Abstract
A large number of diluents were screened to determine the optimum combination between diluent and extractant. Combinations of a C 8 tertiary amine and aromatic diluents or of a C 12 tertiary amine and aliphatic diluents do not lead to third-phase formation. A flow-sheet for a solvent-extraction process for treatment of various qualities of wet-process phosphoric acid solutions is proposed. Based on a cadmium purification level of 1 mg/kg, extraction, stripping and scrubbing sections of the process would contain two, two and one stages, respectively. A solvent pre-treatment stage may be necessary in some cases. Co-extraction of acids such as H 3PO 4, H 2SO 4, HCI, HF and H 2SiF 6 can be decreased to very low values by manipulating process variables such as pre-equilibration, phase ratios, diluent and amine concentration. Co-extraction of cations other than cadmium was also investigated. Iron, aluminium and magnesium are not co-extracted while zinc and calcium are co-extracted to some extent. The proposed process can be used either for pollution abatement or in combination with other purification processes to recover some of the valuable cations such as uranium, or to produce more refined phosphoric acid streams.
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