Oil industry waste based non-magnetic and magnetic hydrochar to sequester potentially toxic post-transition metal ions from water

Solid waste conversion to value-added products is a stepping stone towards sustainable environment. Herein, sesame oil cake (SOC), an oil industry waste was utilized as a precursor to develop hydrochar (HC) samples by varying reaction temperature (150–250 °C) and time span (2–8 h), chemically treated with 10% H2O2 to optimize a sample with maximum yield and Pb(II) adsorption. Highest yield (29.2 %) and Pb(II) (24.57 mg/g at Co: 15 mg/L) adsorption was observed on [email protected] °C/6 h, magnetized ([email protected] °C/6 h) for comparative study. XRD displayed highly crystalline [email protected] °C/6 h and amorphous [email protected] °C/6 h, both having a characteristic cellulose peak at 14.9°. [email protected] °C/6 h displayed superparamagnetic behavior with 11.2 emu/g saturation magnetization. IR spectra confirmed the development of samples rich in oxygen containing functionalities; an additional peak for iron oxides appeared at 586 cm−1 in [email protected]°C/6 h spectrum. Four major peaks at 531.9, 399.9, 348.2 and 284.7 eV, assigned to O 1s, N 1s, Ca 2p and C 1s, respectively were observed during XPS analyses. An additional peak at 710.3 eV, ascribed to Fe 2p was observed in [email protected]/6 h XPS spectrum, while a peak at 143.2 eV for Pb 4f appeared in spectra of both Pb(II) saturated samples. pH dependent (maximum at ∼6.7), exothermic Pb(II) adsorption was found. About 50–70% (at Co: 25 mg/L) adsorption on both [email protected] °C/6 h and [email protected] °C/6 h was accomplished in a minute, attaining equilibrium in 180 and 240 min, respectively. Error functions and superimposed qe, exp. and qe, cal. values supported Langmuir isotherm model applicability, with respective qm values of 304.9 and 361.7 mg/g at 25 °C for [email protected] °C/6 h and [email protected] °C/6 h. Kinetic data was fitted to PSO model. Highest (between 92.2 and 88.9 %) amount of Pb(II) from [email protected] °C/6 h and [email protected] °C/6 h was eluted by 0.01 M HCl.