Elimination of selected heavy metals from aqueous solutions using biochar and bentonite composite monolith in a fixed-bed operation

Abstract

Hydrochar (HC) obtained from hydrothermally synthesized Lepironia articulata (LA) was successfully modified into biochar (LABC) using KOH. Subsequently, Natural bentonite clay was modified using cationic surfactant (bencylhexadecyldimethyl ammonium chloride, (BCDMACl). Both the adsorbents LABC and MB were mixed and bound to make a monolith (LABC-MBm) using two different binders, polyvinylidene difluoride (PVDF) and methylcellulose (MC). The LABC, MB, and LABC-MBm were characterized via wettability parameters, swelling index, strength, Fourier transform infrared spectrometer (FTIR), Brunauer-Emmett-Teller (BET), and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX). The surface area of HC, LABC, MB, and LABC-MBm was calculated to be 69.23, 820.24, 15.57, and 455 m(2)/g, respectively. The efficiency of the LABC-MBm was analyzed in a fixed-bed column operation for the removal of heavy metals, Chromium (Cr3+), Nickel (Ni2+), and Zinc (Zn2+), respectively, by varying bed depth and the flow rate. The column performance with LABC-MBm adsorbent was 82.37%, 81.74%, and 80.64% for Cr3+, Ni-2 +, and Zn2+, respectively, and the saturation capacity was calculated to be 15.58, 11.22, and 10.4 mg/g for Cr3+, Ni-2 +, and Zn2+, respectively. The experimental data were validated using diversified mathematical models and the high regression coefficient values (R-2 > 0.99) were obtained in the case of using BDST and the Yoon-Nelson models and satisfactory fitting at 10% and 50% break-through. The overall results proved that the LABC-MBm can be used as a potential adsorbent for eliminating heavy metals from wastewater and the process is so simple, environmentally friendly, and eco-efficient.