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Novel sawdust-derived cellulose nanocrystals adsorbents for heavy metals removal from water.
Zulu, Confidence
Zulu, Confidence
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Abstract
Environmental problems related to water pollution due to the presence of highly toxic heavy metals poses a significant threat to ecosystems and human health. Numerous studies have
reported that heavy metals, including vanadium (V(V)) and chromium (Cr(VI)), play a significant role in environmental degradation. As a result, effective removal of these metal ions
is of great concern because of their negative health impacts. Among other treatment methods applied in the removal of these heavy metals, adsorption method has been considered as one of the most effective treatments of heavy metals. Of lately, application of lignocellulosic biomass derived adsorbents for environmental remediation has received much attention due to their availability, inexpensive nature and exceptional properties. Moreover, development of sawdust derived cellulose nanocrystals (CNCs) has received extensive attention as a promising nanomaterials adsorbent for heavy metal ions treatments. Therefore, this study investigated the removal of V(V) and Cr(VI) contaminants from synthetic wastewater using cationic surfactant hexadecyltrimethyl ammonium bromide (HDTMA-Br) and sodium alginate modified CNC pellets adsorbent. Both sorption media were characterized using different analytical techniques such as FTIR, SEM, TEM, and XRD in order to confirm the successful functionalization and enhancement of the surface properties. Characterization results confirmed the existence of crystalline structures and the presence of carboxyl and amide groups on the surface of the adsorbents and revealed that modified CNC were in nanosized structure with an average particle size of 6 to 36 nm. In addition, SEM analyses for pelletized materials revealed a rough surface and high porosity morphologies as a prerequisite properties of a good adsorbent. Thereafter, batch equilibrium and kinetics tests were conducted to investigate the adsorption capability of the adsorbent under varying adsorbent mass, solution
pH, initial ions concentration, contact time and temperature of the system. Equilibrium data showed that good performance was obtained at pH of 4.0 and pH 2,0 for V(V) and Cr (VI),
respectively. Furthermore, isotherm studies demonstrated that both vanadium and chromium removal followed the Langmuir model with a maximum adsorption uptake of 47.2 mg/g and
69,4 mg/g at 298K. Meanwhile, adsorption kinetics data was well described by Ho pseudo second order model suggesting chemisorption nature of the process. The spontaneity and endothermic nature of the adsorption process was demonstrated through thermodynamic studies for adsorption of vanadium whereas results showed exothermic nature and nonspontaneous process for Cr(VI) removal. Regeneration of the spent modified CNC was studied and demonstrated that the adsorbent can be reused for three consecutive times in adsorption desorption cycle. Continuous fixed-bed operation was employed to investigate the adsorption performance of sodium alginate modified cellulose nanocrystals (HDTMACNC/SA) pellets in the removal of Cr(VI) ions from aqueous solution by varying the influence of operational conditions like bed height, influent initial ion concentration and flow rate. It was seen that the good column performance was achieved at a lower bed loading of 2,5 g and an influent metal ion concentration of 10 mg/L pumped at flow rate of 2,5 mL/min. Consequently, the breakthrough curve for the fixed-bed data illustrated that the breakthrough points were reached faster when increasing the flow rate and influent concentration, and later by increasing the bed height indicating poor performance at these conditions. The experimental results were satisfactorily described by Yoon–Nelson compared to other applied models. Based on these reported findings, it can concluded that surfactant modified CNC and alginate based CNC can be a suitable candidates adsorbents for the removal of V(V) and Cr(VI) ions from water.
Description
Submitted in partial fulfilment of the requirements for the degree, Doctor of Engineering in the Department of Chemical Engineering Faculty of Engineering and the Built Environment at the
Tshwane University of Technology.
Date
2023-11-01
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Tshwane University of Technology
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Keywords
Adsorption, Sawdust, Functionalized cellulose nanocrystals, Chromium (VI), Vanadium (V), Isotherm, Thermodynamic, Column dynamic, Granulation
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CC0 1.0 Universal