Demand for new and large energy storage systems is increasing for applications such as remote area power systems, wind turbine generators, load-levelling at electric power stations, as well as emergency back-up applications. The use of batteries as portable electrical power sources has also increased dramatically and to some extent technology has not been able to keep pace with demands. Longer cycle life and higher volumetric energy densities are needed for portable energy applications such as electric vehicles while load-levelling applications are more sensitive to cost.
Lithium and nickel metal hydride emerged more recently as excellent high energy density alternatives to conventional lead-acid and nickel-cadmium batteries although the relatively high cost of metal hydride has limited use to smaller-scale portable equipment and hybrid electric vehicles.
The redox flow cell appears to offer great promise as a low cost, high efficiency system for large-scale energy storage and the first generation vanadium redox battery (G1 VRB) is rapidly moving towards full commercialization in a wide range of stationary applications.
The VRB system employs vanadium redox couples in sulphuric acid in both half-cells and was pioneered by Prof. Maria Skyllas-Kazacos and her team at the University of New South Wales in Australia. The electrolyte used in vanadium redox batteries is a mixture of vanadium and sulphuric acid of acidity similar to lead-acid batteries.
Vanadium redox batteries are widely hailed as a strong contender for the alternative energy storage requirements. This technology could also potentially replace lead-acid batteries in UPS and other back-up uses, subject to competitive pricing of the vanadium-based electrolyte. The VRB market promises steady growth over the next few decades constrained mainly by price volatility of vanadium in steel alloying as its primary application. It follows that the successful commercialisation of VRB is contingent on access to low cost vanadium from sources decoupled from cyclical price and demand fluctuations of the construction industry globally.
The challenges with production of electrolyte are well described from the website of Cellenium Technologies: “Vanadium is commercially available as vanadium pentoxide (V₂O₅), or as ammonium vanadate (NH₄VO₃). In both these compounds the vanadium is in the oxidation state V⁵⁺. However, the electrolyte required for first filling vanadium regenerative fuel cells is acid vanadium sulfate with half the vanadium in the oxidation state V³⁺, and half in the state V⁴⁺. Unfortunately, vanadium pentoxide is only slightly soluble in sulfuric acid and water, and the methods used until now for preparing the acid vanadium electrolyte have been complex and costly chemical and electrochemical processes. The overall economics of vanadium fuel cells needs a better method of preparing the electrolyte from solid vanadium pentoxide.”
VENEX has overcome this through the use of ion exchange to enhance the efficiency of vanadium leaching from spent catalysts and other secondary sources. VENEX has developed and demonstrated viable technologies for recovery of vanadium from a number of these alternative sources including;
Recovery of vanadium from calcine residues previously demonstrated at Transvaal Alloys at commercial scales. This technology was also piloted at Vanchem in 2008 over a six month period using a dedicated mobile pilot plant. Potential sources in South Africa include EVRAZ Highveld, Vanchem, Rhovan and Vametco dumps. The EVRAZ Highveld stockpile is 16.5Mt of calcine residue and a detailed study confirmed >22,000 tons of recoverable V₂O₅. A provisional patent for the proposed recovery process is ready for refiling should this be required.
Recovery of vanadium from spent sulphuric acid catalyst
Vanadium-rich tailings from uranium plants processing carnotite deposits
Fly ash dumps from select petrochemical industries (various globally)
Baghouse dust and alumina slag material from ferro-vanadium alloy producing operations