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ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 669.054.8
THERMODYNAMIC PARAMETERS OF PROCESSING COBALT-CONTCAINING ORES AND OF IVESTIGATION OF CONDITIONS OF SEPARATION
COBALT FROM SOLUTION
N.V.Yusifova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 15.04.2019
Kinetics of separation of Co by dissolution of cobalt ores was studied. Using of methods chemical analysis decomposition of cobalt, iron, calcium, manganese and magnesium oxides to simple chlorides with thermal consequence at interacting with ammonium chloride and forming ammonium chloride complexes was confirmed. Optimum yield of cobalt makes up 94% at 3000C for 160 min. To define the mechanism of the process results of thermogravimetric and X-ray phase analysis methods were used. Free energy values of chlorination of cobalt compounds with ammonium chloride were calculated. Change of Gibbs energy value depending on the temperature was calculated. As seen from calculations obtaining of compound CoCl2 is possible from thermodynamic. Separation condition of cobalt and accompanying elements from solutions depending on pH by precipitation was studied.
Keywords: cobalt, ammonium chloride, ore, free energy, thermodynamics, precipitation.
https://doi.org/10.32737/0005-2531-2019-3-88-94
Introduction
Cobalt ores have different mineralogical and chemical compositions and are many-colored. In ores amount of cobalt may change in a wide range - from one hundred per cent -to several per cent. When amount of cobalt is 0.15% or less in non-oxidized complex ores (with sulfide and arsenyl), the production of it is economically profitable. In Azerbaijan the main reserves of cobalt are in Southern Dashkasan deposit. The main mineral of this deposit is co-baltite. In samples the red cobalt mineral can be also seen. Maximum yield of cobalt to solution depends on easy dissolution of its mineral in water or other solvents, i. e., cobalt Co3+ in mineral should be brought to maximum soluble salt form. The reason of partial extraction of cobalt from ore is weak dissolution of its minerals in water, acid and alkali solutions. To bring cobalt to maximum soluble form, crystal cell of its minerals in ore should be decomposed. Ore sample is activated in two ways: by thermal decomposing in inert medium and oxidizing with atmospheric air. As seen from min-eralogical composition of ore most of minerals consist of solid silicates (clinochlorine, andradite) [1, 2]. Since enrichment of this mineral by physical methods is impossible we have used chemical enrichment technique. Recent researches of
chemists and technical-engineers on complex processing of mineral raw materials are of great interest [3-8]. Therefore, authors preferred to use ammonium chloride to extract valuable metals from different ore and processing products.
Analysis of our work [1] showed that when roasting primary materials by mixing them with ammonium chloride positive changes are observed in dissolution mechanism of Fe, Mn, Mg, Zn and Co. Essence of the technology is that when valuable non-ferrous metals (Fe, Mn, Mg, Zn and Co) in ore and concentrates are roasted with ammonium chloride intermediate chlorammonium complexes are formed. If heating continues the complexes decompose into relevant soluble chloride salts and gaseous (NH3, HCl) solutions. It is interesting that valuable non-ferrous metals in raw material form complexes which dissolve with NH7, but mixed metals iron, manganese, calcium do not form complexes under this condition. Ammonium chloride does not interact with silicium and aluminum oxides. Ammonia complexes of iron, zinc, cobalt and manganese have different resistance constants. Using this property they can be separated by boiling the solution and destroying complexes. Unlike copper, zinc and nickel ammonia complex [Co(NH3)4]2+ of divalent cobalt is easily decomposed and the com-
plex of trivalent cobalt is more stable than complex compounds of these metals [3]. Using this property and boiling the solution cobalt can be kept in solution and other ions can be kept in precipitate. Unlike chloride acid ammonium chloride differs in selectivity and is not a hazardous substance.
Experimental part
The studied Dashkesen Cobalt ore is polymineral ore. According to the results of X-ray and mineralogical analysis methods is ore contains the following minerals: cobaltite, erythrite, clinochlore, andradite, a-quartz, hematite, aluminum phosphide. Under the microscope, the major rock-forming minerals such as aluminosilicates (clinochlore, andradite) are observed in the form of large and small grains of irregular shape. Cobaltite in polished sections is characterized by its weak anisotropy effects, it has a pinkish-brown colour. Depending on its location it can be found in the cracks among garnet skarns, sometimes it is intergrown with safflorite accompanied with pyrite. From the results of mineralogical analysis investigated that cobalt ore is also high siliceous aluminum raw material which contains: clinochlore -44.2%, andradite - 23.3%, a-quartz - 11.2%, aluminum phosphide - 2.2%. Despite the low aluminum content (4.5-7.6%), the presence of other valuable components such as Mg, K, Ti, Mn, Cr. Revealed is complexity of this type ore processing is that their enrichment process is difficult associated with presence of both sul-foarsenic and oxidized minerals and interaction their germination and also presence of other metals and impurities. Dashkesen cobalt ore has the following average of chemical composition (in terms of oxide) (mass%): Na2O-1.48; MgO-5.65; Al2O3-14.29; SiO2-44.64; SO3-O.85; K2O-1.32; CaO-7,19; As2O3-5.20; Fe2O3-12,93, MnO-0,43, TiO2-0,54. Established that the CoO content in the ore is in the 3.58-5.48% range
Before processing ore with ammonium chloride cobalt mineral in it should be activated thermally decomposed. Results of thermal analysis are given [1]. As seen from thermogram at temperature up to 7600C serious change is not observed in the material. In X-ray phase analy-
sis of material obtained at 8500C intensities typical for CoS and CoAs are observed. It is supposed that cobalt mineral in ore is thermally decomposed by the following equation:
CoAsS 850 C > 4CoS+ 4CoAs+As4S4. (1)
Cobalt ore was roasted in inert, oxidizing and ammonium chloride in furnaces with horizontal tube. Raw cobalt ore or mixture of ammonium chloride with a burnt obtained from thermal decomposition is added into quartz tube with diameter of 40 mm, and furnace was heated up to given temperature and roasted. After the experiment roasted products were taken out of the furnace and cooled at room temperature. The burnt was weighed in a balance and its composition was analyzed on Fe, Co, As, Cu, Al and other components. Gas (NH3) obtained in the experiments with ammonium chloride were adsorbed with 5% chloride acid. Cooled solution was dissolved at 800C for an hour with water in a magnetic mixer. Obtained solution and dry residue (cake) was analyzed on the above mentioned elements.
Results and discussion
Thermal processing of "Ore-NH4Cl" mixture was carried out. To define the mechanism of the process thermographic and X-ray phase analyses methods were used [1]. The reactions of thermal oxidation and chlorination reaction of cobalt ore with ammonium chloride on cobalt can be expressed by the following chemical equation 1) thermal decomposition of cobalt:
2CoS+3O2->2CoO+2SO2,
CoS+4NH4Cl ^^^ (NH4)2CoCl4+2NH3+H2S,
CoO+2NH4Cl=CoCl2+2NH3+H2O,
CoO+2HCl=CoCl2+H2O,
(NH4)2CoCl4 CoCl2+2NH3+2HCl.
During chlorination of CoO and CoS with NH4Q at 273-600 K the values of isobarthermal potentials of possible reactions were calculated using Temkin-Schwarzman's equation:
AGr = AH2°98 - TAS2°98 - T(M0Aa + MlAb + M2Ac).
Thermodynamic properties of substances (AH, ACp, Sp) in the calculations were taken from reference book [9].
Table 1 shows calculated values of the change of Gibbs energy value of chlorination reactions of CoO and CoS with NH4Cl depending on temperature.
Table 1.Calcualted values of free energies of chlorination cobalt compounds with ammonium chloride
Reactions AGt, kC/mol
298 K 400 K 600 K
CoO+NH4Cl 84.4 27 -21.47
CoS+NH4Cl 232 187 100.9
CoO+HCl -43.21 -71.932 -98.89
As calculations show chlorination of cobalt
oxide occurs faster and more rapidly than cobalt
disulfide, i.e. production of CoCl2 is thermody-namically possible. For full characterization of the peaks observed in effects relevant to different temperatures on thermogram of Ore-NH^l mixture the samples were studied using X-ray phase and IR spectroscopic methods.
Comparison of X-ray analysis showed that the intensity of the minerals in the initial spleen changes partly after chlorination. The peaks which are typical for (NH4)2CoCl4, NH4CoCl3, CoCl2NH4Cl are observed in the material after chlorination. The composition of the chlorinated complex was confirmed using chemical analysis method.
Mass percent of Co:Cl:NH4 in the complex compound formed from CoO and NH4Cl was 17.7:62.1:20.8.
i.0e+003
4.0e+003
3.0e+003
2.0e+000
1.0e+003
0.0e+000
3
s s
s a
1.0e+004:
S.0e+003 ■
2 5 3
3
WW
10
20
30
40
50
a
6
3
b
â.0e+003
4.0e+003
2.0e+000
0.0e+000
2- Theta scale
Fig. 1. The initial oxidized cobalt ore (a) and its mix with NH4Cl (1:1) at 2650C is given X-ray of processing products (b). In the X-ray: 1 - andradite, 2 - hematite, 3 - quartz, 4 - clinochlore, 5 - cobaltite, 6 -albite, 7 - CoCl2, 8 - (NH^CoCL,, 9 - CoCl2(H2O)2.
Calculated molar ratio
17.7 62.1 20.8
58.93 35.5 18 0.3:1.75:1.155=1:5.83:3.85=1:6:4 conforms to the compound CoCl24NH4Cl.
According to the results of experiments interaction mechanism of cobalt dioxide with ammonium chloride can be shown by the following conversions:
CoAsS-CoAs, CoSA CoO +NH# -SO2
CoCh^NHCl 1810C (NH4)3CoCl5
NH4Cl (-NH3, HCl)
NH4CoCl3
> (NH4)2CoCl4
2600
-NH
3090
+nh4
CoCl2.
Basing on these results we may conclude that NH4Cl reagent can be advisable and useful for processing oxidized cobalt ore. With this reagent we may transform oxidized cobalt in ore into chlorinated salt form at 200-3200C [10, 11]. Researches showed that ammonium chloride can be used in processing of cobalt ores. Ammonium chloride is also broken at 3380C. As a result of the interaction of the oxide in the ore with ammonium chloride ammonium chloromethylates are formed.
NH4CI 338 "S NH3+HCI, CoO+2NH4Cl= CoCl2+2NH3+H2O, CoO+2HCl= CoCl2+H2O, Fe2O3+6NH4Cl=2FeCl3+6NH3+H2O, Fe2O3+6HCl=2FeCl3+3H2O, MnO+2NH4Cl=MnCl2+NH3+H2O, MnO+2HCl= MnCl2+H2O, SiO2+NH4Cl - the reaction does not.
For comparison, cobalt(III) oxides were used in the experiments. 2g Co2O3 with 4g NH4Cl at 260, 280, 3 200C burned.
At 2600C (NH4)3CoCl5 complex, and at 2800C NH4CoCl3, (NH4)2CoCl4 complexes are formed. To find out the mechanism of the pro-
cess we used the following analysis methods: thermography, X-ray phase and IR spectroscopy. The product of the interaction of ammonium chloride with a candle of cobalt ore, obtained at 30000C, was studied by IR spectroscopy (Figure 2). The IR spectrum proves the presence of bond
9
oscillations: [CoCl4] - - the chlorammonium
complex at 1754.97 cm-1 (a), 1731.96 cm-1 (b).
Further works were performed on the precipitation of cobalt and accompanying elements in solutions. Cobalt can be found in ores, minerals, alloys and other industrial and natural materials together with iron, nickel, magnesium, copper, chromium, vanadium and other elements. Cobalt(III) is located in analytic cation group. Determination of pH of solution in hy-drometallurgy processes in the processing of ore is important. At different values of pH separation of valuable components from each other occurs. Precipitation was carried out using ammonia water, iron pH=4.5 Fe(III) is separated in solution in a form of Fe(OH)3 hydroxide. Since aluminum has atmospheric property its precipitation occurs at pH=4.5-6, pH=8-8.5 Co2+ ion is separated in the form of precipitate and Mn2+ ions is precipitated in the form of Mn(OH)2; manganese, magnesium, calcium are precipitated at pH 8.5.
During dissolution cations formed in solutions were exposed to stepwise hydrolysis and form hydrocomponents by the following scheme:
Me"+ + H2O —> Me(OH)+("- 1)+H+;
-1
12O
V+ÍB-1),
Me(OH)+(B-1)+H2O —> Me (OH)2+(«-2)+H+;
MeOH0 + OH
► Me(OH)-
«+1.
Metal ions Fe2+, Fe3+,Co2+, Mn2+are in
different ion and molecular forms depending on density and pH. Results of precipitation are given in the following Table 2.
As the results form the table show selective precipitation of metals occurs. Aluminum and iron begin precipitating at pH 4.5. Thicker precipitate appears during precipitation of magnesium at pH 9.5-11. In the range of pH 7-9.5 the complex precipitate of cobalt and manganese is formed.
+
22 20 18 16 14 12 10 8 6 4 2
-2 -4
SP-s
_Sh
s a
Ph
x, cm
4000 3500 3000 2500 2000 1500
Fig.2. a - product of the interaction of ore and NH4Cl, b - IR spectrum of the of the interaction of CoO and NH4Cl. The research showed that annealing process with ammonium chloride can be used in the processing of cobalt ore. The developed method differs by its in effectiveness and can be used for extraction of Co from sulfoarsenide ores.
Table 2. Results of precipitation depending on pH
pH Yield,%
Al Fe Co Mn Mg
4 6.73 11.71 - - -
4.5 43.29 29.43 - - -
5 51.66 14.71 6.54 5.20 2.18
5.5 4.73 49.33 0.27 - -
6 0.171 9.52 - - -
6.5 0.037 0.00008 - - -
7 22.25 - -
7.5 32.70 - 8.46
8 21.25 8.80 2.51
8.5 16.35 14.09 5.02
9 0.58 30.81 2.18
9.5 0.60 33.45 25.69
10 6.25 14.21
10.5 1.33 35.81
12.5 0.008 -
Total yield 99.97 90.48 99.94 99.99 99.80
a
Conclusion
Free energy values of chlorination of cobalt compounds with ammonium chloride were calculated. Calculated values of the change of Gibbs energy value depending on the temperature were given. As seen from the calculations obtaining of compound CoCl2 is thermodynamically possible.
References
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KOBALTTORKiBLi FiLiZLORiN EMALININ TERMODiNAMiKi GOSTORiCiLORi VO MOHLULDA
KOBALTIN AYRILMA SORAiTiNiN TODQiQi
N.V.Yusifova
Kobaltli filizlarin hallolmasi metodu ila Co aynlmasinin kinetikasi tadqiq edilmi§dir. Kimyavi analiz metodlan ila kobalt, damir, kalsium, manqan va maqneziumun oksidlarinin ammonium xloridla qar§iliqli tasirda olaraq ammonium xlorid komplekslari amala gatirarak, termiki ardicilliqla sada xloridlara pargalandigi subut edilmi§dir. Kobaltin optimal giximi 3000С temperaturda 160 daq muddatinda 94% ta§kil edir. Prosesin mexanizminin agilmasi ugun termoqravimetrik va rent-genfaza analiz metodlarinin naticalarindan istifada edilmi§dir. Kobaltli birla§malarin ammonium xloridla xlorla§masinin sarbast enerjilarinin qiymatlari hesablanmi§dir. Gibbs enerjisinin qiymatinin temperaturdan asili olaraq dayi§masinin hesablanmi§ qiymatlari verilmi§dir. Hesablamalardan da gorunduyu kimi CoCl2 birla§masinin alinmasi termodinamiki cahatdan mumkundur.Alinmiij mahlullardan kobaltin va onu mu§ayat edan elementlarin pH-dan asili olaraq gokdurularak bir-birindan ayrilma §araiti 6yranilmi§dir.
Agar sozlar: kobalt, ammonium xlorid, filiz, sarbast enerji,termodinamiki,gokdurm3.
ТЕРМОДИНАМИЧЕСКИЕ ПОКАЗАТЕЛИ ПРОЦЕССА ПЕРЕРАБОТКИ КОБАЛЬТСОДЕРЖАЩИХ РУД И ИССЛЕДОВАНИЕ УСЛОВИЙ ВЫДЕЛЕНИЯ КОБАЛЬТА ИЗ РАСТВОРА
Н.В.Юсифова
Исследована кинетика выделения кобальта методом растворения из кобальтсодержащих руд. С помощью химических методов анализа доказано, что оксиды кобальта, железа, кальция, марганца и магния, образуя комплексы при взаимодействии с хлористым аммонием, последовательно термически разлагаются на простые хлориды. Оптимальный выход кобальта составляет 94% при 3000С и 160 мин. Для установления механизма процесса использованы результаты термогравиметрического и рентгенофазового методов анализа. Рассчитаны значения свободной энергии хлорирования соединений кобальта хлористым аммонием. Приведены также рассчитанные значения изменения энергии Гиббса в зависимости от температуры. Показано, что получение хлорида кобальта термодинамически возможно. Исследованы условия осаждения и отделения кобальта от сопутствующих его элементов в зависимости от pH растворов.
Ключевые слова: кобальт, хлористый аммоний, руда, свободная энергия, термодинамика, осаждение.
