Since the adsorption process and the principle of action involved in activated carbon water treatment are more complicated, there are also many influencing factors. It is mainly related to the nature of activated carbon, the nature of pollutants in water, the process principle of activated carbon treatment, and the selected operating parameters and operating conditions.
Since the adsorption phenomenon occurs on the surface of the adsorbent, the specific surface area of the adsorbent is one of the important factors affecting the adsorption. The larger the specific surface area, the better the adsorption performance.
Because the adsorption process can be regarded as three stages, internal diffusion has a greater influence on the adsorption rate, so the micropore distribution of activated carbon is another important factor affecting adsorption.
In addition, the surface chemical properties, polarity and charge of activated carbon also affect the adsorption effect.
The activated carbon used for water treatment should have three requirements: large adsorption capacity, fast adsorption speed, and good mechanical strength. The adsorption capacity of activated carbon is attached to other external conditions, which is mainly related to the specific surface area of activated carbon. The specific surface area is large, the number of micropores is large, and there are many adsorbates that can be adsorbed on the pore wall. The adsorption speed is mainly related to particle size and fine pore distribution. Activated carbon for water treatment requires transition pores (radius 20~1000A) to be developed, which is beneficial to the diffusion of adsorbate into fine pores. The smaller the particle size of activated carbon, the faster the adsorption speed, but the loss of water head should be increased, generally in the range of 8~30 mesh. The mechanical wear resistance of activated carbon directly affects the service life of activated carbon.
The adsorption capacity of the same activated carbon for different pollutants is very different.
The solubility of the same group of substances decreases with the lengthening of the chain, while the adsorption capacity increases with the series of homologues or molecular weight. The lower the solubility, the easier the adsorption.
For example, the order of activated carbon adsorbing organic acids from water is increased by formic acid-acetic acid-propionic acid-butyric acid.
The size and chemical structure of the adsorbate molecules also have a greater influence on the adsorption. Because the adsorption rate is affected by the internal diffusion rate, the size of the adsorbate (solute) molecule is proportional to the pore size of the activated carbon, which is most conducive to adsorption. In homologues, larger molecules are easier to adsorb than smaller molecules. Unsaturated bonds are more saturated and easy to adsorb. Aromatic organic matter is easier to adsorb than aliphatic organic matter.
Activated carbon can basically be regarded as a non-polar adsorbent, the adsorption capacity of non-polar substances in water is greater than polar substances.
When the concentration of the adsorbate is within a certain range, as the concentration increases, the adsorption capacity increases. Therefore, the concentration of the adsorbate (solute) changes, and the adsorption capacity of the activated carbon for the adsorbate (solute) also changes.