One-Step Preparation of High-Purity Sodium Tungstate from Wolframite via Alkali Fusion and the Mechanism of Impurity Directional Migration

TL;DR

A new method is developed to efficiently produce high-purity sodium tungstate from wolframite with reduced waste and energy use.

Contribution

A novel phase-regulated alkali fusion method is introduced for one-step high-purity sodium tungstate production.

Findings

Sodium tungstate purity of 98.76% and tungsten recovery rate of 98.91% were achieved.

Impurities like Fe and Mn were retained in slag, ensuring product purity.

The method enables phase separation at 1000°C through silicate slag immiscibility.

Abstract

The extraction of high-purity sodium tungstate from complex wolframite concentrates presents significant challenges due to the limitations of conventional processing methods, which are often energy-intensive and generate substantial secondary waste. In this study, we propose a novel phase-regulated alkali fusion approach for the one-step production of high-purity Na2WO4. Using phase-diagram calculations with FactSage in the Na-Fe-Mn-Si-O system, SiO2 was introduced to regulate slag formation, promoting immiscibility between the silicate slag and Na2WO4 melt. This resulted in a clear stratification of the phases at 1000 °C, enabling spontaneous separation of the Na2WO4-rich salt phase from the slag. The optimized conditions achieved a sodium tungstate purity of 98.76%, with a tungsten recovery rate of 98.91%. Furthermore, impurity elements such as Fe and Mn were preferentially retained in stable silicate/oxide phases within the slag, contributing to the high purity of the sodium tungstate product. This method offers a simplified and environmentally friendly alternative to traditional hydrometallurgical and pyrometallurgical processes, with significant implications for the efficient utilization of complex tungsten resources.

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