What exactly is KDF used in water treatment?

1. The function and mechanism of KDF

KDF is a high-purity copper/zinc alloy particle that works for water treatment through a microelectrochemical oxidation-reduction reaction (Redox), where the two metals in the alloy react on a submicroscopic scale when in contact with water Constituting countless small primary battery systems, this material has strong reaction ability and extremely fast reaction speed in water, and can remove up to 99% of chlorine in water and metal ions and compounds such as lead, mercury, nickel, and chromium dissolved in water. It has an outstanding effect on inhibiting the growth of bacteria, fungi, dirt and algae. Used in pretreatment, main treatment and wastewater treatment plants. KDF improves or replaces the existing technology, which greatly prolongs the life of the system, reduces heavy metals, microorganisms, and dirt, reduces the total cost, and simplifies system maintenance.

(1) Removal of strong oxidants (residual chlorine) KDF has a strong reducing ability and can remove various strong oxidants in water, especially effective for residual chlorine. KDF is composed of two different metals, copper and zinc. When in contact with water, the copper with positive potential in the alloy becomes the cathode, while the zinc with negative potential is the anode, forming a primary battery. The zinc anode loses electrons in the reaction, and zinc ions are generated to enter the solution. The reduction reaction of free chlorine occurs on the copper cathode, but the dissolution of metallic copper does not occur. Water and residual chlorine become the final electron acceptors, and simultaneously generate hydrogen ions, The total reaction formula of hydroxide ion and chloride ion is as follows: Zn+HOCl+H2O+2e—Zn2++Cl-+H++2OH- Other oxidants in water, such as ozone, bromine, iodine, etc. and KDF Similar redox reactions can also occur after contact.

(2) Removal of heavy metals KDF treatment media can remove a variety of heavy metal ions in water, such as lead, mercury, copper, nickel, cadmium, arsenic, antimony, aluminum and many other soluble heavy metal ions. Their removal is through Replacement reactions and physical and chemical adsorption reactions to complete. The mechanism of KDF to remove heavy metal ions is as follows: metal ions are adsorbed on the surface of KDF treatment medium and undergo a replacement reaction with zinc in KDF, and the resulting metals may be adsorbed on KDF Phenanthrene (KDF) surface, or into the KDF (KDF) lattice, so that toxic heavy metal pollutants combined on KDF (KDF). For example, lead ions dissolved in water are reduced to insoluble lead atoms, which are adsorbed on the surface of KDF medium, and similar reactions occur between mercury ions and KDF. X-ray diffraction studies have found that mercury removal Is the formation of copper – amalgam. The chemical reaction formula of KDF for treating heavy metal ions is as follows: Zn/Cu/Zn+Pb2+ →Zn/Cu/Pb+Zn2+ Zn/Cu/Zn+Hg2+→Zn/Cu/Hg+Zn2+ Metal ions in water When the pH rises, it hydrolyzes to form metal hydroxide precipitates, which can also remove metal ions.

(3) Removal of hydrogen sulfide When using membrane method for water treatment, if groundwater is used as the water source, hydrogen sulfide may exist in the water. If hydrogen sulfide is oxidized into sulfur, it will pollute the surface of the filter membrane. KDF filter media has The function of removing hydrogen sulfide, the generated copper sulfide is insoluble in water, and can be removed during backwashing of KDF medium. The chemical reaction formula is as follows: Cu/Zn + H2S → Cu/Zn + CuS + H2 2H2 +02 → 2H20

(4) Reduction of suspended solids The average particle size of the KDF treatment medium is about 60 mesh, and the smallest particle is about 110 mesh. It can also play a role in removing suspended substances by physical filtration. Usually, KDF filter The media is capable of effectively removing particles down to 50µm in diameter. When the water delivery pipe fittings made of steel material corrodes, iron oxidizes to form FeO colloid, and FeO contacts with KDF, and redox reaction can also occur, and FeO finally forms Fe2O3 solid and precipitates on the surface of KDF. They can be removed by backwashing method, the chemical reaction formula is as follows: Zn + FeO = ZnO + Fe 2Fe + 3O2=2Fe2O3

(5) Reduce mineral scaling KDF treatment medium has two effects on calcium carbonate scale.

  1. On the one hand, according to the relationship between pH, carbon dioxide concentration and calcium carbonate solubility, when carbon dioxide is removed from the solution, the pH value increases, thereby reducing the solubility of calcium carbonate. KDF also raises the PH value of water through electrochemical reaction and reduces the solubility of calcium carbonate, resulting in easy precipitation of calcium carbonate scale.
  2. On the other hand, due to the dissolution of zinc ions in the KDF treatment medium, the content of zinc ions in the water has increased, and the presence of zinc ions in the water can change the crystal growth mechanism of the scale, so that the calcium carbonate scale in the water is The crystalline form of the calcite precipitates, forming a soft scale on the walls of the vessel, rather than crystallizing as a hard scale of the calcite type. Some people have studied the influence of impurities in water on the growth of calcite crystals, and found that even when the concentration of zinc ions is very low, the formation of calcite crystals can be prevented.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading

25TPH RO water treatment

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