Biosorption efficacy studies of Sargassum wightii and its biochar on the removal of chromium from aqueous solution

Abstract

The aim of the current project is to treat chromium-polluted water economically from an aqueous medium using algal biomass of Sargassum wightii and its biochar through a batch adsorption process. Initially, the dried algal biomass and its biochar were examined by FT-IR, XRD, TGA, SEM-EDX, Elemental analysis (CHNSO), and BET analysis. The highest carbon content was assessed for raw dried algal biomass and at various pyrolysis conditions ranging from 300 °C to 600 °C for 1 hour using a pyrolyzer unit. From the FTIR results, it was revealed that the wavenumber present in the region around 3400 and 1600 cm−1 confirms the existence of NH, OH, amide, COOH groups of the bioactive components of Sargassum wightii and its biochar. XRD, SEM, and BET analyses exhibit the amorphous nature, rough surface morphology, and porous surface of the biosorbent. Batch adsorption studies were carried out to eliminate Cr(VI) ions from the aqueous solution employing dried algal biomass of Sargassum wightii and its biochar by changing the parameters such as pH, residence period, biosorbent dosage, and initial Cr (VI) ion concentrations. Based on the outcomes of the experiment it was found that the optimum adsorption of Cr(VI) ions occurred at pH 5, adsorbent dose 6 g/L, contact time 6 h, and initial concentration of about 50 mg/L for both biosorbents. The equilibrium adsorption is well-suited to the Freundlich isotherm (R2 = 0.9889). The adsorption process follows pseudo-second-order kinetics (R2˃0.99). SEM-EDAX and FTIR analyses were applied to characterize the adsorbed sample, and the results demonstrated that the interaction between the adsorbent and adsorbate was successful. Metal-loaded sorbent was used for desorption investigations. The desorption results demonstrated that the desorption ratio of Cr(VI) ions was higher in HCl compared to EDTA for both the biomass and its biochar. Further, the desorption results concluded that the biosorbents are effective till 5 cycles. Cr(VI) typically exists in anionic forms in aqueous environments, leading to electrostatic attraction to positively charged biochar. In conclusion, this study evaluated the removal efficiency of Sargassum wightii and its biochar which was economical and the results are highly promising.