Abstract
Biosorption of chromium (Cr(VI)) is studied by using raw (chemically not modified) Moringa (Moringa Oleifera) leaf powder without any pretreatment. Cr(VI) is one of the potentially harmful heavy metals found in industrial wastewater. In the Moringa leaf powder, the presence of a significant amount of organic acids form the source for the biosorption of Cr(VI). The concentration of Cr(VI) in the feed solution is varied and different dosages of the proposed biosorbent are used to study its efficiency in the removal of Cr(VI). The concentration of Cr(VI) is varied from 1 ppm to 20 ppm while the amount of biosorbent is varied from 0.5 g to 2.5 g. The equilibrium time for adsorption of Cr(VI) is observed to vary between half an hour and 90 min. The metal removal efficiency varied from 30% to 90% which is a significant achievement compared to other conventional methods which are either energy-intensive or not cost effective. The experimental results are modeled using Langmuir, Freundlich and Redlich–Peterson isotherms. The metal removal efficiency is attributed to the chelating effect of carboxylate and hydroxyl groups present in the moringa leaves and is confirmed from the FTIR analysis. Further molecular docking simulations are performed to confirm the binding of the metal to the speculated sites within the different acids present in the moringa leaves. Untreated green moringa leaf powder used as a biosorbent in this study leads to a sustainable and cheaper option for treating wastewater containing Cr(VI).
Highlights
Heavy metals such as lead, nickel, copper, chromium, cadmium and strontium are commonly found in industrial wastewater [1]
From the FTIR analysis, it showed that the contribution from the chelating effect due to the O-H groups present in the ascorbic acid dominate over the corresponding contribution from the carboxylate groups in the amino acids. All these observations are in complete agreement with the findings reported by Gupta and Balomajumber [32] where they have used water hyacinth as the biosorbent to remove chromium and phenol simultaneously
The chromium in the solution has the possibility of existing as the chromate ion (CrO24−) or in the hydrogenated form (HCrO4−) based on the acid dissociation kinetics given by Equations (1) and (2) [33,34]
Summary
Heavy metals such as lead, nickel, copper, chromium, cadmium and strontium are commonly found in industrial wastewater [1]. An alternate cost-effective technique for heavy metal removal from wastewater is to use adsorption method This has led to explore different types of adsorbents that can be used to efficiently remove Cr(VI) from the waste containing this metal. There are several biosorbents that are developed to separate Cr(VI) and these include mango kernels, peanut hull, banana peels, sugarcane bagasse, sugarcane leaves, Aloe vera leaves, neem leaves, coconut shell [20] Most of these biosorbents are modified or activated using acids to generate the metal capturing sites on the surface of the adsorbent [21,22] which improves the capability of binding the metal to the adsorption site. In our research we use raw moringa leaf powder without any activation or pretreatment with chemicals as a biosorbent to adsorb Cr(VI) from the wastewater containing this metal
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