Chemical treatment of teff straw by sodium hydroxide, phosphoric acid and zinc chloride: adsorptive removal of chromium

Abstract

In this study, teff (Eragrostis tef) straw has been chemically treated and tested as an adsorbent for Cr(VI) removal. Chemically treatment of teff straw was done by NaOH, H 3 PO 4 and ZnCl 2 solutions. Scanning electron micrograph and X-ray diffraction were used for anatomical characterization, whereas Fourier transform infrared spectroscopy was used for surface change characterization of adsorbents. Effects of different experimental parameters like pH (2-12), initial Cr(VI) concentration (100-900 mg/L), adsorbent dose (2.5-20 g/L), contact time (15-360 min) and temperature (288-318 K) were studied. Temperature increment was found to stimulate the adsorption process. Langmuir isotherm was found to give better representation over wide range of temperature for untreated, H 3 PO 4 -as well as ZnCl 2 -treated teff straw, and Freundlich isotherm best represented the isotherm data for NaOH-treated teff straw. Maximum Cr(VI) adsorption capacity of untreated, NaOH-, H 3 PO 4 -and ZnCl 2 -treated teff straw was found to be 86.1, 73.8, 89.3 and 88.9 mg/g, respectively. Respective values of average effective diffusion coefficient (D e ) were found to be 2.8 9 10 -13 , 2.59 9 10 -14 , 1.32 9 10 -13 and 1.14 9 10 -13 m 2 /s, respectively. The negative value of DG o for all the adsorbents indicates Cr(VI) spontaneous adsorption. Isosteric heat of adsorption (DH st,a ) was found to vary with surface coverage (h). DH st,a increased for untreated, H 3 PO 4 -and ZnCl 2 -treated teff straw, and decreased steadily with h for NaOH-treated teff straw.

Reducing Sugar Production from Teff Straw Biomass Using Dilute Sulfuric Acid Hydrolysis: Characterization and Optimization Using Response Surface Methodology

“…The exposure of internal structures of Teff straw with acid increases the accessibility of cellulose for further processing [ 10 ]. The results of SEM analysis ( Figure 1(b) ) indicated that acid hydrolysis of T eff straw showed significant surface modification, i.e., developed honeycomb-like rough surfaces, nonuniform pores, and cavities caused by the reaction between H 2 SO 4 and ester bonds, which led to removal of lignin and hemicellulose with cellulose domination [ 7 ].…”

“…Even though they are strong agents for cellulose hydrolysis, concentrated acids are toxic, corrosive, and hazardous and thus require reactors that are resistant to corrosion, which makes the pretreatment process very expensive. In addition, the concentrated acid must be recovered after hydrolysis to make the process economically feasible [ 6 , 7 ]. Dilute acid hydrolysis has been widely used for pretreatment of lignocellulosic biomass.…”

Formation of improved activated carbons from sugarcane bagasse as environmental materials for adsorption of phenolic pollutants

“…Therefore, AC adsorbents cannot be regenerated (Magne and Walker 1986). Thus, different thermo-chemical methods have been investigated for the conversion of biomass of agricultural residues, as renewable and non-expensive starting materials for AC adsorbents formation (Açıkyıldız et al 2014;Gundogdu et al 2012;Angin 2014;Khenniche and Benissad-Aissani 2010;Gonçalves et al 2014;Wassie and Srivastava 2016;Karri et al 2017b;Khalil et al 2017).…”

Simultaneous Biosorption of Arsenic and Cadmium onto Chemically Modified Chlorella vulgaris and Spirulinaplatensis

“…Moreover, sodium ions can be easily replaced by heavy metal ions without affecting the subsequent biosorption process. The ZnCl 2 modification could separate hemicellulose, which contains a variety of functional groups that are beneficial to the biosorption process, from biomass and cause biomass swelling [22]. It has been reported that iron-based adsorbents exhibited a strong affinity for arsenate [23], thus FeCl 3 was used to enhance the efficacy of the adsorbent for the effective removal of the As.…”