外文翻译---用选择性氧化或溶解分离非金属矿物和硫化砷铜矿.docx

separation of enargite and tennantite from non-arsenic copper sulfide minerals by selective oxidation or dissolution d. fornasiero , d. fullston , c. li, j. ralston a ian wark research institute, the arc special research centre for particle and material interfaces, uniersity of south australia, the mawson lakes campus, mawson lakes, s.a. 5095,australia rio tinto technology development, research ae., bundoora, vic., 3083, australia received 10 march 2000; accepted 19 july 2000 abstract selective oxidation of minerals was investigated as a means to separate by flotation the copper sulfide minerals of chalcocite, covellite and chalcopyrite from the arsenic copper sulfide minerals of enargite and tennantite in mixed mineral systems. it was found that a separation of these minerals could be feasible after selective oxidation of their surfaces in slightly acidic ph conditions, or after oxidation and selective dissolution of the surface oxidation products with a complexant in basic ph conditions. q2001 elsevier science b.v. all rights reserved. keywords: selective flotation; copper sulfide minerals; tennantite; enargite; oxidation; x-ray photoelectron spectroscopy 1. introduction arsenic is an undesirable element that causes serious toxicological and environmental problems in smelting of arsenic-containing minerals e.g., padilla et al., 1998; dutre and vandecasteele, 1995 . although hydrometallurgy or pyrometallurgy could be used to remove this element, increasing severity of environmental legislation has resulted in a progressive reduction of the amount of arsenic allowable in processing bi-products（morizot and ollivier, 1993）. as a result, high financial penalties are imposed by smelters to treat copper ores containing higher than 0.2 wt.% arsenic （wilson and chanroux, 1993 . ） it would be more economically and environmentally beneficial to remove the minerals containing arsenic at an earlier stage such as during flotation. their separation is nevertheless difficult as they generally have similar flotation behaviour to the valuable minerals with which they are associated. this is the case in separating arsenopyrite (feass) from pyrite, or removing enargite（cu3 ass4）and tennantite（cu12 as4 s13）from covellite （cus ）, chalcocite（cu2 s） and chalcopyrite（cufes2）. apart from arsenopyrite, the amount of literature dealing with the separation of arsenic minerals is scarce. one of the potential separation methods relies on the selective oxidation of sulfide minerals due to differences in their electrochemical properties （e.g., tolley et al.,1996; byrne et al., 1995; kydros et al., 1993; wang et al., 1992; beattie and poling, 1988; guongming and hongen, 1989; chander, 1985）.oxidation can promote the adsorption of collectors, such as xanthate, at low to moderate levels of oxidation, or prevent their adsorption at high levels of oxidation by creating a physical barrier of oxidation products for their diffusion to the mineral surface. the oxidation behaviour of non-arsenic copper sulfide minerals(chalcocite, covellite and chalcopyrite) is well established (e.g., richardson and walker, 1985; hamilton and woods, 1984) ,whereas only a limited amount of literature is available on the oxidation of enargite and tennantite (fullston et al., 1999a; cordova et al., 1997; mielczarski et al., 1996a) . a recent study on these minerals has shown that their rate of oxidation at ph 11.0 follows the order: chalcocite tennantite enargitecovellite chalcopyrite (fullston et al., 1999b) .this order, for the non-arsenic minerals, is in agreement with that of their rest potential value or their flotation response in the absence or presence of collectors(crozier, 1995; majima, 1969) . furthermore, it was reported that xanthate collector adsorbs more on chalcopyrite than on tennantite (mielczarski et al., 1996b) .for a similar flotation system containing antimony copper sulfides, a satisfactory separation of chalcopyrite from tetrahedrite (cu12sb4s13 , the antimony analogue of tennantite). was obtained and was attributed to the faster oxidation rate of tetrahedrite than chalcopyrite(byrne et al., 1995) . enargite and tennantite often occur at various quantities in copper deposits with chalcocite, covellite or chalcopyrite. being the major copper minerals. in this study, the separation by flotation of chalcocite, covellite or chalcopyrite from enargite or tennantite was investigated in mixed mineral systems by means of oxidation treatments. a two mineral system was preferred in this investigation to identify the flotation performance of each non-arsenic mineral gainst that of enargite or tennantite. to obtain a better understanding of the surface reactions occurring during oxidation, the surface of these minerals was monitored after the conditioning and flotation stages by x-ray photoelectron spectroscopy(xps).xps is a powerful surface sensitive analytical technique that can identify the surface species responsible for flotation. in general, flotation performance is closely related to the overall hydrophobicity of a mineral surface with a balance of hydrophobic contribution from collector coverage and hydrophilic contribution from oxidation products such as oxidesrhydroxides. the layer thickness of these oxidation products is not only a measure of the extent of surface oxidation, but also an important indicator of the ability of the collector to interact electrochemically with the mineral surface. 2. experimental all chemicals were of analytical grade quality. high purity gas (nitrogen or oxygen from cig ltd). was scrubbed by bubbling it through a silica dispersion. high purity water, produced by reverse osmosis, two stages of ion exchange and two stages of activated carbon prior to final filtration, was used in all experimental work. this water was pretreated at the required ph with kno3(0.01 mol dm-3) . as electrolyte and by bubbling the required gas into it. chalcocite, covellite and chalcopyrite samples were purchased from wards natural science establishment(usa ). enargite and tennantite samples were supplied by continental minerals(usa) . the chemical analysis of these samples is reported in table 1. no significant amount of impurities were detected on the mineral surface by xps measurement before and after the grinding stage, except for a noticeable amount of iron in the enargite and tennantite samples. optical microscopy examination of polished surfaces of these minerals confirmed the purity of the chalcocite, covellite and chalcopyrite samples, however this technique revealed the presence of a small amount of bornite and chalcocite in the enargite and tennantite samples. flotation was conducted using a modified partridge and smith column (partridge and smith,1971) .the mineral combinations used in mixed mineral flotation experiments were enargitechalcocite,enargitecovellite,enargitechalcopyrite,tennantitechalcocite,tennantitecovellite and tennantitechalcopyrite(1:1 weight ratio) . mineral samples (5 g dm -3) . were wet ground separately in pretreated kno3 solution with a ceramic mortar and pestle (d50 of 16 mm). and, then transferred into a stirred conditioning vessel. the temperature inside the conditioning vessel was maintained at 21.0+0.20c. the ph was kept constant by adding small quantities of concentrated potassium hydroxide or nitric acid solutions. minerals were conditioned either for 20 min with nitrogen gas or for 60 min with oxygen gas and hydrogen peroxide（0.013% w/v）. at the end of the conditioning period, diethyl dithiophosphate (dedtp;95% pure). was added to the mineral slurry at a concentration of 2 10-5 mol dm-3 . after a 1-min table 1 collector adsorption time, the mineral slurry was transferred into the flotation column. nitrogen gas was introduced into the flotation column at a flow rate of 50 cm3 miny1. concentrates were collected after 1, 2, 4 and 8 min of flotation time and filtered through pre-weighed filters. the amount of copper and arsenic was determined by inductively coupled plasma (icp). analysis. the ratio of arsenic to copper was then used to calculate the experimental percentage recovery of copper and copperarsenic minerals. xps measurements were obtained with a perkin elmer physical electronics division (phi). 5100 spectrometer using an mgk a irradiation x-ray source operated at 300 w. a pass energy of 17.9 ev was used for all elemental spectral regions. the pressure in the analyser chamber was 10-7 pa. the energy scale was calibrated using the fermi edge and the 4f7/2 line (be s84.0 ev) for gold,whilst the retardation voltage was calibrated with the position of the cu （2p3/2） peak(be s932.67 ev) and the cu （3p3/2）peak( be s75.13 ev ). an accelerated ar ion beam at 3 kv was used to etch the mineral surface for 5 min. for the xps analysis, the minerals were prepared in a similar way as in the flotation experiments. after decantation, the mineral slurry was washed once with pretreated water to remove any suspended colloidal particles and was introduced immediately into the fore-chamber of the spectrometer on a stainless steel sample holder as a slurry. a turbo-molecular pump was used to evacuate the sample before it entered the main chamber at an ultra high vacuum of approximately 10-9 torr. the procedure used to analyse the xps spectra of the minerals has been presented in details in our previous xps study of these minerals( fullston et al., 1999a) . 3. results and discussion3.1. mineral flotation in non-oxidising conditions at ph 5.0, n2 conditioning resulted in high flotation recoveries of all the minerals without selectivity for all the pairs of minerals fig. 1 without h2o2 . under these non-oxidising conditions, only a small amount of oxidation products was found on the surface of all the copper minerals investigated (table 2) . as an example, the as (3d) and cu (2p) xps spectra of tennantite are shown in figs. 2 and 3, respectively. each spectrum was deconvoluted into individual components, namely those attributed to sulfide and oxide species (fullston et al., 1999a) . from this spectral deconvolution, the proportions of copper and arsenic oxide on the tennantite surface were calculated and are shown in tables 2 and 3 as a function of oxidation conditions. at ph 11.0, the flotation results were more complex with relatively good separations of covellite from tennantite, tennantite from chalcopyrite, enargite from chalcopyrite and enargite from chalcocite (fig. 4 without h2 o2) . although these results are satisfactory only for an ore system containing some of the minerals present in these pairs of minerals, they also indicate that a poor copperarsenic mineral separation will be obtained if the full suite of copper minerals is present in a real flotation system. furthermore, it is often preferable to reject the arsenic minerals with the gangue minerals. fig. 1. flotation recoveries of the empty circles. chalcociteenargite, empty squares. covelliteenargite, empty triangles. chalcopyriteenargite, fill ecircles. chalcocitetennantite, filled squares. covelliteten- nantite and filled triangles. chalcopyritetennantite mixed mineral system sat 1, 2, 4 and 8 min at ph 5.0. without 20 min n2 conditioning and with 0.013% wrv h2o2(60 min o2 conditioning) . (mineral=s5 g dm -3; dedtp= 2 10-5 mol dm-3 ) 3.2. mineral flotation in the presence of hydrogen peroxide a high degree of oxidation of the copper and arsenic surface species occurred when the minerals were conditioned in oxygen and with h2o2 . as an example, tables 2 and 3 shows the trends in surface oxidation for tennantite as the oxidising condition was changed from nitrogen to oxygen and to hydrogen peroxide. these surface analysis results are in agreement with the depression of the flotation of all the minerals observed in the presence of h2 o2 at a ph value of 11.0, with maximum recoveries lower than 20% (results not shown ). fig. 1 shows that, conditioning the minerals with h2o2 at ph 5.0 generally produced a higher flotation recovery of the non-arsenic minerals than the arsenic minerals, and therefore a good mineral separation. this was particularly the case for the mineral systems containing enargite. recoveries achieved for the non-arsenic minerals ranged table 2 proportions of copper and arsenic oxidation products measured by xps on the surface of tennantite at ph 5.0 as a function of conditioning treatment 【h2 o2】 = s0.013%. fig. 2. as（3d ）xps spectra of tennantite conditioned for 60 min with oxygen gas and h2o2. the dots represent the experimental spectra and the full lines represent the calculated spectra obtained by summing gaussian bands . from 47% to 82%, and from 40% to 53% for the arsenic minerals. the xps results in figs. 2 and 3, and tables 2 and 3 show that the proportion of copper oxide on the fig. 3. cu(2p3/2) xps spectra of tennantite conditioned for 60 min with oxygen gas and h2o2. the dots represent the experimental spectra and the full lines represent the calculated spectra obtained by summing gaussian bands . table 3 proportions of copper and arsenic oxidation products measured by xps on the surface of tennantite at ph 11.0 as a function of conditioning treatment (h2 o2 = s0.013%). mineral surface is less at ph 5.0 than at ph 11.0, hence the higher flotation recoveries of the non-arsenic copper minerals obtained at ph 5.0 than at ph 11.0. the increased mineral separation observed at ph 5.0 than at ph 11.0 is also the result of an increased proportion of surface arsenic oxide species at ph 5.0 figs. 2 and 3, and tables 2 and 3 . this last result is in agreement with the decrease in dissolution of arsenic oxide observed by marasinghe and koleini 1994. with decreasing ph values. more importantly, a comparison of the proportion of surface oxidation species before and after etching in tables 2 an 3 indicates that the arsenic oxide layer is thicker than the copper oxide layer. similar trends were observed for enargite. the flotation and xps results are also supported by thermodynamic calculations on the copperarsenicoxygen system showing that copper oxide is not a stable species at ph values lower than 7 while arsenic oxide is stable over a wider range of ph values (e.g., brookins, 1988 ). fig. 4. flotation recoveries of the (empty circles). chalcociteenargite,(empty squares). covelliteenargite, empty triangles. chalcopyriteenargite, filled circles. chalcocitetennantite, filled squares. covellitetennantite and filled triangles. chalcopyritetennantite mixed mineral systems at 1, 2, 4 and 8 min at ph 11.0 without 20 min n2 conditioning. and with 0.013% w/v h2o2(60 min o2 conditioning; edta= 4.510-4 mol dm-3.mineral =5 g dm-3; dedtp=210 -5 mol dm-3. ethylene diamine tetra-acetic acid edta , a strong complexant, has been commonly used in mineral processing to give information about the amount and type of oxidation products covering the surface of minerals, but also to remove these surface ductsclarkeetal.,1995a. fig. 5 shows that a separation between chalcocite and tennantite only occurred at intermediate edta concentrations. at high edta concentrations, surface oxidation products were removed from both minerals resulting in high recoveries but no selectivity. fig. 4 shows that the addition of 4.5 =10y4 mol dm-3 edta before collector addition produced higher recoveries of the non-arsenic minerals than enargite or tennantite, hence the greater mineral separation obtained in these conditions although this edta concentration is optimum for the chalcocitetennantite system, other concentrations may provide a better separation for the other mineral systems . the xps analysis was also conducted on the flotation concentrate and tail fractions of the chalcociteenargite system to confirm the previous interpretations. for mineral mixtures, a detailed analysis of the xps spectra, as in figs. 2 and 3, is rather complicated clarke et al., 1995b. and therefore only the proportion of surface elements will be considered. it is shown in table 4 that the concentrate samples containing 52% chalcocite and 17% enargite at ph 5.0, and 50% chalcocite and 25% enargite at ph 11.0 had more collector represented by the p 2p signal of dedtp on their surface than the tail samples. the reverse is true for the amount of oxidation products represented by the o 1s signal. this difference between concentrate and tail samples was also evident after etching the surface. the observation that the intensity of the o 1s signal of the concentrate was decreased approximately by a factor of 4 while that of the tail was only decreased by a factor of 2 after etching indicates that the oxidation product layer on the mineral surface is thicker in the tail than in the concentrate samples. these xps results showing that more copper and, more importantly, less arsenic are found in the concentrate than in the tail samples are in a good agreement with the flotation results. furthermore, the xps results have revealed that the higher flotation fig. 5. flotation recoveries 8 min. of chalcocite and tennantite in a mixed mineral system at ph s11.0 with h2o2 as a function of edta concentration mineral s5 g dm ; h2 o2 conditioning time s60 min; w