Abstract:
With the rapid advancement of technology, the demand for elements such as rare earth metals (REMs) has increased considerably during the last decade. Many countries are facing problems securing sustainable supplies, a fact acknowledged in many publications. Due to the ever-growing demand and supply problems, REMs are now considered to be some of the most critical elements. This has focused attention towards their recovery from end-of-life products and industrial waste streams, with fluorescent lamps being one of the targets. However, despite the research published on the recovery of REMs from fluorescent lamp waste, large scale applications are scarce, mainly due to the lack of sustainable processes.
The research presented here is aimed at developing a sustainable hydrometallurgical process for the treatment of fluorescent lamp waste, with the goal of recovering the REMs that these lamps contain.
In comparison to other efforts in this field, these investigations were carried out using real waste samples originating from a discarded lamp processing facility. The complexity of the material (a mercury contaminated mix of glass, metallic and plastic parts, phosphors, remaining electronics and other impurities) makes already proposed methods a challenge and makes additional research necessary.
Cerium, europium, gadolinium, lanthanum, terbium, and yttrium were the REMs identified in the studied material. The leaching of metals was investigated using organic and mineral acids under various conditions (temperature, ultrasound-assisted digestion, solid to liquid ratio, and leaching agent concentration). Partial selective leaching of europium and yttrium is possible using diluted mineral acids at room temperature. An increased acid concentration and increased temperature, and also ultrasound-assisted digestion improved the leaching efficiency for the other investigated REMs. The recovery of REMs from nitric acid media was studied using commercial trialkylphosphine oxides. The extraction potential of REMs and the advantages/disadvantages for a possible industrial scale-up process were investigated. The separation of heavier elements (terbium, yttrium, europium and gadolinium) from lighter ones (cerium and lanthanum) is possible due to larger separation factors. A selective stripping of REMs from the co-extracted elements (iron and mercury) was easily achieved using concentrated hydrochloric acid. Further recovery of the extracted iron and mercury (with either oxalic acid or nitric acid solutions) allows the subsequent re-use of the organic phase in the process.
|
