RECOVERY OF Cr(VI) BY QUATERNARY AMMONIUM COMPOUNDS

The extraction of chromium (VI) from aqueous solutions of 0.1 ionic strength by trioctylmethylammonium compounds (Aliquat 336) in a mixture of kerosene and xylene was investigated. The results indicate that the extraction efficiency of Cr(VI) in acidic aqueous solution is good. In these experiments, the relative affinities of different anions to Aliquat 336 were in the order order of NO3− > Cl− > SO4−2. Experimental results showed that hydrogen chromate ion (HCrO4−) is the major extractable species of Cr(VI) at pH 3.53–3.75, expressed by the mechanism + HCrO4− = + NO3−. The equilibrium constant for the reaction is 102.078 (at 25°C). A computer program has been developed to simulate Cr(VI) extraction results under various conditions, the results of which fit the experimental data very well. The strippant is composed of 0.1 sodium hydroxide and 1.0 , sodium chloride and completely strips Cr(VI) from the loaded solvent ([Cr] = 0.0092 , A/O = 0.5). Thus, the recovered solution, by reducing the A/O ratio, contains a 10-times-higher concentration of Cr(VI). The stripped solvent (Aliquat 336) can then be reused for extracting Cr(VI). After five extraction cycles, the Aliquat-336/kerosene/xylene solution shows no significant loss in volume and retains the same extracting ability. © 1998 Elsevier Science Ltd. All rights reserved