European Journal of Chemistry 13 (1) (2022) 78-90 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2022 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.13.1.78-90.2189 European Journal of Chemistry View Journal Online View Article Online Kinetic studies and adsorptive removal of chromium Cr(VI) from contaminated water using green adsorbent prepared from agricultural waste, rice straw Izaz Ul Islam 1 , Mushtaq Ahmad 1 , Maqbool Ahmad 1 , Shah Rukh 2 and Ihsan Ullah 1, * 1 Department of Chemistry, Government Post Graduate College Mardan, Higher Education Department, Khyber Pakhtunkhwa, 23200, Pakistan 2 Department of Chemistry, Government Girls Degree College Takht Bhai Mardan, Higher Education Department, Khyber Pakhtunkhwa, 23200, Pakistan * Corresponding author at: Department of Chemistry, Government Post Graduate College Mardan, Higher Education Department, Khyber Pakhtunkhwa, 23200, Pakistan. e-mail: ihsan.chem@tju.edu.cn (I. Ullah). 10.5155/eurjchem.13.1.78-90.2189 Received: 29 September 2021 Received in revised form: 11 November 2021 Accepted: 27 November 2021 Published online: 31 March 2022 Printed: 31 March 2022 Water pollution caused by heavy metals is of great concern because of rapid industrialization, lack of wastewater treatment, and inefficient removal of these metals from wastewater. The present project was designed to develop a green adsorbent from rice straw and to investigate it for the removal of chromium from chromium-contaminated water. Rice straw biochar was prepared and then modified with FeCl3·6H2O and FeSO4·7H2O to enhance its Cr removal efficiency. Modified and unmodified biochar were characterized by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR). Batch sorption experimentations were performed to inquire about adsorption kinetics, isotherms, and Cr(VI) adsorption mechanism onto iron-modified rice straw biochar (FMRSB). The results specified that the apex adsorption capability of the adsorbent for chromium was 59 mg/g and the maximum removal efficacy was 90.9%. Three isotherm models, Sips, Freundlich, and Langmuir models were applied to the experimental data. Among them, the Sips isotherm model reveals the most excellent fitting with a maximum correlation coefficient (R 2 = 0.996) that was adjusted to the experimental data. Regarding kinetic studies, the Pseudo second-order (PSO) exhibits the best fitting with a higher correlation coefficient (R 2 = 0.996). The kinetic equilibrium data expressed that the adsorption of Cr(VI) on the FMRSB surface was chemisorption. The mechanism of adsorption of Cr(VI) on FMRSB was predominantly regulated by anionic adsorption through adsorption coupled reduction and electrostatic attraction. The present study demonstrated that the use of modified biochar prepared from agricultural wastes is an environmentally safe and cost-effective technique for the removal of toxic metals from polluted water. Pyrolysis Rice straw Chromium Adsorption Raw rice straw biochar Iron modified rice straw biochar Cite this: Eur. J. Chem. 2022, 13(1), 78-90 Journal website: www.eurjchem.com 1. Introduction The acquit of a large number of toxic substances i.e., heavy metals into the water bodies are a consequence of rapid industrialization and swift in commercial and anthropogenic activities. Due to these toxic substances, the biotic components of the environment are at high risk. Even at low concentrations, they are extremely toxic because of their accumulation in the human body and therefore very harmful to living organisms and human beings. Once the heavy metals are introduced into the food chain, they are biomagnified regularly and their concentration is increased to a harmful level. Zinc, arsenic, chromium, nickel, copper, mercury, lead, and cadmium are heavy metals that are frequently released by various industrial operations. 0.050, 0.006, 0.05, 0.25, 0.01, 0.08, 0.00003, and 0.2 are the maximum contaminant limit (MCL) for arsenic, lead, chromium, copper, cadmium, zinc, mercury and nickel, respect- tively. Chromium, among the heavy metals, is one of the most toxic, carcinogenic, and mutagenic metals that adversely affect all the biotic components of the ecosystem [1,2]. The toxicity of chromium is due to its non-degradable nature [3]. Chromium exists in multitudinous valencies from -2 to +6, however, Cr(III) and Cr(VI) forms of chromium are most profuse [4]. Chromium (VI) and its compounds are comparatively more toxic than trivalent and metallic chromium. In developed countries, the Cr(VI) concentration in industrial effluents is 0.5 ppm [5]. The chromium contamination of the water reservoir is because of the uncontrolled release of effluents from various industrial operations, such as electroplating, production of glass, metal coating, pigments, leather making, textile, and paint industries that are laden with a considerable amount of chromium waste [6,7]. According to USEPA and WHO, the acceptable Cr(VI) limit in drinkable and wastewater from various industrial operations is 0.05 and 0.5 mg/L, respectively [8]. Chromium entry into the human body occurs via eating, breathing, drinking, or contiguity of the skin with chromium and its compounds. The adverse consequences of chromium exposure include infection of the respiratory tract, cancer of the lungs, rashes on the skin, ABSTRACT RESEARCH ARTICLE KEYWORDS