Pyrochlore, which contains some rare metals such as tantalum and niobium and many yttrium group rare earths such as erbium and ytterbium, is of very high commercial value. Therefore, it is very important to efficiently recover valuable metals from pyrochlore.
To date, tantalum-niobium ores such as pyrochlore have been treated by using various methods including alkali digestion, acid leaching and chlorination. At present, NaOH or KOH melting digestion method is not applied to the industry due to its low digestion rate, high energy consumption, high reagent consumption and dangerous operations. The consumption of alkali in the pressure leaching is lower than that in the melting digestion, but it is also not applied to the industry due to its operation difficulties. Concentrates are digested at 120-200℃ with concentrated sulfuric acid in the sulfuric acid leaching, which has some drawbacks such as low digestion rate, complex process and high reagent consumption. In the hydrofluoric acid leaching, concentrates are leached at 90-100℃ with 60% HF. This method is now widely used in the industrial processes due to its high tantalum leaching rate (>85%) and easy production of high-purity tantalum. However, the wastes of about 10-15 tons containing fluorine are produced when 1 ton of concentrates is treated, which leads to serious environmental pollution. What is more, the tantalum leaching rate decreases below 85% when low-grade niobium-tantalum concentrates are treated, so this method causes wastage of resources.
Recently, the KOH sub-molten salt (SMS) leaching has been applied to treating ilmenite, vanadium slag, chromite ore and fergusonite, bringing successful results. This technology has several advantages including low environmental pollution, low reagent consumption, mild degradation conditions and high recovery of valuable metals.
Considering all the preceding studies, Kang Chung Su, a section head at the Institute of Analysis, investigated a new decomposition method of pyrochlore concentrate into high KOH solution in order to effectively recover tantalum and niobium from pyrochlore concentrates while reducing environmental pollution at the same time.
The results showed that when the pyrochlore concentrate with a particle size of less than 75㎛ is added to 80% KOH solution in a mass ratio of KOH to concentrate 3:1, and decomposed at 300℃ for 2h at the stirring rate of 80r/min, 95% decomposition rate of pyrochlore concentrate is guaranteed.
You can find more information in his paper “Study on the Environmental Friendly Decomposition Method of Pyrochlore Concentrate in High KOH Solution” in “Proceedings of KUTIC-2025”.