An experimental study on the solubility of copper bichloride in water vapor

Chinese Science Bulletin@ 2007 Science in China PressSpringer-VerlagAn experimental study on the solubility of copperbichloride in water vaporSHANG LinBo*, BI XianWu, HU RuiZhong & FAN WenLingState Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002,ChinaUsing the solubility method, the solubility of CuCl2 in liquid-undersaturated HCl-bearing water vaporwas investigated experimentally at temperatures of 330- 370C and pressures of 4.2- 10 MPa. The re-sults have shown that hydration could significantly enhance copper solubility and the concentrationsof copper were positively correlated with Pr,o. The solubility of copper in vapor phase increased withincreasing Pr,o at the constant temperature. CuCl2 was transported as hydrated species CuCl2(H2O)ngasin water vapor. The formation of complexes is proposed to be the result of the following reaction: .CuClzaolid + nH2Oas = CuCI2 (H2O),gasThe hydration number n decreased slightly with increasing temperature. Statistical hydration numbersare 4.0, 3.6 and 3.3 at 330, 350 and 370"C, respectively.CuCl2, water vapor, solubilit, experimental studyThe vapor transport of metals is an important geo-solubility of metals in vaporThe high concentra-chemical process. For example, the condensates of vol-tions of the transition metal copper in vapor can be takencanic gases commonly contain appreciable concentra-as a typical example. The highest concentration of cop-tions of metalst- ; the high concentrations of metalsper reported is 8.4x10 in the condensates of volcanichave been detected in vapor -rich fluid inclusions8-12]gases", and recent LA-ICP-MS analyses have revealedand the condensates of metal compounds usually exist in that its concentrations are as high as 3.3wt% in vapor-the dash of flue in the process of metallurgyl'5s. Previousrich fluid inclusions' 10. The available copper volatilityexperimental research on metals in vapor focused on the data can not explain the high concentrations of copper involatility of metals or their compounds, and it was con-vapor-rich fluid inclusionst19. In order to shed light onsidered that only highly volatile metals could be trans- the mechanisms of the dissolution and transport of cop-ported in vapor.per in vapor, more experiments need to be done. Up toBut more and more weakly volatile metals (Cu, Au,now, only Archibald et al."4 described the behavior ofZn, Pb, Fe and so on) have been detected in vapor,copper in water vapor at 280 to 320C. The resultswhich makes researchers have to think about whether orshowed that water vapor could enhance the solubility ofnot the metal transport in vapor is solely related withcopper in vapor. But at higher temperatures, little isthe volatility of metals. In addition to the voltility ofknown about the behavior of copper differing in valencemetals, which factors enhance the solubility of metalsin vapor. This paper presents the results of experimentsin vapor? How significant are the metallic elementsReceived April 12, 2006; accepted June 13, 2006transported in vapor? In recent years, the vapor transportdoi: 10.1007/s11434-007-0039-xof metals has attracted ever increasing attention, andCorresponding author (email: s 2000@sina. com)results of experimental research have shown that sol-Supported jointly by the Knowledge Innovation Program of the Chinese Academy ofSciences (Grant No. KZCX3-SW-125), the National Natural Science Foundation ofvents such as H2O, HCl and H2S could enhance theChina (Grant Nos.40503007 and 40373020) and the Westem Light Programwww.scichina.com www.springerlink.comChinese Science中国煤化工no. 3 | 395-400MYHCNMHG.for the solubility of CuCl2 in HCl-bearing water vapor at330 to 370"C.1 Experimental methodThe experimental method used in this study is identicalto that employed by Migdisov et al.l4] and Archibald etal.!I7!. The experiments were conducted in titaniumautoclaves at temperatures between 330°C and 370°Cand pressures up to 10 MPa. Each of the autoclaves wasconditioned with nitric acid to produce a protective layerof TiO2 on the inner surface. Autoclave volumes were( H,0determined by flling the autoclaves with 25°C distilled( HCIwater from a Teflon flask, and this flask was weighedbefore and after flling. This pressure was calculated inCuC,(H,O);和terms of the autoclave volume and the equation of statefor water of Kestin et a1.44 . The autoclaves were heatedin a forced draft oven (Sx2-6-6). The temperature gra-dient in the furnace was less than 0.5C over the height( H,Oof the autoclave. .The autoclave was loaded with one open quartz am-HCIHC)poule containing CuCl2 2H2O (Figure 1). A known massof H2O-HCl solution (HCl, optima -grade) with a prede-(HO)termined composition was placed at the bottom of theautoclave using a syringe in order to prevent contact ofCuclgdsolid CuCl2 and liquid. Care was taken to ensure that themass introduced did not saturate the system with liquidunder the experimental conditions, and CuCl2 only dis-solved in dry vapor. After each run, the autoclaves wereremoved from the oven and quenched in cold water, andthe condensates were collected for analysis. Several mil-liliters of 1:5 HNO3 were added to dissolve any copperprecipitated on the walls of the autoclaves. The concen-58mm，trations of dissolved copper in the condensates andwashing solutions were determined by atom absorptionFigure 1 Sketch of a titanium autoclave used in this study. The auto-spectroscopy (PE5 100).clave contains a CuCl2 reagent-bearing quartz capsule.2 Experimental resultsTable 1 Solubility of CuCl2 in vapor phase as a function of timeTime (d)_T(C)_fruo(x10'Pa)Cuyapor (ug/g)To determine the duration required for the reaction to3303.914.22reach equilibrium, a series of kinetic experiments were3.92118.78performed for 1 to 16 days. At the given temperature,3337.02equilibrium was attained 8 days later (Table 1 and Fig-53.11ure 2). Figure 2 shows that once equilibrium wa8.69.21070.90reached, the solubility of CuCl2 was reproducible to ap-13.565..50proximately +5%. On the basis of the results of kinetic3.9268.00experiments, all subsequent runs were conducted for 9fiuo is the fugacity of H2O; Curapor is the concentration of dissolved Cudays.in the vapor phase.396SHANG LinBo et al. Chinese Science Bulletin | February 2007中国煤化工MHCNMH G.110 |70900}i 70T重40言5(330C.1.o=-3.921x10 Pa350Cofic=2x10 PaMr0=4.169*10* Pa3(02 4 68101214 16 18104.Time (d)logfhcFigure 2 The solubility of copper in vapor as a function of time.Figure 3 The solubility of copper in vapor versus logfincu at constantfuo.The dependence of the concentrations of CuCl2 inwater vapor on the partial pressure of HCl is illustratedin Table 2 and Figure 3. In this figure, the slope is equalperatures, experiments specially designed to investigateto zero, so it is evident that CuCl2 solubility is inde-the dependence of solubility on fi,o were conducted overpendent of fuc within the limit of experimental errors, atthe same restricted range of fuc. At temperatures ofconstant temperature and partial fugacity of H2O. This330°C, 350°C, and 370"C, the concentrations of copperindicates that in the dominant gaseous copper species in the vapor phase determined from our experiments arethe stoichiometrical ratio Cu:Cl is equal to 1:2.listed in Table 3, and shown as a function of PH,O andIable 2 Concentration of copper in water vapor versus the partial pres-fr,o in Figures 4 and 5, respectively. From both figures,sure ofHClit can be seen that the isothermal concentrations of cop-T(Cfuo(x10Pa)logfra(Pa) Cu0(x105)per in vapor tend to increase sharply with increasing3504.1690.04.8667.471.093.8573.08H2O fugacity, that is to say, copper fugacity correlates73.00positively with the fugacity of water vapor. At the same70.5066.60time, from Figure 4, it can also be seen that the solubi-3.0274.75ity of copper in vapor increases slightly with increasing68.00temperature at constant PH2O, but the effect of water va-fno is the fugacity of H2O; logfucis the log of the fugacity of HCI invapor phase; Cu'apor is the concentration of dissolved Cu in the vaporpor density on the solubility of copper is higher than thatphase.of the temperature.Table 3 Solubility and mole fraction of CuCl2 in the vapor phase at 330C, 350C and 370CT(C)PaH,o)(x 10°Pa)logPH.o)oH2Ologf,oCup0(μug/g)logXcu3306.686.6480.00-4.64 .5.5826.750.8926.70104.17-4.53306.3536.800.878142.50- 4.397. 2006.866.7923 1.25-4.186.890.852 .276.60-4.114.4686.656.61-4.706.720.909111.25-4.506.7456.836.78210.94-4.22508.1016.910.8636.84264.50-4.134.6506.676.6390.72-4.593705.4856.740.915120.42- 4.476.1070.906172.50-4.317.0626.850.892 .187.03- 4.28189.53- -4.278.5186930.871328.13-4.036.970.858 .385.00-3.9610.0487.000.8496.93411.90-3.9311.0877.040.835503.75-3.85P is the partial pressure of H2O; pH2O is the fugacity coefficient of H2O; Cu'apor is the concentration of dissolved Cu in the vapor phase; logXcu is thelog of the Cu mole fraction in vapor phase.SHANG LinBo et al. Chinese Science Bulletin I February 2007中国煤化工397MYHCNMH G.500450log K = log XxcaCl,(H2O)。-(n- l)og ft,o - logfcucrglu.00一(2)While holding temperature constant, differentiating ec50(2) with respect to logfr.o, we obtained00so t( 0log xn(l(H2),≌n-1,00 t350C0log fim,os0where n-1 is the slope of log Xcu(h(H,O)，versus00)▲370C■350Clog fr,o, as shown in Figure 5. At the temperatures of●330C330°C, 350"C and 370C, the slope values are ~3.0,0.010.020.030.040.05~2.6, and ~2.3, respectively, so the substituted hydrationp(H2O) (g/cm)numbers are ~4.0, ~3.6, and ~3.3 and the dominant cop-per species in vapor are CuCl2(H2O)4.8*， CuCl-Figure 4 The concentrations of CuCl2 in water vapor versus water vapor(H20O)3.62as, and CuCl2(H2O)3.3Eas. .density obtained in experimental runs at 330C, 350"C and 370"C.-3.9330C.fnc=2xI0Pa3 Discussion- 4.3-3.1 Data analysisy 2.9866x-9. 5661R?= 0.9749In our calculations, we assumed that fuc and fcu werenegligible (when HCl was present in the experiments)4.9Lcompared to PH,o. Values of PH,o were calculated from6.606.656.70 6.75 6.80 6.85 6.90the equation of Kestin et al.2, and the mole of copperlogfH2O)in vapor was calculated from the concentrations of cop-- -3.9per in quenched condensates. The mole fraction of cop-350CJfrc=2x10'Paper is therefore given by the equation:4.3-McuC1,Mcucl2y= 2.5541x- 8.8025XcuCl2MH,o +Mcucl, M2o-4.7R2= 0.9823where Xcucl, is the mole fraction of copper in vapor, and6.55 6.60 6.65 6.70 6.75 6.80 6.85 6.90M is the mole concentrations of the corresponding com-log/(H2O)pound.-3.7As the concentrations of copper in vapor increase3.9- 370C.fucn=2xI0Pawith increasing PHo, it can be assumed that the domi-4.1nant species has the stoichiometrical CuCl2(H2O).8as.4.3= 2.2861x -8.3406The formation of this species can be described by theR2= 0.9846reaction:4.74CuC1g2lid + nH2Oas= CuCl2(H2O);as，(1)6.60 6.65 6.70 6.75 6.80 6.85 6.90 6.95 7.00 7.05where n is the hydration number of the copper species inlog. AH2O)vapor. Our experiment data were interpreted on the as-Figure 5 Diagram of logXCc.cC.J versus log/fa.o) at constant fica and tem-sumption that the vapor was an ideal mixture ofperatures of 330"C, 350C and 370"C.non-ideal gases, and therefore it obeyed Raoult's Law.So the fugacity of copper in vapor is expressed as3.2 Comparison with other studiesJcucl(H2O)n≌JH2O x XCuCl(H2O)n.Results of these experiments show that CuCl2 is trans-The equilibrium constant for reaction 1 is given byported as hydrated species CuCl2(H2O),gas in water vapor.398SHANG LinBo et al. Chinese Science Bulletin | February 2007中国煤化工MYHCNMH G.With increasing temperature from 330C to 370C, the show that interaction between vapor solvent and copperhydration number tends to decrease from 4.0 to 3.3. Thiswould enhance the solubility of copper in water vapor.situation is similar to what was reported in previous re-Therefore，in special geological environments (e. g.search.1o.1. Migdisov et al.'4 concluded that AgCl has .magmatic degassing process or evolution of mag-a hydration number of three between 300C and 360C.matic-hydrothermal fluid), vapor-phase fluid may playArchibald et a.16.] reported a variable hydration numberan important role in the formation of copper deposits.for AuCl, from 5 at 300°C to 3 at 360"C; for CuCl，from7.6 at 280C to 6 at 320"C. As proposed by Archibald et4 Conclusionsal!taln for gold and copper, the decrease of hydration Results of these experiments show that the CuCl2 of ap-number should be attributed to the decrease of stability ofpreciable concentrations can be transported in chlo-the solvation shell with increasing temperature.ride-bearing water vapor. At the constant temperature,Through experimental studies, it is discovered that thethe solubility of copper in the vapor phase tends to in-behavior of CuCl2 is similar to that of CuCl7 in watercrease with increasing fHo, but under the same experi-vapor, their solubility all correlate positively with themental conditions, the solubility of CuCl2 is about twowater vapor pressure, but the concentrations of CuClorders of magnitude higher than that of CuCl in waterare two orders of magnitude higher than those of CuClvapor. Relatively, CuCl2 is more easily dissolved in wa-under the same experimental conditions, and are at leastter vapor than CuCl.ten orders of magnitude higher than those of CuC1h1 inThe increase of solubility of CuCl2 is attributed to thethe water-free system. Relatively, CuCl2 is more easilyinteractions between copper and water vapor, and copperdissolved in water vapor than CuCl.is dissolved as hydrated species in water vapor. ThIn the process of magmatic-hydrothermal evolution,complexes are proposed to have been formed throughlow density vapor will appear, which contains manythe reaction:volatile components (H2O, HCI, H2S, SO2, CO2 and soCuCisgld + nH2Oas = CuCl2(H2O)as.on). In addition, the data obtained from our experimentsshow that the chloride- bearing water vapor can enhanceThe hydration number n decreases slightly with increas-the capacity of copper transport in vapor, and other re-ing temperature. At the temperatures of 330"C, 350"Csearchers also suggest that copper may exist as a and 370C, the dominant copper species in vapor areHS- bearing complex in the vapor-23- 29]. Which ligand isCuCl2(H2O)4.0，CuCl2(H2O)3.6 and CuCl2(H2O)3,3, re-dominant in copper transport? This needs more experi-spectively.mental researches. 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