Chemically modified nanoparticles usage for removal of chromium from sewer water

Abstract

In this work, multiwall carbon nanotubes (MWCNTs) were chemically modified to yield products that speciate and selectively remove trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from wastewater. The surface of MWCNTs were modified with cationic surfactant cetyl trimethyl ammonium bromide (CTAB), and yielded a product (MWCNTs-CTAB) that can remove Cr(VI) with 98 % efficiency at optimum conditions. Surface modification with anionic surfactant sodium lauryl sulfate (SLS) after magnetization with magnetite (M) yielded a product (MWCNTs-M-SLS) that can remove Cr(III) with 99 % efficiency at optimum conditions. Removal of Cr(III) by MWCNTs-M-SLS and Cr(VI) by MWCNTs-CTAB best fitted to Langmuir isotherm model with an adsorption capacity of 66.2 and 27.8 mg/g, respectively. Adsorption kinetics for removal of Cr(III) by MWCNTs-M-SLS and Cr(VI) by MWCNTs-CTAB, demonstrated that adsorption is very fast (< 5 min). Thermodynamic studies indicated that adsorption of Cr(VI) by MWCNTs-CTAB is an endothermic process with enthalpy, entropy and free energy of adsorption of 14.1 KJ/mol, 51.6 J/mol.K and -1.30 KJ/mol, respectively. Adsorption-desorption study of chromium from impregnated MWCNTs-CTAB was performed at different temperatures. At 25 °C, removal efficiency dropped from 98 % to 73 % to 60 %, and at 35 °C, removal efficiency dropped from 98 % to 75 % to 61 %, indicating that temperature did not have a significant effect on the regeneration process. Results indicate that a sequential plant can be designed and engineered for simultaneous speciation and removal of both ions from wastewater.