Recovery of scandium from synthetic red mud leach solutions by solvent extraction with D2EHPA

The extraction of scandium from an Australian red mud by selective acid leaching was explored and preliminary leaching tests showed that diluted sulphuric acid can be used to leach scandium from the red mud. The recovery of scandium from a synthetic leach solution of the red mud using solvent extraction was studied. A number of extractants were investigated for the extraction of scandium and its separation from the other metals in the synthetic leach solution. It was found that amongst the three acidic organophosphorus extractants studied, D2EHPA performed best. With the organic system consisting of 0.05 M D2EHPA and 0.05 M TBP in Shellsol D70 under an A/O ratio of 5:1 at pH 0.25 and 40 °C, over 99% scandium was extracted and almost no iron and aluminium were co-extracted. The scandium extracted can be stripped from the D2EHPA/TBP system with 5 M NaOH to obtain Sc(OH)3 product. A conceptual flowsheet for the recovery of scandium from red mud is proposed.

► Preliminary leaching scandium red mud using diluted sulphuric acid conducted.
► A number of solvent extraction systems studied.
► D2EHPA showed high selectivity and extraction of scandium at low pH.
► Scandium stripped using strong caustic solution and precipitated by dilution.