Recovery of valuable metals from spent HEV NiMH battery leach solutions
Abstract: As the demand on resources is increasing worldwide, the process of recycling material has become more important. The specific recycling of metals used in car batteries, and more specifically in the large batteries used in hybrid electric vehicles, is a rising concern where the industrially implemented recycling processes concerning these batteries that exist today are often highly pollutant and energy consuming. In the present study, an alternative hydrometallurgical recycling process of the previously and to some extent presently widely used battery type for hybrid electric vehicle applications, namely the Nickel Metal Hydride (NiMH) battery, has been investigated. The focus was to evaluate different routes of recovering Ni, Co, Mn, Zn, Al and residual Y from a NiMH battery leach solution as obtained in a priorly conducted leaching study. Three different possible products were chosen for closer investigation, a mixed metal hydroxide where all of the metals would be precipitated together, a new NiMH cathode material where a controlled precipitation of Ni, Co and Zn together would be implemented and last a pure Ni salt product where a selective separation of Ni from the other metals would be required. Two of the three products, the mixed metal hydroxide and the pure Ni salt, were found suitable for the specific system and it was concluded that a pure Ni salt production would be most justifiable. The separation of Ni from the other metals present in the solution was here proposedly achieved by an extraction process using supported liquid membranes. A mathematical model was used in Matlab in order to evaluate the separation efficiency and to determine the optimum process conditions for the extraction process and a hydroxide precipitation experimental study was conducted in order to determine both the process streams in the production of a mixed metal hydroxide and the solution behavior during the pH increase in the Ni salt production extraction process. The results suggested a low loss of valuable metals and due to this, both the process of producing a mixed metal hydroxide and the process of producing a pure Ni salt could be found to be economically justifiable.
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