外文翻译---金属离子和闪锌矿存在下的黄铁矿浮选.docx

附a 英语论文pyrite flotation in the presence of metal ions and sphalerite【canada】 q. zhang, z. xu, v. bozkurt, j.a. finch abstractthe effect of cu 2+, fe 2+ and ca 2+ ions on pyrite floatability with xanthate as a function of ph in the presence and absence of sphalerite was studied. in the alkaline ph region, these ionsactivated the pyrite when alone but not when sphalerite was present. zeta-potential measurementsand infrared surface characterization confirmed the different interaction with xanthate dependingwhether the pyrite was alone or with sphalerite. 1997 elsevier science b.v.keywords: pyrite; sphalerite; flotation; mineral interaction; metal ions: introductionsulphide mineral ores remain the major source of base metals. the flotation ofvaluable minerals of copper, lead and zinc from pyrite, the main sulphide gangue, hasreceived considerable attention (forssberg, 1985; dobby and rao, 1989). recently, there has been growing suspicion that metal ions play a role in limiting selectivity of sulphide flotation. these metal ions result from the use of recycle water, the presence of semi soluble minerals and from superficial oxidation of sulphide minerals and steel grinding media. their detrimental effect is associated with either depression of the target minerals or activation of the unwanted mineral (e.g. pyrite).1. experimental section1.1. mineralsthe sphalerite (sp) and pyrite (py) samples (37-74 txm size fraction) were isolated from ore samples from brunswick mining and smelting (new brunswick, canada) by alternate use of a shaking table and a mozley separator. the single minerals obtained were treated three times with a 5% hc1 solution to remove soluble impurities. residual sulphur, formed as a result of the acid treatment, was removed by washing the samples with acetone, followed by de-oxygenated-distilled water. the product was then dried in a vacuum oven at 70c and stored under nitrogen. for both sphalerite and pyrite, x-ray diffraction analysis showed that no significant amounts of other mineralogical phases were present. chemical analysis indicated a purity over 97% for pyrite while sphalerite contained 63.8% zn and 2.8% fe. the sample of this size range was used inthe flotation and ir studies. for zeta-potential measurements, it was further ground (in an agate mortar and pestle) to ca. 20 immediately prior to use.1.2. chemicalssodium iso-propyl xanthate iprx, (ch3)2chocs2na from american cyanamidwas further purified using standard procedures and stored in petroleum ether (rao,1971a,b), acs reagent grade copper sulphate, zinc sulphate, ferrous sulphate and calcium chloride (fisher scientific) were used as received. hydrochloric acid andsodium hydroxide used as ph modifiers were also of acs reagent grade.de-oxygenateddouble distilled water was used in all the experiments.1.3. microflotationthe set-up for conditioning the pyrite (fig. 1) permitted the mineral to be treatedalone (as mineral 1) or in the presence of sphalerite (as mineral 2), where the two minerals were in separate compartment but shared the same solution. one gram of mineral was conditioned for 10 min in 30 ml of de-oxygenated water at a given metal ion concentration, after which the supernatant was replaced with a premeasured amount of xanthate stock solution, and conditioning continued for another 10 min. conditioning was provided by a laboratory shaker (new brunswick scientific co., inc., usa) at 200 rpm. to ensure that the minerals in the separate compartments shared the same solution in the case of the mixed-mineral tests, the level of the solution in the beaker was maintained above the top of the glass partition, as indicated in fig. 1. the pyrite along with the supernatant was then transferred to a modified hallimond tube (fuerstenau et al., 1957), and flotation was conducted for 2 min with an air flow rate of 74 ml/min.the solids in floats and tails were weighed separately after filtration and drying, and there covery was calculated.1.4. zeta-potentialzeta-potential of pyrite was measured using a lazer zee tm meter (model 501: penkem, inc., usa). all measurements were conducted in a 0.1 m nac1 backgroundelectrolyte solution. a 0.05 g sample of pyrite, alone or mixed with sphalerite (whichwas of much greater size), was placed in a 100 ml beaker and mixed, for 5 min, with 80ml distilled water containing the metal ions of interest. (in some of the experiments, apre-determined amount of xanthate was added at this stage and mixing continued foranother 5 min.) the coarse sphalerite particles were then allowed to settle andsupernatant containing the fine target mineral particles was taken for zeta-potentialmeasurement. the results presented in this paper are the average of three independentmeasurements with a typical variation of +2 mv. repeat tests showed that theconditioning procedure was capable of producing reproducible mineral surfaces suitablefor studying the effect of various treatments.1.5. ftir-spectrumthe attenuated total reflectance (atr) spectroscopic technique was used to characterizethe surface species on the mineral particles treated. (sample preparation was thesame as used for the microflotation tests.) a sample of the mineral along with somesolution was taken using a pipette and placed on a strip of filter paper. this was repeatedtill the filter paper was covered by a thin layer of particles. the sample was then liftedalong with the filter paper and pressed onto a zinc selenide (znse) atr crystal. irspectra were obtained using an ifs-66 ftir spectrometer (bruker) with a baselinehorizontal atr sampling unit (spectra tech). the clean atr crystal was used asbackground for the spectra presented in this communication. the spectrum was obtainedby accumulating 200 scans using an mct detector at a wavenumber resolution of 4 cm-1 and presented without any baseline correction. as a check, a spectrum from the znse crystal in contact with 10 a m xanthate solution was acquired: no characteristic bands were observed in the spectral region presented in this communication. the crystal was cleaned with acetone, exposed to ultraviolet radiations for 10 min (to decompose any residual xanthate species), rinsed with 100% ethanol, and blow-dried with filtered dry nitrogen after each measurement.for the purpose of ir band identification, the spectrum was also collected usingexternal reflectance infrared spectroscopy (at a fixed incident angle of 45 ) using acopper foil pre-treated in a 0.5 m m i prx solution, rinsed with petroleum ether and dried with dry nitrogen. this treatment removes all dixanthogen components and leavescopper xanthate on the foil. the spectrum was collected using the same instrumentalparameters as in atr experiments, and polished copper foil was used as background.the experiments for the mixed-mineral system were designed to eliminate galvaniceffects which otherwise would complicate the analysis. this system is therefore differentfrom that encountered in practice, but nevertheless it is a step closer compared to thetraditional single mineral studies. our focus in this work is to examine the effect of metal ions and a second mineral on xanthate interaction with a target mineral (pyrite).the effect of galvanic interaction and redox potential was not examined, but for thepurpose of comparison, we kept the redox potential relatively constant by usingde-oxygenated water with a low solid-to-liquid ratio. in the case of mixed-mineralsystems, quantifying the adsorption of metal ions or xanthate on individual minerals isdifficult even if semi-quantitative xps analyses were used. for this reason, we usedzeta-potential measurement as an analytical tool to provide in situ semi-quantitativeinformation, which proved satisfactory.2. results2.1. flotationpyrite alone (i.e. in the absence of metal ions and sphalerite) exhibited the well known flotation response: a minimum around ph 7, with increasing floatability in acid conditions and a maximum in alkaline (ca. ph 8) (steininger, 1968;fuerstenau et al., 1985). the addition of cupric ions enhanced pyrite floatability significantly over the ph range 6 to 10. in contrast, in the presence of sphalerite along with metal ions, the floatability of pyrite decreased significantly over the whole phrange, with the recovery at ph 5 being lower than that for pyrite alone without copper activation. this reduced floatability suggests competition for xanthate when the two minerals share the same solution. it appears that when copper-activated sphalerite ispresent, it consumes most of the xanthate available, leaving a lower xanthate concentrationfor pyrite flotation than if the sphalerite were not present. this was indirectlyconfirmed by the observation that the flotation of pyrite in the presence of sphalerite butabsence of cupric ions remained unchanged, because in the absence of activating metal ions, sphalerite is largely unresponsive to xanthate. this suggests that the presence of sphalerite under these conditions should have little effect on pyrite flotation, as observed.the effect of ferrous ions on pyrite flotation. similar to cupric ions,ferrous ions increased floatability of pyrite alone, in particular in alkaline media with amaximum recovery at ca. ph 9. again, in the presence of sphalerite, pyrite flotation was depressed. an activation effect of calcium ions (10 -5 m) on single pyrite flotation was found although it was less than that of either cupric or ferrous ions (fig. 4). whensphalerite is present, however, pyrite is virtually unfloatable above ph 7.the above flotation results all show a common feature: metal ions promoted flotation of pyrite alone, but the presence of sphalerite along with the metal ions depressed the floatability. 2.2. zeta-potentialpyrite alone had an iso-electrical point (iep) at ca. ph 3. this value is lower than that reported by fuerstenau and mishra (1980), but similar to that by fornasiero et al. (1992). the discrepancy appears to be related to the initial oxidation state of pyrite: the more oxidized the pyrite, the higher the iep. by comparison with the iep of pyrite oxidized to various degrees as reported by fomasiero et al. (1992), the pyrite sample used in this study appears to be slightly oxidized.in the presence of iprx, the zeta-potential of pyrite decreased marginally (byinspection of the data points), probably reflecting adsorption of negatively chargedxanthate anions. a similar observation was made by fomasiero and ralston (1992) although cases et al. (1993) suggest a much larger decrease in zeta-potential in the presence of xanthate. cupric ions increased the zeta-potential significantly, in particular above ph 6. this increase can be attributed to the adsorption of a cupric ion species (probably cu(oh) from reference to the solution stability diagram (stumm and morgan, 1996) on the negatively charged pyrite surface. upon subsequent addition of xanthate at alkaline ph, the zeta-potential decreased significantly. the reduction can be attributed to either the adsorption of negatively charged iprx ions and/or to partial removal of adsorbed cupric ions from the pyrite surface. the increased flotation recovery of pyrite with iprx in the presence of cupric ions suggests that the former is more likely to be the case, i.e. the presence of cupric ions on the surface attracts the negatively charged iprx.the effect of the presence of sphalerite. the zeta-potential in the presence of cupric ions remained the same whether sphalerite was present or not. the subsequent addition of iprx did not change the zeta-potential, which is in marked contrast to the case in the absence of sphalerite. by comparison with fig. 5, copper ions appear to be still adsorbed on pyrite in the presence of sphalerite, but subsequent xanthate adsorption did not occur. this finding is consistent with the observed flotation behaviour, namely that a significant reduction in pyrite flotation occurred when sphalerite was present (fig. 2).the zeta-potential results in the presence of ferrous ions and calcium ions, respectively. similar to the case with cupric ions, these ions increased he zeta-potential of pyrite significantly. in the presence of sphalerite, however, the zeta-potential response resembled that of pyrite alone and the subsequent addition of iprx had little effect. this suggests that ferrous and calcium ions have much less affinity for pyrite compared to sphalerite and adsorbed preferentially on sphalerite when these two minerals are present in the same solutions. the competition mechanism tbr theobserved suppression of metal activation in the presence of sphalerite seems to depend on the metal ion: in the case of cupric ions, xanthate adsorption was suppressed while in the case of ferrous and calcium ions, adsorption of the metal ions was suppressed. the overall effect, however, is similar, namely, the presence of sphalerite retarded the flotation of pyrite.2.3. infrared spectrainfrared spectroscopy was used to identify and quantify the surface species resulting from interactions between the minerals and iprx. fig. 9 shows the spectra obtained withpyrite in the presence of cupric ions. (only part of the spectral region, from 1350 to 950 cm -1, is shown, over which the characteristic xanthate bands appear.) a featureless spectrum was obtained for the pyrite conditioned in de-oxygenated water (a). six broad bands at ca. 1267, 1256, 1142, 1088, 1026 and 1008 cm were observed when pyrite was conditioned in 5 10- 5 m prx solutions (b), suggesting the adsorption of i prx on pyrite. comparing these bands with those (1239, 1227, 1216, 1090 and 1016 cm -t) on copper foil (e), it is evident that the adsorbed species is dixanthogen, as expected in the case of pyrite (ball and rickard, 1976; woods, 1984). the dixanthogen bands corresponded to those of ethyl dixanthogen (leppinen et al., 1989; yoon et al., 1995), but with a slight shift as shown in table 1. these spectral shifts are associated with substitution of the ethyl group by iso-propyl which is a stronger electron donor. when cupric ions were present (c), the intensity of dixanthogen bands increased slightly and three additional bands at ca. 1237, 1227 and 1216 cm-l were observed. these indicate the formation of copper iprx as there was a close spectral match with the external reflectance spectrum of copper foil treated in i prx (e). these observations confirm the zeta-potential results showing the adsorption of copper ions and collector on pyrite. in the presence of sphalerite, the spectrum (d) becomes featureless, resembling that of the pyrite baseline spectrum (a). these spectroscopic observations further confirm that pyrite is not activated by copper ions when sphalerite is present. it implies that adsorption of xanthate is preferentially on activated sphalerite, which reduces the amount of xanthate available for the pyrite.table 1positions of corresponding principal bands (cm- 1 ) of copper xanthate and dixanthogen formed from ethyl and iso-propyl xanthateswavenumbecm-1fig.3.3. frlr/atr spectra of particles treated with cupric (c), ferrous (d) and calcium (e) ions in the presence of 5 10 -5 m iso-propyl xanthate as compared to that untreated (a) and treated with xanthate only(b)(b).the spectra of pyrite treated with the ferrous and calcium ions are shown in fig. 3.3(for reference, the spectrum of pyrite treated with cupric ions is also included.) spectra(d) and (e) showed similar features as in the absence of these metal ions, but with someincrease in band intensity. in contrast to copper ions, no additional bands were observed,3. discussion3.1. general observations3.1.1. pyrite alonethe results show that the metal ions, cu 2+, fe 2+ and ca 2+, activate pyrite. theactivation is through either the formation of metal xanthate (copper), and/or a catalyticeffect of metal ions on dixanthogen formation (all ions studied). in the case of cupric ions, the formation of metal xanthate seems responsible for the increasedfloatability although the slight increase in dixanthogen formation may be a contributing factor. whether the copper ions were incorporated into pyrite lattice to induce the copper xanthate formation remains to be determined. the zeta-potential measurement suggests that copper ions were chemisorbed on pyrite.the dixanthogen bands were enhanced when metal ions were present. the observed enhancement appears to be related to the variable valencies of copper and iron ions. ferric or cupric ions may initially be reduced to a lower oxidation state while adsorbed xanthate is oxidized to dixanthogen. in the case of ferrous and calcium ions, it appears that adsorbed cations (as confirmed by zeta-potential measurements) provided a high density of surface active sites which electrostatically attract negatively charged xanthate. as a result, the xanthate concentration in the surface region may be increased sufficiently to promote the redox reaction in the boundary layer. it is also possible that the adsorbed metal ions reduce the electrochemical potential of xanthate oxidation, although this remains to be explored.3.1.2. mixed-minerals competitive adsorptionthe presence of sphalerite did not materially affect pyrite flotation when metal ions were absent. however, with metal ions present, sphalerite decreased pyrite flotation significantly, the floatability being even lower than for pyrite alone in the absence of q. zhang et al./ int. j. miner. process. 52 (1997) 187-201 199 metal ions. this implies that when in competition with sphalerite, adsorption of xanthate is not favoured on pyrite. competition is either for activating ions which appears to be the case for ferrous and calcium ions, or for collector, which is apparently the case for cupric ions. the end result is, however, the same: the less competitive pyrite is depress