KINETIC AND THERMODYNAMIC STUDY OF THE ADSORPTION OF MANGANESE (II) ON ACTIVATED CARBON

Abstract

Recent studies revealed the Bay of Algiers was being polluted by manganese. Similar pollution was also reported in Azemmour, Morocco alongside the estuary of Oum Er Rbia, but also in the waters of developed countries (i.e. Canada, especially following the replacement of tetraethylplumbane in gasoline by methylcyclopentadienyl manganese). Treatment of polluted waters by manganese is therefore essential prior to their release, which is within the purpose of the present study. Commercial activated carbon (AC) was used for treating synthetic aqueous solution containing different concentrations of Mn. Adsorption kinetics was studied under agitation at different temperatures between 295 and 318 K. Results show that there are two areas where adsorption occurs according to a first-class model. In the first one, rate constant is k1 = 0.001610 min-1, meanwhile in the second, it is k2 = 0.000488 min-1. Equilibrium is reached in 7 hours. The obtained adsorption isotherm is a V type and follows Freundlich model for low concentrations and Langmuir model for high concentrations. The isotherm part described by Freundlich model lessens with the rise of temperature, increasing adsorption maximum capacity from 3.49 mg Mn/g AC (at 295 K) to 4.78 mg Mn/g AC (at 318 K). Adsorption is endothermic. Standard enthalpy (14.4869 kJ•mol-1) and standard entropy (36.25 J•mol-1•K-1) have been calculated. The free energy was positive in all the studied temperatures range. The values of adsorption heat indicate a physical adsorption.

Keywords

• activated carbon
• adsorption
• enthalpy
• entropy
• manganese