Preparation of single-phase ammonium dimolybdate by combination process

RARE METALSVol. 31, No.5, Oct. 2012, p.517DOI: 10.1007/s12598-012-0550-3Preparation of single-phase ammonium dimolybdate by combination processZHANG Bao,XIA Xiaomei.ancLI OianSchool of Metallurgical Sclence and Engineering, Central South University, Changsha 410083, ChinaReceived 25 October 201 1; received in revised form 12 January 2012; accepted 24 March 2012◎The Nonferrous Metals Socicty of China and Springer-Verlag Berli Heidelberg 2012AbstractA novel method for the preparation of single phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in-fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NHz/Momolar ratio, and stiring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ay diffrac-tion XRD) analysis and chemical analysis show that the product is single phase ammonium dimolybdate, and no impurity phases exist. Thescanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no aggiomeration between particles.Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the mainphases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidificationproduct can be used as a raw material to produce single-phase ammonium dimolybdate.Keywords: single-phase ammonium dimolybdate; combination process; crystallization rate; phase cormposition; total molybdenum recovery1 Introductioncontent of impurities, owing to the dissolved impurities to-gether with the separated filtrate returning to the reactionMetallic molybdenum (Mo) is a refractory metal com-system completely. Moreover, this technology has otherbined with remarkable high temperature strength, highproblems such as low recovery, long production cycle, andthermal and electrical conductivity, high corrosion resis-needing to recrystallize more than twice to increase recoverytance, high elastic modulus, and low coefficient of thermal[15- 16]. Combination process is a relatively new techniqueexpansion [1- 3]. Because of these outstanding properties,to produce ammonium dimolybdate. The improvementmetallic molybdenum is utilized in a variety of applications,comparing to the traditional evaporation crystallization issuch as electronics, metallurgy, aerospace, lighting technol-that after recovering element molybdenum in the form ofogy, and coating technology [4 -7]. The production of me-ammonium molybdate by adding acid into separated filrate,tallic molybdenum is a complicated physical and chemicalthe residual solution with dissolved impurities is not re-process including calcinating， deoxidizing, and so on.turned to the reaction system. The recovered ammoniumTherefore, the raw material plays a key role in the manufac-molybdate can be used as raw material. Consequently, theturing process [8]. Ammonium dimolybdate is the chief rawproduct of combination process is low impurity, and there ismaterial to producc mctallic molybdenum due to low con-no need to recrystallize due to the high total molybdenumtent of impurities, uniform particle size, and good particlerecovery of acidification [17]. In addition, combinationflowability [9- 10]. The production of mtallic molybdenumprocess has other advantages, such as easy control of pro-is mainly accomplished in two ways all over the world [1].duction process, less agglomerated particles, and narrowAmmonium dimolybdate is first reduced to molybdenumgranularity distribution. Although the production of ammo-trioxide and the latter is then reduced in the second step tonium dimolybdate has been widely applied in China onmetallic molybdenum. The other is the direct reduction ofcommercial scale, there are few researches on combinationammonium dimolybdate by a single stage.process. Meanwhile, few literatures have reported the effectUp to now, evaporation crystallization has been the es-of reaction conditions on the crystallization rate and phasetablished method for the production of bulk ammonium di-compoition!中国煤化工e-phase ammoniummolybdate in China [12- -14]. Recent studies show that theIn this paYHevaporation crystallization with closed cyclc leads to highdimolybdate. CNMH G was ivesigtede.Corresponding author: ZHANG BaoE-mall: csuzb@vip.163.com包Springer518RARE METALS, Vol. 31, No.5, Oct. 2012The effects of reaction temperature, reaction time, initialwere added into the beaker while stirring the content of themolybdenum concentration, initial NH3/Mo molar ratio, andbeaker at a certain speed. Reaction time began from initialstiring speed on the crystallization rate and phase composi-addition of ammonia solution. The supemnatant was vacuumtion of product were studied systematically. Moreover, asfiltered after cooling. The acidification was performed in aacidification was the key of combination process, the total150 ml beaker immersed in a thermostatic water bath. Nitricmolybdenum recovery and the phase composition of acidi-acid was dropped into the beaker containing 100 ml ammo-fication product were studied.nia reaction filtrate with a fixed stiring speed of 100 rmin 'at 50 °C. The pH value was controlled during the reaction.When the required pH value was reached stably, the slurry2 Experimentalwas filtered. The dissolved molybdate of acidification fil2.1 Materials and analysistrate was recycled by solvent extraction or ion exchange,The industrial ammonium molybdate used as raw mate-and the residual solution could be used to produce ammo-rial was procured from Jiangxi Copper Corporation, Jjiangxi,nium nitrate. The filter cakes of ammonia reaction andChina. The X-ray diffraction (XRD) analysis of industrialacidification were dried prior to subsequent ICP and XRDammonium molybdate is shown in Fig. 1. Except for theanalyses. Figure 2 shows the flowsheet of the experimentalcharacteristic peaks of ammonium tetramolybdate, there areprocedures.also the characteristic peaks of ammonium trimolybdate inAmmonium molybdatethe diffraction patterm. Ammonia solution and nitric acidused were of analytical grade, and distilled water was usedAmmonia reactionin experiment.25 r●(NH,)Mo,OnFiltrate Ammonium dimolybdate20 t▲(NH)2Mo,Ow台15Acidification10-↓Ammonium molybdate Acidification filtrates|Recycle山Fig. 2 Flowsheet of combination process of ammonium dimo-10203lybdate production20/(°)Fig. 1 XRD pattern of the industrial ammonium molyb-3 Results and discussiondate3.1 Ammonia reactionThe phase composition was determined by XRD (D/max2550, Rigaku, Japan) with Cu Ka X-ray radiation at 40 kV3.1.1 Effect of reaction tempcratureand 250 mA in the scanning range of 5°~ 50°. The concentra-The reaction temperature effect on the crystallization ratetion of element was analyzed by inductively coupled plasmaand phase composition of product was examined in theatomic emission spetroscopy (ICP-AES, PS-6, BAIRD,range of 50~ 90 °C for 3 h with the initial molybdenum con-USA). The microstructure was observed by a scanning elec-centration of 310.00 gL-, the initial NHz/Mo molar ratio oftronic microscope (SEM, JSM- 5600LV, JEOL, Japan).2.77, and the stirring speed of 100 rmin-. The results areshown in Table 1 and Fig. 3.2.2 Experimental proceduresAs shown in Tablc 1, the crstallization rate increasesThe ammonia reaction was carried out in a 250 ml beakerwith increasing reaction temperature. However, by increas-immersed in a thermostatic water bath equipped with a digi-Table 1 Effect of reaction temperature on crystallizationtally controlled thermometer. Firstly, the required amount ofdistilled water was put into the beaker and heated to a pre-Reaction temp中国煤化工)300determined temperature. Then, 50 g industrial ammoniummolybdate and the required amount of ammonia solutionCrystallizationYHC N M H G.9599.1298.69空SpringerZHANG Bao, et al, Preparation of single phase ammonium dimolybdate by combination process519●(NH)Mo,O,●(NH)Mo2O,▲(NH),Mo,O2&▲(NH)oMo,O2+90°C80°C70°C60°CA semuhnA50 °C2050300201(9)Fig3 Effect of reaction temperature on phase compositionFig. 4 Effect of reaction time on phase composition(XRD patterns)ing the reaction temperature over 80。C, the crystallizationevaporated increases with the reaction time extending. Morerate is almost 100%. The solubility of ammonia becomesammonium dimolybdate is crystallized due to the decreasesmaller with the increasing reaction temperature; thus, am-of solution volume. Figure 4 shows the product reacted for 1monia volatilizes in greater quantities. The reduction oh has main phase with ammonium dimolybdate and a smallammonia leads to produce more ammonia and ammoniumamount of secondary phase with ammonium heptamolyb-dimolybdate by decomposing ammonium monomolybdate.date. The phases of products reacted for 2~4 h are single-The main reaction is expressed as follows:phase ammonium dimolybdate, and no impurity phases exist.(NH4)2Mo4Oj3+6NH2OH=4(NH4)2MoO4+3H2O(1Accordingly, a reaction time of3 h is selected to investigate2(NH)MoO4+H2O=NH)2Mo2O+2NH4OH(2)the effects of other factors on the ammonia reaction process.When the temperature is over 80。C, there is lttle solu-3.1.3 Effect of initial molybdenum concentrationTablc 3 and Fig. 5 show the effect of initial molybdenumtion left. The dissoluble impurities migrate into product in-concentration on the crstallization rate and phase composi-stead of being removed with solution, which results in thetion of product at 70 °C for 3 h with the initial NH3Mo mo-relatively high impurity content of product. Figure 3 revealslar ratio of 2.77 and the stiring spced of 100 rmin-.that the product reacted at 50 °C is composed of ammoniumdimolybdate and ammonium heptamolybdate. The phases ofTable 3 Effeet of initial molybdenum concentration on crysta-products reacted at 60~90。C are singlc-phase ammoniumlization ratedimolybdate, and no impurity phases exist. Based on theseInitial molybdenum232.50 253.64 279.00 310.00 348.75results, 70 °C can be considered as the optimal reactionconcentration/(gL )temperature.Crystallization rate/% 41.48 49.49 71.70 86.95 98.443.1.2 Effect of reaction timeThe relationship between crystallization rate and phase com-●(NH)2Mo2O,position of product and reaction time was studied at 70 °C,▲(NH.)sMo2O2sawith the initial molybdenum concentration of 310.00 gL",348.75 gL-the initial NHy/Mo molar ratio of 2.77, and the stiring speedof 100 rmin '. The results are shown in Table 2 and Fig. 4.310.00gLTable 2 indicates that the rystallization rate becomeshigher with the increase in reaction time. The amount of279.00gL-ammonia volatilized increases with the reaction time ex-232 50gLtending. More ammonium dimolybdate is generated becauseof the ammonia loss. Moreover, the amount of water大u232 50gL-1Table2 Effect of reaction time on rstallization rate40Reaction time/h1_2中国煤化工Fig. 5 Effleentration on phaseCrystallization rate/%31.51 65.70 86.9599.32comp;YHCNMHG包Springer.520R4RE METALS,VoL.31, No. 5, Oct 2012Table 3 shows that the crystallization rate increases withthe production conditions of ammonium dimolybdate andincreasing initial molybdenum concentration. The final mo-ammonium heptamolybdate are discussed. The product islybdenum concentration decreases with the decrease in ini-ammonium dimolybdatc, when the initial NH3/Mo molar ra-al molybdenum concentration under the same reactiontio is above 1.86. The crystallization rate is determined byconditions, so more product is dissolved instcad of crystal-the amount of ammonium molybdate, as the amount oflizing. Therefore, the crystallization rate decreases. Mean-ammonia is relatively excessive. Because the added ammo-while, more energy is needed with small initial molybdenumnium molybdate is constant, the crystallization rate changesconcentration to reach the same crystallization rate. Figure 5little. The product is ammonium heptamolybdate with theshows that the product with initial molybderum concentra-initial YH3/Mo molar ratio of 1.41. The production mecha-tion of 232.50 gL-' is composed of ammonium heptamo-nism is different between ammonium dimolybdate and am-lybdate and ammonium dimolybdate. The phases of prod-monium heptamolybdate; as a result, the crystallization rateucts with initial molybdenum concentration in the range ofdecreases obviously. Figure 6 shows the phases of products253.64~348.75 g:L- are single-phase ammonium dimolyb-with the initial NHyMo molar ratio in the range ofdate, and no impurity phases exist. Therefore, the optimum1.86~3.22 are single-phase ammonium dimolybdate, and noinitial molybdenum concentration is determined to beimpurity phases exist. The product with the initial NHz/Mo310.00 g:L-' to minimize energy consumption.molar ratio of 1.41 has main phase with ammonium hepta-3.1.4 Effect of initial NH3/Mo molar ratiomolybdate and a small amount of secondary phase withThe experiment for evaluating the effect of initialammonium pentamolybdate. The optimum initial NHy/MoNH3/Mo molar ratio on the crystallization rate and phasemolar ratio is determined to be 1 .86 to minimize ammoniacomposition of product was conducted at 70。C for 3 h withconsumption.the initial molybdenum concentration of 310.00 gL+ and3.1.5 Effect of strring speedthe stiring speed of 100 rmin '. The results are shown inThe effects of stiring speed on the crytallization rate andTablc 4 andFig. 6.phase composition of product at 70 °C for 3 h with the initialThe initial NHz/Mo molar ratio is an important factor onmolybdenum concentration of 310.00 gL~ ' and the initialthe crystallization rate and phase composition of product.NH/Mo molar ratio of 1.86 are shown in Table 5 and Fig. 7.Table 4 shows that the change of initial NH3/Mo molar ratioTable 5 shows that the crystallization rate increasesin the range of 1.86~3.22 has no obvious influence on theslightly with increasing stiring speed. Stirring benefits thecrystallzation rate. However, the crystallization rate de-diffusing of solvent molecular and the volatilization of am-creases significantly with the initial NH3/Mo molar ratio ofmonia, so the crystallization rate increases. Meanwhile, stir-1.41. This result is in agreement with a study [18] in whichring improves the dispersity of product particle, which de-creases the particle agglomeration. However, the high stir-Table 4 Effect of initial NHyMo molar ratio on erystallizationring speed leads to more energy consumption. Figure 7rateInitial NH/Mo molar ratio 1.41 1.86 2.31 2.77 3.22Table5 Efect of stirring speed on crystallization rateCrystallization rate/%76.90 85.23 84.43 86.95 84.00Strring speed/rmin) 80 100 120 140 160Crytallization rate/%84.21 85.23 85.82 87 2290.7- ;●(NH4)2Mo2O,▲(NH)Mo,O2，■(NH)AMo;O,●(NH,)Mo,O,::.2.2.160 rmin-'2.77.140 rminr120 rmin1.86100 rmin小众1.4180 rmin:|12050201()0中国煤化工Fig. 6 Effect of initial NHy/Mo molar ratio on phase composi-tion (XRD patterns)Fig.7 EffeceMYHC N M H Gmposition(XRD patterns)包SpringerZHANG Bao, et al, Preparation of single-phase ammonium dimolybdate by combination process521shows that the phases of products with different stirringcrystallinity. In addition, the main phases are the same asspeed are single-phase ammonium dimolybdate, and no im-those of raw material. The result indicates that the recoveredpurity phases exist. Therefore, the stirring speed of 100ammonium molybdate with final pH value in the range ofrmin' is chosen.1.0-~2.5 can be used as a raw material to produce sin-gle-phase ammonium dimolybdate. Considering the total3.2 Acidificationmolybdenum recovery, the best result is obtained when theIn order to study the effects of final pH value on the totalfinal pH valucis 1.5.molybdenum recovery, a series of experiments were carriedout at 50。C with the stirring speed of 100 rmin . The re-.3 Characterization of the productsults are shown in Table 6 and Fig.8.Under the optimum conditions of ammonia reaction, thecrystallization rate of product is 85.23%. Figure 9 displays theTable 6 Effect of final pH value on total molybdenum recov-XRD pattern of product. As shown in Fig. 9, the diffractionerypeak positions of product are the same as those of ammo-Final pH valuc0.51..52.0niumdimolybdate shown in PDF card 37-0379. It revealsTotal molybdenumthat the product is single-phase ammonium dimolybdate, and98.1398.72 99.40 99.03 99.02recovery/%no impurity phases exist. Mcanwhile, the XRD pattern ofproduct with sharp diffraction pcaks and high peak intensity, (NH)2Mo,O;indicates that the product has a high degree of crystallinity.▲(NH)2Mo,Ow .ile。_ 众in m Rawnaterial3530pH=2.5|台25pH=2.02 20pH=1.5H-10pH- 0.510205020137-03 79 (NH)Mo2O,Fig. 8 Effeet of final pH value on phase composition(XRD patterns)201(9)Table 6 shows that the total molybdenum recovery firstFig. 9 XRD pattern of single phase ammonium dimolybdateincreases and then decreases with the increase of final pHvalue. The total molybdenum recovery reaches a peak valueof 99.40% when the final pH value is 1.5. The additionThe chemical analysis shows the molybdenum content ofamount of nitric acid is the key factor of total molybdenumproduct is 56.38%. The molybdenum content of single-recovery. By adding nitric acid, the following reaction canphase ammonium dimolybdate is 56.44%. The result showsoccur in the solution:that the ammonium dimolybdate content of product is 99.9%.4(NH)MoO4+6HNO3=Figure 10 shows the SEM image of product. The particle(NH4)2Mo2O132H2O+6NH4NO3+H2O(3)size is uniform and good particle dispersion appears. TheThe total molybdenum recovery increases as more mo-morphology of product particles takes on irregularity and nolybdenum is reacted with nitric acid to produce ammoniumagglomeration between particles exists.The acidification experiment at 50 °C with the final pHmolybdate. The molybdenum cannot be precipitated com-pletely with the lack of nitric acid, whereas the precipitate isvalue of 1.5 and the stirring speed of 100 rmin-' was con-redissolved, as the added nitric acid is more than needed.ducted, and the total molybdenum recovery reached toFigure 8 shows that the XRD patterm of product with final99.40%，Figure 11 shows the phase comparison between thepH value of 0.5 is unsatisfactory with irregular diffractionacidification product and the raw material. As shown in Fig.peaks, high background value, and low peak intensity. The11, the main phases of acidification product are the same asXRD patterms of products with final pH value in the range ofthose of raw中国煤化工nes that the acidi-1.0~2.5 show sharp diffaction peaks and high peak intensity,cation produ:rial to produce sin-which indicates that all the phases have a high degree ofgle-phase amMYHCNMH G'包Springer.522RARE METALS, VolL. 31, No. 5, Oct 2012It ensures that the acidifcation product can be used as rawmaterial to produce single-phase ammonium dimolybdate.AcknowledgementThis work is financially supported by the National Natu-ral Science Foundation of China (No.51072233).References1] Primig S., Leitner H, Clemens H, Lorich A, Knabl W., and5 umStickler R., On the rerstallization behavior of technicallypure molybdenum, Int. J. Refract. Met. Hard Mater, 2010,Fig. 10 SEM image of single-phase ammonium dimolybdate28 (6): 703.2] Abbas Q, and Binder L, The electrochemical dissolution of●(NH)Mo2O;molybdenum in non-aqucous media, Int. J. Refract. Met.▲(NH)Mo;OnoHard Mater, 2011, 29 (4): 542.[3] Tan W, Guo M.X, Cao L.F, Shen K, and Wang M.P, Theannealingcharacteristics of pure molybdenum bars manufac-tured by a modified technique, J. Alloys Compd, 2008, 462Raw material(1-2): 386.4] Ohser-Wiedemann R., Martin U., Seifert HJ, and Miller A,登Densification behaviour of pure molybdenum powder byspark plasma sintering, Int. J. Refract. Met. Hard Mater,2010, 28 (4): 550.pH= 1.55] An G, and Liu GJ, Preparation of ultramicro molybdenumcarbide powders and study on wear properties of their coating,Rare Met, 2011, 30(3): 262.14050》) 26201(9)6]Wang X.Q, He X.X, and Guo H.L., Influence of Mo on themicrostructure and mechanical properties of TiC-based cer-Fig. 11 Comparison of XRD patterns7] Song x, Wang L, Liu Y, and Ma H.Q, Precipitation char-acteristics and La effects on precipitates of a nev4 Conclusion22Cr-14W-2Mo superalloy, Rare Met, 2010, 29 (2): 132.8] Sun YJ, Xie H, and Sun J. Influence of ammonium moThe experiment results show that single-phase ammo-lybdate precursor on Mo powder preparation and workingnium dimolybdate can be prepared by combination processproperties, Mater. Sci. Eng. A, 2008, 483- 484 (1-2): 168with industrial ammonium molybdate. The crystallization9] Mendenhall R.G, Chereslowsky M.J, and Scheftic J.L.,rate of product increases and the phase composition trans-Method for Producing Fine Size Yellow Molybdemum Triox-ide. Powder, United States Patent, 5185133, 1993.forms from ammonium molybdate mixture to single-phase[10] Tuominen S.M, Preparation and sintering of fine molybde-ammonium dimolybdate with the increase of reaction tem-num powder, Powder Technol, 1981, 30 (1): 73.perature, reaction time, and initial molybdenum concentra-[11] Manukyan K, Davtyan D., Bossert J, and Kharatyan S, Directtion. The crystallization rate and phase composition ofreduction of ammonium molybdate to elemental molybdenumproduct change obviously with the initial NHyMo molar ra-by combustion reaction, Chem. Eng J, 2011, 168 (2): 925.12] Li w.C, Production practice of large crytalline ammoniumtio shifting in the range of 1.41~1.86. The effect of stiringdimolybdate, Chin. Nonferrous Met, 2007, (4): 40.speed is not significant. The optimum experimental condi-13] Li F, Production process of high water solubility ammoniumtions are determined as 70。C, 3 h, initial molybdenum con-dimolybdate, Shanxi Chem. Ind, 2007, 27 (5): 41.centration 310.00 gL"', initial NH/Mo molar ratio 1.86,[14] Li x.W, Kao Y, and Yang WJ, Modifying traditional de-vice and improving products quality of ADM and AHM,and stirring speed 100 rmin~'. Under the conditions, theChin. Moly. Ind, 2006, 30 (6): 26.crystallization rate of product can achieve 85.23%, and the[15] Xiang T.G, Molybdenum Metalurgy, Central South Univer-product is single-phase ammonium dimolybdate. Moreover,sity Press, Changsha, 2002: 127.the particle size is uniform and no agglomeration between[16] Wang z.C, Study and production of ammonium heptamo-particles exists.lybdate for reagent with ammonium quadvimolybdate, Chin.Additionally, in the present work, the final pH of acidif-Moly. Ind, 2000, 24 (5): 27.[17] Zhang.Molybdenuim Metal-cation is determined to be 1.5 as the total molybdenum re-中国煤化工g 2005: 208.covery reaches a peak value of 99 40%, and the main phases[18] Li H.G,IHC N M H Geallurgical Industyof acidification product are the same as those of raw material.包Springer