Solvometallurgical recovery of antimony from waste polyvinyl chloride plastic and co-extraction of organic additives

Abstract

Antimony is a critical raw material in Europe wherein for 43% of its market share it is applied in the form of antimony trioxide as a fire retardant in plastics. Currently, antimony recycling from waste plastics does not take place and has been scarcely studied. In this work, a process was developed to extract antimony from a soft PVC material and recover it as Sb₄Cl₂O₅. Antimony was extracted by means of an ethanolic hydrochloric acid solution, prepared by diluting fuming HCl with ethanol to achieve the desired concentration. The addition of an organic solvent, such as ethanol, is known to enhance the chloride ion activity and promote metal chloride complex formation. This study confirms that the use of aqueous ethanol as a solvent increased the solvation of antimony at moderate temperature (i.e. 80 °C) as opposed to aqueous HCl solutions. The optimised leaching process showed high antimony extraction yields (94%) in the presence of an aqueous ethanol solution containing 4 M HCl at 80 °C for 4 h. Furthermore, the addition of the organic solvent ethanol to the reaction mixture caused organic additives to be co-extracted from the PVC (71% di-n-octyl phenyl phosphate, 51% di-iso-nonylphthalate, 76% 2-ethylhexyl diphenyl phosphate, 30% 9-octadecanamide and 15% butylated hydroxytoluene). The pregnant leaching solution was subsequently distilled to recover ethanol and washed with n-hexane to recover the extracted organic additives. Finally, water addition to the obtained solution led to the precipitation of 95% of antimony from the solution as Sb₄Cl₂O₅ with a high purity (≥99.8%). The residual PVC was not degraded and could be suitable for recycling.