Antimony recovery from the halophosphate fraction in lamp phosphor waste: a zero-waste approach
Antimony is becoming an increasingly critical element as the supply-demand gap is expected to exceed 10% over the period 2015–2020. Antimony production is primarily concentrated in China (90%) and as the industrial demand for this metal surges, attention has to turn towards the recovery of antimony from (industrial) waste residues and end-of-life products in order to guarantee a sustainable supply of antimony. Although lamp phosphor waste is usually considered as a source of rare earths, it also contains significant amounts of antimony in the form of the white halophosphate phosphor (Ca,Sr)5(PO4)3(Cl,F):Sb3+,Mn2+ (HALO). HALO phosphor readily dissolves in dilute acidic conditions, making antimony far more accessible than in the main production route which is the energy intensive processing of stibnite ore (Sb2S3). HALO makes up 50 wt% of the lamp phosphor waste, but it has been systematically overlooked and treated as an undesired residue in the efforts to recover rare earths from lamp phosphor waste. In this paper, the feasibility of antimony recovery is discussed and an efficient process is proposed. The HALO phosphor is first dissolved in dilute HCl at room temperature, followed by a selective extraction of antimony with the ionic liquid Aliquat® 336. The remaining leachate is valorized as apatite which is a feed for the phosphate and fertilizer industry. A zero-waste valorization approach was followed, meaning that no residue or waste was accepted and that all the elements were converted into useful products. This paper thus emphasizes the potential of lamp phosphor waste as a secondary source of antimony and describes a sustainable process to recover it. The process can be integrated in lamp phosphor recycling schemes aimed at recovering rare earths.