EXTRACTION OF ANIONS WITH TERTIARY AMINE FROM AQUEOUS-SOLUTIONS OF MIXED ACID AND SALT

Amine extraction was made in aqueous solutions of HCl (0-0.5 M), H2SO4 (0-0.4 M), and H-3-PO4 (0-0.3 M) with their corresponding salts (0-0.08 M), i.e., NaCl, MgSO4, and Na2HPO4, respectively, covering a wide pH range (i.e., 0.4-8.6). The organic phase comprised 15% (w/w) Alamine 336 (tri-C-8 to C-10 alkylamine) in the diluent, n-hexadecane or oleyl alcohol. The common extraction mechanism involving the protonated tertiary amine was observed in the systems of pure or concentrated acid. The presence of salts was found to enable a nonprotonated extraction mechanism where the anions were postulated to couple with the metallic cations for partition into the organic phase. Among the anions studied, the nonprotonated mechanism was most significant for phosphate extraction and least for chloride extraction. Experimental results have been modeled with simultaneous extraction by protonated and nonprotonated mechanisms, and the best-fit apparent extraction constants are reported.