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The development of efficient and environmentally friendly technological processes for processing zircon concentrate is an urgent problem in the technology of producing reactor-pure zirconium and hafnium used in nuclear power. The review presents the environmental, technical and economic characteristics of zircon decomposition processes using existing industrial technologies and provides data on the environmental safety of each technology. It is shown that current industrial technologies do not meet the criteria of sustainable development and allow emissions of toxic reagents into the environment. New applications of particularly pure zirconium and hafnium compounds which have emerged in recent decades, with impurity content of 10-3–10-5%, require less corrosive reagents than chlorine and fluorine, new resource-saving processes and equipment. Today, technical zirconium oxide with a purity of 98% is the main industrial product of zircon processing, but it allows for losses of hafnium, scandium and silicon. This is equivalent to financial losses of over USD 150 million per year. Based on the analysis of promising halogen-free technologies, a new integrated zircon processing technology is proposed which allows producing scarce hafnium, scandium and silicon compounds along with reactor-pure zirconium and its high-purity chemical compounds. The chemicals consumed in the zircon processing process are utilized in the production of mineral fertilizers, eliminating environmental pollution. The use of the highly efficient refining extraction process in a nitric acid environment using centrifugal extractors with an available tributilphosphate extractant allows us to obtain reactor metals with a purity of 99.95%. The production of high-purity zirconium, hafnium, scandium and silicon oxides meets the demand for non-nuclear products, which expands the volume of integrated zircon processing and meets the growing market demand for new functional materials. The integrated approach to zircon processing can reduce the cost of zircon by producing by-products, recycling consumed reagents and eliminating non-recyclable solid and liquid waste. This will ensure environmental protection even with relatively small volumes of reactor-pure metal production.
The development of efficient and environmentally friendly technological processes for processing zircon concentrate is an urgent problem in the technology of producing reactor-pure zirconium and hafnium used in nuclear power. The review presents the environmental, technical and economic characteristics of zircon decomposition processes using existing industrial technologies and provides data on the environmental safety of each technology. It is shown that current industrial technologies do not meet the criteria of sustainable development and allow emissions of toxic reagents into the environment. New applications of particularly pure zirconium and hafnium compounds which have emerged in recent decades, with impurity content of 10-3–10-5%, require less corrosive reagents than chlorine and fluorine, new resource-saving processes and equipment. Today, technical zirconium oxide with a purity of 98% is the main industrial product of zircon processing, but it allows for losses of hafnium, scandium and silicon. This is equivalent to financial losses of over USD 150 million per year. Based on the analysis of promising halogen-free technologies, a new integrated zircon processing technology is proposed which allows producing scarce hafnium, scandium and silicon compounds along with reactor-pure zirconium and its high-purity chemical compounds. The chemicals consumed in the zircon processing process are utilized in the production of mineral fertilizers, eliminating environmental pollution. The use of the highly efficient refining extraction process in a nitric acid environment using centrifugal extractors with an available tributilphosphate extractant allows us to obtain reactor metals with a purity of 99.95%. The production of high-purity zirconium, hafnium, scandium and silicon oxides meets the demand for non-nuclear products, which expands the volume of integrated zircon processing and meets the growing market demand for new functional materials. The integrated approach to zircon processing can reduce the cost of zircon by producing by-products, recycling consumed reagents and eliminating non-recyclable solid and liquid waste. This will ensure environmental protection even with relatively small volumes of reactor-pure metal production.
To date, reactor-grade zircon is produced on an industrial scale using metallothermic and electrochemical methods. Electrolytic production of reactor-purity zirconium in a sealed electrolyzer is more cost-effective than metallothermic production, as it does not require iodide refining and the use of reducing metals (Na, Mg, and Ca). Despite the importance of this production, its features are not fully described in the literature. This study presents the results of industrial tests of the electrolysis process in a sealed electrolyzer with a current load of 10 kA from the molten electrolyte KCl–KF–K2ZrF6. Based on the achieved technological indicators, the current efficiencies of the main cathode and anode reactions were determined and the factors influencing them were evaluated. We analyzed the composition of nutrient salts and the mechanism of accumulation of potassium fluoride in the electrolyte, an increase in which concentration leads to an anode-destroying effect. We considered possible mechanisms of the electrochemical formation of freons and compiled material balances for all starting substances and reaction products. The change in the electrolyte density during electrolysis was calculated, which allowed justifying the volume of its daily drainage. Fine carbon and zirconium powder formed in the electrolyte due to the interaction with potassium metal are not separated and are removed for chemical redistribution, which reduces the productivity of the electrolysis process.
The paper analyzes promising industrial processes for obtaining electrolytic hafnium powder. It is shown that extraction and iodide refining are the main processes used to purify hafnium from impurities, achieving both reactor-grade and high purity. The conducted studies have demonstrated the possibility of creating an alternative, more economical, and environmentally safe technology for hafnium recovery, compared to the current magnesium-thermal method. Production of reactor hafnium by electrolysis from molten electrolyte K2HfF6–KCl–KF is possible due to obtaining hafnium oxynitrate salt of nuclear purity and the creation of a hermetic electrolyzer. It is shown that the process of electrolysis leads to the accumulation of potassium fluoride in the electrolyte and requires its periodic draining with deterioration of technological indicators associated with increased recycling of the electrolyte. It was found that along with hafnium, metallic potassium is released on the cathode, which additionally worsens the technical and economic indicators of production. Sealing the electrolyzer makes it possible to create an overpressure of anode gas and determine its quantitative and chemical composition. Processing hafnium cathode sludge with potassium carbonate solution preserves the potassium cycle in the system and eliminates the effluents generated by ammonium carbonate.
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