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Membrane Separation Technology Introduction
- Apr 03, 2018 -

Membrane separation technology introduction


Membrane separation methods can be divided into gas (steam) separation and liquid separation according to their separation objects, and can be divided into reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) according to their uses. Dialysis (D), electrodialysis (ED), gas separation (GS), pervaporation (PVAP), emulsion membranes (ELM), and membrane separations and membrane extractions in combination with other processes. Among them, the separation process of reverse osmosis, ultrafiltration, microfiltration and electrodialysis has matured. The use of the membrane as a membrane separation process for electroplating wastewater treatment typically involves ultrafiltration, nanofiltration, reverse osmosis, high pressure reverse osmosis.


Depending on the classification method, it can be homogeneous or heterogeneous; symmetric or asymmetric; solid or liquid; neutral or charged. Its thickness ranges from a few microns (even 0.1 μm) to several millimeters. Membrane separation is the process of selectively permeating the membrane as the separation medium, through the permeation of the membrane, by means of external energy or some kind of driving force (such as pressure difference, concentration difference, potential difference, etc.) existing on both sides of the membrane. The process of separation, fractionation, purification, and enrichment of one or more mixed gases or liquids.


Membrane separation technology is used in wastewater treatment and reuse, mainly microfiltration, ultrafiltration and reverse osmosis. Microfiltration and ultrafiltration belong to the sieving mechanism and are mainly used for the treatment of organic pollutants such as membrane bioreactors and waste water. Reverse osmosis is the solution of solvent (such as water) under pressure through a pair of solvents. A water-permeable selective semi-permeable membrane enters the low pressure side of the membrane while other components of the solution, such as salt, are trapped on the high pressure side of the membrane and concentrated. That is, the use of reverse osmosis membranes to retain metal ions and organic additives, allowing water molecules through the membrane, so as to achieve the purpose of separation and concentration.


If the combination of reverse osmosis and nanofiltration processes is used, nickel plating rinse water can be recycled. The first stage nanofiltration was concentrated 10 times, the second stage nanofiltration was concentrated 5 times, the third stage nanofiltration was concentrated twice, the total concentration factor was 100 times, and the Ni2+ rejection rate was >99.5%. Ni2+ mass concentration> 20g/L concentrate is reused in the electroplating bath, or the nickel sulfate crystals are sold after vacuum distillation; the permeate is used as rinse water, or as other process water. The water reuse rate of the entire system is >98%, and the nickel recovery rate is >97%. Membrane separation system processing power consumption per ton of waste water is 1.112kW ̇h, the system is generally cleaned 3 to 6 months, cleaning 1,2,3 membrane separation system at the same time. Therefore, the consumption of chemical agents is also very limited. After accounting (taking into account the depreciation of the membrane components), the investment recovery period of this system is about 2 years, which realizes the recycling of wastewater, and has achieved very good economic and environmental benefits.