Abstract
Clinoptilolite modified by hexadecyltrimethylammonium bromide (HDTMA-Br) was used to simultaneously remove copper and hexavalent chromium from aqueous solutions. The surface properties of HDTMA-modified natural zeolite (HMNZ) were characterized using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), zeta potential and Fourier transform infrared spectroscopy (FTIR) techniques. SEM images showed that surfactant is adsorbed on the surface of the zeolite, which is confirmed by the FTIR result. The results from BET demonstrated a reduction in the specific surface area and pore volume due to the presence of surfactant molecules on the external surface of zeolite. The effects of important parameters on adsorption efficiency of Cu2+ and Cr (VI) were evaluated by Box-Behnken design. The Langmuir isotherm provided the best fit to the equilibrium data of Cu2+ and Cr (VI), with the maximum adsorption capacity of 0.068 and 0.0093(mmolg-1), respectively. The film diffusion mechanism was found to control the mass transfer, and the adsorption reactions were computed as endothermic for Cu2+ (ΔHads ° = 17.58 kJmol-1) and exothermic for Cr (VI) (ΔHads ° -26.18 kJmol-1). The results indicated that surfactant modification changes the surface charge of zeolite from negative to positive, which makes zeolites economic adsorbents with the possibility of simultaneous removal of cations and oxyanions. The results also showed that the removal efficiency of Cr (VI) increases in the presence of copper cations due to there being more positive sites on the adsorbent surface.
Highlights
Today, due to the growth of industries and the advancement of technology, various pollutants have been widely introduced into the environment and have created a lot of problems (Li et al )
Natural zeolite was modified by HDTMA, and simultaneous adsorption of Cu2þ and Cr (VI) ions was investigated
The specific surface area of treated zeolite reduced from 14.85 m2gÀ1 to 9.55 m2gÀ1 in comparison with raw zeolite, which was due to coverage of the surface pores
Summary
Due to the growth of industries and the advancement of technology, various pollutants have been widely introduced into the environment and have created a lot of problems (Li et al ). Chromium must be removed from wastewater or needs to be modified into its less toxic form before it is discharged into the environment because of the destructive effects such as skin inflammation, liver and kidney failure, vomiting and so on. Zeolites are known adsorbents that can remove metal cations from aqueous solutions due to their negative surface charge. After modifying zeolites by HDTMA with a concentration above CMC, a bilayer structure is formed at the outer surface of the zeolite This structure contains functional groups with a positive charge, which can be effective in adsorption of hexavalent chromium oxyanions. HDTMA-modified natural zeolites (HMNZ) can adsorb cationic and anionic trace elements from wastewater simultaneously (Chao & Chen ; Huang et al ). Our results showed that HMNZ is an economical adsorbent with the ability to remove cations and anions from aqueous solutions simultaneously
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