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MEI Online: Hydrometallurgy: Latest News: October 3rd 2005


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:: Vanadium Solvent Extraction Successfully Piloted at Vanchem

Because of numerous oxidation states and narrow regions of species stability, vanadium has eluded efforts to develop a robust refining process over many years. Anglo American Research Laboratories (AARL) has been working with Highveld Steel and Vanadium Corporation (Vanchem) to address this and recently brought together many years' work in this field to successfully pilot a vanadium solvent-extraction (SX) circuit.This process will produce a high purity ammonium decavanadate electrolyte intermediate product from which the AMV and vanadium pentoxide are produced.

Following evaluation of various SX and ion-exchange options by AARL, a tertiary amine extractant was selected for a pilot-plant trial to produce an upgraded high-purity vanadium electrolyte from the Vanchem desilicated liquor.The four-week piloting campaign was carried out at the Witbank site during February 2005. Desilicated liquor was sourced from Vanchem and approximately 1 mVday processed through the SX circuit. The loaded strip liquor (LSL) produced a high-purity ammonium decavanadate solution which was returned to Vanchem for processing with ammonia to yield ammonium metavanadate. As necessary, this product can be calcined to yield V2O5.

The objective of the piloting campaign was to commission and run the process under continuous conditions to assess the suitability of the proposed flowsheet for the treatment of the desilicated liquor with respect to chemistry, operability, and process control. The design and operating parameters for a full-scale circuit were confirmed and sufficient mass-balance data obtained to be used in the design and costing of a full-scale circuit.

The vanadium SX process is strongly influenced by pH in both the extraction and strip circuits, and inadequate control of this variable can cause irreversible precipitation of either the so-called "red cake" in the extraction circuit or "yellow cake" in the strip circuit. Essential to the success of this piloting campaign was the use of more sophisticated monitoring equipment than has been previously available. Excellent pH stability control was achieved using modern pressurised gel-based pH probes linked to automatic dosing controllers, and as a result an AMV product well within the target specification was produced.




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