Removal of chromium and lead from synthetic wastewater by neyveli lignite and neem biochar

Abstract

Some of the heavy metals extensively used in industry are toxic and harmful to the environment and produce huge negative impacts. In this study, the removal of Cr(VI), Pb(II), and F ion existing in synthetic wastewater was achieved by using the surface-modified Neyveli Lignite (NL) and Neem Biochar (NBC) as an adsorbent. Neyveli lignite was converted into hydrophilic type by employing alkylation and Friedel Crafts alkylation. NBC was prepared by pyrolysis of neem leaves after soaking in 0.1 N phosphoric acid followed by pyrolysis. The prepared adsorbents were characterized by utilizing various techniques such as X-ray diffraction study, Atomic Force Microscopy, FESEM with EDAX mapping method, FTIR, Zeta potential measurements, BET surface area analysis, WCA measurement, and XPS. Cr(VI) and F ions present in the synthetic wastewater have been removed by hydrophilic NL, and the NBC was used to remove Cr(VI) and Pb(II) in an independent manner. After agitating the NBC with synthetic wastewater containing Cr(VI), the char effectively removes Cr(VI) through adsorption. The quantity of Cr(VI) adsorbed on NBC was 58.54 mggand#8722;1 and also found to be pH-dependent. The adsorption process involved between NBC and Cr(VI) followed a Langmuir-type adsorption isotherm. The removal of Cr(VI) by NBC was analyzed through batch and fixed-bed column experiments. The adsorption isotherm, adsorption kinetics, and all other relevant parameters were evolved with reference to Cr(VI) removal by NBC. The adsorption efficiency was found to decrease from 96% to 57% while using the regenerated NBC as an adsorbent. The removal efficiency of Cr(VI) by NBC proves that the adsorption process was cost-effective. The removal of Pb(II) by NBC from synthetic wastewater was analyzed through batch experiments. With the help of the Design of Experiments (DOE) technique, the Central Composite Design (CCD) of Response Surface Methodology (RSM) was used to find out the optimum level of Pb(II) removal by NBC. In the RSM study, three different variables namely pH, initial concentration, and contact time were used. The validation of the studies was confirmed by the experimental results obtained. The experimental and predicted values of Pb(II) adsorption on NBC were 98.54% and 98.07%, respectively. The optimum conditions for the removal of Pb(II) were optimized as initial concentration = 325 mgL 1, pH = 5, and contact time 120 mins. From these studies, it is ensured that the removal of Cr(VI) and Pb(II) was found effective while utilizing low-cost surface-modified coal and NBC as adsorbents. newline