Abstract
The biosorption of Cr (III) onto the leaf biomass of Calotropis procera popularly known as ‘bom bom’ in western Nigeria, over a wide range of reaction conditions were studied. The batch experimentsshowed that the biosorption of Cr (III) onto Calotropis procera leaf biomass is a rapid process reaching equilibrium within 10 minutes at an optimum pH value of 5. Other reaction conditions such as biomass dosage, initial metal ion concentration and temperature were also found to influence the biosorption process. Both Langmuir and Freundlich isotherms were employed to describe the biosorption process and both proved to beapplicable. However, Langmuir gave a better fit with an R-Squared value of 0.967 (closer to unity than that of freundlich), Langmuir constant, KL of 0.0188 and monolayer adsorption capacity, qm of 32.26 whereas the Rsquared value for the freundlich plot was 0.948 with adsorption capacity Kf and adsorption intensity, n of 1.156 and 1.146 respectively. The biosorption process followed the pseudo-second order kinetic model evident by an Rsquared value of 0.999 and the pseudo second order rate constant, K2 of 0.3668 gmg-1min-1. Thermodynamic studies revealed negative value of change in free energy, G0 (- 4.046KJmol-1) as an indicator of feasibility and spontaneity of the Cr (III) biosorption process. A positive value of enthalpy, H0 (26.099 kJmol-1) was obtainedwhich indicated the endothermic nature of the biosorption process. FT-IR studies of the biosorbent before and after the biosorption process indicated that carboxylate, amino and nitro functional groups were involved in the sorption of Cr (III) onto Calotropis procera leaf biomass. These findings indicate that the leaf of biomass of Calotropisprocera could be employed in the removal of Cr (III) from aqueous solutions and industrial effluents.
Highlights
Chromium is one of the most abundant elements on earth and is of considerable environmental concern as it is widely used in leather tanning, electroplating, metal finishing, chromate preparation, wood preservation and manufacture of dyes and pigments (Krishna et al, 2004; Shali and Indu 2005)
Various kinds of biomaterials have been investigated for chromium removal and have been found efficient under various conditions such as pH, biosorbent dose, agitation time and initial metal ion concentration
Effect of pH: pH is an important parameter that affects the biosorption of heavy metals from aqueous solutions
Summary
Chromium is one of the most abundant elements on earth and is of considerable environmental concern as it is widely used in leather tanning, electroplating, metal finishing, chromate preparation, wood preservation and manufacture of dyes and pigments (Krishna et al, 2004; Shali and Indu 2005). The effect of pH on the biosorption of Cr (III) ions onto Hyloconium splendens biomass showed that Cr3+ adsorption increases with increase in pH from 3 -5 with maximum adsorption occurring at pH 5 This pH, there is dramatic decrease in the amount of Cr (III) adsorbed (Sari et al, 2008). Though maximum binding of most metals occur rapidly within the first 10 – 15 minutes and remain fairly uniform in the 120 minutes, Baig et al, 1999, reported a gradual increase in binding of Cr (III) over time on biomass of silverleaf nightshade (Solanum Elaeagnifolium). This study is aimed at increasing the biomass data bank by checking the efficiency of biosorption of Cr3+ onto Calotropis procera which is known to be locally used in coagulation of milk to cheese This implies that it might have some abilities to coagulate or adsorb metallic macromolecules and expected to sorb heavy metals from aqueous solutions containing them. A deeper knowledge by which this takes place will be necessary; this work has looked at the kinetics of the sorption process, equilibrium modeling and thermodynamics of the system as well as the means by which the process takes place
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