Vitaliy P. Guro, Matluba A. Ibragimova, Edgorjon T. Safarov

235

Journal of Chemical Technology and Metallurgy, 51, 2, 2016, 235-241

Organic-mineral binder fOr mOlybdenum cOncentrate granulatiOn

Vitaliy P. Guro, Matluba A. Ibragimova, Edgorjon T. Safarov

Institute of General and Inorganic Chemistry Academy of Sciences of Uzbekistan77 a, Mirzo-Ulugbek avenue 100170, Tashkent, UzbekistanE-mail: vpguro@rambler.ru

abStract

Process of pyrite cinders production from Mo middlings consists of molybdenite concentrate granulation, firing to oxidize sulfide minerals and to recover Re-oxide. If kaolin binder is used a pyrite cinders dilution with Mo takes place. So, the development of organic binding agents, alternative to kaolin, is an actual issue. The approach is based on the com-parison of the hydrophilic, strength and technological features of the hydrometallurgical processing of pellets. The new batch is developed. It differs from the traditional mixture by polymer burning and minimizing Mo dilution, thus aiming to maximize Re, Au, Ag recovery. The composition of the new organic-mineral batch is as follows: 97.3 % of molybdenite concentrate, 2 % of kaolin and 0.7 % of SK polymer.

Keywords: molybdenum middlings, binder, organic additive, batch, granulation.

Received 20 April 2015Accepted 08 January 2016

intrOductiOn

It is common practice in mining industry to pel-letize finely ground mineral ore concentrate to facilitate ore shipping. After screening, a binding agent is added to the wet ore concentrate and the binder/mineral ore composite is conveyed to a balling drum for ore pel-letizing. The binding agent serves to bind the mineral ore together until after firing. For many years, bentonite was used as a binding agent in exclusive usage mode for iron ore concentrates because the pellets obtained pos-sessed good wet and dry strengths. The use of bentonite, however, had disadvantage referring particularly to the additional silica content introduction. Organic binders have proven to be an attractive alternative to bentonite because they do not increase the silica content providing the pellets best mechanical properties. They also burn out during ball firing operations thus causing pellets mi-croporosity increase. Accordingly, the pore volume and

surface/mass ratio of the pellets produced in presence of organic binders is greater than that of pellets produced with bentonite participation. This provides more ef-ficient reduction of metallic oxides such as iron oxide. Examples of some commonly mentioned organic binders include polyacrylate, polyacrylamide and copolymers thereof, methacrylamide, polymethacrylamide, cellulose derivatives such as alkali metal salts of carboxymethyl cellulose and carboxymethylhydroxyethyl cellulose, poly(ethylene oxide), guar gum, dairy wastes, starches, dextrins, alginates, pectins, etc.

An invention is offered which refers to a binder for agglomeration of particulate material, especially iron ore, in the presence of water. It comprises an amount of a water-soluble polymer acting as an effective binder and an amount of caustic [1] enhancing the binding. Another one discloses a composition for iron ore ag-glomeration which includes 10 % - 45 % (mass) of a water-in-oil emulsion of a water soluble vinyl polymer,

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55 % - 90 % (mass) of a polysaccharide, 0.001 % - 10 % (mass) of a water soluble surfactant and 0 % - 15 % (mass) of borax [2]. Different binder agents are used in patents [3 - 5] disclosing accordingly contents of water soluble sodium carboxymethylhydroxyethyl cellulose with sodium carbonate, carboxymethyl cellulose with a weak acid salt or with sodium tripolyphosphate. Wood related products such as sulfonated cellulose, lignine, lignosulfonates are recommended as binding agents too [6 - 7]. Another invention discloses a process for making iron ore pellets. The water-soluble polymer applied may be of any typical type, e.g., natural, modified natural or synthetic. The mixture may optionally comprise sodium citrate [8] as a pelletizing additive. Organic binder com-positions have their own disadvantages. They do not generally impart adequate dry strength to the pellets. Thus, there is an ongoing need for economical binders of improved properties.

It is not superfluous to emphasize and to draw the attention to the fact that the patent and scientific litera-ture specific information on binders used for mineral metallic ore agglomeration refer primarily to iron ores and concentrates. There is no information concern-ing molybdenite concentrate application. Therefore, the objective of this study is to select an alternative to kaolin mineral-organic binder in the composition of Mo concentrate batch’s aiming to outperform the hydrometallurgical properties through providing (i) strength to the pellets during their granulation and fir-ing; (ii) molybdenum dilution elimination. The further requirements are as follows: it should not contain any

“technological poisons” (such as phosphates) adversely affecting the redistribution of cinder: leaching, Mo(VI) ions sorption on an ion-exchange resin, reduction to metal, sintering rods. This requires the comparison of the hydrophilic, strength and technological properties in case of introducing kaolin or its alternatives of organic and organic-mineral nature to a batch composition for pyrite cinders for molybdenum middlings production at JSC “Almalyk GMK” (Uzbekistan) [9].

experimental

The batches used for Mo concentrate granulation had the compositions listed in Table 1.

The limiting wetting angle of the batch material compacted under pressure of 20 MPa (Æ 12, height: 4 mm) was determined on the ground of the profile of water droplets thereon [10]. The granules were obtained in a disc pelletizer and then dried for 24 h at 20°C. Their crushing strength was evaluated on the ground of (i) the integrity of the granules dropped from a height of 2 m onto concrete; (ii) the compression fracture. The comparison carried out provided to outline the strength criterion: F ³ 1.2 MPa. The elements content in the raw materials and the technological solutions was determined using AAS "Perkin-Elmer" 3030V with a flaming atom-izer, and Aligent 7500 ICP-MS. Thus, Au and Ag in the samples were determined at wavelengths of 242.8 nm and 328.1 nm with preconcentration extraction in a tolu-ene solution of sulfide oil at a ratio of organic/aqueous phases = 1/10, respectively.

Table 1. Batches used for Mo-concentrate pelletization (b - bentonite, k - kaolin, LG - liquid glass, CS - sulfonated cel-lulose, CMC – carboxymethylcellulose, PVA - polyvinyl acetate, SC - polyacrylonitrile fiber production waste).

No Binder composition, %

Mo concentrate,

%

No Binder composition, %

Mo concentrate,

% Mineral

component Organic binder

agent Mineral

component Organic

binder agent b k lg SC Na-

CMC PVA CS b k lg SC Na-

CMC PVA CS

1 - - - - - - - 100 10 - - 1,5 1,5 - - - 97 2 - 10 - - - - - 90 11 2 - - 1,5 1,5 - - 95 3 - - - 3 - - - 97 12 - 2 - 1,5 1,5 - - 95 4 - 2 - 3 - - - 95 13 - - 3 - - - 97 5 2 - - 3 - - - 95 14 2 - - 1,5 - - 96.5 6 2 - - - 2 - - 96 15 2 - - 0,5 - - - 97.5 7 2 - - - - 2 - 96 16 - 2 - 0,5 - - - 97.5 8 2 - - - - - 2 96 17 1 - - 0,5 - - 98.5 9 - - - 1 - - - 99 18 1 - - 0,5 - - - 98.5

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IR absorption spectra were recorded in the range of 400 cm-1 - 4000 cm-1 with AVATAR-360 spectrometer Nicolet. Thermograms were recorded by derivatograph Paulik Erdey at a gradient of 10 degrees per min. The sample mass was in the range of 0.200 g - 0.250 g. A corundum crucible of Æ of 10 mm with T-900 and TG-200 was used. This referred also to the DTA-1/10 and DTG1/20 sensitive galvanometers. Al2O3 was the standard applied. Röntgenograms were recorded by DRON-2.0 X-ray crystal analyzer with Cu-anticathode. A table of ASTM standard card index was used to cal-culate the interplanar distances. The relative intensity of the lines I/I (J, %) was determined as a percentage of reflex expressed at the maximum.

reSultS and diScuSSiOn

The Mo concentrate’s composition used for the granulating is as follows, %: Mo - 38; Re - 0.7; Cu - 2.5; P - 0.009; Sb - 0.025; WO3 - 0.05; S - 25.2; SiO2 - 10.8; humidity of 0.42; the Au and Ag quantities refered to Mo concentrate are presented there too. The limiting wetting angles of the batches prepared on the ground of Mo-concentrate are compared to those pointed in ref. [10]. They are also included in Table. 2.

Table 2 shows that sample No 1 is identified as hydrophobic. The decrease of its hydrophobicity is facilitated by binders’ introduction which provides its granulation. The selection of the best of them is carried out comparing the strength of the corresponding pellets of a diameter of 3 mm - 5 mm after their drying at 20°C, 250°C and 600°C (Table 3).

The requirement to the durability of pellets in manufacturing Mo middlings candle end is revealed empirically. It is adjusted by the mode of balling in a home made stainless steel balling drum for pelletizing the concentrate with a diameter of 2 m, as well as by batch composition used: 92 - 90 % of Мо-concentrate, 8 - 10 % of kaolin. The drum inclination angle, the speed of its rotation and water introduction, the time of balling were selected empirically too aiming the production of pellets of optimal size and durability. Their resistance to abrasive wear on the way to the furnace is expected to decrease, while their oxygen permeability (О2 is neces-sary for oxidation of molybdenite to Мо trioxide) has to be blocked: in both cases the sulfur content at the candle end is expected to conform to that of GOST 2677-78.

Thus, one of the problems of this investigation was the quantitative description of the empirically revealed requirements pointed above. The approximate accept-able range of pellets’ durability is established to be ap-proximately: Р = 1 - 4 MPa. The criterion specification demands additional study. The sulfur content at the candle end could can exceed its norm of 1,5 % [9] in case of under- or overestimation of this parameter.

Table 3 reveals the current charge mixture based on kaolin No 2, as well as a mixture based on kaolin or bentonite, i.e. No 4, 5, 15 - 16, 18. The required pellets’ strength of P = 1 - 4 MPa is provided.

Granules and corresponding powders obtained by abrasion to 0.074 mm are placed in a laboratory boat after 45 min of heating at 600оС in a current of oxygen. They are analyzed to determine their sulfur content. The latter is essential importance for the powders because

Table 2. Wetting of quartz, talc, batch mixtures (No listed above). Batch, No quartz* talc* 1 2 3 4 5 17 18

Limiting wetting angle 0 69 95 36 33 32 30 34 33

Table 3. Pellets’ strength depending on the batch’s composition and drying temperature.T,

ОC Durability of pellets ∅ of 3 mm – 5 mm under loading prior to destruction, MPa

Batch pelletizing based on Мо-concentrate, batch mixture’s No

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

20 0.7 1.1 2.0 1.9 0.2 1.6 0.9 0.5 1.5 1.6 1.8 2.8 0.3 1.5 1.5 0.3 1.2

250 2.4 1.6 1.8 3.2 0.5 0.2 0.8 0.6 1.9 2.2 2.7 2.5 0.4 3.1 1.9 0.9 1.8

600 6.4 1.2 4.1 8.4 0.6 0.6 1.2 0.7 0.1 0.2 0.2 0.3 0.7 7.3 4.0 1.1 4.5

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of the superficial crust which affects the oxygen access. It is found that the exclusion of a mineral compo-

nent of the binding mix (kaolin or bentonite), as seen in samples No 3 and No 9, results in decrease of the burnt granules durability, their destruction in the furnace, their sticking to the walls and incomplete sulfides oxidation or dusting. Therefore, its exclusion, for the benefit of only one polymer, is inexpedient for molybdenite. The similar conclusion has been earlier made in respect to magnetite [11]. Agglomeration and granulation of iron ore is suggested to be carried out in presence [12] of at least one colloid agent providing mineral particles cohe-sion and a synthetic polymer acting as a dispersing agent.

SC polymer replacement by CMC (No 6, 14, 17) results in worsening of the strength values. However, in case of high concentration of bentonite and CMC (No 6, 14) they do satisfy the strength requirements. At low concentration of both binder agents in No 17 mixture, the durability is dissatisfying. SC replacement by sul-fonated cellulose (No 8) or water glass (No 11, 13) in presence of a mineral binder (kaolin or bentonite), as well as in presence of SC (No 3, 9), decrease of pellet’s strength is observed. The increase of the temperature treating from 20°C to 600°C results in pellets’ strength increase. The advantage of the compositions based on an organic binder, for example, No 15 - 18 in respect to mixtures with no supplement consists in the fact that the organic additives SC, CMC, PVA burn up to the ground at thermal treating causing no calcine dilution. The latter is observed in presence of mineral binders (bentonite, kaolin) irrespectively of their beneficial effect in respect

to pellets strength. The addition of WG decreases the strength of granules dried at 600°C.

It is of interest to compare the technological proper-ties of mixtures No 1, 2, 16 used for pellets formation and their subsequent drying and ammonia leaching. Au and Ag are recovered cyanide leaching from the cakes obtained. At all stages the samples are analyzed to determine the content of Mo, Re, Au, Ag. It is found out that pellets of a batch No 16 has been relatively enriched with Mo prior to and after their firing. Their content of unoxidized MoS2 is minimal, while that of MoO3 is maximal. Ag and Au contents in the cinder are maximal facilitating their removal from the cakes. At 600°C rhenium in the form of Re2O7 sublimates to a maximum extent (Table 4).

Pellets of Mo concentrate batches No 2 - 5 prior to and No 2t - 5t after firing at 600oC, as well as SC, kaolin, bentonite are subjected to IR spectrometry (Fig. 1) and grav analyses (Fig. 2).

The IR spectra of the individual components show the specific characteristic frequencies, while those of their mixtures indicate frequencies’ and bands intensi-ties’ changes. The latter provide to suggest the existence of interactions. The samples treatment at 600oC gives thermolysis products of valence frequencies and defor-mation oscillation characteristic for Al2O3, MoO3, SiO2, Fe2O3 and calcium carbonate.

Derivatograms (grav) of the samples reveal the in-teraction between the components and the difference in the composition and content of the thermolysis products. They indicate the disappearance of MoS2 at 560 - 600оС

Table 4. Effect of firing of pellets made of mixtures No 1, 2, 16 on metals recovery (Re - from the gas phase, Mo - from the pyrite cinder of molybdenum middling by means of ammonia leaching, Au, Ag - from the cinder’s cake after Mo recovery by means of cyanide leaching). Conditions designation: I – metal’s content in a batch prior to firing; II – after the firing; III – metal’s recovery (%); batches sulfides were preliminary oxidized by nitric acid in case of No 1 (without firing-roasting) and by oxygen at firing in case of No 2, 16.

Element Batch No 1 (no binder) Batch No 2 Batch No 16

I II III I II III I II III

Mo, % 41,3 - 97% 37,7 39,1 97% 39,9 42,2 99%

Re, % 0,07 - - 0,06 0,05 15% 0,07 0,05 30%

Au 38,1 g/t - 94% 34,7 g/t 36,1 g/t 92% 36,7 g/t 38,2 g/t 95%

Ag 62,2 g/t - 95% 56,9 g/t 59,2 g/t 93% 60,0 g/t 62,0 g/t 95%

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accompanied by transition of Мо into МоО3. Derivato-grams of the pellet’s samples prior to and after roasting

at different temperatures show full decomposition of organic polymers at 300оС.

Fig. 1. IR-spectra of the samples (curves 1 - 4, 5 - 8 correspond to batches No 2 - 5 and 2t - 5t, curves 9 - 12 correspond to Мо-concentrate, kaolin, bentonite, SC polymer).

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cOncluSiOnS

Effective binder compositions for Мо-concentrate granulation are developed as a result of the comparative colloid-, physical and chemical, mechanical, technologi-cal tests carried out. They provide the required gran-ules strength being alternative to existing kaolin batch mixture (Mo concentrate of 90 - 92 %, kaolin of 10 - 8

%). They are based on two combinations: 1) kaolin (2 %), SC polymer (0.7 % - 1,0 %), Mo concentrate; 2) bentonite (0,7 % - 1,0 %), SC polymer (0.7 % - 1,0 %), Mo concentrate. The organic SC polymer may be replaced either by CMC or PVA in the concentration range of 0.7 % - 2 %, but it is preferable in terms of strength. The results of the comparative molybdenum leaching from the molybdenum middling pyrite cinder

Fig. 2. Derivatograms (grav) of the samples No 2, 5, 2t, 5t.

TG

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DTA

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0∆Р, mg t, Co

t, min

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0

t, Co

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0∆Р, mg

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DTA

T

Sample Nr 2 Sample Nr 5

25 50 75 100t, min

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produced on the ground of traditional and the advanced mineral-organic batches by means of ammonia leaching and the precious metals cyanide leaching from cinder’s cake after Mo recovery show explicitly that the advanced batch compositions provide better hydrometallurgical processing features.

AcknowledgementsThe research was carried out with the financial

support provided by government’s grant 7 FҚ-0-19005.

referenceS

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