Thermodynamic and Equilibrium Studies of Dextrin Adsorption on Modified Coal

Abstract

Dextrin produced from cassava was investigated for adsorption on coal during processing. Aluminium ion (Al3+) and nitrate ion (NO3-) were employed for adsorption test to improve coal surfaces. The effect of initial concentration, adsorbent dose and pH on dextrin adsorption onto modified coal surface was investigated. Studies concerning the adsorption equilibrium and thermodynamics are presented; the equilibrium data was modelled using Langmuir and Freundlich isotherms. The adsorption equilibrium data was well explained by Freundlich isotherm. The percentage removal was found to be 93.75% and 90.75% at adsorbent dose of 0.2 g for both aluminium sulphate coal bituminous (ACB) and aluminium sulphate coal lignite (ACL) respectively. There was a rapid increase in adsorption of dextrin from low pH of 2 to about pH of 4 with a plateau region from pH 4 to pH 6. Adsorption capacity of 61.25 mg/g and 55.00 mg/g was achieved at initial concentration of 200 mg/L for ACB and ACL respectively. For a better interpretation, the nature of the adsorption of dextrin on the prepared coal samples was predicted from thermodynamic point of view by estimating the thermodynamic parameters. The determination of basic thermodynamic parameters: enthalpy of adsorption, Gibb’s free energy and entropy of adsorption are important. The negative value of ∆Gad indicates the feasibility and spontaneity of the adsorption process and the magnitude is an indication of the involvement of salt link, electrostatic interaction and hydrophobic bonding in the adsorption.