Several factors affecting the adsorption efficiency of activated carbon
Since the adsorption process and the principle of action involved in the treatment of activated carbon water are complicated, there are 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.
First, the nature of activated carbon
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, the internal diffusion has a great influence on the adsorption speed, so the micropore distribution of activated carbon is another important factor affecting the adsorption.
In addition, the surface chemistry, polarity and charge of the activated carbon also affect the adsorption effect.
Activated carbon for water treatment should have three requirements: large adsorption capacity, fast adsorption speed, and good mechanical strength. The adsorption capacity of activated carbon is related to the specific surface area of ​​activated carbon, and the specific surface area is large, the number of micropores is large, and the adsorbate adsorbed on the pore wall is more. The adsorption rate is mainly related to the particle size and pore distribution. The activated carbon for water treatment requires a transition hole (radius 20~1000A) to be developed, which is beneficial to the diffusion of the adsorption mass into the micropores. The smaller the particle size of activated carbon, the faster the adsorption speed, but the head loss 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.
Second, the nature of the adsorbate (solute or pollutant)
The same activated carbon has great differences in the adsorption capacity of different pollutants.
(1) Solubility
The solubility of a substance of the same group decreases as the chain lengthens, and the adsorption capacity increases as the series of homologues rises or the molecular weight increases. The smaller the solubility, the easier it is to adsorb.
For example, the order in which activated carbon adsorbs organic acids from water is increased by formic acid-acetic acid-propionic acid-butyric acid.
(2) Molecular structure
The size and chemical structure of the adsorbate molecules also have a large effect on 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 favorable for adsorption. In homologues, molecules larger than molecules are easily adsorbed. The organic matter of the unsaturated bond is more soluble than the saturated one. Aromatic organics are easier to adsorb than aliphatic organics.
(three) polarity
Activated carbon can be regarded as a non-polar adsorbent, and its adsorption capacity for non-polar substances in water is greater than that of polar substances.
(4) Adsorption sanctions (solute)
When the concentration of the adsorbate is within a certain range, the adsorption capacity increases as the concentration increases. Therefore, the concentration of the adsorbate (solute) changes, and the adsorption capacity of the activated carbon for the adsorbate (solute) also changes.
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