Extraction of vanadium from stone coal by modified salt-roasting process

Cent South Univ Technol( 2011)18: 1940-1944DoI:10.1007/s1177-011-0926-9Extraction of vanadium from stone coal by modified salt-roasting processWANG Ming-yu(王明玉), WANG Xue-wen(王学文, SHEN Ji-feng(沈继峰, WU Ri-na(乌日娜)School of Metallurgical Science and Engineering, Central South University, Changsha 410083, Chinao Central South University Press and Springer-Verlag Berlin Heidelberg 2011Abstract: In order to reduce the pollution of Cl2 and HCl released during extracting vanadium from stone coal by sodium chlorideroasting, a modified salt-roasting process was proposed by adding calcined lime in roasting process followed by H2So. leaching. Theeffects of parameters including roasting temperature, roasting time, addition mass ratio of NaCl, calcined lime upon leaching rate ofranadium and curing rate of chlorine were investigated, and the effects of leaching time and leaching temperature on leaching rate ofvanadium were also studied. The results show that the vanadium leaching rate and the curing rate of chlorine are 67. 3% and 51.5%(mass fraction), respectively, at roasting temperature of 750C, roasting time of 4 h, 15% sodium chloride and 8%(mass fraction)calcined lime, leaching temperature of room temperature, and leaching time of 4 hKey words: vanadium; stone coal; salt-roasting chlorine curingbeen taken for industrial applicatione northwest1 Introductionregion of China [12], while the recovery is low(about60%). Although the vanadium leaching rate of otherChina is rich in mineral resources of vanadium.extraction processes is high (70%), they are still notMore than 87% vanadium existing in stone coal, is applied to industrial application because of high cost orwidely deposited around the Southern China [1]. With rigorous reaction system. For example, the vanadiumthe rapid growth of vanadium products demand, theleaching rate of pressure acid leaching can reach 76%,tudy on extraction of v2Os from stone coal attracted based on the condition of reaction system with themore and more attentions.special material (titanium) and high temperatureThe traditional vanadium extraction technique from (180C). Therefore, the sodium chloride roasting-lowstone coal is roasting with a source of sodium chloride acidity leaching technique is still used to extractunder oxidizing conditions in a flat kiln, and then vanadium from stone coal in some placesvanadium in stone coal will be converted to solubleIn order to reduce the pollution of exhaust gassodium salt [2]. After roasting, the calcine is leached during sodium chloride roasting, and the difficulty ofwith low acidity solution. Due to the simple flow and treating the exhaust gas, a modified sodium salt roastinghigh recovery of vanadium, this technology has beenprocess is presented. about half of chlorine can be curedwidely applied to treat stone coal in many places for over and the rest of chlorine is easy to be absorbed by lime40 years. However, the released exhaust gas containing pellets deposited in the chimney flue in this process [13]Cl2 and HCl pollutes the environment seriously. In recentyears,several other processes have been proposed to2 Experimentalrecover vanadium from stone coal, such as oxidizingroasting-alkaline leaching [3], dilute sulfuric acid2. 1 Materials and procedureleaching [4], calcium salt roasting-sulfuric acid leachingThe stone coal used in experiment was taken from[5], direct acid leaching-solvent extraction [6], pressure Tongren District in Guizhou Province, China. XRFcid leaching [7-8], sulfuric acid with villiaumite (X-Ray Fluorescence) analysis result of stone coal isaching [9-10] and low temperature sulphatinglisted in Table 1. As shown in Table 1, the Ca content inroasting-water leaching [11]. However, there is no an raw stone coal is very low. The reagents includingall-purpose process for the extraction of vanadium from sodium chloride used for roasting, sulfuric acid used forstone coal. Among all the above extraction proccessesleaching and sodium hydroxide, ammonium ferrousonly direct acid leaching-solvent extraction process nassulfate etc used in chemical analysis were of analyticalFoundation item: Project(2007GHo01) supported by Development and Reform Commission of Guizhou PrReceived date: 2010-12-31: Accepted date: 2011-03-28中国煤化工Corresponding author: WANG Ming-yu, Professor, PhD; Tel: +86-731-88830247; E-mail: wmyd@163CNMHGJ. Cent. South Univ. Technol (2011)18: 1940-1944Table 1 XRF analysis results of main composition in raw stone 2Ca(on2+2Cl2=2CaCI2+2H2o1+O2tcoal(mass fraction, %It can be seen from Eq (4)and Eq (6)that Cl2 andHCI can be absorbed by calcined lime to produce CaCl26.7439200.550.200.26which can reduce chlorine element volatilization duringroasting. In practice, Cao can also react with vanadium2.490.020.660.39152to produce calcium vanadate, and the reaction may befollows [14]grade. Additive agent was industry calcined lime and the V205+Cao-Ca(vO3)2main composition is 95.41% Cao, 1.98% MgO, 0.82%Al2O3, 0.36%Fe2O3 and 0.82%SiO2(mass fraction)V205+V203+4Ca0-+022Ca2 V2O7After crushed and ground, the particle size of stone V2O5+V2O3+6Ca0-+O2=2Ca3(VO4)2coal and calcined lime is less than 0.089 mm accountingSoluble sodium vanadate in roasted stone coal isfor 80% and 85%, respectively. Experiments were easy to be leached out with water, and for calciumcarried out in 100 g raw stone coal scale. The charge wasvanadate, it can be leached out by sulfuric acid solution,composed of a weighed amount of stone coal, sodiumand the reactions can be expressed as follows:chloride and calcined lime. This charge was put in acrucible and heated gradually in an electric muffle Ca(VO3)+2H2SO4CasO4l+(VO2)SO+2H20 (10)furnace at a predetermined temperature with the door Ca v20,+3H2 S04-2CaSO4l+(VO2)2SO4+3H,0 (11)open to maintain an oxidizing atmosphereThe leaching procedure was performed in a beaker,Ca3(VO4)2+4H2so43CasO41+(VO2)SO4+4H2O(12)the liquid-to-solid ratio was 2 mL/g, the adding sulfuric3 Results and discussionacid was 3.5 mL, and the leaching temperature was roomtemperature. The contents of vanadium in the stone coalsamples and the leached residue were analyzed by3.1 Effect of roasting temperature on vanadiumammonium ferrous sulfate titration. Titration withleaching and chlorine curingammonium sulfocyanate was used to determine theThe roasting temperature was varied in the range ofcontent of chlorine in the residue and the concentration 700-900oC, with an interval of 50C. The roasting timeof chlorine in the solution. The curing rate of chlorine iswas constant of 4 h. the mass ratio of stone coal. sodiumexpressed aschloride and calcined lime was 100: 15: 8. The leachingcondition was constant,, and the results are illustrated in(1) Fig.1. It can be seen that, at around 800C, the vanadiumCLAleaching rate is maximal. a further increase inwhere Pa means the curing rate of chlorine, QaR meanstemperature leads to obvious decrease in vanadiumthe quantity of Cl in residue, @cus means the quantity ofleaching, which may be attributed to the sintering ofCl in solution, and ClA means the total quantity of stone coal. With increasing temperature, curing rate ofadded clchlorine decreases rapidly. This may be attributed to theincreased volatilizing of NaCl and CaCl2. The vanadium2.2 Experimental principleThe main reactions taking place in the roastingprocess with sodium chloride addition can be expressedas follows:yV205)+2xNaC1+(x/2)O2-xNa20-yV2O5+xCl t (2)y(V2O5)2+2 xNaCHxh2。→xNa2Oyv2O+2xHCl↑(3)where(V205e is a generic term for the vanadium bearingoxide in stone coal. The numerical values x and y in theproduct xNa20r yV2Os are correlative with roastingcondition, and the product can be NavO3, Na,v207 andNa3vO4. When calcined lime is added, the followingreaction will take place7007508008509002HCH+CaO=CaCl2+H2O↑中国煤化工Fig 1 Effect of roastCao+H20=Ca(OH(5) curing of chlorineHCNMHG1942J. Cent. South Univ. Technol(2011)18: 1940-1944leaching rate is 70. 1%, and 67.3% at 800C and 750C, which may be caused by two factors: one is the increaserespectively, while the curing rate of chlorine are 35.9% of the released Cl2 and HCl during roasting processand 51.5% respectively. The decrease of the curing rate absorbed by the calcined lime to form CaCI, and theof chlorine is more obvious compared with the increase other is the increase of unreacted NaCl with the increaserecovery of vanadiumm temperature of NaCl additionof 750C is chosen for further experiments3.2 Effect of roasting time on vanadium leaching andchlorine curingIn order to study the effect of roasting time onvanadium leaching and chlorine curing, the roasting timewas varied from 2 h to 6 h with an interval of 1 h, whilekeeping sodium chloride and calcined lime additionconstant. The experimental results are shown in Fig. 2. Itis observed that there is a rapid increase in vanadiumleaching rate with the increase in roasting time up to 4 h30With further increase in roasting time, there is a fall invanadium leaching rate. The longer the standing time ofANacI%stone coal in high temperature zone is, the more severe Fig 3 Effect of NaCl addition on vanadium leaching and curingthe enwrapped stone coal will be, which is unfavorable of chlorinefor the leaching of vanadium. For the curing of chlorine,with the increase of roasting time, curing rate of chlorine 3. 4 Effect of addition calcined lime on vanadiumdecreases rapidly. Thus, roasting time of 4 h is found toleaching and chlorine curingbe optimum for maximum extraction of vanadiumThe effect of calcined lime addition was studied fora period of roasting for 4 h at 750C, with 15%(massfraction) of NaCl addition, and the results obtained arepresented in Fig 4. It can be seen that the curing rate ofchlorine increases with the raise of calcined limeaddition. However, with an increase in calcined lime. thevanadium leaching rate decreases. In roasting process,the more the calcined lime is added, the more theunreacted calcined lime is remained in roasted stone coalUnder the condition that the amount of sulfuric acid used45for leaching is invariable, the increase of unreactedcalcined lime can consume more H2SO4 to join in theneutralization reaction. In addition the more the calcined123456lime is added, the more the CaSO4 will be producedFig2 Effect of roasting time on vanadium leaching and curingof chlorine583.3 Effect of addition of NaCl on vanadium leachingand chlorine curingThe effect of sodium chloride addition on leachingof vanadium and curing of chlorine was studied for aperiod of roasting for 4 h at 750C, with 8%(massfraction) calcined lime addition. The Nacl addition wasvaried from 9% to 17%(mass fraction), and the resultsobtained are presented in Fig 3. The graph shows that,with more than 15%(mass fraction) of NaCl in the feedmixture,the increase of vanadium leaching rate is notobvious. Thus, 15%(mass fraction) of NaCl addition is中国煤化工chosen for extraction of vanadium. The curing rate of Fig 4 Effect of calcichlorine increases with the increase of Nacl additionCNMH Gm leachingand curing of chlJ Cent. South Univ. Technol (2011)18: 1940-19441943which can wrap the stone coal particles and hinder the 60C. With the increase in leaching temperature, theleaching of vanadiumvanadium leaching rate and silicon concentrationobviously decrease. The concentration of SiO2 in leach3.5 Effect of leaching time on vanadium leachingliquor is 5.90 g/L at room temperature leaching, whileThe effect of leaching time on vanadium leaching only 1.99g/L at 95oC. When the leaching temperature iswas studied, and the results are presented in Fig. 5. Thehigher than 60C, the silicon can be condensed androasted stone coal used for leaching was got at 750Cprecipitated. The precipitate can adsorb vanadium fromroasting for 4 h, and the mass ratio of stone coal, sodium the liquor [15], which results in the decrease ofchloride and calcined lime was 100: 15: 8. As shown invanadium leaching, and thus high temperature isFig. the vanadium leaching rate increases with the unfavorable for the leaching of vanadium.tending of leaching time, But4 h, the vanadium leaching rate rises slowly. Thus, 4 h is4 Conclusionschosen as the leaching time in experimental process74D)The modified salt-roasextract vanadium effectively from stone coal but alsoreduce the environmental pollution.2)The vanadium leaching rate of 67. 3% and thechlorine curing rate of 51.5%(mass fraction)areobtained under the experimental condition of roastingtemperature of 750C, roasting time of 4 h, 15%(massfraction) sodium chloride and 8%(mass fraction)calcined lime addition to stone coal. leachitemperature of room temperature, and leaching time of4h.ReferencesTime/hig.5 Effect of leaching time on vanadium leaching[1] DENG Zhi-gan, WEI Chang, FAN Gang, LI Min-ting, LI Cun-xiong3.6 Effect of leaching temperature on vanadiumLI Xing-bin. 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