Integrating life cycle assessment and life cycle costing of fluorescent spent lamps recycling by hydrometallurgical processes aimed at the rare earths recovery

Abstract

This study compared the sustainability of two recycling treatments of fluorescent powders aimed at recovering rare earths. The analysis has been performed to evaluate the environmental impacts and economic aspects by using Life Cycle Assessment (LCA) and Life Cycle Cost (LCC). The first process includes a thermal pretreatment at 950 °C of powders, followed by sulfuric acid leaching, precipitation with oxalic acid and recovery of rare earths as oxides, and wastewater treatment. The second one differs only for the preliminary treatment; a mechanical activation has been proposed as an alternative to thermal pretreatment. The LCA proved the advantage of secondary production of rare earth oxides (REOs), compared to the current supply from ores. Furthermore, an environmental advantage of process A was estimated for combining the highest recovery and the lowest hazardous level of waste to dispose of, thanks to the preliminary removal of mercury. The potential benefit of REO recoveries was mainly highlighted in the categories of climate change and resource use, energy carriers and the leaching phase was identified as the main burden in most of the analyzed environmental categories. The final oxide from Process A contains more terbium than the product obtained from Process B. Labor is the main item of operating costs, and electric energy represents around 99% and 73% for Process A and Process B, respectively. The sensitivity analysis shows that varying the plant's capacity, the net profit increases. The main factor that influences the economic feasibility is the prices of rare earths.