Removing ions from nickel electroplating rinse water This study investigated the performance of nanofiltration (NF), which is more economic than reverse osmosis (RO) and requires lower pressure, for the removal of cations and anions in simulated nickel electroplating rinse-water environments. Reraoval rates according to changes in basic parameters, such as pressure, cross-flow velocity, pH, ion types and ion concentrations were observed. In single-salt system experiments NF removed more Ni 2+ in NiSO 4 solution than in NiCI 2 solution. As concentration increased in single-salt systems, the removal rate of sulfate salts and some chloride salts (in the system with cations of +1 valency) decreased, whereas chloride salts with cations of +2 valency increased. In the experiment with multi-salt systems, the removal rate of ions showed a logarithraic increase with pressure until 3 kgf/cm 2 (0.294 MPa), and beyond this value the removal rate stabilised. A change in cross-flow velocity did not affect the ion removal, but a change in pH was a significant factor for C1 removal rate. Furthermore, the removal rate of Cl was heavily dependent on the amount of SO4- present in the same system. In experiments using simulated nickel electroplating rinse water below a pressure of 3 kgf/cm 2, the removal efficiencies of ions increased greatly with increased influent salt concentration and pressure, whereas beyond 3 kgf/cm 2, the removal efficiency stabilised. This result indicated that 3 kgf/cm 2 is the optimum pressure for NF application against nickel electroplating rinse water. K.-H, Ahn, K.-G. Song, H.-Y. Cha, 1.-T. Yeom: Desalination 122(1) 77-84 (25 May 1999).
Nanofiltration applied to electrolyte and non-electrolyte solutes The behaviour of two different nanofiltration membranes (NF45 and NF70) was studied. Experiments were carried out under various trans-membrane pressures, concentrations and solutes (NaC1, Na2SO 4 and PEG200) in the absence of the effect of concentration polarisation. The experimental data were processed using the dynamic permeability model and the generalised Kimura-Sourirajan model. The experiments, run with charged and uncharged membranes and solutes allowed us to gain a clear understanding of the relative contributions of steric and surface interactions on the separation characteristic. Furthermore, the experimental results show that there exists another type of surface force interaction other than the electric repulsion which can dominate the transportation of solute. The results show that the strongly pronounced dependency of the separation factor, the dynamic permeability, as well as the solute transportation parameter on
the electrolyte concentration, are only the characteristics of a charged membrane. Y. Xu, R.E. Lebrun: Desalination 122(1) 95-106 (25 May 1999).
Differentiation of organic matter by cross-flow UF and UVspectrofluorescence Cross-flow ultrafiltration (UF) of samples taken from the Rio Negro basin (Amazon) was undertaken with tangential flow equipment, producing concentrated fractions on which UV-fluorescence produced information about the individual characteristics of the organic matter in different size fractions. O f major interest is that conductance (ionic strength) and fluorescence were both linearly (r > 0.95) correlated with total organic carbon (TOC) determined at each individual station. The physico-chemical characteristics (fluorescent sensitivity and electro-mobility) of the organic carbon seem to be constant within each size fraction (particulate, colloidal and dissolved). The "complexing" capacity of copper was found to be elevated, and as a consequence, more than 80% of the metal transport occurred in the dissolved phase. By comparing these various results, it has been deduced that the functional groups responsible for "complexation" are not the same as those responsible for fluorescence and conductance. S. Mounier, R. Braucher, J.Y. Bena~im: Wamr Research 33(10) 2363-2373 (1 July 1999).
Effect of pH on protein transport through UF membranes Although a number of previous studies have demonstrated that solution pH can have a dramatic effect on protein transport through ultrafiltration (UF) membranes, the exact origin of this behaviour is still unclear. Experimental data were obtained for the transport of a broad range of proteins with different surface charge and molecular weight. The effective hydrodynamic size of the proteins was evaluated using size-exclusion chromatography. The membrane charge, both before and after exposure to a given protein, was evaluated using streaming potential measurements, in most cases, the electrostatic interactions were dominated by the distortion of the electrical doublelayer surrounding the protein, leading to a distinct maximum in protein transmission at the protein isoelectric point. Attractive electrostatic interactions did occur when the protein and membrane had a large opposite charge, causing a second maximum in transmission at a pH between the isoelectric points of the protein and membrane. The sieving data were in good agreement with
theoretical calculations based on available models for the partitioning of charged solutes in cylindrical pores. D.B. Burns, A.L. Zydney: Biotechnology & Bioengineering 64(1) 27-37 (5 July 1999).
SO~ transport through supported liquid membranes Facilitated transport of SO 2 through supported liquid membranes, containing water as a carrier, was studied experimentally and theoretically in the range of SO 2 partial pressure pF(SO2) from 3.5 Pa to 2 kPa. The permeance of SO 2 at p~.(SO 2) = 3.5 Pa was as high as 6 x 10 -4 mol/m 2 s kPa, and the contribution of gas-phase mass transfer resistance to the overall mass transfer resistance was found to be significant. The observed SO 2 permeance was analysed on the basis of the theory of facilitated transport which had been developed by the authors for the facilitated transport of carbon dioxide using amine as a carrier. The theory could quantitatively explain the effect of various experimental conditions such as the SO 2 partial pressure and the membrane thickness on the permeance of SO 2. Comparison of the present facilitated transport membrane with polymeric membranes showed that the present membrane is much more effective at removing SO 2 at low partial pressures encountered in flue-gas desulfurisation processes. M. Teramoto, Q. Huang, T. Maki, H. Matsuyama: Separation & Purification Technology 16(2) 109-118 (12 July 1999).
Ethanol-water mixture separation by membrane distillation The effect of membrane distillation process parameters on ethanol-water separation has been investigated using a comprehensive mathematical model. Three mass transfer solutions are considered in the model. These are the exact solution of the Stefan-Maxwell equations developed by Krishna and Standart; the approximate solution of the Stefan-Maxwell equations suggested by Krishna and Wesselingh; and the binary Fickian solution. Temperature and concentration variation along the flow and diffusion paths are accounted for in the model. Although the exact and approximate solutions of the Stefan-Maxwell equations are coincident with each other, some differences are noticed between them and the Fickian-based solution. The difference between the three mass transferbased solutions, as well as the process performance under several process parameters, are discussed. EA. Banat, EA. A1-Rub, M. Shannag: Separation & Purification Technology 16(2) 119-131 (12 July 1999).