The creation and development of new science-intensive industries of high processing stages (5th, 6th and 7th stages) requires the expansion of production and the use of rare and rare earth metals. At present, these metals may well be obtained from coal or its waste, including accumulated ash and slag waste. At the same time, the approach aimed at extracting exclusively REM from ash does not seem promising, since in this case, the meaning of the complexity of the use of raw materials is lost. Given that the main components of the ash are oxides of aluminum, silica and iron, it is necessary to take into account the possibility of extracting the entire spectrum of metals. In this perspective, of great interest for practice can be a highly efficient technology for processing ash with a complex extraction of silica, aluminum oxide, iron and rare-earth metals into commercial products. Issues related to the study of the theoretical aspects of this technology are of great interest.
Creation of an innovative environmentally friendly, highly efficient waste-free technology for processing ash from coal combustion to produce high-purity silica, special pure aluminum oxide (Tabular Alumina), an iron-containing product and REM.
- Ensuring the reduction of ash waste through their complete utilization to obtain commercial products with high added value;
- exclusion of the use of expensive materials and reagents;
- exclusion of the formation of additional solid and / or liquid waste;
- improving the efficiency of CHPPs by involving ash waste in the processing as an additional source of raw materials for obtaining marketable products;
- expanding the range of commercial products;
- reduction of CHP costs by reducing the volume of accumulated ash and reducing existing energy and material costs spent on storage and storage of ash;
- ensuring stable conditions for complex ash processing through the use of new technical solutions («know-how»).
The results obtained for the 1st stage of the schedule:
1) New data on the thermodynamics of interaction reactions between ash components and calcium chloride have been obtained. A high probability of decomposition of mullite by calcium chloride in an oxidizing atmosphere to gehlenite (Ca2Al2SiO7) has been established. It has been established that the Gibbs free energy of the studied reaction sharply increases with increasing temperature from 1073 to 1373 K from ∆G1073K = -1226.0 kJ/mol to ∆G1373K = -2317.57 kJ/mol. It is shown that the formation of gehlenite increases in the presence of water, as evidenced by the high values of the Gibbs free energy, which at 1073 and 1373 K are: ∆G1073K = -1309.74 kJ/mol and ∆G1373K = -2524.42 kJ/mol.
2) It is shown that the formation of anorthite is less significant, due to the low negative values of the Gibbs free energy, which for temperatures of 1073 and 1373 K are: ∆G1073K = -46.39 kJ/mol and ∆G1373K = -55.74 kJ/mol.
3) New data on the thermodynamics and kinetics of the process of leaching the cinder with hydrochloric acid have been obtained. The mechanism of the leaching process has been established, which is described by the reaction of the interaction of anorthite and gehlenite with HCl with the formation of AlCl3 with its further transition to the mother liquor. It has been established that the rate of interaction reactions between anorthite and gehlenite with HCl increases at a temperature of 60 ºС and T:L=1:3.
4) The possibility of enrichment of iron from ash (up to 80%) by magnetic separation with the production of a commercial iron-containing product with a high iron content of ~50% has been experimentally proven. The material balance of the process was compiled, the elemental and phase composition of the magnetic and non-magnetic ash fractions were determined.
5) The optimal parameters for firing the non-magnetic ash fraction together with calcium chloride in an oxidizing atmosphere were determined: temperature - 1100 ºС, CaCl2 consumption - 2 times higher than its stoichiometric consumption required for mullite decomposition, firing duration, τ = 60 min. A maximum of more than 98% decomposition of mullite to easily soluble aluminum compounds - gelenite and anorthite has been achieved.
6) New data have been obtained on the leaching of cinder with hydrochloric acid with the selective transfer of aluminum, calcium, iron, non-ferrous metals and REM into the mother liquor and the release of silica in the form of a commercial product. The optimal parameters of the leaching process were determined - T:L=1:3, temperature, T=60 °C, leaching time, τ=60 min. Achieved the maximum extraction of aluminum into solution and silica into a commercial product - 99.92 and 99.8%, respectively.
7) For the first time, new data on the forms of finding the main components of ash in the cinder and leaching products have been obtained. It has been established that during the burning of ash with CaCl2, the quantitative ratio of the formed easily soluble compounds - gelenite and anorthite in the cinder, is 5:1.
8) New data on the distribution of Al, Ca, Fe, non-ferrous metals and rare-earth metals between the solid precipitate of silica and the mother liquor have been obtained. It has been established that under the conditions of the optimal leaching regime, only silica is precipitated, and the remaining metals, almost completely, pass into the mother liquor.
9) As a result of processing CHP ash according to the scheme "magnetic separation - roasting of the non-magnetic fraction of ash together with CaCl2 - leaching of the cinder with hydrochloric acid", an iron-containing commercial product and pure silica of the composition, wt %: 99.5 SiO2; 0.02Al; 0.07Ca; 0.02 Fe. Sediment whiteness - 92%, specific surface area (BET) - 165 m2/g, oil saturation (linseed oil) 140 g / 100 g.
List of performers :
- Dosmukhamedov Nurlan Kalievich - Scientific adviser
- Egizekov Maksut Gusmanuly - Chief Researcher
- Kaplan Valery Aronovich - Leading Researcher
- Zholdasbay Yerzhan Yesenbayuly - Senior Researcher
- Kurmanseitov Murat Bauyrzhanuly - Senior Researcher
List of publications:
- Kaplan V., Dosmukhamedov N., Zholdasbay E., Daruesh G., Argyn A. Alumina and Silica Produced by Chlorination of Power Plant Fly Ash Treatment // JOM. – 2020. – Vol. 72(10). – P. 3348–3357. (Web of Science, Scopus, Q-2, Процентиль-84-й.)
- Досмухамедов Н.К., Каплан В.А., Жолдасбай Е.Е., Даруеш Г.С., Аргын А.А. Выделение железа в железосодержащий продукт из золы от сжигания Экибастузских углей // Уголь. – 2021. – №1. – С. 56-61. (Scopus, Q-3, Процентиль-30-й.)
- N. Dosmukhamedov, V. Kaplan. Flue gas purification from SO2 and NOx using molten mixture of alkali metal carbonates // International Journal of Coal Preparation and Utilization. – 2021. – P. 1-12. (Web of Science, Scopus, Q-3, Процентиль-58-й.)
- Досмухамедов Н.К., Егизеков М.Г., Жолдасбай Е.Е., Курмансейтов М.Б., Аргын А.А. Поведение NOx при очистке отходящих газов ТЭС карбонатным расплавом щелочных металлов // Международный журнал прикладных и фундаментальных исследований. – 2021. – № 1. – С. 30-35. (РИНЦ, IF-0,58)
- Досмухамедов Н.К., Каплан В.А., Жолдасбай Е.Е., Курмансейтов М.Б., Аргын А.А. Электрохимическое восстановление CO2 до СО в условиях электролиза карбоната лития при 900 ºС // Международный журнал прикладных и фундаментальных исследований. – 2021. – № 3. – С. 59-66. (РИНЦ, IF-0,58)
- Dosmukhamedov N.K., Zholdasbay E.E., Daruesh G.S., Argyn A.A., Kurmanseitov M.B. Study of the mechanism of pre-burned ash leaching by hydrochloric acid // Complex Use of Mineral Resources. – 2021. – Volume 4, Issue 319. – Р. 72-80.
- Жолдасбай Е.Е., Курмансеитов М.Б., Даруеш Г.С., Аргын А.А., Досмухамедов Н.К., Егизеков М.Г. Концепция технологии комплексной переработки золы на основе хлорирующего обжига // II Международная научно-практическая конференция International scientific innovations in human life, 25-27 августа 2021 года Манчестер, Великобритания. – С. 130-136
- Жолдасбай Е.Е., Даруеш Г.С., Курмансеитов М.Б., Аргын А.А., Досмухамедов Н.К. К комплексной технологии переработки золы: Термодинамика хлорирующего обжига // III Международная научно-практическая конференция Modern scientific research: achievements, innovations and development prospects, 29-31 августа 2021 года Берлин, Германия. – С. 94-102