Abstract
The present work verified the adsorption of hexavalent chromium (Cr (VI)) from synthetic aqueous solution using synthesized highly efficient low-cost adsorbent prepared from H2O2-modified olive seed residue solid waste/Anthracite/Chitosan (MOSR/An/CS) composite. Characteristics of the fabricated MOSR/An/CS composite were estimated by XRD, SEM, TGA, DSC, FT-IR, SBET and zeta potential tools. The entire chromium uptake study was conducted via batch adsorption mode under various operating conditions. Kinetics data were analyzed using five kinetic models, while empirical equilibrium data was fitted using three isotherms. The results clarified that Langmuir best described the adsorption of Cr (VI) ions with maximum monolayer coverage of 137.7 mg/g. Pseudo-first-order mode nicely fitted the kinetics adsorption. Further, Elovich, intraparticle diffusion, and Boyd models validate that more than one mechanism contributed to the adsorption of Cr (VI). The positive ΔH (110.11 kJ/mol), suggesting that the method of adsorption is endothermic and favorable at low temperatures, also indicated the chemisorption of Cr(VI). The positive value of ΔG varying from (14.53 to 8.1115 kJ/mol) at the temperature range measured confirms the possibility of the process as a non-spontaneous adsorption reaction. The Ea value was found to be 110.11 kJ mol−1 which mean that the adsorption of Cr(VI) onto MOSR/An/CS composite is chemisorption. The developed MOSR/An/Cs composite exhibited decent reusability after five sequential adsorption cycles and showed higher adsorption affinity towards Cr (VI) ions. MOSR/An/CS composite could also be effectively used as an effective eco-friendly and recyclable sorbent for the elimination of Cr (VI) from wastewater.
Highlights
Chromium (Cr) a long-standing environmental heavy metal pollutant in waste-water is generated widely by mining, electroplating, chemical manufacturing, dyeing, steel fabrication, printing, fertilizers and electronics industries
The crystalline structure of modified olive seed residue (MOSR)/An/Cs composite was indicated by the broad peaks at 24°−29° and 42°−45°
As shown in the figure, the small pore diameter distribution of the composite MOSR / An / Cs in the range of 1,5-5 nm with wide pores ranging from 5 nm to more than 50 nm. The results showed that the curing formed more pores; in the porous structure the mesoporous materials may predominate and the curing results in an increase in the composite MOSR / An / Cs total surface area, which is qualitatively consistent with the modification in the (BET) surface area
Summary
Chromium (Cr) a long-standing environmental heavy metal pollutant in waste-water is generated widely by mining, electroplating, chemical manufacturing, dyeing, steel fabrication, printing, fertilizers and electronics industries. Some examples are seaweed bio-adsorbent [Karamipour et al, 2019], rice husk, tannin-gel [Nokano et al, 2000], wood, coconut husk and shell, lingo-cellulosic wastes, charcoal and residue of olive-mill product [Bhatnagar et al, 2014]. In order to enhance their adsorption capacity, CS has been frequently incorporated with different materials such as clay [Foroutana et al, 2020], activated carbon, carbon nanotubes [Alawady et al, 2020] and graphene oxide [Mei et al., 2020 ] to fabricate composites with different functionalities surface. In this study, an innovative H2O2-modified olive seed residue/anthracite/chitosan (MOSR/An/CS) composite has been fabricated for the adsorptive removal of Cr(VI) from aqueous solution. A special study on the isotherm, kinetics, and thermodynamics features was reported to understand the adsorption performance of Cr(VI) using MOSR and MOSR/An/Cs composite
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