The separation of cadmium from zinc with a synergistic mixture of nonylsalicylic acid and triisobutylphosphine sulphide

Abstract

Metal pH 50 and ΔpH 50 values were determined and compared for a number of organic systems to select a synergistic system for the separation of Cd from Zn. The largest ΔpH 50(Zn–Cd) value was obtained with HRJ-4277 (nonylsalicylic acid)/Cyanex 471X (triisobutyl phosphine sulphide or TIBPS) system and reached 1.53 pH units, indicating excellent separation of Cd from Zn with this system. Shellsol 2046 was chosen as the diluent of the system due to its larger ΔpH 50(Zn–Cd) and excellent phase separation compared with other diluents. Distribution isotherms and subsequent McCabe–Thiele diagrams indicate that 99% Cd could be extracted in two stages at pH 3.80 and A / O ratio of 1.5 : 1. The extraction kinetics and stripping kinetics of Cd and Zn were very fast with > 97% metal transferred within 30 s. In a three-stage batch continuous extraction test, > 99% Cd and 0.4% Zn were extracted. The loaded organic solution contained 3.87 g/L Cd and only 12 ppm Zn. In a two-stage batch continuous scrubbing test, all the co-extracted Zn was removed with the scrubbed organic containing < 1 ppm Zn. Nearly 99% of cadmium was stripped in two batch contacts with 20 g/L sulphuric acid. Excellent separation of Cd and Zn can be achieved in three stages of extraction, two stages of scrubbing and two stage of stripping with this synergistic SX system.