Reasons why ultrafiltration membranes cannot remove calcium and magnesium ions from water
Reasons why ultrafiltration membranes cannot remove calcium and magnesium ions from water
Ultrafiltration membranes have a strong filtration and purification effect, mainly used to retain harmful substances in water while keeping the pH value of the product water unchanged. Ultrafiltration can effectively remove large proteins and bacteria-like substances. If you need to remove calcium and magnesium ions, it is recommended to use nanofiltration membranes or reverse osmosis membranes.
In membrane treatment, it is generally divided into ultrafiltration, nanofiltration, and reverse osmosis. The ultrafiltration membrane you mentioned generally has a pore size of 0.1-0.01 μm, and the molecular weight retained is between 1000 and 300,000. However, the diameter and molecular weight of calcium and magnesium ions are much smaller than this value. Therefore, they pass through the ultrafiltration membrane.
1. The concept of ultrafiltration
Ultrafiltration is the process of filtering a solution containing macromolecules or fine particles using an ultrafiltration membrane with a pore size of 1.0～20.0 nm or larger, separating the macromolecules or fine particles from the solution.
2. Characteristics of ultrafiltration
Similar to reverse osmosis, the driving force of ultrafiltration is also pressure difference. Pressure is applied to the solution side to allow the solvent to pass through the membrane for separation. Unlike reverse osmosis, in the ultrafiltration process, small molecule solutes will pass through the ultrafiltration membrane along with the solvent.
3. The essence of ultrafiltration
The essence of ultrafiltration is sieving, adsorption, and blockage of particles in the micropores on the membrane surface.
Ultrafiltration membranes are asymmetric membranes. Their surface active layer has micropores with a pore size of 10-9～2×10-8 m, which can retain macromolecules and colloidal particles with a relative molecular weight of 500 or more. The pressure difference used is 0.1～0.5 MPa.
However, ultrafiltration and reverse osmosis membranes can remove scaling cores such as colloids from water, which can reduce the degree of scaling to some extent.
4. Advantages of ultrafiltration membranes
Due to serious water pollution and secondary pollution, it is difficult to achieve deep purification of drinking water using ordinary filter media. Ultrafiltration membrane purification technology uses a high-precision, purely physical filtration principle, without adding any chemicals. It relies on the micropores densely distributed on the surface of the ultrafiltration membrane for sieving, thereby retaining harmful substances and achieving filtration, purification, and purification effects.
For various reasons, the development of membrane technology and the scale of production have made ultrafiltration membranes more stable in performance. However, ultrafiltration membranes are not the mainstream technology for removing calcium and magnesium ions from water
