Removal of Cr and Mn from aqueous medium using bentonites and their derivatives
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Ó Indian Academy of Sciences Sadhana (0123456789().,-volV)FT3](0123456 789().,-volV)
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Removal of Cr and Mn from aqueous medium using bentonites and their derivatives SOURAV MAJUMDERa,*
and ASHOK KUMAR JHAb
a Department
of Chemistry, Kaliachak College, Malda 732 101, West Bengal, India Department of Chemistry, Tilka Manjhi Bhagalpur University, Bhagalpur 812 007, Bihar, India E-mail: [email protected] b University
MS received 18 May 2020; revised 14 July 2020; accepted 29 July 2020
Abstract. Bentonite minerals of Rajmahal Hills and Hazaribagh district along with their derivatives have been used to remove hexavalent chromium and manganese from aqueous medium. Bentonites are smectite group of minerals having swelling power and cation exchange properties. Blue colour with benzidine solution indicates the presence of montmorillonite unit having SiO2, Al2O3, K2O, Fe2O3, FeO and traces of TiO2 also. The adsorption isotherm and removal performance of hexavalent chromium and manganese have been examined by shaking 100 mL 2 ppm solution with 1 gram of bentonite and their derivatives up to different intervals of time and also with varying amount of bentonite up to fixed time intervals. The percentage removal of chromium (VI) ranges from 12% to 67.7% whereas percentage removal of manganese (VII) varies from 09% to 92.5%. Experimental data showed that the removal of Cr (VI) and Mn (VII) represented both Freundlich and Langmuir adsorption isotherms. Adsorption of Cr (VI) and Mn (VII) on to bentonites and their derivatives follow first-order kinetics. It is concluded that locally available bentonites may be exploited as a low-cost feasible adsorbent for removal of Cr (VI) and Mn (VII) in the laboratory as well as industrial level too. Keywords. Isotherms; Bentonite; Langmuir; Adsorption; Hexavalent chromium.
1. Introduction Hexavalent chromium concentration in drinking water has attracted the attention of scientists due to carcinogenic characteristics.1–4 Chromium (VI) exists in the aquatic medium as HCrO4- at pH 4 to 6 or CrO42at pH 8-10 whereas Cr(III) exists as Cr?3, Cr(OH)3 5,6 and Cr(OH)Chromium is released into water 4. bodies through metallurgical operations, metal finishing, steel alloy and chrome plating.7 Various techniques for removal of hexavalent chromium from an aqueous medium such as ion exchange, coagulation, membrane filtration, electrodialysis are available but adsorption is considered the most appropriate method of removal especially by the use of bentonites.8,9 In addition to this, bacteria may also be used to mitigate heavy toxic elements from aqueous medium. Use of adsorbents e.g., yeast biomass and fungal biomass have been adopted due to its being low cost and
abundance in nature. The binding capacity of orange peel powder, rice husk and maize stem powder has already been investigated. Natural herbs and wastes from agricultural operations have the potential to be used as an effective adsorbent of Cr (VI). Many literatures available suggest that active carbon prepared from wal
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