Removal of Cr (III) from wastewater by using raw and chemically modified sawdust and corn husk

Abstract

Abstract The contamination of water resources by heavy metals (HMs), mainly introduced by anthropogenic resources, has been considered as a serious environmental issue in the recent era. Therefore, the conventional methods for heavy metal removal have various drawbacks in terms of cost, toxicity, and efficiency. The novel study investigated the biosorption intensity of raw and chemically modified sawdust (SD) and corn husk (CH) to eliminate chromium (III) from the aqueous solutions. SD and CH were used as biosorbents and were treated chemically with sulfuric acid (H2SO4), sodium hydroxide (NaOH), and detergent powder. The biosorption potential was estimated based on percentage removal efficiency (% RE) of chromium (III) and the adsorption intensity (qmax). The characterization of surface morphology and functional groups of biosorbents was studied by SEM and FTIR. Moreover, the adsorption isotherm models (Langmuir and Freundlich), kinetic models (pseudo-first-order kinetics and pseudo-second-order kinetics), and thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were also assessed to predict the biosorption process. The results of % RE revealed that detergent-treated SD (DTSD) and detergent-treated CH (DTCH) showed highest % RE of 9.27 ± 0.15 (%) and 99.16 ± 0.08 (%) for elimination of chromium (III), respectively. Similarly, base-treated SD (BTSD) and base-treated CH (BTCH) exhibited 95.53 ± 0.18 (%) and 92.43 ± 0.22 (%) of % RE compared with 77.87 ± 1.64 (%) and 81.96 ± 0.34 (%) removal efficiency of acid-treated SD (ATSD) and acid-treated CH (ATCH), respectively. The raw SD (RSD) and raw CH (RCH) showed lower % RE of 23.68 ± 1.52 (%) and 35.52 ± 4.74 (%) for Cr (III) removal. Further, the porosity on the biosorbent's surface and attached functional groups increased after chemical treatment and this variation resulted in increased removal efficiency after chemical treatments. The Langmuir isotherm model and the Freundlich isotherm model were employed to predict the biosorption process, and both these models are best-fitted. The pseudo-second-order kinetic model was promising representative of the biosorption data. The process was endothermic and the parameters indicated that Cr (III) biosorbtion was thermodynamically favorable. Therefore, the obtained results highlighted that detergent-treatment enhanced the % RE, and DTSD and DTCH are highly efficient biosorbents for eliminating Cr (III) from aqueous solutions. Thus, detergent-treated biosorbents are proved to be a promising sustainable, eco-friendly, and cost-effective way to treat HMs from aqueous solutions as they utilize natural agriculture waste products and also handle issues related to excessive solid waste management.