Comprehensive evaluation of Moringa oleifera seed as a low-cost adsorbent for removal of manganese (Mn) from aqueous solutions

Abstract

Adsorption of heavy metals from wastewater using agricultural waste materials has been implemented over the years due to their inexpensiveness and abundance. Manganese (Mn) is a heavy metal used in several industries which can pollute the groundwater significantly. The dried seeds of Moringa oleifera, a drought-resistant tree, grown in several parts of Saudi Arabia were selected for the removal of Mn from aqueous solutions. The seeds of three different particle sizes were utilized under two different acidic pH to establish the adsorption of the metal with different dosages. The optimum adsorption properties were observed at a pH of 3, time of 2 hours, and particle size of 250 μm for a dosage of 0.2 g at room temperature with metal removal efficiency higher than 92 %. The adsorption data were utilized to plot adsorption isotherms. The powder was characterized by Fourier Transform Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) before and after adsorption experiments. Both techniques confirmed the presence of Mn (II) ions after adsorption experiments in the Moringa powder which corroborates the hypothesis that these kinds of agricultural wastes can remove the heavy metals easily due to the presence of several organic groups in them. The adsorption kinetic studies showed that both Freundlich and Langmuir isotherms fit well the experimental data obtained. Moreover, the intra-particle diffusion model of the kinetic studies can explain the adsorption process of Mn ions from water.

Keywords

• Agricultural wastes
• Heavy metal
• Moringa oleifera
• Isotherms
• Kinetics