Alumina recovery from spent Bayer liquor by methanol

Available online at www.sciencedirect.comTransactions of骂PScienceDirectNonferrous MetalsScienceSociety of ChinaELSEVIER PressTrans. Nonferrous Met. Soc. China 20(2010) s165-s168===== =www .tnmsc.cnAlumina recovery from spent Bayer liquor by methanolZHANG Ying(张盈):2, ZHENG Shi-1i(郑诗礼), DU Hao(杜浩),WANG Shao- na(王少娜), PENG Ying(彭鹰), ZHANG Yi(张懿)'1. National Engineering Laboratory for Hyrometallurgical Cleaner Production Technology,Key Laboratory of Green Process and Engineering, Institute of Process Engineering,Chinese Academy of Sciences, Bejing 100190, China;2. Graduate University of Chinese Academy of Sciences, Bejjing 100049, China;3. Beijjng Tungsten and Molybdenum Material Factory, Beijing General Research Intitute, Beijing 102206, ChinaReceived 6 July 2009; accepted 30 December 2009Abstract: Decomposition of sodium aluminate solution is the key step for alumina production; however, approximately only 55%alumina yield is obtained by seeded precipitation. So, it is difficult to obtain sodium aluminate solution with high caustic ratio. In thisstudy, a method was explored to recover alumina from spent Bayer liquor by deep decomposition with methanol. A variety ofconditions, including reaction temperature, reaction time, mcthanol amount and seed cofficient were elaborately investigated. Theresults showed that the appropriate conditions were 1:1 in volume ratio of methanol to spent Bayer liquor, more than 1.0 seedcofficient and in a40 C water bath for 24 h. By characterizing through XRD, the crystal products were found to be Al(OH)3. Withthis method, the molar ratio of Na2O to Al2O3 of the spent liquor can be increased from about 3.0 to 10.0 due to the recovery ofalumina, which is beneficial for the treatment of red mud.Key words: spent Bayer liquor; methanol; alumina; decompositionrecycling from red mud have been done worldwide,1 Introductionamong which hydrothermal treatment is considered to bethe most promising way. KLAN[5] pointed out that,Aluminum bydroxide, 90% of which is efined bywith the condition of high caustic ratio (10-11) (MR, theBayer process, has a wide application in manymolar ratio of Na2O to Al2Oz) of spent Bayer liquor,contemporary technical domains[1- -2]. About 90% ofhydrothermal treatment could be used to treat red mud byaluminum hydroxide is calcined and electrolyzed toBayer process. According to research results fromproduce aluminum[3]. The production of aluminaZhengzhou Research Institute of Chalco[6], a recycleincreases rapidly in recent years, reaching 19.45 millionratio of 50%-70% of Al2O; and 90% of Na2O can betons in 2007 and 22.78 million tons in 2008. It isrealized by using caustic liquor with MR higher than 8.expected that the productivity would increase to 35Even though hydrothermal method is effective in Al2O3million tons in 2010. However, with the fastand Na2O recycling, it bas not been applied widely indevelopment, the production of red mud becomes 8industries because of the difficulty to obtain sodiumsignificant problem. 1.0-1.3 t of red mud will be outputaluminate solutions with MR higher than 8. In Bayerwhen 1 t Al2O; is produced, which contains more thanprocess, the highest MR obtained is only about 3.2 from20% of alumina and 8% of sodium oxide by massthe spent Bayer liquor.fraction, respectively[4]. The release of red mud not onlyCurrently, there are mainly three ways to preparecauses environmental pollution, but also leads to aluminahigh MR caustic liquor. One is sodium aluminateresource waste.crysallization method[7]. This method requiresA great number of researches on Al2O3 and Na2Ovaporization of the spent Bayer liquor to an alkaline中国煤化工Foundation item: Projc(50874099) supported by the National Natural Science Founcppred by the Natinali-tich Rescarch and Development Program of China; Projcts(20:YH; by the National BasicResearch Program of China; Projct(KGCX2-YW-321-2) supporteCN M H GrChine paeBesSciences; Project supported by the Scientific Research Foundation of State Education Ministry for tbe Retumed Overseas ChineseScholars, ChinaCorreaponding autbor: ZHENG Shi-i; Tel: +86-10- 62520910; E-mail: slzheng@bome ie.c.cns166ZHANG Ying, et al/Trans. Nonferrous Met. Soc. China 20(2010)s165-s168concentration ofabove 500 g/L， followed bysolution and a liquid feed pump was used to addcrystallization of sodium aluminate, and a caustic liquormethanol. The reactor was beated by a thermostaticwith high MR is obtained consequently. But this processwater bath with a precision of +0.1 C, and a condenserhas the disadvantage of large amount of waterwas used to condense the liquid.vaporization (12 t water per ton alumina) and highenergy consumption. Another one is calcium aluminatehydrate method, which is adding lime into the sodiumaluminate solution, synthesizing calcium aluminate andsimultaneously obtaining the needed caustic liquor. Butthis method could only be used to treat low concentrationcaustic solutions. The third, extraction treatment[8], is animmature method that uses extractant to capture sodium3東ions and eventually separates sodium ions from thesodium aluminate solution. But high phase ratio,excessive extraction stages and complicated operationFlg,1 Schematic diagram of experimental installation: 1limit its application.According to WANG et a[9-10] and ZHANG etFastening stand; 2 Condenser; 3 Thermostat water bath; 4 Flaskal[11]，the introduction of methanol can break thereactor; 5 Feed dosing pump; 6 DC electromotor; 7 Voltageregulator; 8 Digital multimeterequilibrium of seeded precipitation, lead to a significantincrease in the driving force for crystallization, and in theAfter the temperature reached the pre-set value, theend, obtain high MR caustic solution. Further, methanolspent Bayer liquor mixed with a certain amount of seedscan be efficiently recycled by distilation. In this work,were poured into the precipitation reactor. Then, a certainthe deep decomposition of spent Bayer liquor withmethanol is systematically studied. The effects ofamount of methanol (nmtanop:Vohuiothe samereaction temperature, reaction time, methanol amounttemperature was added into the solution. The solutionwas kept stirring with a speed of 300 r/min underand seed amount on the final MR are investigated.atmospheric pressure. At appropriate time intervalsduring a nun, 5 mL of the filtrate was taken out and2 Experimentaldiluted to determine the concentrations of Na2O andAl2O3 by ICP-OES.2.1 MaterialsThe precipitation ratio (n) was calculated from theAll reagents, including methanol(99.5%，increase of MR according to Eq.(1)[3]:manufactured by Beijing Chemical Works), sodiumhydroxide (96%， from Beijing Chemical Reagents力= R-R(1)Company), aluminum hydroxide (with water contentbetween 32.0% and 35.0%， produced by Beijingwhere Ro denotes the caustic ratio of initial solution andChemical Reagents Company), were of analytical purity.R。denotes the caustic ratio of the solution afterHigh-purity Milli-Q water, with a resistivity of abovedecomposition.18.2 MQ2:cm at ambient temperature, was used in allexperiments. The Al(OH)3 seeds, with an average3 Results and discussiondiameter of 29.6 um, were produced using methanoldecomposition method,3.1 Effect of reaction temperatureThe solubility of alumina in sodium hydroxide2.2 Preparation of spent Bayer liquorsolution greatly depends on temperature. The effect ofThe spent Bayer liquor with Na2O concentration oftemperature on R, was investigated in this research. The175.0 g/L and MR of 3.0 was prepared by dissolving aexperiments were performed with Vnmchan:V5ohutio of 1:1certain amount of Al(OH)3 into hot sodium hydroxideand a seed coefficient of 2.0. The temperatures weresolution in a polytetrafluorethylene vessel. The solutioncontrolled to be below the boiling point of methanol. Thewas filtered twice and reserved for use in an oven at aresults are shown in Fig.2 and Fig.3.constant temperature of80 C.from Fio ? that MR increases sharplywith中国煤化工. Large gap exsts2.3 Precipitation reactor and procedurebetweCNMH(11.7 for40 C and，Fig.l ilustrates the experimental apparatus used in.3 f山icopouvcly. The distinctionthis work. The batch reactor used was a three neck flask.between 40 c and 50 C could be the Co- efects ofA two-blade mechanical sirrer was used to stir thesupersaturation degree which favors AI(OH)3 precipitationZHANG Ying, et al/Trans. Nonferrous Met. Soc. China 20(2010)s165-s168s167Table 1 ffcts of volume ratio of methanol to spent Bayerliquor on R= 40V:K2R,(12 h)R。(24 b)-60C0.5:13.924.0710l:19.8611.691.5:111.4512.982.0:111.5913.59experiments was 2.0.It can be seen from Table 1 that, MR is greatlydependent on the amount of methanol and it is25 30 35remarkably increased with the increase of V:Vz,Time/hespecially when the ratio is lower than 1.0. MR valuesFig.2 ffets of temperature onRare all above 10 when V:Vz is not less than 1:1 after 24 h.When the volume ratio is higher than 1:1， furtherincrease of MR becomes less appreciable. There is no7S十:much difference between 1.5:1 and 2:1. The most。70probable explanation for this observation is that theincrease of methanol not only intensifies the dilutioneffect, which leads to the decrease of the amount ofg 60water molecules per unit volume, but also increases thebinding of solvent molecules, which decreases theamount of free water molecules used to dissolve Na2O1一30Cand Al2O3[13]. They both promote the precipitation of●一40C4..- 60公Al(OH)3. Undoubtedly, a higher MR must be weighedagainst a higher cost of raw materials and higher energy406 - 5101520253035consumption for recycling methanol. With acomprehensive consideration, a volume ratio of methanolFig3 Effects of temperature on precipitation ratioto spent Bayer liquor of 1:l was selected.at low temperature and mass transfer which favors3.3 Effect of seed coefficientsAl(OH)3 precipitation at high temperature. It appears thatIn the seeded precipitation process of supersaturatedsupersaturation plays more significant role than masssodium aluminate solution, a large amount of seeds weretransfer. MR gradually increases as temperature increases,added, which can reach a seed coefficient of 2.0. Thisand reaches platforms after 24 h. The highest MR is 12.5means that double amount of Al(OH)3 by mass is circledat30CandthelowestMRis7.1at60C.in this process. The effect of seed cofficients which is inCorrespondingly, the solution reaches the highestthe range from 0.5 to 3.0 is also investigated in this study.precipitation ratio of 76% at 30 C and lowestOther conditions are V:V2=1:l, temperature of 40 Cprecipitation ratio of 58% at 60 C. From these results, it and reaction time of 24 h. The corresponding results areis clear that in order to obtain a caustic solution with MRshown in Table 2.higher than 10, the temperature should not be higher than40 C. In the following experiments, the temperatureTable 2 Effects of seed coefficients on R.was fixed at 40 C and the reaction time was 24 h.Seed coeficicntR.(12 b)R(24 h)_0.57.317.833.2 Effect of volume ratio of methanol to spent Bayer1.09.7310.62liquor2.0Due to the difference in physicochemical propertyand ability to dissolve Na2O and Al2O3 between water3.0 .12.4012.96and methanol[12], the volume ratio of methanol to water中国煤化工is an important factor. In this work, the volume ratio ofIHCNMHGble 2 that seed .methanol to spent Bayer liquor (V:V2) was in the rangecofficlem grcaly allecls une MK ana precipitation ratio.from 0.5:1 to 2.0:1 and the corresponding results areWith a seed cefficient no less than 1.0, the ultimate R,shown in Table 1. The seed coefficient in thesecan be higher than 10. It has been known that fragmentss168ZHANG Ying, et al/Trans. Nonferrous Met. Soc. China 20(2010) s165- -s168produced by micro-abrasion on seed surface is the originreadily distilled from the liquor and recycled whilst thefor the secondary crystal nuclei. Consequently, seedscaustic liquor with high MR can be used to treat redreduce the resistance of crystal formnation and shorten themud.induction period. Because more seeds mean largerThe experiments have shown that many factors,surface area, higher seed coefficient leads to higherincluding the reaction temperature， time, methanoleventual MR.amountand seed coefficient influence the final causticratio. The optimum conditions are: an equal volume of4 Product characteristicsmethanol to spent Bayer liquor, 1.0 seed cefficient, 40C and 24 h. Under these conditions, the final MR canFrom the above mentioned experiments, thereach a value higher than 10. XRD spectra indicate thatoptimum condition to recover alumina from spent Bayerthe precipitate is Bayerite type of aluminum hydroxide.liquor by methanol was mixing the spent Bayer liquor(175.0 g/L Na2O, MR 30, and seed coefficient 1.0) withReferencesmethanol of the same volume at40 C for 24 h.The precipitated product was characterized by[] WANG Er-xing, LIU Jiao-ping, WU Fu-yun. The application ofmeans of XRD. The XRD result exhibits a typicalA(OH)3 in papermaking and organic material fields [机Non-Meallie Mines, 199, 22(5): 27- 29. (in Chinese)Bayerite type of aluminum hydroxide, as shown in Fig.4.[2] SLEPPY W C, PEARSON A, MISRA C, MACZURA GNon-maeallurgical use of alumina and bauxitc [] Light Metals, 1991:117-124.(间)[3] BI Shi-wen. The alumina prodution proces [M] Beijing; ChemicalIndustry Press, 2006. (in Chinese)[4LIU Wan-chao, YANG Jia-kuan, XIAO Bo. Recovering iron andpreparing building material with residues fom Bayer red mud小The Chincse Journal of Nonferrous Mctals, 2008, 18(): 187-192.(in Chinese)[5] KLAN P. JCSOBA [R].1971, 3: 163-173.[6] ZHOU Jie-fang, CHEN Wan-kun, GU Song qing, YIN Zhong lin,YANG Tian-xi. Hydrothermnal treatment of Bayer red mud fromGuangxi Filiale of CHALCO [R]. Guangxi Filiale of CHALCO,Mwlmtmn n1989. (in Chinese)[7] SHAREN B C. The crsalization of sodium aluminate [C]/ LU(b)Wen-qi. Chemistry and Process of Alumina. Beijing: China IndustryPress, 1964: 48- -54.[8] GU Song-qing, YIN Zhong-lin, BAI Wan- quan, QI Lijuan, HANDong-zhan. A method of Bayer mother liquor exraction: China,200610140858.3 [P]. 2006-10- 13. (in Chinese)[9WANG Xue, ZHENG Shili, ZHANG Yi. Decomposing sodiumaluminate by solventing out process to prepare aluminium hydroxide0 Noferrous Metals (Extractive Malurgy), 2008(1); 18-21. (inChinese)[10] WANG Xue. ZHENG Shi-li, ZHANG YL. Preparation of aluminumhydroxide with dssolution of sodium aluminate in methanol-watersolvent [切Chinese Joumal of Process Engineering, 2008, 8():01020304050607809072-77. (in Chinese)20/(*)[1] ZHANG Ying, ZHENG Shi-ti, DU Hao, XU Hongbin, WANGShao-na, ZHANG Yi. Improved precipitation of gibsite fromFig.4 XRD spectra of Bayerite standard and product preparedsodium aluminate solution by adding methanol [0]. Hyromcailurgy,2009, 98(1/2): 38-44.at optimum condition: (a) Product; (b) Bayerite standard[12] WILLIAM F L. Solubilities [M]. Stamford: American ChemicalSociety, 1965.5 Conclusions[13] BORISSOVA A. DASHOVA z, LAI x, ROBERTS K J. Examinationof the semi-batch crysallization of benzcopbenone from sauratedThe addition of methanol deepens the crystallizationmethanol solution via aqueous antisolvent drowning-out aof spent Bayer liquor, which has the potential to obtainmonitored in-process using ATR FTIR spectroscopy [U] CrystalGrowth and Desien 2004. 4(5): 1053-1060.high MR (> 10) caustic solution. Methanol can be中国煤化Ited by FANG Jigbua)FYHCNMHG