The efficient recovery of highly concentrated cadmium (44.55 g/L) from zinc smelting dust leachate is recognized as a significant metallurgical challenge. In this study, we focused on the selective separation of Cd from coexisting arsenic and zinc using trioctylamine (N235) as the extractant. Accordingly, key operational parameters including initial pH, extractant concentration, phase ratio, and temperature were optimized in a systematic manner. Under the optimized conditions of 30% N235, 15% TBP, and 55% sulfonated kerosene by volume, together with an initial pH of 0.5, an organic to aqueous phase ratio of 1 to 1, and a temperature of 20 °C, a three-stage countercurrent extraction process was found to dramatically enhance the Cd extraction efficiency to 99.80% while successfully rejecting As. Subsequently, stripping with 0.7 mol/L aqueous ammonia achieved an 81.4% stripping efficiency in a single stage, and washing with 1.0 mol/L HCl ensured complete regeneration of the organic solvent. Furthermore, Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS) analyses corroborate that the extraction proceeds via an anion exchange mechanism. Specifically, within the chloride rich acidic environment, protonated N235 was shown to preferentially coordinate with the tetrachlorocadmate anion CdCl42− to form the highly stable and lipophilic complex (R3NH)2CdCl4. Overall, this work provides a scalable technological framework and a robust theoretical foundation for the extraction of highly concentrated heavy metals from complex secondary metallurgical resources.
Li et al. (Tue,) studied this question.