Equilibrium, Kinetic, and Thermodynamic Studies on the Adsorption of Cadmium from Aqueous Solution by Modified Biomass Ash

Abstract

Natural biomass ash of agricultural residuals was collected from a power plant and modified with hexagonal mesoporous silica and functionalized with 3-aminopropyltriethoxysilane. The physicochemical and morphological properties of the biomass ash were analyzed by ICP-OES, SEM, TEM-EDS, FTIR, and BET analysis. The adsorption behavior of the modified product for Cd2+ in aqueous solution was studied as a function of pH, initial metal concentration, equilibrium time, and temperature. Results showed that the specific surface area of the modified product was 9 times that of the natural biomass ash. The modified biomass ash exhibited high affinity for Cd2+ and its adsorption capacity increased sharply with increasing pH from 4.0 to 6.0. The maximum adsorption capacity was 23.95 mg/g in a pH 5 solution with an initial metal concentration of 50 mg/L and a contact time of 90 min. The adsorption of Cd2+ onto the modified biomass ash was well fitted to the Langmuir model and it followed pseudo-second-order kinetics. Thermodynamic analysis results showed that the adsorption of Cd2+ was spontaneous and endothermic in nature. The results suggest that the modified biomass ash is promising for use as an inexpensive and effective adsorbent for Cd2+ removal from aqueous solution.

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“…Although this definition is not so rigorous from the thermodynamic point of view, it was widely used in the literature …”

“…Although this definition is not so rigorous from the thermodynamic point of view, it was widely used in the literature. [22][23][24][25][26][27] On the basis of Equation (10), one can consider a conditional ΔG ad (standard Gibbs energy change related to the adsorption) as follows:…”

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“…The quantity of residual pigments Y 1 The quantity of raw material carbonized and Y 2 The quantity of AC obtained…”

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“…In fact, in [13] the researchers have changed the reaction chain as well as employing KNO3 instead of NaOH for mercerization process. Unlikely, they did not present the thermodynamics analysis that is essential to observe nature and spontaneity of the reaction [14] as well as exhaustive kinetic analysis by virtue of this maiden adsorbent.…”