Adsorptive retention of citric acid onto activated carbon prepared from Havea braziliansis sawdust: Kinetic and isotherm overview

Retention of citric acid, an organic ligand, from aqueous phase was studied using activated carbon (15% K2CO3 treated) prepared from Havea braziliansis saw dust obtained from a local timber industry at Kodangavila, Trivandrum, Kerala, India. Batch adsorption studies were performed to evaluate the effect of various parameters such as pH, contact time, initial citric acid concentration and adsorbent dose for the adsorptive retention process. The mechanism of citric acid adsorption from aqueous solution was investigated by conducting pH as well as kinetic studies. The maximum adsorption of citric acid onto activated carbon occurred at a pH value around 5.0. The kinetic adsorption data was in close agreement with pseudo-first-order than pseudo-second-order expression. The solution pH, zero point charge (pHzpc) and citric acid speciation played important roles in the extent of citric acid adsorption onto activated carbon from water and wastewaters. The equilibrium data obtained from isotherm studies explains the L-type adsorption process and follows a Langmuir type isotherm model.