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DEVICES AND METHODS OF EXTRACTING COLORFUL AND NOBLE METALS
INVENTION
Patent of the Russian Federation RU2293134

METHOD FOR EXTRACTING RARE-EARTH METALS AND YTTRIUM FROM COALS AND SULFUR WASTES FROM THEIR INJECTION

METHOD OF EXTRACTING RARE-EARTH METALS AND YTTRIUM
FROM COAL AND SLUDGE WASTES FROM THEIR INCINERATION

The name of the inventor: Kuzmin Vladimir Ivanovich (RU); Pashkov Gennady Leonidovich (RU); Kartseva Nadezhda Vladimirovna (RU); Okhlopkov Semen Semenovich (RU); Kichkin Vladimir Romanovich (RU); Suleymanov Albert Mikhailovich
The name of the patent holder: Institute of Chemistry and Chemical Technology of the SB RAS (IHTT SB RAS) (RU); OAO Nizhne-Lenskoye
Address for correspondence: 660049, Krasnoyarsk, K. Marksa, 42, Institute of Chemistry and Chemical Technology SB RAS, Patent Department
Date of commencement of the patent: 2005.05.26

The invention relates to the field of hydrometallurgy, in particular to the technology of extracting rare and rare-earth metals from natural organic raw materials - coal and its combustion products - ash-and-slag wastes. The technical result of the invention is to reduce the consumption of reagents (acids) for leaching rare-earth elements from coals or ash-and-slag wastes and to simplify the process of extraction and purification of these metals during processing of leach solutions. It is achieved through the use of nitric acid for leaching, selective isolation of rare earth nitrates by extraction with organic solutions of tributyl phosphate and the use of part of the heat from the combustion of coals for the regeneration of nitric acid by thermal decomposition of raffinates and calcium, aluminum, iron and other metal nitrates contained therein.

DESCRIPTION OF THE INVENTION

The invention relates to the field of hydrometallurgy, in particular to the chemical technology of extracting rare and rare earth elements from natural organic raw materials (coals) and products of its combustion - ash and slag wastes.

Various methods of extracting valuable elements (including rare earths) from the mineral part of coals are known, which consist in the chemical treatment of ash and slag waste after the combustion of coal with various chemical reagents. The main method for processing ash and slag wastes is to open them with acidic reagents, which can be used both as mineral acids and as organic cation exchangers in the H + -form.

With sulfuric acid opening of ash and slag wastes from the burning of Ekibastuz coals, extraction of up to 98-99% of rare-earth metals into solution is achieved / VF Borbat, LN Adeeva and others. Investigation of the possibility of obtaining rare-earth elements from the fly ash of CHPP // Tez. Doc. Int. Conf. "Rare earth metals: processing of raw materials, production of joints and materials based on them". Krasnoyarsk. 1995. P.108-1091. The basis of Ekibastuzsky ash consists of: SiO 2 - 61.5%, Al 2 O 3 - 27.4%, Fe 2 O 3 - 5.6%, CaO - 1.2%, MgO - 0.5%, other elements less 4%. The process is carried out at 50 ° C and the concentration of sulfuric acid is 100 g / l.

A method for the sulfuric acid leaching of radioactive, rare and rare-earth elements is also known, by treating the ash with a solution of sulfuric acid with the addition of 0.5-25 g / l to the sodium chloride solution in order to intensify the process / Pat. 213839. Russia, IPC 6 B 03 B 9/06, C 04 B 7/28. VF Borbat, LN Adeeva, OA Nechaeva, Yu.L. Mikhailov. Method of preparation of fly ash from combustion of coals for use as building materials. The process is carried out at a sulfuric acid concentration of 50-300 g / l at a ratio of T: H = 1: 4-10 and a temperature of 18 to 90 ° C. The recovery can be carried out in a stirred tank reactor during 1-6 hours or in heap leaching. In the latter case, the process temperature is maintained at 18-40 ° C.

A method is known for the extraction of scandium and yttrium from ash-and-slag wastes with hydrochloric acid / AA Kontseva, AD Mikhnev, GL Pashkov, LP Kalmykova. Extraction of scandium and yttrium from ash and slag wastes. ZhPH. - 1995. - T.68, issue 7. - From 1075-1078 /. The extraction is carried out from ash-and-slag waste from burning of brown coal, composition: SiO 2 - 40,1%, Al 2 O 3 - 10,6%, Fe 2 O 3 - 8,5%, CaO - 7,4%, MgO - 8 , 3%. It is proposed to leach scandium and yttrium in 2-3 stages by reusing leachate filtrate. Leaching is carried out with 10% HCl solution when heated. At the same time, the degree of extraction into the solution is reached: scandium - 84% and yttrium - 92%. It was found that this cross-leaching leads to a significant saturation of the solution with salts of calcium, magnesium, iron and aluminum. The high concentration of salts makes it difficult to separate the solid from the liquid phases.

The process closest to the proposed method for extracting rare-earth metals from ash-and-slag wastes is the GG Pashkov, RB Nikolaeva et al. Sorption leaching of scandium from ash-and-slag wastes from the combustion of brown coals of the Borodino section / Tez. Reports of the International Conference "Rare-earth metals: processing of raw materials, production of compounds and materials based on them". Krasnoyarsk. 1995. P.104-106 /, combining leaching and sorption (sorption leaching). According to this method, the acidified pulp of ash-and-slag wastes is mixed with sulphocathionite KU-2 at a temperature of 40-60 ° C. This provides a transition to scandium ionite and rare earth metals. At the same time, calcium was leached out, its residual concentration in the ash does not exceed 0.2% with a content of about 20% in the initial ash. A considerable part of iron does not leach out under these conditions.

To remove the bulk of the calcium, the sorbent is then treated with a 1 M sodium sulfate solution acidified to 0.1 M sulfuric acid. In this case, the ion exchanger is transferred to the H-form, and calcium is separated in the form of gypsum.

The disadvantages of the known processes of extracting rare-earth metals from ash-and-slag wastes are: a large consumption of acids to neutralize the oxides of macroelements (calcium, magnesium, strontium, aluminum, iron) ash-and-slag wastes and the problems of separating rare-earth metals from complex solutions.

Thus, the most abundant ashes of rare earth metals contain 100-1000 g / kg (0.01-0.1%) of rare earth elements with a content of only one calcium oxide of 10-20% or more, the neutralizing ability of which is much higher than the neutralizing ability of rare earth oxides Metals. For such ash-and-slag waste, acid overexposure due to their reaction with calcium compounds alone will be 200-5000 times or more, respectively. The use of sorption leaching does not eliminate this drawback, since the practical use of sorption leaching involves a complete regeneration of the cation exchanger, which is achieved at the stage of desorption of cations by treatment of ion exchangers with the same mineral acids.

Another significant drawback of known processes is the problems of separating rare-earth metals from sulfuric and hydrochloric acid solutions, taking into account the complexity of the salt composition.

The known sulfuric acid processing schemes for rare-earth concentrates are generally multi-stepped and include operations for precipitation of sparingly soluble rare earth sulfates with sodium, subsequent hydrolysis of precipitation with sodium hydroxide, dissolution of the rare earth hydroxides formed by nitric acid, and purification by extraction.

The closest analogue to the set of essential features is RU 93051055 A (IPC C 22 V 59/00, published on September 27, 1996), which discloses a method for extracting rare earth metals and yttrium from coals and ash and slag wastes from their combustion, including acid leaching and extraction Rare earth metals and yttrium from solutions with alkyl phosphate. The technical result is a reduction in the consumption of reagents (acid) for leaching and simplification of the extraction and purification process in the processing of leach solutions.

The technical result is achieved by the fact that rare earth metals and yttrium from coals and ash and slag wastes from their combustion and extracted by acid leaching and their extraction from solutions by tributyl phosphate, but unlike a similar analogue, rare earth metals and yttrium are leached with nitric acid, which is regenerated by utilization of associated heat From combustion of coals by thermal decomposition of raffinate nitrates obtained after extraction and absorption of waste gases by water.

The use of nitric acid for leaching provides, first of all, the possibility of using a universal, highly selective to rare earth metals and the most widely used in practice process of extraction with tributyl phosphate. This process is well studied and can be used for the selective separation of rare-earth metals from most elements. Moreover, such basic macroimpurities from the leaching of ash and slag wastes with nitric acid, such as calcium, aluminum and iron nitrates, are salting out agents when extracting rare-earth metals with tributyl phosphate, facilitating their extraction into the organic phase. The reextraction of metal salts and the regeneration of the extractant are not very complicated and are carried out with water.

On the other hand, the use of nitric acid in the leaching stage of rare earth metals makes it possible to use part of the excess heat from burning coal for acid regeneration due to the thermal decomposition of nitrates. This process for calcium nitrate begins to flow at a temperature of 500-600 ° C and intensively at 600-700 ° C. Aluminum and iron nitrates decompose at a lower temperature. The decomposition of these salts leads to the formation of oxides of the corresponding metals, nitrogen dioxide and oxygen, as, for example, for calcium nitrate (1):

Absorption of formed gases by water provides regeneration of the initial nitric acid by the reaction (2):

The theoretical heat consumption for regeneration of the acid required for leaching 1 ton of calcium oxide, calculated from the enthalpy of reaction (1), is about 1.6 × 10 6 kcal / ton. With an average caloric value of 4000 kcal / kg, the specific coal consumption will be 400 (kg of coal) / (t CaO). With an ash content of 10% and an acid soluble mineral content of not more than 50% (calculated on calcium oxide), the consumption of coal for acid regeneration will be about 2% of its total combustible mass.

Example 1 . The ash from coal combustion in the Chaidakh-Yuryakh river basin (Sakha-Yakutia Republic) containing: 0.11% yttrium, 0.25% lanthanum, 0.52% cerium, 0.022% dysprosium, 0.008% ytterbium, etc. The rare earth elements are heated with stirring With a 3M (~ 17%) solution of nitric acid at T: F = 1: 8, at a temperature of 90 ° C for 1 hour. The yield of cake is 61%. 91% of yttrium, 75% of lanthanum, 72% of cerium, 90% of dysprosium, and 93% of ytterbium are extracted into the solution. The solution is evaporated 1.5-2 times and emulsified with 80% tributylphosphate in kerosene at O: B = 1: 1. The distribution coefficients in the organic phase are, respectively: 40 for yttrium, more than 5 for lanthanum and cerium, more than 30 for dysprosium and ytterbium. When the extract is contacted with water in the ratio O: B = 5: 1, a complete reextraction of the rare-earth metals is achieved.

The raffinate is further evaporated and the precipitate is calcined at 700 ° C. for 1 hour. The degree of decomposition of salts is more than 98%.

Example 2 . The ash from the burning of brown coal from the Borodino Basin (Krasnoyarsk Territory) containing 0.008% of yttrium is heated with stirring with 4M (~ 17%) nitric acid solution at T: H = 1: 5, at 90 ° C for 1 hour. The yield of cake is 49%. 89% of yttrium is recovered in the solution. The solution and washings are evaporated to the original volume and mixed with 80% tributyl phosphate in kerosene at O: B = 1: 1. The coefficients of the distribution of yttrium into the organic phase are more than 20. When the extract is contacted with water in a ratio of O: B = 5: 1, a complete reextraction of the salts of rare-earth metals is achieved.

The raffinate is evaporated, the precipitate is calcined at 700 ° C for 1 hour. The degree of decomposition of salts is more than 98%.

Example 3 . The ash from coal combustion in the Chaidakh-Yuryakh river basin (Sakha-Yakutia Republic) containing: 0.15% yttrium, 0.27% lanthanum, 0.085% cerium, 0.025% dysprosium, 0.0079% ytterbium and other rare earth elements, heated at Stirring with 4.5M (~ 25%) with a solution of nitric acid at T: F = 1: 3, at a temperature of 90 ° C for 1 hour. The yield of cake is 67%. The solution is extracted: 90.8% of yttrium, 72% of lanthanum, 70% of cerium, 97.5% of dysprosium, and 91.3% of ytterbium. In extractors of the "mixer-settler" type, counter-current extraction of REM with 80% tributyl phosphate in kerosene is carried out at O: B = 1: 1 (3 stages), washing the extract with 1M nitric acid solution at O: B = 30: 1 (2 stage with recirculation of water Solution) and reextraction with water O: B = 10: 1 (2 steps). The recovery of rare earth metals from the solution after leaching into the re-extract is more than 95%. A rare-earth product with an impurity content of less than 10% (mass) to REM oxides is obtained.

The raffinate is evaporated and the precipitate is calcined at 700 ° C. in a rotary kiln for 2 hours. The nitric acid vapor is captured in the absorption column by water. As a result, a 25% nitric acid solution is obtained with a yield of 92% of its initial amount taken for the leaching of the ash.

Example 4 . Coal of the Chaidakh-Yuryakh river basin (Republic of Sakha-Yakutia) containing 149 g / t-yttrium, 160 g / t-lanthanum, 380 g / t-cerium, 28 g / t-dysprosium, 16 g / t-ytterbium And other rare earth elements are heated with stirring with a 1M solution of nitric acid at T: H = 1: 5 at 90 ° C for 1 hour. The recovery into the solution, respectively, is: 74.3% for yttrium, 80.1% for lanthanum, 85% for cerium, 80% for dysprosium, 69% for ytterbium. After evaporation of the solution, the rare earth nitrates are extracted with tributyl phosphate and reextracted with water. The extraction of the REM for 1 stage of extraction is more than 75%.

Thus, the proposed method makes it possible to extract rare-earth metals from coals or ash-and-slag wastes, isolating them into a concentrate with high extraction rates (over 80%) and purification. The quality of a rare-earth product with respect to the content of impurities in it by using the extraction of rare-earth metals from nitrate solutions with tributylphosphate can be brought to practically any level, depending on the number of stages of washing and re-extraction. At the same time, the use of available heat from coal combustion and thermal instability of nitrates allows the main chemical reagent, nitric acid, to be regenerated and reagent costs reduced many times.

CLAIM

A method for extracting rare earth metals and yttrium from coals and ash and slag wastes from their combustion, including acid leaching and extraction of rare earth metals and yttrium from tributyl phosphate solutions, characterized in that rare earth metals and yttrium are leached with nitric acid, which is recovered by utilization of associated heat from coal combustion By thermal decomposition of the raffinate nitrates obtained after extraction and water absorption by the exhaust gases.

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Date of publication 14.03.2007gg