Development and Application of Teff Straw Supported Nano Zero-valent Iron for Removal of Hexavalent Chromium from Aqueous Solution

Abstract

Waste water released to the environment is causing adverse effect on our ecosystem. There are various toxic heavy metals that are released with industrial waste water to the environment, hence worsening the life of biodiversity and increasing environmental pollution. Hexavalent Chromium (Cr(VI)) is a highly toxic pollutant which needs to be removed from the waste water. Conventional methods for remediation of Cr(VI) are usually costly and difficult to operate. Green synthesis provides advancement over chemical and physical method because it is cost effective, environmentally friendly, easily scaled up for large scale synthesis. In this study, zero valent iron, a strong reducing agent that transforms Cr(VI) to nontoxic trivalent chromium (Cr(III)), was synthesized, characterized and tested for adsorption of Cr(VI). Zero valent iron (Fe0 ) nanoparticles were synthesized by reduction of Ferrous Sulphate (FeSO4.7H2O) in the presence of polyphenol extracted from Eucalyptus Camaldulensis leaves. The synthesized particles were identified as iron nanoparticles using UV visible spectrophotometer. X-ray Diffraction (XRD) was used to determine the crystallinity of synthesized nano zero valent iron (nZVI) particles, hence, the formed polyphenol based iron nanoparticles have no crystalline structure. FT-IR spectra revealed the existence of -OH stretching vibration of polyphenols and Fe-O bond formation in the prepared nanomaterials. The batch adsorption experiments for the removal of hexavalent chromium has been conducted using nZVI-TS dosage, initial concentrations of Cr(VI), solution pH and contact time as parameters and the process was significantly affected by these parameters. The highest removal efficiency obtained was 99.79%. Langmuir isotherm model was better to fit to the experimental data and favored adsorption process. Response Surface Methodology using Central Composite Design was applied to analyze statistical experimental analysis for the data obtained from laboratory experiments and its optimal condition was identified. The optimal conditions selected using design tool were nZVI-TS dosage of 0.972 g/100 ml, initial Cr(VI) concentration of 21.034 mg/1000 ml, pH of 4.166, and contact time of 6.99 min providing predicted value of 99.984% removal efficiency