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ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 546.881.542.61
THE STUDY OF THE CONDITIONS FOR THE RECOVERY OF VANADIUM, GALLIUM AND NICKEL FROM THE ASH RESIDUE AT BURNING OF FUEL OIL BY SINTER
AND LEACHING METHODS
L.T.Tagiyeva
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 10.06.2019 Accepted 21.11.2019
The conditions for the extraction of gallium, vanadium and nickel from the ash residues resulting at the burning of high-sulfur chemicals by sintering with soda and leaching with water have been examined. A new technology has been developed, characterized by higher extraction of gallium, vanadium and nickel, which is environmentally friendly for extracting Ga, V and Ni from the ash residue of heavy oil. In order to completely extract Ga, V and Ni from the ash residue, its thermal oxidation with alkaline (Na2CO3) additives was previously carried out. Installed the optimal conditions of the process. The results showed that the degree of leaching of vanadium and gallium was 98.8 and 97.5%, respectively, in the experimental conditions the sintering temperature was 8000 C, the sintering time was 1.5 hours, the optimum amount of soda needed for sintering was 1:1 by weight, the leaching temperature was 90-950C, the ratio of the liquid-solid phase was (5-10):1 and the leaching time was 2 hours. After the recovery of Ga and V, the residue was followed leaching with a sulfuric acid solution to recover nickel.
Keywords: gallium, vanadium, nickel, recovery, leaching, sintering, ash.
doi.org/10.32737/0005-2531-2020-1-46-52 Introduction
More attention has recently been paid to the integrated use of waste and environmental protection, to the development of a rational technology for the extraction of valuable elements, including vanadium, nickel and gallium from ash residues generated by combustion of sulfur fuel oil [1-4]. The urgency of the problem of vanadium and gallium extraction from oil refining products is determined by the deficiency of these metals. Currently, the mineral part of the fuel oil is a waste that accumulates in huge quantities, occupying large production areas and creating a threat to the Environment. In the literature, there is information about the methods of extraction of vanadium and gallium from the ashes, boiler slag and sediments formed on the heat and power plants [5-10].
It is known many technological schemes to obtain Ga, V, Ni and so forth from ash residues of combustion of fuel oil and coal, but most of the literature on this issue is presented in the form of patents [2, 3].
Extraction of vanadium and nickel from fly ash is carried out by various processing: acid [11], alkali [1], soda solutions, ammonium salts [12-14].
Vanadium in fly ash coal and heavy oilfield products is in the trivalent state and is embedded in the crystal lattice of aluminosilicate minerals in the composition of the raw materials. In general, most of vanadium in stone coal, basically, exists as trivalent vanadium [V(III)], isomorphic replacing trivalent aluminium [Al(III)] in the octahedral crystal lattice of mica minerals [15, 16]. In the lattice of mica minerals, trivalent vanadium is not able to directly dissolve and oxidize to a state of higher valence [16]. Fly ash is characterized by a relatively high content of Ga and V, is mainly in the form of Ga2O3, as well as Ga3 + and V3 +, replacing Al3+ in the fly ash matrix Al-Si [1]. The data of this research dedicated to the extraction of the maximum amount of Ga, Ni and V from these types of fly ash.
The principle of obtaining vanadium and gallium from the fly ash of a heavy oil fraction consists in the decomposition of the crystalline lattice of aluminosilicate clay minerals by oxidation of insoluble forms of vanadium(III) to soluble acid-alkaline method. One of the most rational methods for obtaining vanadium, gallium, and nickel from the ash residue at burning fuel oil is the sintering method with soda [9]. The introduc-
tion of soda to the charge is intended to convert trivalent metals (Al3+, Ga3+, V3+) into a soluble form from the crystal lattice of aluminosilicate minerals included in the raw material.
The purpose of this work is to extract vanadium, nickel and gallium from fly ash, using Na2CO3 as an annealing agent, followed by leaching the mass with water. The optimal conditions for the separation of Ga and V from an alkaline solution are systemically investigated.
Experimental part
Materials and methods. As the object of research is taken ash residue from Baku electrical power station, which has the following chemical composition (mass.%) (Table 1).
The total mass loss at calcination to 1000°C was 7-8%. It was established that in the composition of the ash residue along with other elements contain such valuable components as vanadium (22.65%), nickel (3.4%) and gallium (0.01%). As can be seen from Table 1, the content of vanadium, nickel and gallium in the ash residue is quite significant, therefore, their extraction seems necessary. The content of gallium, vanadium, nickel and other components of the ash residue and the products of its processing were determined on X-ray fluorescence spectrometer a "Bruker C2 Picofox" (Germany).
Table 1. Chemical composition of crude fly ash, mass.%
The mineral composition of the ash residue and its products was determined by X-ray phase analysis (Figure 1).
By its mineralogical composition, ash residue is a mixture of various natural minerals. It is established that the mineral composition of the sample includes: alumina, anhydrous calcium sulfate, hematite, galena Ca2Al[(Si,Al)2O7], anortite Ca[(Al2Si2)Og], kaolinite H4AhSi2O9, vanadium oxide (V2O3). Vanadium(III) and nickel(III) in the ash is in the form of spinels.
Results and discussion
At the beginning of the research, a processing attempt was made of the raw ash residue (without pre-sintering) with water. At the same time, as shown by the results of experiments, the main part of gallium, vanadium and nickel remains in the insoluble residue. It was established that during water leaching of the crude ash residue, the output of V, Ga and Ni is in the limits of 0.7-2.24%.
Preliminary studies have shown that treatment of the ash residue with a solution of sulfuric acid (concentration - 15%) at a temperature of 900C and a leaching time of 2 hours leads to the extraction of 25.8% gallium, 7.6% vanadium, 25.4% aluminum and 78.4 % iron.
Component V2O5 SiO2 M2O3 Fe2O3 CaO MgO K2O Na2O NiO Ga2O3 Stotal
Content 22.65 14.54 9.9 16.4 5.9 3.92 3.8 2.5 3.4 0.01 7.85
Fig. 1. The radiograph of a) ash residue of fuel oil, (b) calcined ash residue: 1 - V2O3, 2 -
V2O5, 3 - CaSO4, 4 - Ca[(Al2Si2)O8], 5 - Ca2Al[(Si,Al)2O7], 6 - Fe2O3,7 - H4Al2Si2O9. AZERBAIJAN CHEMICAL JOURNAL No 1 2020
At the same time, the solution in a considerable amount polluted with iron, aluminum and other impurities. The leaching of the ash residue with a solution of sodium hydroxide also did not produce the desired result (Table 2). The extraction of vanadium and gallium in the solution did not exceed 30-43%.
Table 2. Influence of concentration of NaOH on the degree of extraction of vanadium and gallium from the ash residue (T = 80-900C, leaching time - 24 h, T:L=1:10, the amount of sample is 5 g)_
№ Concentration NaOH, % Recovery, %
V Ga
1 5.0 32.10 31.20
2 10.0 39.70 36.0
3 15.0 43.20 42.4
4 20.0 43.55 43.6
Under alkaline treatment, the bulk of the elements of the R(OH)2 and R(OH)3 groups, (R = Fe, Ti, Ni, Cr, Ca, Mg and others) remains in the solid residue, while vanadium, gallium and aluminum go into solution.
Insufficient recoverability of vanadium and gallium in a solution is connected with that in structure of ash residue the most part of vanadium and gallium is in the form of Spinels or is included in the structure of aluminosilicate compounds which are difficult to decompose. Authors of work [1] was also concluded that Ga and V in the ash residue are in the trivalent
3+
form, replacing Al3+ in the crystal lattice of aluminosilicate compounds.
Influence of sintering temperature on the extraction of V and Ga
Due to the fact that gallium and vanadium are leached efficiently in alkaline medium, the effect on the degree of gallium and vanadium extraction from the ash residue was studied during their thermal oxidation with alkaline additives (Na2CO3).
For the purpose of full extraction vanadium and gallium from the ash residue, their thermal oxidation with alkaline (Na2CO3) additives was previously carried out. The ash residue was mixed with pre-crushed Na2CO3 and sintered at various temperatures. During sintering, vanadium and gallium contained in the ash residue turn into a highly soluble form of vana-date and sodium gallate.
In Table 3 present the data on the dependence of the extraction of vanadium and gallium in solution on the sintering temperature of the material with soda.
Table 3. The influence of sintering temperature on the extraction of vanadium and gallium in solution,% (mass of ash residue - 2.5 g)_
№ Sintering temperature,^ Recovery,%
V Ga
1 500 50.00 49.80
2 500 50.10 50.20
3 600 56.90 56.90
4 600 56.50 57.20
5 700 62.00 66.40
6 700 63.10 65.00
7 750 71.30 82.00
8 750 77.80 82.30
9 800 91.70 91.00
10 800 91.90 92.40
11 900 90.10 90.20
12 900 89.60 90.40
As can be seen from the data given in Table 3, the degree of extraction of vanadium and gallium into a solution from a speckle ash residue during aqueous leaching reaches 91.90% for V, 92.40% for Ga. Apparently the preliminary thermal treatment of the ash residue with soda (8000C) contributes to the destruction of its silicate component, due to the oxidation of spinel particles, that intensifies the process of water leaching. When the temperature rises to 9000C, the degree of extraction of both elements decreases. This is due to the formation of ferritic compounds of vanadium and gallium, which are poorly soluble in water. Therefore, the optimal firing temperature should be considered 800° C.
Influence of duration of the sintering on the recoverability of vanadium and gallium
The influence of duration of sintering time at a temperature of 8000C on the recoverability of vanadium and gallium from the ash residue with soda was studied. The firing duration ranged from 30 to 120 minutes. The results of these experiments are given in Table 4.
As can be seen from Table 4, an increase in the duration of sintering from 30 to 120 minutes leads to an increase in the degree of extraction of both vanadium (98.60%) and gal-
lium (97.5%). At 30 min the duration of sintering, the degree of extraction of vanadium is 86.20% (for gallium 85.0%). Thus, the optimal duration of sintering should be considered 1.5 hours.
Table 4. The influence of the duration of sintering on the extraction of vanadium and gallium in solution (temperature - 8000C, the amount of soda - 2.5 g, the mass of the sample - 2.5 g).
Sintering time, hour Recovery rate, %
V Ga
0.5 86.71 85.0
1.0 90.00 89.2
1.5 98.60 97.5
2.0 98.60 97.5
The influence of the amount of soda during sintering on the extraction of vanadium and gallium in the solution
The influence of the amount of soda at sintering on the recoverability of vanadium and gallium from ash residue was investigated at a temperature 8000C and at the duration of sintering 1.5 hours. As can be seen from the data given in Table 5, an increase in the amount of added soda during sintering significantly affects
the recoverability of both elements (Ga, V) in the solution. It is established that the optimal amount of soda required for sintering is 1:1 (by mass). At the same time, the degree of extraction of vanadium and gallium reaches 98.6 and 97.5% respectively.
Table 5. The influence of the amount of soda during sintering on the extraction of vanadium and gallium in the solution (T- 8000C, time - 1.5 hour, ash mass - 2.5
№ Amounts of soda, gr Recovery rate , %
V Ga
1 1.0 42.04 43.5
2 1.25 51.50 52.0
3 2.0 93.60 92.5
4 2.5 98.60 97.5
5 3.0 98.60 97.4
Thermographic and thermo gravimetric methods of analysis were used to study the process of the ash cintering chemistry. In Figure 2. shows the derivatogram of the crude ash residue (a), as well as the ash residue, when mixed with soda in a mass ratio of 1:1. As can be seen from Figure 2 (a, b), a series of thermal effects (endo and exothermic) are recorded on the DTA curves.
t,0C
t,0C
1000 800 600 400 200
20 40 60 80 100 time, min
900 800 600 400
200
TG
DTG 730
-v 810
DTA
120
T ~>t ■ ■ ■ ■
10 30 50 70 90 time, min
a b
Fig. 2. a - derivatogram of the ash residue of fuel oil, b - derivatogram of ash and soda mixture (1:1).
On the DTA curves studied by us of both samples in the temperature range from 50 to 2000C there are three endothermic effects indicating that their decomposition occurs in three stages. The first stage, with endo-effect, at a temperature of 900C, refers to the release of moisture from the material, the second at 1400C, the third at 1800C, all endo-effects correspond to the dehydration of minerals contained in the ash residues. At temperatures above 3000C to 7300C, there are no significant changes in the condensed phase. Starting from 8000C, gases are released, that is marked on the DTA curves by abrupt mass loss. On the DTA curves, the endo-effect at 7300C belonging to the ash residue mixed with soda at a mass ratio of 1:1 was recorded at high speed. The cinder obtained at a sintering temperature of 8100C is easily and intensively dissolved in water, that indicates transforms V and Ga contained in the ash residue into the form of vanadate and sodium gallate, well soluble in water. Apparently the preliminary thermal treatment of the ash residue (780-8000C) contributes to the destruction of its silicate component, as well as due to the oxidation of spikelide, that intensifies the process of water leaching.
The sintering of the ash residue with soda was carried out at a temperature of 750-8000C, with air supply as an oxidizer. The maximum sintering temperature should not exceed 8500C. Above this temperature, the material melts, turning into an amorphous glassy mass, from which it is very difficult to extract vanadium and gallium. Fusion with soda and oxidizing sintering increases the degree of transition of valuable elements into a water-soluble form. After sintering, the cooled and calcined ash residue goes to leaching. The calcined material, after cooling, is leached out with water at 90-950C, with the ratio t: l, 1:5-10. It should be noted that under static conditions during the filtration all the formed hydroxides of iron, nickel, magnesium and calcium remain on the filter along with soot, and only vanadates, gallates and sodium aluminates soluble in water pass into the solution. Thus, based on the studies of all the kinetic factors affecting the recoverabil-
ity of vanadium and gallium from the ash residue at fuel oil burning, an optimal variant of soda treatment is proposed, which allows 9498% of vanadium and gallium to be extracted into the solution.
Under optimal conditions, the degree of extraction of vanadium and gallium in the solution is 96-98%. In the Table 6 presents the average chemical composition of the alkaline solution after the separation of R(OH)„, n = 2 and 3, (R = Fe, Ti, Ni, Cr, Ca, Mg).
Compounds V2O5 SiO2 AI2O3 Na2O Ga
Content, g/l 10.40 63.23 0.56 54.75 0.180
Alkaline solution containing 10.4 g/l V2O5, 63.23 g/l SiO2, 0.56 g/l Al2O3, 54.75 g/l Na2O and 180 mg/l Ga was neutralized with a solution of 1N sulfuric acid to pH 10.5. Thus more than 90% of leached Al and Si is precipitated as Al(OH)3 and H2SiO3, and more than 98.0% of Ga3+ remains in solution:
SiO2~+2H+^H2SiO3 ^ 2AlO^2H++2H2O=2Al(OH)3 I
In the processes of desiliconization, as mentioned above, the yield of silicon in the sediment reaches 97.9%, while the loss mass of vanadium is 3.4%. The composition of the purified solution obtained at pH = 10.5 is presented in table 7.
Table 7. The composition of the solution purified from Al and Si
Components V2O5 SiO2 AI2O3 Na2O Ga
Content, g/l 10.10 0.066 0.075 54.35 0.180
After separation of the Al(OH)3 and H2SiO3 precipitate, the solution is again neutralized to pH=7.5 with sulfuric acid and gallium oxide hydrate is precipitated from it. The precipitate of Ga(OH)3 is dissolved in hydrochloric or sulfuric acids and then gallium is extracted by the extraction [17].
From Table 7 it is seen that at pH=7.5 vanadium is in solution. On correcting the solution pH to 5-6 with sulphuric acid then 1 M ammonium chloride (NH4Cl) is added to the solution under sterring. The reaction (under sterring at 500C) is set to about 24 hours. Vanadium is
precipitated as ammonium metavanadate (NH4VO3). The obtained red colored cake of metavanadate is filtered, washed with distilled water, dried at 1000C for 24 hours and calcined at 7500C to obtain black vanadium oxide.
The residue obtained after alkaline treatment was additionally treated with a solution of sulfuric acid in the found optimal conditions (CH2SO4=5M, T=980C, x=3h, l/t=4), at the same time, 80% of nickel goes into solution in the form of sulfate. After separation of an empty breed, the resulting solution was neutralized with 8M NaOH to pH=5-6, Fe was precipitated from the solution by adding Na2CO3, at pH=7 NiCO3 was precipitated.
Conclusions
1. It is shown that gallium and vanadium can be completely extracted from the ash residue during sintering the material with soda at a temperature of 8000C and with a duration of 1.5 hours.
2. Extraction of gallium and vanadium into a solution at 90-950C from the burnt mass, at leaching by water in the investigated conditions, makes more than 97.5% for Ga, 98.8% for V. After the recovery of Ga and V, the residue was followed leaching with a sulfuric acid solution to recover nickel.
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MAZUTUN YANMASINDAN ALINAN KÜL QALIQLARINI SODA ÜSULU ÍLO BͧÍRMOKLO VO SUDA HOLL ETMOKLO VANADÍUM, QALLÍUM, VO NÍKELÍN ÇIXARILMASI SORAÍTÍNÍN TODQÍQÍ
L.T.Tagiyeva
Maqalada mazutun yandinlmasindan alinan kül qaliginin soda ila termooksidlaçmasi va biçirilmiç kütlanin suda hall olunmasi naticasinda qallium, vanadium va nikelin çixarilmsi çaraiti tatqiq edilmiçdir. Tadqiqatlar naticasinda agir neftin kül qaligindan V, Ga, va Ni-in yüksak çiximini tamin edan ekoloji tamiz yeni texnologiya taklif olunur. Prosesin optimal çaraiti tapilmiçdir. Müayyan edilmiçdir ki, biçirilma temperatura 8000C, kütlaca zol:soda nisbati 1:1, yanma vaxti 1.5 saat, hall olma temperatura 90-950C, bark:maye nisbati 1:(5—10), hall olma müddati 2 saat olduqda qallium va vanadiumun mahlula çiximi müvafiq olaraq 97.5 va 98.8% taçkil edir. Ga va V ayrildiqdan sonra qalan kül qaligi turçu ila içlanmakla Ni çixanlmasi çaraiti araçdirilmiçdir.
Açar sozter: qallium, vanadium, nikel, zol, hallolma, yanma, çixim faizi.
ИЗУЧЕНИЕ УСЛОВИЙ ИЗВЛЕЧЕНИЯ ГАЛЛИЯ, ВАНАДИЯ И НИКЕЛЯ ИЗ ЗОЛЬНОГО ОСТАТКА ПРИ СЖИГАНИИ МАЗУТА МЕТОДАМИ СПЕКАНИЯ И ВЫЩЕЛАЧИВАНИЯ
Л.Т.Тагиева
Исследованы условия извлечения галлия, ванадия и никеля из зольных остатков, образующихся при сжигании высокосернистых мазутов путем спекания с Na2CO3 и выщелачивания водой. Разработана новая технология, характеризующаяся более высоким извлечением галлия, ванадия и никеля, являющаяся экологически чистой для извлечения Ga, V и Ni из зольного остатка тяжёлой нефти. С целью полного извлечения Ga, V и Ni из зольного остатка предварительно проведено его термоокисление с щелочными (Na2CO3) добавками. Установлены оптимальные условия проведения процесса. Результаты показали, что степень выщелачивания ванадия и галлия составляет соответственно - 98.8 и 97.5%, в условиях эксперимента температура спекания составляла - 8000С, время обжига - 1.5 ч, оптимальное количество соды, необходимое для спекания, 1:1 по массе, температура выщелачивания - 90-950С, соотношение жидкой-твердой фаз составлялa( 5-10):1 и время выщелачивания - 2 ч. После отделения Ga и V, остаток золs дополнительно обрабатывался раствором серной кислоты для извлечения никеля.
Ключевые слова: галлий, ванадий, никель, извлечение, выщелачивание, спекание, зола.
