A Novel Coupling Technology Of Complexation-Ultrafiltration And Its Models

A novel coupling technology of complexation-ultrafiltration has been studied, in which poly (acrylic acid) sodium salt (PAASS) was reacted with metal ions to form metal complexes and polysulfone hollow fiber ultrafiltration membrane was used to concentrate the complexes. Based on the disclosure of ultrafiltration behavior during filtrating metal ions and PAASS solutions respectively, the coupling process has been investigated systematically, including rejection coefficient of complexation systems, selective separation of metal ions, and decomplexation of complexes. The process operational parameters, reaction kinetics and mathematic models are also concerned. At last, it has been discussed to apply the technology to the treatment of wastewater containing copper ions discharged from a printed wiring board factory.1. Ultrafiltration of metal ion solutions. After the charge properties of the membranes were known fully, the relationships between membrane permeability, ion transmission and streaming potential were further investigated in the process of metal ion solution ultrafiltration. It was found that isoelectric points (IEP) of the membranes were 2.9±0.1, 3.5 ± 0.1, 3.8 ± 0.1 respectively in the solution of Na⁺ or K⁺, Ca²⁺ or Mg²⁺, Al³⁺. At the IEP, The permeability of the membrane reached maximum value, and rejection coefficient of metal ion increased with increasing streaming potential. For heavy metal ions, it could be seen that the affinity to membrane followed Hg²⁺> Cu²⁺> Cd²⁺.2. Ultrafiltration of PAASS solutions. Effects of operational parameters on PAASS solution ultrafiltration have been studied. The resistance model for membrane fouling was established on the basis of PAASS adsorption on membrane surface. The results showed that since the membranes could adsorb PAASS remarkably at pH<4.5, permeate flux declined rapidly. A pseudo-second-order model could describe the adsorption kinetics, and the Langmuir equation fit perfectly to the adsorption isotherm. Membrane total resistances depended respectively on membrane resistance R_m or irreversible fouling resistance R_f at high or low pH values. On the other hand, reversible and irreversible concentration polarization resistances R_p,r and R_p,ir could be neglected.