10–20, and 20–40 μm galena fractions was studied. For uncleaned galena a given collector coverage produced better floatability with increasing grain size. Nitrogen had a detrimental effect only for the < 10 μm fraction, producing at a given collector coverage a recovery smaller than that obtained with air.Galena cleaned with 400 g/l ammonium acetate had very poor floatability, although xanthate abstraction was fairly high; this confirms that strong xanthate adsorption is necessary for flotation. Formation of monothiocarbonate was small in all cases, which points to a very minor influence, if any, of this compound in the flotation process.In blank flotation tests, or for very low residual xanthate concentrations, a peak at 208 nm and a shoulder at 255 nm were observed. The former was assigned to the uncomplexed Pb²⁺ ion, and the latter was tentatively attributed to the PbOH⁺ ion.Lead in solution results from dissolution of the oxidation products of galena, as galena itself has an exceedingly low solubility. The curve for total lead in solution vs. initial xanthate concentration, had a minimum for an initial xanthate concentration of 10^?5M, the further increase in dissolved lead is attributed to formation of complexes such as PbX⁺ (X = xanthate). Dissolved lead concentrations were nearly as high for cleaned as for uncleaned galena, which indicates a high oxidation rate of the mineral.     

Flotation of germanium n and p with potassium ethyl xanthate

Steady-state potential of the germanium electrode, flotation tests and results of spectrophotometric ATR (Attenuated Total Reflection) measurements of germanium surface in the presence and absence of potassium ethyl xanthate are presented.On the basis of the steady-state potentials of the germanium electrode in ethyl xanthate solutions, the standard potential E⁰ of the reaction: Ge + 2EtX^? = Ge (EtX)₂ + 2e is estimated. The pH ranges of the dixanthogen (EtX)₂ and the germanium xanthate Ge(EtX)₂ species predominance in the bulk solution are calculated. It has been established that flotation of germanium is greater than the natural floatability (in the absence of collectors) in the pH ranges where (EtX)₂ or Ge (EtX)₂ are present in the bulk solution. Spectrophotometric results reveal the presence of (EtX)₂ and Ge (EtX)₂ on the surface in the same pH ranges as is calculated for the bulk reactions.No significant differences in the surface properties and the flotation behaviour between germanium n and p have been found.     

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.     

Influence of frothers on floatability. II. Flotation of chalcocite and quartz mixtures

Influence of frothers (α-terpineol or n-amyl alcohol) on the floatability of chalcocite and quartz mixtures, with potassium ethyl xanthate as a collector at pH 5.5–6, was investigated with a Hallimond tube.Activation of quartz by the presence of chalcocite was observed and interpreted as due to copper ionic species originating from chalcocite oxidation products. Best selectivity of separation between chalcocite and quartz was obtained when the frother concentration was kept sufficiently low. Collector—frother interactions during formation of three-phase mineral grain/solution/gas bubble contacts were observed.     

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.     

Influence of frothers on floatability. I. Flotation of single minerals (quartz and synthetic chalcocite)

The flotation and sorption properties of chalcocite and quartz in potassium ethyl xanthate (EtXK), frothers (α-terpineol and n-amyl alcohol), and (xanthate + frother) mixed solutions were investigated. Surface tension and frothing properties of the solutions were also measured.Floatability and sorption properties of the minerals investigated strongly depended on any controlled or uncontrolled change occurring at the mineral surface. Surface oxidation of chalcocite was shown to be an especially important parameter.The frothers studied showed some collecting properties in respect to chalcocite and quartz and influenced the xanthate sorption on chalcocite.Comparison of the flotation recoveries in frother solutions respectively with and without xanthate indicated an occurrence of noticeable collector-frother interactions during formation of the bubble/chalcocite grain aggregate. No such interactions were found for quartz.Influence of the frothers on floatability of the minerals was observed at different frother concentrations but at close values of surface pressure (π) and of retention time (rt).     

Depression mechanisms of sodium bisulphite in the xanthate-induced flotation of copper activated sphalerite

The effect of sodium bisulphite on the xanthate-induced flotation of copper-activated sphalerite has been studied using batch flotation testing, surface analysis techniques (XPS and ToF-SIMS), and FTIR. The various techniques have been used to identify the mechanisms of interaction of sulphite ions with both collector and the sphalerite surface. The results indicate that sodium bisulphite depressed the flotation of sphalerite particles pre-treated with copper and xanthate at pH 9 with nitrogen and air purging. It was found that sodium bisulphite interacts with the sphalerite surface, as well as with xanthate in its adsorbed state. Based on the evidence obtained in the present study, and in conjunction with previous work, the mechanisms involved in the depression of the xanthate-induced flotation of copper-activated sphalerite by sulphite are proposed. It is suggested that copper xanthate decomposition on the surface of the activated sphalerite and the decomposition of the hydrophobic copper-sulphide-like species on the sphalerite surface are the active mechanisms for sphalerite depression by sodium bisulphite.     

Effect of surface oxidation and iron contents on xanthate ions adsorption of synthetic sphalerites

Abstraction of xanthate ions from solution by copper-activated synthetic sphalerites with various iron contents was measured. It was found that raising the iron content in the samples caused a decrease in xanthate ions abstraction. For sphalerite samples characterized by the same percentage of iron deoxidized surfaces took up more xanthate ions than oxidized surfaces.Surface coverage by EtX^? ions was determined to be less than one monolayer. These values were compared with copper ion coverage at sphalerite surface. The amount of EtX^? ions abstracted from solution was noted to be independent of the pH of the solution in the range from 6 to 10 pH units, above $\text{pH}\text{=10}$ a decrease in the abstraction was observed.     

A method for determination of fine-particle flotability

The modification of a Hallimond tube enabling flotation of very fine particles at low recovery by mechanical entrainment is described. Flotation yields of closely sized fractions of quartz and chalcocite are presented.     

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.