No abstract

This paper looks at the pyrochlore-monazite-goethite ores of the Chuktukonsk deposit (0.98wt.% Nb2O5) and their processing with the help of acidbased (HNO3, H2SO4) and sulphatization techniques. Nitric-acid pressure leaching was found to be an efficient processing technique for this type of ore: ore size –0.074 mm; CHNO3 = 25%; CH2O2 = 5%; τ = 2 h; solid-to-liquid = 1:9; heat treatment mode: 1 h at 160 oC followed by 1 h at 230 oC. As a result, rare earth metals and manganese are leached to the solution while all of the contained niobium remains in the cake. Two different techniques were tested to recover niobium from the cake. One is based on the use of alkali (NaOH sintering), the other is an extractive leaching technique that combines acid leaching with liquid-liquid extraction of tributyl phosphate in one stage. It was established that niobium mi nerals can be efficiently decomposed when using a mixture of hydro fluoric and sulphuric acids with the concentrations of 4.08 and 8.46 mol/L, correspon dingly, as a leaching agent. At the weight ratio of 1:2:1 of the solid to aqueous to organic phase and after the slurry has been stirred intensively for 5 minutes, niobium fluorides, which form as a result of interaction between hydrofluoric acid and the cake components, can be recovered with a 50% solution of tributyl phosphate in octane. After that they transfer to an organic phase while impurities get accumulated in the solid residue. As niobium-containing cake has a high concentration of silicon, it is recommended to first remove silicon from the cake using a strong alkaline solution.

Исследование посвящено созданию люминофора на основе фторида кальция, легированного редкоземельными элементами: 5% Yb, 1% Er, с использованием методики синтеза из раствора в расплаве. В качестве растворителя использован нитрат натрия NaNO3, в качестве фторирующего агента – фторид натрия NaF. Полученные образцы охарактеризованы методами рентгенофазового анализа, рентгеноспектрального микроанализа, растровой электронной микроскопии и люминесцентной спектроскопии.В ходе работы исследовано влияние параметров синтеза на фазовый состав и морфологию частиц. Было установлено, что для формирования однофазных образцов – твёрдых растворов на основе фторида кальция – необходимо проводить синтез при температуре не ниже 400 °C, оптимальное время выдержки составило 3 ч. Установлен состав полученных образцов, он отличается от номинального и может быть записан как Ca0.88(Yb, Er)0.06Na0.06F2. 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The article is dedicated to finding out the specific features of the behavior of rare-earth metals in hydrometallurgical processing of pyrochlore-monazite-goetite ores of the Chuktukonsky ore field is shown in the work. Chuktukonsky ore field is a potential source of rare earth metals. The mentioned ores are practically unenforceable. Hydrometallurgical methods for their complex processing were suggested. Agitational and autoclave nitric acid leaching depending on such technological parameters as temperature, HNO3 concentration, process duration, S:L ratio and the use of H2O2 were studied. The possibility of transferring manganese (that is present in a significant amount in the ore) into a nitric acid solution by hydrogen peroxide was considered. Based on the results of the conducted studies, the distribution of REM in the products of the hydrometallurgical conversion of pyrochlore-monazitegoetite ore was estimated. It was found out that incomplete opening of the ore material was observed during agitational leaching: average REM recovery into the solution is 60%. The study made it possible to solve the problem of purifying nitric acid solutions from phosphorus that hinders the subsequent extraction and separation of rare earth metal ions forming strong complexes with rare earths. Removal of phosphorus from the solution was achieved by conducting the process under pressure at elevated temperatures (200-230 0C). It was found that the optimal decomposition conditions ensuring the transfer of almost 99% of the REM into the nitric acid solution are: 25% solution of HNO3, ore size - 0.071 mm; 5% by volume H2O2; t(160 0С) = 1 h; t(230 0С) = 1 h, gradual temperature increase from 160 to 230 0С; S:L = 1:8. Autoclave nitric-acid leaching allows selecting rare earth metals from the main part of iron, phosphorus and niobium.