Removal of aluminum from pickling bath liquids by tertiary and quaternary amine extractants

In this work, several extractants and solvents have been investigated for the selective removal of aluminum from a pickling bath, containing HF and H₃PO₄ as its main active components, each at a concentration of 0.01-0.30 M. The final aim of the research is to increase the lifetime of the pickling bath, resulting in reduced operating costs, in a decreased environmental burden, and in a more constant and better pickling performance. Several tertiary amines and one quaternary amine salt have been examined as extractants, Shellsol D70, paraffine and Marlowtherm S have been examined as solvents and Exxal 13 has been examined as a modifier. None of the aluminum extractions were completely selective as phosphorus was co-extracted; selectivities obtained were 0.16-1.1. Aggregation took place in many shake tests, but adding Exxal 13 to the organic phase decreased the aggregation in most cases. Of the solvents tested, Shellsol D70 showed the lowest aggregation. The best conditions for SLM were found to be 1.0M Alamine 308/Alamine 336 with 50 g/1 Exxal 13. In almost all shake tests, [Al]: [P] ≈ I : 1.3-1.9 in the organic phase.