Abstract
The presence of toxic metals in surface and natural waters, even at trace levels, poses a great danger to humans and the ecosystem. Although the combination of adsorption and coagulation techniques has the potential to eradicate this problem, the use of inappropriate media remains a major drawback. This study reports on the application of NaNO2/NaHCO3 modified sawdust-based cellulose nanocrystals (MCNC) as both coagulant and adsorbent for the removal of Cu, Fe and Pb from aqueous solution. The surface modified coagulants, prepared by electrostatic interactions, were characterized using Fourier transform infrared, X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS). The amount of coagulated/adsorbed trace metals was then analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). SEM analysis revealed the patchy and distributed floccules on Fe-flocs, which was an indication of multiple mechanisms responsible for Fe removal onto MCNC. A shift in the peak position attributed to C2H192N64O16 from 2θ = 30 to 24.5° occurred in the XRD pattern of both Pb- and Cu-flocs. Different process variables, including initial metal ions concentration (10–200 mg/L), solution pH (2–10), and temperature (25–45 °C) were studied in order to investigate how they affect the reaction process. Both Cu and Pb adsorption followed the Langmuir isotherm with a maximum adsorption capacity of 111.1 and 2.82 mg/g, respectively, whereas the adsorption of Fe was suggestive of a multilayer adsorption process; however, Fe Langmuir maximum adsorption capacity was found to be 81.96 mg/g. The sequence of trace metals removal followed the order: Cu > Fe > Pb. The utilization of this product in different water matrices is an effective way to establish their robustness.
Highlights
Introduction iationsA significant amount of heavy metals from industrial effluents ends up in the environment and adversely affects the quality of water [1]
The details of the physicochemical properties of the pristine and modified Cellulose nanocrystals (CNC), such as functional groups, structures and surface charge, have been previously reported, the current study focuses on the properties of the floccules obtained in the subsequent trace metal ions removal
X-ray diffraction analysis of the coagulants revealed the presence of peaks associated with the coagulant material, and additional phases appeared after the coagulation process that were ascribed to sodium nitrite and sodium bicarbonate used for modification
Summary
A significant amount of heavy metals from industrial effluents ends up in the environment and adversely affects the quality of water [1]. Some major industrial sources of toxic metals include surface treatment processes and coating of industrial products involving the use of metals such as Cu, Fe, Ni and Pb [2]. Heavy metals are non-biodegradable, and remain in both the environment and biological systems for a long period. Traces of heavy metals could slowly accumulate in the human body over a long period of time [3,4], thereby exerting negative health effects on human tissues. The use of these metals in the industries is in high demand due to their various applications and benefits, their prevention from reaching downstream processes and subsequently ending up in the receiving waters remains a major challenge. The consumption of copper within the allowable limit could improve the human immune system, aid digestion, and Licensee MDPI, Basel, Switzerland
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