Principal Of Nanofiltration And Its Application In Electroplate Waste Water

Nanofiltration is a new technology of membrane on the ground of ultrofiltration and reverse omission and extensively applied since it is been known. The scope of film nears to member level and the electricity characteristic, which made the separation mechanism of nanofiltration very complicated. Now we can't directly accurate the bore structure and nanofiltration film' effective membrane volume charge, so it is very difficult to describe the separation mechanism of nanofiltration film. If we can get the bore structure and nanofiltration film' effective membrane volume charge by model, then it is very important to analyze the separation mechanism of nanofiltration film, estimate film of separation function and provides the theories instruction for the actual application of nanofiltration.This paper discusses the concentration polarization development along the bulk flow direction in crossflow NF using a theoretical model, and taking the NaCl as example to investigate the relationship between the transport coefficient (k) and the concentration polarization. The result implies that the transport coefficient (k) increases by the increasing of the velocity, and the concentration polarization in correspond to descend, meanwhile the rate of permeating flow J have certain influence to the concentration polarization. When the rate of permeating flow increases the transport coefficient (k) decrease and the concentration polarization increases.This essay carries on the taken of structure of the NF90 - 2540 films and the bore path r_p of the film is 0.45 nm, the rate of porosity of the membrane and effective membrane thickness is 0.34.Aim at solving the complexity of DSPM (Donnan steric partitioning pore model) model calculation, this essay carries on a simplification of DSPM model and deduce process in details, which bases on the assumption of negative ionic density is greatly lower than the anti- ionic' in attached negative nanofiltration film. Taking NF90 -2540 nanofiltration films to carry on the experiment of the NaCl electrolyte, and taking the DSPM model to calculate the nanofiltrationfilm' effective membrane volume chargethe resultcertificates NF90 film will be good at keeping small member dissolute and high salt system.We can know the NF90 film have tiny bore structure and effective membrane volume charge, ion in the electric bores effected by the function of convection and electric ,the heavy metals ions (Ni²⁺,Cu²⁺,CrO₄^2-Zn²⁺ etc) belongs to two price ions, compared with the unit price ion (Na⁺ ) , they have the bigger radius and smaller diffusive coefficient, the solute rejection is higher.This text chooses the treatment of electroplate polluted water, the experiment results certificate solute rejection hardly influenced by the density of heavy metal ion. If we can control the ion (Ni²⁺,Cu²⁺,CrO₄^2-,Zn²⁺ etc) density well, after the nanofiltration the water can reach a mark to exhaust or return to use;But actually electroplate density is 100～200 mg/L in the waste water, after the nanofiltration processing the Water can exhaust. If the nanofiltration cooperate with reverse omission as an integration, then we can attain the recovery of the poisonous heavy metals ion and the water return to use, The method not only have an economic effert, but also have environment effert, save the manpower and material resources effectively which have the expansion application value in the engineering.