Adsorptive separation of Cu(II) ions from aqueous medium using thermally/chemically treated Cassia fistula based biochar

Abstract The present study demonstrates the adsorption of Cu(II) ions by Cassia fistula seed derived biochar materials. The activation and surface modification were done by pyrolysis and chemical bath in a different acidic medium. The quality of the prepared adsorptive materials was analysed using different analytical techniques. An appropriate surface characteristic was observed which mediates the adsorptive removal. The possible operating conditions for Cu(II) removal is as follows: pH = 5.0; Cu(II) ion concentration at initial = 50–200 mg/L; adsorbent dose = 2.5 (Hydrochloric acid treated Cassia fistula biochar, HTCF), 1.5 (Physically treated Cassia fistula biochar, PTCF) and 0.6 g/L (Sulphuric acid treated Cassia fistula biochar, STCF); temperature = 303 K; time of contact = 30 min. Among various adsorption equilibrium models, Redlich-Peterson and Freundlich models exhibited best fit (R2 > 0.99) to the adsorption equilibrium data. Langmuir adsorption capacities of HTCF, PTCF and STCF have been found as 72.9, 115.4 and 303.5 mg/g respectively. The adsorption process was exothermic and spontaneous resulted from the thermodynamic analysis. Pseudo first-order best fits the kinetic data with higher correlation coefficient and low error values. Overall, STCF can be a viable option for the commercial adsorbents to treat the industrial wastewater.