Simultaneous removal and recovery of cadmium (II) and CN− from simulated electroplating rinse wastewater by a strip dispersion hybrid liquid membrane (SDHLM) containing double carrier

A novel liquid membrane system, denoted strip dispersion hybrid liquid membrane (SDHLM) with a double carrier (TRPO, trialkyl-phosphine oxide, and D2EHPA, di-(2-ethylhexyl) phosphoric acid) membrane phase, basic stripping aqueous phase and weak acidic waste water phase, was reported for the simultaneous removal and recovery of Cd(II) and CN− from simulated electroplating rinse wastewater. The basic stripping solution containing the concentrated Cd(CN)42− could be again used in the electroplating tanks. The experiments verified that CN− was more quickly transported from the feed phase into the stripping solution than cadmium (II) when the organic phase only contains TRPO. In order to reach the same transport rate for CN− and Cd(II) D2EHPA was added in the organic phase only containing TRPO. Effect of various factors on the transport of CN− and Cd(II) were systematically investigated by orthogonal test of the extraction or membrane transport. The analysis of mass transfer resistances in SDHLM indicates that the mass transfer resistance due to the membrane-phase diffusion is dominant in the overall mass transfer process. The accumulation of coordination compound of CN−-carrier or Cd(II)-carrier in membrane for SDHLM shows that the transfer in SDHLM possesses the characteristic of nonequlibrium mass transfer in this study. According to the optimized condition, after the transport of 6 h for SDHLM the content of CN− or Cd(II) in the feed phase is 0.05 and 0.02 mg/L, respectively. The uptake of membrane solution into an adjacent aqueous phase for SLM is 2.1–2.6 times as high as that in SDHLM. In the experimental comparison of permeability coefficient, recovery percentage or concentration of solute in stripping solution, loss of membrane solution, the accumulation of coordination compound between CN−-carrier or Cd(II)-carrier in membrane, and transport efficiency of membrane for the two types of liquid membrane, SDHLM has superiority over SLM.