IMPORTANT VARIABLES

In general, the most important variables that affect adsorption are:

Temperature, P.H., and the size of the particle.

• TEMPERATURE
  A higher temperature generally makes reaching equilibrium faster; yet, the amount of adsorbed impurity is lower. That means that if time were not important, more adsorption could be achieved at a lower temperature; rarely practical at an industrial level, so increasing the temperature -when possible- is generally beneficial.

• PH
  Many compounds that originate color vary in structure and color when the PH changes. In most of the cases discoloration to a lower PH is more efficient because of two reasons:
  - Compounds that generate color are generally highly dependent on the PH, becoming less intense at a lower PH.
  - Adsorption is possibly more efficient at a lower PH. When you are not sure about the behavior, it is better to modify the PH and find an activated carbon with a PH that is close to that of the process.

• CARBON PARTICLE SIZE
  As mentioned before, the carbon area is internal and consequently the size of the particle does not have any effect on the adsorption capacity of the carbon itself. Yet, it does affect the velocity to reach the equilibrium.
  For example: On a certain application, several hours of contact might be needed when using granular carbon in order to get the same results that might have been obtained using powdered carbon during a 30 minute contact. The disadvantages of using a smaller particle are:
  - With granular carbon: A higher pressure drop
  - With powdered carbon: Less filtration capacity.

Carbon Purity: ashes
Ashes are inorganic compounds present in the raw material from which the activated carbon was produced and that did not volatilize during the activation process.

The ash content is associated to the quality of a carbon; yet, this is not entirely so because what is important is the part of the ashes that is soluble in the product that is being purified.

There are many applications in which ashes are not important; nevertheless, there are some processes in which the presence of inorganic compounds, for example, calcium, magnesium, and iron can cause an unwanted reaction.

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Also visit:
[ The Mystery of Activated Carbon | Activation Process | Classification of Activated Carbon | Liquid Fase Purification | Gas Fase Purification ]