Abstract
Current methodologies for the extraction of tantalum and niobium pose a serious threat to human beings and the environment due to the use of hydrofluoric acid (HF). Niobium and tantalum metal powders and pentoxides are widely used for energy efficient devices and components. However, the current processing methods for niobium and tantalum metals and oxides are energy inefficient. This dichotomy between materials use for energy applications and their inefficient processing is the main motivation for exploring a new methodology for the extraction of these two oxides, investigating the microwave absorption properties of the reaction products formed during the alkali roasting of niobium-tantalum bearing minerals with sodium bicarbonate. The experimental findings from dielectric measurement at elevated temperatures demonstrate an exponential increase in the values of the dielectric properties as a result of the formation of NaNbO3-NaTaO3 solid solutions at temperatures above 700 °C. The investigation of the evolution of the dielectric properties during the roasting reaction is a key feature in underpinning the mechanism for designing a new microwave assisted high-temperature process for the selective separation of niobium and tantalum oxides from the remainder mineral crystalline lattice.
Highlights
Current methodologies for the extraction of tantalum and niobium pose a serious threat to human beings and the environment due to the use of hydrofluoric acid (HF)
The industrial treatment of Columbite group minerals (CGM) concentrates consists of the digestion of the concentrate using a mixture of sulphuric and hydrofluoric acid at temperatures between 250 and 300 °C to form niobium and tantalum fluorides, which are selectively separated by solvent extraction (SX) using an organic medium
In the context of engineering a novel technique for the extraction of niobium-tantalum oxides from columbite-tantalite minerals, we have reviewed the importance of dielectric properties of these two oxides for microwave processing, and on this basis we propose a combination of alkali roasting using microwave heating source as a first step in the conservation of energy and approaches for waste minimization
Summary
Current methodologies for the extraction of tantalum and niobium pose a serious threat to human beings and the environment due to the use of hydrofluoric acid (HF). The current processing methods for niobium and tantalum metals and oxides are energy inefficient. This dichotomy between materials use for energy applications and their inefficient processing is the main motivation for exploring a new methodology for the extraction of these two oxides, investigating the microwave absorption properties of the reaction products formed during the alkali roasting of niobium-tantalum bearing minerals with sodium bicarbonate. The industrial treatment of CGM concentrates consists of the digestion of the concentrate using a mixture of sulphuric and hydrofluoric acid at temperatures between 250 and 300 °C to form niobium and tantalum fluorides, which are selectively separated by solvent extraction (SX) using an organic medium. The organic extractants used in the SX processes are not optimized. The use of HF and organic solvents leads to potentially dangerous operations and serious environmental pollution. The process generates a substantial solid and liquid waste, which are difficult to dispose of because of their chemical reactivity
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