VI SHMMT I XVIII ENTMME- 2001 -Rio de Janeiro/Brazil

PROCESSING OF RARE AND NON-FERROUS METAL RA W MATERIALS USING MECHANICAL ACTIVATION

S. V. Chizhevskayc/, A.M. Chekmarev1, V.A. Mikhailov2, E.G. Avvakumov3

1Chair of R are and Dispersed Elements , D. Mendelcyev Univcrsity of Chemical Technology of Russia, Miusskaya sq., 9, 125047 Moscow, Russia, e-mail: chizh@rctu.ru, chekmarev@rctu.ru

2Chair of Inorganic Chcmistry, M. Lomonosov State Acadcmy of Fine Chemical Technology, Vernadskiy prospekt, 86, 117571 Moscow, Russia, c-mail: vamikh@orc.ru

3Institutc of Solid State Chemistry and Mechanochemistry, Siberian Branch of RAS, Kutateladze, 18, 630128 Novosibirsk, Russia, e-mail: avvakumov@solid.nsk.su

ABSTRACT

Mechanical activation has becomc a powcrt'ul and llcxihle technique for intensitication of treatment processes of various mineral raw materiais of rarc and nonferrous metais. ln the present papcr the studics of Russian scientists, including those performcd by thc authors, and some practical aspects of U1e acti vation i n high-cnergy apparatus of centrifugal-planetary type are discussed.

INTRODUCTION

Dccomposition and lcaching are thc stages requiring thc most cxpcnditurc of reagents, energy and time in processing tlow-sheets of rare and non-ferrous mineral raw materiais . Therefore, it is necessary to improve etTiciency of these stages.

Mcchanical activation is a promising method, which allows to improve technological parameters, to accelcrate U1e process, to increase Ule recovery of metal values and to reducc thc numbcr of processing stagcs. Mechanical activation not merely increases specific surface of solids but significantly aftects the structure by dcterioration and partia! destruction of crystal lattice forming dcfccts of various types. That lcads to an increase or reactivity of solids and also intluences on kinctics of subsequent treatment (Avvakumov, 1986; Boldircv et ai., 1983).

Thc application of mechanical activation allows not only to improve technical and economical rates of conventional tlow-sheets but also to involve lower-gradc and more complex raw materiais into Ule trcatment.

Currently, there are many cxamples of such innovations applied to mineral raw materiais of various types, some or them were dcscribed in monographs and rcviews (Avvakumov,19S6; Boldirev et ai., 1983; Chizhevskaya et ai, 1999; Kulebakin , 1988; Lapteva ct ai., 1982;

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Mechanochemical Phenomcna, 1971; and Yusupov,1981; Molchanov Zelikman et al.,l987)

Molchanov et al.,1988;

It is worth to underline that Ule efticiency of mechanical activation is to a large extent determined by a type of Ule devicc used as well as by regime of action of operating bodies on Ulc material subjected to treatment: abrasion, vortex, impact. For planetary mill the regime is determincd by a ratio of rotating rates of Ule bowl and the carrier. Mass ratio of operating bodies and treated material, weight and properties of a chargc, configuration of operating bodies etc also significantly affect the results of mechanical acti vation.

According to statistical model of grinding and activation in thc apparatus with milling bodies Yosel et ai., 1986,p.l 02; 111) an average pulse recurrence frcquency (t) of mechanical action on a particle is an import

S. V. Chizhevskaya, A.M. Chekmarev, V.A. Mikhailov, E.G. Avvakumov

preliminary mechanical activation decreases caking temperature and duration of the process, increases lhe erticiency of decomposition of cake and extraction of its soluhle components in course of suhsequent leaching and simplities preparation of a charge (Kulebakin, 191\1\; Lapteva et ai., 191\2; Mechanochemical Phenomena, 1971 ; Mulchanov and Yusupov, 191\1; Molchanov ct ai., 1988; Zelikman et ai., 1987). Mechanical activation of zircon charge with calcite (added at I :2 mole ratio) in presence of water (S:L = 1:1) during 5-7 min using planetary mill ensures total decompusition of the mineral hy just 2-h caking at 1000°C even without an addition ot· mineralizing agenl (CaCI2), whereas non-activated mineral reacts with CaC03 at satisfactory rate only at 1400-1500"C (Zelikman, et ai, 1979).

ln a numher of cases the technique enahles to avoid l'usion. Mechanical activation of zircon concentrate by planetary mill before lhe caking with K2SiF6 guarantees total subsequent decomposition at lower temperature. The decomposition of activated zircon starts at 580 "C and completes at 650 oc eluring 30 min, whcreas, oU1er conditions being equal, non-activated mineral lcnds itself to lhe decomposition only to 67 % (Zelikman et al , l982). Because U1e reaction belween soliel components of U1e charge occurs before liquid phase formalion (T -640 "C) and actually accomplishes hy U1en, it is possible to conduct the process by caking or briquett.ed charge containing activated zircon without risk o r melting o r lhe hriquettes .

INTENSU~ICATION OF SULFATIZATION

A signiticant resistance lo mineral acids and al kalis fcatures cassiterite, which is the major mineral of tin ores. Only partia! dissolution of the mineral using a mixture of HF and H2S04 is possible. According to (Shashura, 1966) total dissolulion of cassilerite (oblained from various layers) in H2S04 was allained at 310-325"C in 170-300 h elepeneling on lhe layer of origin. At the lemperature :s: I OO"C the recovcry was about 0.12%. Mechanical activation of cassiterite concentralc ( - 60'k Sn02) under thc regime providing amorphizalion of thc mineral (30 min in planetary mill) allows to increase the recovery of tin at subsequent H2S04 leaching up lo ~ 90% (Mechanochemical Phcnomena,l971 , p.l35-146; Molchanov and YUSllflOV,l981) . Mechanical activation in presence of abrasive results in deeper changes in slructure of the mineral (Mechanochemical Phenomena, 1971; Molchanov anel Yusupov, 191\ I). Activation of fine cassiterite slime in presence of quartz (at -1.5 mass ratio)

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eluring 60 min allows conelucting the decomposition of cassiterite even by concentrated HCI. Reactivity of cassiterite to HCI increases under carrying out the activation in presence of solid reelucing agents (Mokhanov and Yusupov, 191\ I), in particular in presence of ferrosilicon (Butyagi n et ai., 1974 ). lt is worth to mcntion that presence of residual tlotation agenls ( e.c. aliphalic acids) retards mechanochcmical transformations (Molchanov and Yusupov,1981).

Baddeleyite (Zr02) is another mineral, which is resistant to decomposition. Mechanical activation ( 15 min) of baddelcyite using centrifugai planetary mill (CPM) leads lo 60"C-decrease of temperature, at which the reaction with ammonium sulfate occurs, that, in turn, leaels to considerable reduclion of (NH4) 2S04 consumplion in course of conversion of zirconiurn dioxide lo waler-soluhle sul rate (Medvedev et al., 1991).

H was established (Kodin el ai., 1981) U1ett the oplimum conditions for sulfatization of tine powdercd haddeleyile, which guaranlee total decomposition of the mineral are as follows: 300"C, S:L=1:3 and 3 h duralion of the process. ln our sludies (Chizhevskaya el ai., 1990; 1991: 19Y5) the regimes of mcchanical activalion allowing to decrease boU1 sul falizatio n temperature (ln 250°C) and duration of the process (to I h) were dctermined. It was demonstrated that lhe incrcase of reactivity o r haddeleyile is related to a lransformation or monoclinic modification of Zr02 to tetragonal onc.

Mechanical activalion nf lantalile-niohates (pyrochlorc. tantalite, columhit.e, and wodginite) also results in signit'icant reducing of lemperature and requireel amounl of sul furic ac iel (Chizhevskaya et al.,2000). At tJ1c same time gaseous emissions of S02 and H2S04 acrosol as well as an amount of wastc were decreascd.

Reactivity of pyrochlore under sulfatization was also increased by eonducting mechanical activation in presence of small additions of water (Batzuev et ai., 1977).

Mechanical activation allows to utilize ali uset'ul components of aluminosilicate mineral raw material. Lepidolite KuA I15fAISi 30 10](F,OH )2 is usually considered only as Iithium-potassium raw material hut it is possihle to ohtain also alumina anel sílica as commercial products. Decomposition was coneluctcd either by sul faling of powelered molten (1090°C) mineral using H2S04 al 320 ''C or using K2S04 at 850-950"C. Mechanical activalion during 10 min in planetary mill allows to recover actually ali aluminum and alkaline metais in course of suhsequent lcaching with sulfuric acid (20 'fr, H2S04, 90 "C, I h) . Washing wilh water and elehydration of lhe cake rcsults in commercial sílica (Lapteva el ai. , 191\2).

VI SHMMT I XVIII ENTMME- 2001 -Rio de J aneiro!Brazil

INTENSIFICATION OF LEACHING

Zircon ZrSi04 is also the mineral, which is very resistant to decomposition. ln conventional industrial processing transformation of t11e mineral to acid-soluble form is carried out solely by means of pyrometallurgical techniques: caking with NaOH, Na2C03, K2SiFó or by chlorinating. A 15-min mechanical activation of zircon using CPM results in tl1e incrcasc of reactivity to mineral acids: 2 h of lcaching witl1 H2S04 (300 g/dm

3) or HCl

(370g/dm3) at (S:L=l:IOO, T=80°C) showed 12% zirconium rccovery in comparison with -1% for initial (non-acti vatcd) zircon (Medvedev ct al., llJlJI ).

lt was dcmonstrated in our studies (Chizhevskaya et ai., 1998; 1998) that tl1c application of high-energy planetary activator (designed by Institute of Solid State Chemistry and Mechanochcmistry, Russia) allows total decomposition of zircon by mineral acids tlms excluding the stagc of preliminary caking or fusion. Zircon being mechanically activated during 60 min can he totally dccomposed hy 9 mole/! H2S04 (S:L= l :20, T= 140 "C) in 1 O minutes.

Mechanical activation in aqueous mcdium is a promising variant of the technique that in addition eliminatcs the prohlems related to dust catching. Mechanical activation of lead cake (31.44% Ph, 10.56'!!~ Zn, 6.5% Fe, O.OlJ8'7,, ln, 0.204'1b Cd) in CPM in presence of water (S:L=1:1) during 15 min and subsequent leaching with H2S04 (230 g/dm\ S:L= 1:3, T=90 "C, 1=6h) results in a product enriched with lead (Pikul et ai., 1986). The purilication of lead cake from admixtures of zinc, indium, cadmium and irclll occurs due to decay of ferrite structure aml formation of elementary oxides.

Preliminary mechanical activation of scheelite concentrate in dillerential planetary mil! undcr optimum conditions during 2 min cnahles to increase W01 recovery in coursc of autoclave soda leaching (sodium carhonatc equi valcnt value 3, S:L= 1:4, T=225 "C, 1=2h) from 82.8% (non-activated conccntrate) to lJ6.5'fr,. 6 min of thc activation results in 9lJ.3'/í, recovery (Mikhailov et ai., 1lJ85). Under the ahove-dcscrihed conditions W01 recovcry trom wolframite concentrate increases lrom 20.7% (non-activated concentratc) to 40.lJ% and 44.6'/u for 2-and 6-min of activation, rcspcctively. The mcchanical activation allows either to increasc tungsten recovery at fixed soda consumption or to reduce soda consumption, the recovcry bcing the samc.

Similar results werc ohtained in the study (Zelikman et ai., 1lJ79) on activation of scheclite concentrates.

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It was demonstrated (Mikhailov et ai., 1985) tlHlt the increasc in reactivity of schcclitc occurs due to accumulation of structural dcfects. Line broadening of Mn2+ (isomorphic admixture in CaW04 crystal lattice) in electron paramagnetic resonance spectra was found to be a useful measure for both quantitative evaluation of concentration of defects and for estimation of t11c increase of chemical reactlVlty of scheelite (spin-probe technique ).

The int1uence of mechanical activation on reactivity of titanium raw material to sulfuric acid was also studied (Pryakhina et ai., 1985). Leucoxene and ilmenite are railier resistant to sulfuric acid. Mcchanical activation of leucoxene concentrate in planetary-centrifugal mil! providcs actually total decomposition (98.5%) hy 89% H2S04 at 200°C in 1 h, whercas total decomposition of initial concentrate requires more enforced conditions: 93-lJ5% H2S04 at 250-270°C. The increase of reactivity is related to microstrains of the lattice and change in composition of rutile moditication of leucoxcne. '

ln coursc of processing of arsenic-containing ores and concentrates preliminary withdrawal of As trom thc material is often neccssary. Bacterial leaching combined with preliminary mechanical activation was found to he prospective for tl1is purpose. Thus bactcrial leaching of tin concentrate (Sn- 24.7%, S- 18.3%, As -7.1%) during 4 days eliminates only 14.1% of As (Kulehakin, 1lJ78). A 5-min activation in planetary mill in air results in the increase of arsenic recovcry up to 78.5%. The activation in aqueous medium requires somewhat longer term (15 min) for similar result.

ln processing of sulfide zinc concentrates zinc-hearing residues containing signiíicant amount of zinc ferrite ZnFe20 4 generally occur after leaching of ashcs from roasting furnace. That hinders furthcr treatment. Mechanical activation of ilie residues followcd by leaching with diluted sulfuric acid allows to transform into solution up to 87% Zn, 93% Fe and 87 100% Cu (Molchanov and Yusupov, 1981 ). Müsshaucr spectroscopy showed a change of tetrahedral Zn2+ surrounding to octahedral one under mechanical activation of zinc ferrite (Boldirev et ai., 1983 ). It was established t11at thcrc is a liminal value of howl rotating frequency of planetary mill, ahovc that a sharp transformation of zinc ferrite into activated state occurs. Adjusting the rotation of opcrating bowls enablcs to govern the selectivity of leaching.

Preliminary mechanical activation significantly promotes leaching of iliose raw materiais, which are rather easy to decompose hut containing high amount of silica. ln our studies it was demonstratcd on an examplc of eudialyte whosc thc general motive of t11e crystal structure can he reprcsented hy

S. V. Chizhevskaya, A.M. Chekmarev, V.A. Mikhailov, E. C. Avvakumov

the formula : Na12ül(;Fe3ZrJ[Si 30 9h[Si 90 24(0H)Jh that it is possible to improve leaching by means of preliminary mechanical activation under the conditions providing, from one hand, high dispersion and from another - preservation of main structural motive of the mineral (Chizhevskaya et al., 199X; 1998). Mechanical activation allows to decrease a capture of solution by sílica cake and thus to increase the recovery of metal values. The mechanical activation carried out in presence of small amount of conccntrated HN03 enables more tlHtn twicc to reduce t11e acid consumption (from 800 to 350 % of stoichiometrically required) and in three times to decreasc tl1e duration of leaching (from 3 h to I h) (Chizhevskaya et ai., 1998).

Jn our studics carried out in scope of ISTC Project N 1332-99 it was established that the 1-min mechanical activation of eudialyte in planetary activator considerahly increases the selectivity of Zr and REE rccovery at subseque11t leaching with 100% TBP saturated with HN03 (CorgHNOJ = 4.2 mole/!) and decreases the capture of organic phase by cake.

Combination of mechanical activation of mineral raw material with leaching is also effective. For example, in the production of V20 5 of pure grade from the oxide of tcchnical grade such comhination of stages using planetary mil! allowed to rcduce the process duration to 10 min (instead of 1.5-2 h of preliminary grinding of initial concentrate in a hall mil! in NaOH solution) and to carry outthc process in single stage instead of 3 stages. The time requi~ed for filtration and washing of slime was also reduced (Mcchanochemical Phenomena, 1971 , p.l20-134).

Mechanical activation of baddeleyite concentrate i11 presence of small amount of water (4-6%) (Chizhevskaya et ai., 1995; 1998) allows to remove admixtures i11 Lhe course of subsequent leaching in fact totally, while thc main component-zirconium bcing actually unaffected. Purc commercial product was thus ohtained through signiticantly more fast process.

CONCLUSIONS

Thc abovc review on the in11uence of mechanical activation in the apparatus of centrifugai- planetary type 011 processing of rare and nonferrous metais mineral raw material demonstrates that tl1is technique is very efficient tool for inte11sifying dccomposition (caking, fusion, sulfatization) and lcaching processes. Mechanical activation allows to improve tl1e processes of hydrometallurgical trcating of rare and nonferrous metais: to increase the recovery of metal values , to decrease the consumption of chemicals, to reducc requirccl numbcr of stagcs of hydrometallurgical

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processing and the loss of liquor occurring in filtration due to comhination of operations of mechanical activation anel leaching (or solvent extraction). This method allows conduct selective withdrawal of admixtures from concentrates. The results of thcse studies provide prospects for involving low-grade complex sources (ores of tine-embedded type, slimes, slags and othcr wastes) to hydrometallurgical processi11g. The application of modern advanced mechanical activation techniques allows overall utilizing of mineral raw material that will also promotc t11c solution of environmental problems. The data demonstratc an oprortunity for devclopment of nove I tcchnologies altcrnati ve to t110se currently in use.

ACKNOWLEDGEMENT

The studies on the inlluence of mcchanical activation 011 reactivity of silicate (cudialytc) and oxide (baddcleyitc. tantalite-niobatcs) raw materiais have been supported by ISTC (Grant 1332-99).

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VI SHMMT I XVIII ENTMME - 2001- Rio de Janeiro/Brazil

Chizevskaya, S. V., Sharonov, A. V., Povetkina, M.V. et ai. Chcmistry and Tcchnology of Rare and Dipersed Elements. ln: Mezhvuz. Sb. Nauchn. Tr., L TI, Len ingrad, p.l 05. 1991.

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S. V Chizhevskaya, A.M. Chekmarev, VA. Mikhailov, E.G. Avvakumov

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