Diatomaceous earth is the sediment of the remains of ancient aquatic algae plants. After tens of thousands of years of burial, a fossil rock and soil layer is formed. After mining, screening, crushing, washing, and high-temperature flint burning, it is made into commercial diatomaceous earth.
Its main component is SiO2, the general content is about 90%, and contains a small amount of Fe2O3, A”., CaO, M gO, and organic impurities.
After acid foaming or melting agent is fired into diatomaceous earth, the product quality with fewer impurities and a large specific surface area is superior.
Pre-spread diatomaceous earth on the filter medium (filter cloth, filter paper, microporous plastic, etc.) to form a filter cake, which can remove 1 or even 0.1 of particles and bacteria, and obtain a satisfactory filtration rate.
Therefore, diatomaceous earth is the best filter aid today, and it is widely used in the fine filtration of solutions such as beer, liquor, wine, beverages, fruit juices, medicines, vegetable oils, paints, chemicals, electroplating, and water treatment.
The Principle Of Diatomite Filter
There are many small holes, small grooves, and small cells on the shell wall of diatomaceous earth. These small holes, small grooves and small cells after being burnt at high temperature are more obvious, complete and clean, and form macroscopic loose and microscopic hard solids with a large specific surface area. structure.
Its particles are generally about 2-40/zm. When pre-applied on the filter medium, a filter layer with a particle size distribution from large to small is formed. The large particles are close to the filter medium and play a bridging role.
Because the particles are irregular, the mesh of the filter medium cannot be blocked. Therefore, criss-cross and tortuous pores are formed.
Under the action of the pressure difference, when the suspension passes through the diatomaceous earth filter layer (ie filter cake), the large particles in the suspension are blocked on the surface of the filter cake, and the small particles enter the filter cake and are bent by the curved pores and channels. The small holes, small cavities, and small grooves on the surface of the particles are caught and trapped in the filter cake.
The filtered liquid flows into the container through the filter medium, thereby achieving the effect of solid-liquid separation.
Because the diatomaceous earth particles are hard, the filter cake has very little compression deformation, and the viscous material in the filtrate is captured and trapped before it reaches the surface of the filter medium, and cannot block the medium mesh.
Therefore, after the filter medium is pre-coated with diatomaceous earth, it can maintain a satisfactory filtration speed, flow rate, and filtration accuracy for a long period of time. The above is the filtration mechanism of diatomaceous earth.
Application Of Diatomite In Electroplating
According to relevant information, but 5g of diatomaceous earth sample into 100 mL H2SO4 with a pH of about 1.5 and heat it in a constant temperature bath for 1 hour. Under such severe conditions, the dissolved FezOa is 0.01% to 0.02%.
Similarly, put 5 g of diatomaceous earth sample into 100 mL of sodium hydroxide aqueous solution with pH 10.5, and put it in a constant temperature bath for 1 h. Under these conditions, the amount of SiO? dissolved is about 0.2% to 0.5%.
This shows that the physical and chemical properties of diatomaceous earth are quite stable. Coupled with the excellent filtering performance of diatomaceous earth, it can be used for the filtration of electroplating solutions.
Used for circulating filtration of bright fetters plating solution
In the shackle plating process, due to the impure shackles and chemical raw materials, there is a lot of anode mud. Directly filtering with the filter medium of the filter will cause the following two situations:
The filter medium is a filter cloth because the mesh is large, the solution is not clear, and the effect is extremely poor. As time increases, the mesh is basically blocked, although the filtering effect is a little better.
However, the flow rate and filtration rate are already very small, and the filter cloth has reached the cleaning cycle. If the filter medium is a wound filter element or filter paper, although the filtering effect is better, it will be clogged quickly and the flow rate will decay quickly.
The above situation causes headaches for electroplating engineering technicians and operators. At this time, if the filter area is 0.5kg/m2, diatomaceous earth is pre-applied on the filter cloth (usually a closed-loop cycle is about 10 minutes).
The formed diatomaceous earth filter cake will be firmly adsorbed on the filter medium.
At this time, recirculation filtration is performed. The filtrate is very clean. No suspended matter can be observed in the filtrate, and the filter paper cannot filter any solid particles.
This shows that diatomaceous earth has excellent filtration performance and can maintain satisfactory filtration speed and flow for a long time.
The filter with a filtration area of 5 m2 and a maximum flow rate of 12 m3/h generally takes 8 hours to clean once.
What needs to be explained here is: if the machine is stopped midway (such as a power outage or other reasons), remember to close the outlet before turning it on again, perform a closed loop, and wait for the outlet solution to be clear and transparent before putting it into normal filtration.
In circulating filtration, after pre-coating diatomaceous earth on the filter medium, if a certain amount of powdered activated carbon is pre-coated on it, it can achieve the dual purpose of filtration and purification and can achieve the effect of continuous non-stop production and automatic treatment of the plating solution. This is very common abroad.
Filter plating solution containing a large amount of activated carbon
After a stage of use, the organic impurities in the solution increase. A proper amount of activated carbon and other treatment agents must be put into the bath for large-scale treatment, and then the activated carbon particles that have adsorbed organic impurities must be filtered out.
Due to the large mesh size of the filter cloth, if only the filter cloth is used, it needs to be repeated 7 to 8 times. It is often difficult to ensure that the solution does not contain activated carbon particles, resulting in a waste of manpower and material resources.
If the filter medium is pre-coated with diatomaceous earth as a filter-aid layer for treatment of activated carbon, only one filter can be used to obtain satisfactory results, and the benefits are quite obvious.