Abstract
Tantalum, niobium, and their oxides are important precursor materials, essential for high-temperature alloys and electronic devices. The primary hydrometallurgical extraction technique to extract tantalum and niobium from minerals involves hydrofluoric acid (HF) digestion of the concentrates, followed by solvent extraction as an oxide separation and purification step. Solvent extraction, on the other hand, releases organic solvents which are lost irreversibly via natural evaporation during the process. This research demonstrates a novel chemical process for the extraction and refining of columbite and tantalite concentrates (29% Ta2O5 and 16% Nb2O5). In this process, the concentrates are reduced using carbon and alkali in the temperature range of 800–950 °C, which helps in reducing and magnetically separating the iron oxides present in the concentrates as metallic iron. The remaining residue is rich in alkali complex (e.g., sodium tantalates and niobates) formed during the roasting process which was reclaimed as a purified mixture of oxides of Nb2O5 and Ta2O5, by using oxalic acid leaching, followed by sodium bisulphate roasting.
Highlights
Niobium, tantalum, and their oxides are considered strategic mate rials due to being key components in the manufacturing of energy de vices and systems
The largest end-use market for niobium is in HSLA steel, for which the demand is expected to grow at 5–7% per year in the building and construction sector (Moreno, 2011)
The samples used in this study were supplied by the TantalumNiobium International Study Centre from the Democratic Republic of Congo (DRC)
Summary
Tantalum, and their oxides are considered strategic mate rials due to being key components in the manufacturing of energy de vices and systems These two metals remain in large demand for developing advanced structural steels (Moreno, 2011), nu clear (El-Genk and Tournier, 2005) and aerospace alloys (Upadhya et al, 1997). To remove or minimize the use of HF in the process, chlorination, and carbo-chlorination with gaseous mixtures of N2-Cl2 and N2-Cl2-CO, the use of sodium salts as complexing agents in mixtures such as NaF-HF and Na2C2O4-HF and digestion of the concentrates with NH4NF2 have been investigated (Brocchi and Moura, 2008; Gonzalez et al, 1998; Kabangu and Crouse, 2012; Mudzanapabwe et al, 2004; Rodriguez et al, 2016) These improvements have been focused on decreasing the amount of HF employed or its replacement for chlorine gas which still do not meet the sustainability criteria required in modern societies due to the toxic nature of chlorine gas and fluoride salts (Deblonde et al, 2019). The Ta and Nb oxides obtained can be used as feed for their respective metal/alloy production
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