Recovering germanium from coal ash by chlorination with ammonium chloride

RARE METALSvo,2I,No.4,Dec2002,p.278Recovering germanium from coal ash by chlorination with ammoniumchlorideZHU Guocai SHI Wenzhong), and TIAN Jum h1)Institute of Nuclear Energy Technology. Tsinghua University. Beijing 102201, Chinachang 340000, China(Received: 20m2-01-12Abstract: A new process of enriching germanium from coal ash was developed. The process involves in mixing the coalash and ammonium chloride and then roasting the mixture to produce germanium chloride that is then absorbed by dilutehydrochloric acid and hydrolyzed to germanium oxide. The germanium recovery reached to 80. 2% at the optimum condition: mass ratio of NH, CVcoal ash is 0.15, roasting temperature 400C and roasting time 90 min.Key words: germanium; recovery coal ash; chlorination; lignite[This project is financially supported by the National Nature Science Foundation of China (No. 598040) and(No.50274046)1 Introductioneconomic reasons. Zhu Guocai et al.(5-8] haveGermanium and germanide are important raw been working on chlorination of rare earth ores bymaterials for the semiconductor, information and salts such as NH,Cl or NaCl, many useful resultsphotoelectron material, and so on [1, 2]. With the have been achieved for chlorination of rare earth.development of information technology and A new process of enriching germanium from coalcommunication, the consumption of germanium ash is proposed on the basis of RE chlorinationincreased rapidly in recent years. Whereas there is investigation in this paper. The new process hano individual deposit of germanium in the world, the advantages of simplicity and low operationmost germanium exists in other ores such as zinc cost, and it is favorable for the environment pror zinc- lead ores Recovery of germanium in Chna mainly comes from the zinc smelting. But 2 Experimentalmost germanium resources in the world exist inor lignite in practice. To date, several 2.I Roasting principlpossible ways have been proposed for the recov-The Yunnan lignite of China contains 0.005%ery of germanium from coal ash, for example, 0.02% of germanium. Most of germanium existsextraction by DHYA [3], precipitation with tannin, as germanide such as sulfide, oxide and organicchlorinating distillation etc [4]. However, those germanide. These germanides would be invertedmethods have not been universally used in the to oxide in burning the lignite. The germanide suhproduction of germanium for technical and fide mainly exists as the Ges, ges, and gesCorresponding author: ZHU GuocaiE-mall: zhuge@ mail. tsinghua.edu.中国煤化工CNMHGZhu G C et al, Recovering germanium from coal ash by chlorination with ammonium chloridethey can be converted each other 191decomposed to NH, and HCI2GeS, + Ge S,+S+> 2GeS+S) L4Cl-32C-NH3t+HC1↑5)The resulting HCl would chloridize the metalGes begins to be oxidized to GeSO4 at 350 Coxides(IL, III and Iv valences)in the coal ash asGes+20 =Ge sO aand further be oxidized to geO, at above 350 C.MO+2HCl=MCI+H,O6)3M+2Hc=3Mo+H0GeO is oxidized to GeO, at 550 C2Ge 0+0=2GeO,MO2+2HCI= MCl+HOwhen the mixture of NH,CI and coal ash is The gibbs free energy of these reactions in chlo-heated, the NHCl in the mixture would be easily ridizing coal ash could be calculated in tableTable 1 Tbe Gibbs free energy of possible chlorinating reactions in the coal ash [101Chlorinating reactions400K1/2 GeO+2HCl=l/2 GeCL+H20-197511.17112 SiO2+2HCl=1/2 SiCl+H20855096.40106.901/3 Al,O3+2HCI=2/3 AICI3+H2010540109701/3 Fe, O,+2HCl=2/3 FeCl,+H,O40.40173V2O5+2HCl=2/3 VOCl3+H,O29.39Ca0+2HCl=CaCl2+H0-173.80148.20125.80MgO+2HCl=Mg Cl2+H2O-49200.10MoO+2HCl=MnCl2+H,O104.3077,40-51.80The results in table I show that the Gibbs free Therefore the dilute hydrochloric acid can notenergy of Ge, Ca, Mg, and Mn oxide are negative only absorb the NHa and surplus NH,CI in thevalue and that of Si, Al, Fe and v oxides are chlorination roasting, but also separates outpositive value. It illustrates that the Ge, Ca, Mg, enrichment of germanium by hydrolysis of GeCldand Mn oxides could be easily chloridized while 2.2 Materials and analytical methodsthe Si, al, v, and Fe oxides could not be chlori-dized under the calculated temperature range. TheThe coal ash sample was from Lincang, Yun-results further approve that the chlorination of nan Province; its content of GeO2 is 0.63%.Am-coal ash with NH,Cl would selectively chloridizemonium chloride used in enrichment was induS-the metal elements and elementary separation of trial material. The chlorination roasting exper-purities Si, Al, V, and Fements were carried out in a quartz tubular fumaceCoal ash of 10 g and determined amount of am-The boiling point of GeCl is only 83 1C monium chloride were mixed by grinding each(3561k), so it is easily evaporated in chlorination time. The mixture was fit into pot and put it intoprocess. At the same time, GeCL is easily hydro- the tubular fumace. The furnace was heated, andlyzed to GeO in hydrochloric acid with a con- at the same time, nitrogen(n2)was inlet to the tu-centration lower than 6 molL:bule to take away the GeCl formed by chlorinaGeCl+2H,O-GeO24 +4HCI(9) tion. The GeCL4 was absorbed by dilute hydro-I蝨■翻L::中国煤化工CNMHGRARE METALS, VoL 27, No 4, Dec 2002chloric acid and hydrolyzed to GeO2. The NH, the recovery ratio of germanium could be calcu-and the surplus NH4Cl were also absorbed by di- lated. The content of germanium was analyzed bylute hydrochloric acid.the phenlyfluorone spectrophotometryBy analyzing the germanium content of calcineFlow sheet of the process is shown in figure 1Coal ashMixtureRoastingHydrolysisRecovered Ne c]FiltrationHGcO, enrichmentFigure1 The eperimental flow sheet of recovering germanium from3 Results and discussionmation and evaporation of GeCl4. Thereforethe dosage of NH4Cl could be determined to3.1 Eiect of CIl dosagebe15%Coal ash of 10 g is mixed with different 3.2 Effect of roasting temperatureamount of NH Cl, and masted 90 min at 400C10 g coal ash(mp) and 1.5 g NH CI are weight-each time. The relationship between germanium ed respectively, mixed by grinding and roasted 90recovery ratio(Ge /%)and amount of NHCI min at different temperature. By determining themHA/g)is presented in figure 2.content of germanium in the calcine, the relationship between the recovery ratio and roasting tem-perature would be obtained as shown in figure 3emg"I5g0.51.01.52.02.53,0t=90 minFigure 2 The eect of NH Cl doser/t"450500The results in figure 2 show that the recoveryFigure 3 The effect of roasting temuperature on germanium recovery ratiratio increases with the increase of the dosage ofNH,Cl, and reaches the peak when mNHac equalsThe results in figure 3 indicate that a maximum1.5 g and then declines when mNHaci is over value is observed at the roasting temperature 400that the surplus Nh,CI will prevent the for- would not be suitable for the chlorination of ger-TH中国煤化工CNMHGZhu G C ef al., Recovering germanium from coal ash by chlorination with ammonium chloridemanium of coal ash. It can be explained that oxide. The germanium recovery reaches 80chlorination has not completed at low temperature the optimum condition: mass ratio of NH-Owhile the GeCl may be decomposed to geO at ash=0. 15, roasting temperature 400C and roastgh temperature. The optimum temperature in ing time 90 minthe experiment is400℃References3.3 Ehect of roasting timeThe experimental sample is roasted at 400C. Qiu G. W Recovering germanium and zinc from theand the relationship between the recovery ratio ofzinc oxide flue dust containing germanium P] Yungermanium and roasting time is shown in figure 4.an Metallurgy (in Chinese), 2000, 29(3): 17It could also be explained that the reaction would [2] Zhang S L,, Study on occurence mode of ger-not be completed at less than 90 min while sur-anium in lignite in Yunnan Bangmai Basin [J]plus roasting time would cause the further de-Deposit Transaction (in Chinese), 1988, 6(3): 29composition of GeCL4[ 3]Li YS,Li P and Liu G. H, a review on the reabroad Jiangsu Chemical industry(in Chinese)200028(4] LiY. S, Extraction of germanium from coal ash with10gdihydroxa mic acid []. Modern Chemical Industry=1.5 g(in Chinese), 2000, 20(8): 34.t=400℃[5] Zhu G. C, Tian J, Chi R, and Xu S M, Extractionof rare earth with NH CI masting from bastnasite40608010012014016ough ore [] Trans. Nonferrous Met. Soc. China nr/ minChinese2000,0(5):701Foure 4 The elect of[6] Zhu G. C and Chi R. A, A recovering method dfnre earth carbonate by roasting bastnasite concentBased on the above experiment, the optimumtrate with NH CI [Pl, Chinese patent, No, CNconditions of chlorination991061497ash are NH CI dosage 15%(mNa/m), roastingm如加G.C, ChiRa, and Tian J.eta, Recovery oftime 90 min and roasting temperature 400 Crare earth with NHC roasting from bastnasite J].The recovery of germanium could reaches 80.2%Nonferrous Metals(in Chinese), 2000, 52(1): 66.under the optimum condition. Therefore it is an[8] Zhu G C, Tian J, Chi R. A, and Xu S M, Theffective process to recover the germanium fromgreen chemistry progress on extraction of rare earthcoal ash.from bastnasite [], Progress in Chemistry (n Chinese)200,12:64 Conclusions[9] Zhou N. Z, Metallurgy of Rare Metals(in ChineseA novel process of enriching germanium fromIM] Metallurgical Industry Press, Beijing, 1988coal ash was developed. The process involvesmixing the coal ash and ammonium chloride and [10J Qu D J and Ying w.J. Handbook of Rare Metalsthen roasting the mixture to produce germanium(in Chinese)[M, Metallurgical Industry Press, Bei-chloride, which is then absorbed with dilute hydrochloric acid and hydrolyzed to germanium中国煤化工CNMHG