A hydrometallurgical process for the recovery of rare earth elements from fluorescent lamp waste fractions

Artikel i vetenskaplig tidskrift, 2016

Rare earth elements (REEs) are presently regarded to be some of the most critical elements, being essential in future sustainable applications. One of the many examples is fluorescent lighting, which relies on REEs such as cerium, europium, gadolinium, lanthanum, terbium and yttrium. The high demand for REEs, low supply, price fluctuations and geopolitical factors have contributed to an increased interest in reclaiming these elements from end-of-life products. This publication reports on a new potential hydrometallurgical route to reclaim REEs in fluorescent lamp waste. The investigations were carried out at bench scale and laboratory pilot scale to assess the potential of a process based on leaching and solvent extraction. Real waste fractions of various compositions, originating from several companies that use different mechanical, physical and chemical processes to treat lamps, were studied. A multi-step leaching process that selectively dissolves different groups of metals in the waste was investigated. Removal of mercury, one of the vital constituents of fluorescent lamps and an undesired contaminant in the waste, was carried out using leaching with iodine in potassium iodide solutions. Selective leaching of impurity metals e.g. calcium and selective leaching of REEs was performed with nitric acid, taking advantage of the significant differences in their leaching kinetics. Separation of REEs was achieved with Cyanex 923, a commercial mix of trialkylphosphine oxides, in a counter-current mixer setter system comprising three extraction and four stripping stages, respectively. The product, a yttrium/europium concentrate, was treated with oxalic acid, followed by thermal treatment, to produce an oxide containing 99.96% REEs, of which 94.61% was yttrium and 5.09% was europium.