Extraction of platinum(IV) by hydrophobic deep eutectic solvents based on trioctylphosphine oxide

In this paper, trioctylphosphine oxide (TOPO) was combined with some environmental-friendly molecules to form hydrophobic deep eutectic solvents (HDESs) for platinum (Pt) extraction from secondary resources. Due to the formation of HDESs, the loss of TOPO content in the aqueous solution obviously decreased. Then, the extraction behaviors under different vibrating time, acidity and salinity (NaCl/NaBr) were investigated and discussed. Among all the constructed HDESs, the TOPO/1-butanol showed the best Pt(IV) extraction performance (98.9%) in 5.6 mmol·L −1 Pt(IV) solution. Ion-association mechanism in the extraction process was proposed through the analysis of UV–vis and FT-IR spectra. In addition, the HDESs exhibited excellent selectivity to Pt(IV) in the experiments of multi-metal selective extraction. The extracted Pt(IV) could be easily and completely stripped by adding 3 mL 0.5 mol·L −1 NaOH solution, and the extraction ability of recovered extractants remained constant after 4 cycles of extraction tests. Furthermore, by using RSM-CCD optimization, the operating concentration of acidity and salinity was obtained: 1.27 mol·L −1 HCl and 2.65 mol·L −1 NaCl. Under optimal experimental conditions, the designed processes of Pt(IV) extraction further improved recycling efficiency.