A study of the factors affecting the removal of humic acid by activated carbon prepared from biomass material

A biomass agricultural waste material, rice husk (RH), was used for preparation of activated carbons by chemical activation using phosphoric acid. The effect of various factors, e.g., carbon type, carbon dosage, pH, initial concentration, temperature, particle size of carbon and various inorganic ions on the adsorption capacity, were quantitatively determined. The two-parameters equilibrium models (Langmuir and Freundlich equations) were discussed. It was found that the monolayer capacity is increased by 38% in the presence of Ca2+ and only 4% of the adsorbed humic acid (HA) is desorbed. Temperature effect at 25, 35 and 45 °C prove that the adsorption is endothermic process. Cations, e.g., Ca2+, Mg2+, Na+ and Al3+ taken as nitrate were tested on the humic acid uptake, and it was found that the capacity of activated carbon can be markedly enhanced by certain cationic species and Ca2+ has the greatest effect. A mixed effect of “electrostatic attraction” and “surface complex formation” is suggested to be responsible for the adsorption of humic acid on the surface of carbon.