Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions

ABSTRACT

In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L⁻¹ and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g⁻¹, respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R² = 0.97) and O-mont (R² = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the –OH, –COOH, –NH₂, and for O-mont intercalated amines and –OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.

KEYWORDS:

• biosorption
• organo-clays
• modeling
• FTIR
• remediation
• contaminated water

Funding

The authors are thankful to the Grand Challenges Canada – Stars in Global Health (Round 5, Grant No. 0433-01), International Foundation for Science (W/5698-1, IFS, Sweden) for the financial assistance, and University of Agriculture Faisalabad. Dr Irshad Bibi acknowledges the Postdoctoral Research Fellowship awarded by Alexander von Humboldt Foundation at the University of Bremen, Germany. This research (the SEM-EDX and FTIR analyses) was partly supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2012R1A1B3001409). The first author is thankful to Dr. Zara Jabeen.