Biocomposite of hydrochar and Lindnera jadinii with magnetic properties for adsorptive removal of cadmium ions

The aim of the work was to check the possibility of obtaining a biocomposite with magnetic properties capable of removing cadmium ions from aqueous solutions. The biocomposite consists of hydrochar obtained by hydrothermal carbonization of raffia fibers, Lindnera jadinii yeast and Fe3O4 nanoparticles. The obtained biocomposite was characterized by SEM, FTIR, VSM, XRD, TGA and BET analysis. The study examined the effect of sorption time, initial concentration of cadmium ions, temperature, the pHZPC and the reusability of the biocomposite. Based on the obtained results, non-linear equilibrium and kinetic models were selected. The equilibrium model with the highest matching factor describing the sorption of Cd(II) by the bionanocomposite was the Temkin isotherm model R2 = 0.9960 and ARE = 2.06%, while the kinetic model with the best fit was the Elovich model R2 = 0.9928 and ARE = 5.44%. The results showed that the maximum Cd(II) adsorption capacity of the biocomposite was equal to 16.34 mg/g at 25 °C and increased with increasing temperature up to 26.22 mg/g at 40 °C. The performed Cd desorption tests showed a significant efficiency of the biocomposite for five successive cycles of the sorption-desorption process with the use of HNO3, obtaining a leaching degree of 96–98.8%. The conducted research provides new data on the use of composites obtained from biomass, microorganisms and Fe3O4 in the bioremediation of heavy metals from water media and proves the effectiveness of removal and potential use in real environmental conditions of the biocomposite due to its easy recovery from contaminated aqueous solutions.