The influence of pH value of the solution on adsorption should be considered comprehensively with the influence of activated carbon and adsorbate (solute). The pH of the solution controls the degree of dissociation of acidic or basic compounds. When the pH reaches a certain range, these compounds will dissociate and affect the adsorption of these compounds. The pH value of the solution will also affect the solubility of the adsorbate (solute) and the charging of the colloidal substance (solute). Because activated carbon can absorb hydrogen and oxygen ions in water, it affects the adsorption of other ions.
The effect of activated carbon in adsorbing organic pollutants from water generally decreases with the increase of the pH value of the solution. When the pH value is higher than 9.0, it is not easy to adsorb. The lower the pH value, the better the effect. In practical applications, the optimal pH range is determined through experiments.
Because the heat of adsorption is small during liquid phase adsorption, the effect of solution temperature is small. Adsorption is an exothermic reaction. Adsorption heat, that is, the total heat released by activated carbon to adsorb a unit weight of adsorbate (solute), in KJ/mol. The greater the heat of adsorption, the greater the effect of temperature on adsorption. On the other hand, temperature has an effect on the solubility of a substance and therefore also has an effect on adsorption. When activated carbon is used to treat water, the effect of temperature on adsorption is not significant.
When applying the adsorption method to treat water, usually the water is not a single pollutant, but a mixture of multi-component pollutants. During adsorption, they can be co-adsorbed to promote or interfere with each other. In general, the respective adsorption capacity of multi-component adsorption is lower than that of single-component adsorption.
Because the speed of external diffusion (liquid film diffusion) has an effect on the adsorption during the liquid phase adsorption of activated carbon, the type of adsorption device and contact time (water flow rate) have an impact on the adsorption effect.
In summary, there are many factors that affect the adsorption, which should be comprehensively analyzed, and the best adsorption conditions should be selected according to the specific situation to achieve the best adsorption effect.