Technical comparison of activated carbon in different industries
Activated carbon is a porous structural substance, which is obtained by impregnating raw materials with chlorides and acids, then carbonizing at low temperature, then burning and activating or purifying pure carbon in a gaseous medium at a high temperature. The powder surface area of â€‹â€‹1g activated carbon is as high as 500-1500m2, and has excellent adsorption performance. In the purification of various plating solutions, its main role is to remove oils, organic impurities and decomposition products of various additives. The following points should be noted when using activated carbon to purify the bath:
1) Select a suitable activated carbon product. The activated carbons on the market are granulated and powdery. It is convenient to use granular activated carbon for filtration, but the treatment effect is far less than that of powdered activated carbon. The reason is that the powder has a much larger specific surface area than the granular one. Choose according to the degree of contamination of the plating solution.
2) Activated carbon should contain no impurity ions harmful to the plating solution. At present, the raw materials for the manufacture of activated carbon are mainly the shells of wood, coal and hard shell nuts (such as coconut). Practice has proved that in the purification of plating solution, activated carbon made from hard husks is superior to activated carbon products made from coal. Inferior activated carbon often contains more impurities such as zinc and should not be used. If activated carbon containing zinc impurities is used in the purification of nickel plating liquid, it will cause more serious pollution results (such cases are not uncommon).
3) The dosage should be sufficient. For plating solutions with different levels of organic impurities, appropriate input should be taken, generally 2~5g/L. If the dosage is insufficient, the treatment effect is not good. The amount of activated carbon can also be determined by a small test using a small process test tank or a Hull tank.
4) The Î¸ and pH of the treated bath should be appropriate. Most of the plating solutions have a good treatment effect with a Î¸ of 55 to 70 Â° C and a pH of 5 to 6. Î¸ and pH should remain stable throughout the treatment.
5) Stirring should be sufficient and uniform. It is advisable to use intermittent filtration and compressed air for intermittent strong agitation. If manual agitation is used, it should be carried out continuously in the plating tank without leaving a dead angle. t stirring should generally be 2 ~ 4h.
6) Rest time. After the adsorption process is completed, the plating solution should be allowed to stand for a period of time and then filtered, t is still for 6 to 12 hours; after sufficient precipitation, it is filtered 2 to 3 times until there is no residual carbon powder in the plating solution, and the plating solution is in bulk color (none Charcoal black) so far.
7) Prevent detachment. When the activated carbon is continuously filtered by the electroplating process, when the activated carbon is saturated, the activated carbon in the filter element should be cleaned and replaced in time to prevent desorption and impurities from re-contaminating the plating solution.
Application of activated carbon in tap water supply
The adsorption of activated carbon can be divided into physical adsorption and chemical adsorption. Physical adsorption occurs mainly in activated carbon-rich micropores for the removal of impurities in water and air. The molecular diameter of these impurities must be smaller than the pore size of activated carbon. Different raw materials and processing techniques result in different microporous structures, specific surface areas and pore sizes of activated carbon, which are suitable for different needs. The activated carbon contains not only carbon but also a functional group on its surface, which chemically reacts with the adsorbed substance, so that the adsorbed substance often occurs on the surface of the activated carbon. The impurities in the medium continuously enter the porous structure of the activated carbon through physical adsorption and chemical adsorption, so that the activated carbon is saturated and the adsorption effect is decreased. The activated carbon after adsorption saturation needs to be activated and regenerated, and its adsorption capacity is restored and reused. The adsorption performance indexes of activated carbon are mainly methylene blue value, iodine value and caramel adsorption value. The larger the adsorption capacity, the better the adsorption effect.
Activated carbon is a charcoal with a large specific surface area and a porous structure. According to its raw material classification, it can be divided into coal-based activated carbon, wood charcoal, shell charcoal and bone charcoal; according to its form, it can be divided into columnar carbon, broken carbon, powdered carbon and fibrous activated carbon. The main raw material of activated carbon is carbon, organic materials such as coal, wood, and husk, which are activated to form a complex pore structure with adsorption capacity. The pores having a radius greater than 20,000 nm are large pores, 150-20000 nm are mesopores, and less than 150 nm are micropores. The adsorption of activated carbon mainly occurs on these voids and surfaces. A large number of molecules on the pore walls of the activated carbon can generate strong gravitational force to attract impurities in water and air into the pores.
Activated carbon can be used in air purification and feed water, wastewater treatment to separate or collect impurities in air and water media. Granular activated carbon and powdered carbon have the same effect and can be used for water treatment. Granular carbon is not easy to be lost, can be reused and reused, and is used for water treatment processes with light pollution and continuous operation. Powdered carbon is not easy to recycle, and is generally used for single-use use in intermittently polluted water treatment processes. The activated carbon of the feed water is generally developed with micropores and mesopores, and should meet three requirements: large adsorption capacity, fast adsorption speed, and good mechanical strength. Powdered activated carbon requires that in addition to the above characteristics, the smaller the particle size, the better the adsorption effect.
Activated carbon laboratory technology
Add different amounts of activated carbon to the two-necked flask containing the solution to be purified, and make the adsorption reach equilibrium at the specified contact time as close as possible to the actual operating conditions. In this way, we can get the relationship between the amount of activated carbon used and the final concentration of the compound we are concerned with. Usually the performance of activated carbon under actual conditions can be well simulated. From the test results, we can choose: the most expensive and effective activated carbon species (the best price performance ratio); optimize the working conditions (contact time, pH, temperature).
Below is a useful laboratory technique based on our experience that will help you measure more reliable data.
The amount of solution that had been volatilized during the test was examined and the well was calibrated for volume before measuring the impurity content. This is important in high temperature atmospheres.
Make sure all activated carbon is filtered out.
When testing volatile materials, use a stoppered two-cornered bottle.
If your solution is pH sensitive, measure the pH of the solution before using activated carbon and after using activated carbon.
If there are strict restrictions on the mineral impurities in the liquid to be treated, check it before and after the activated carbon treatment.
In the recording and evaluation data, the use rate of activated carbon is often used. The term is defined as the mass of activated carbon required for each unit of measurement to be purified. For example, in the field of sugar refining, this unit of measurement is the dry basis weight of the substance, which is used for glycerin refining. This unit of measurement is volume.
It is important that the adsorption isotherm covers a range of concentrations, especially the Freundlich adsorption isotherm.
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