Adsorption performance of heavy metal ions from aqueous solutions by a waste biomass based hydrogel: comparison of isotherm and kinetic models

The rice husk biochar (RHB), Ca-alginate (CA), and biochar/ca-alginate composites (CA-RHB) was synthesised for the removal of aqueous Cu(II) and Zn(II) and characterised by BET, SEM, EDS, and FT-IR analysis. The adsorption experiments of Cu(II) and Zn(II) ions by RHB, CA, and CA-RHB were studied on effects of initial concentration, pH, and contact time. The purpose of characterisation the adsorption behaviours of Cu(II) and Zn(II) ions on RHB, CA, CA-RHB1, CA-RHB2, CA-RHB3, and CA-RHB4, the Langmuir, Freundlich, Temkin, Redlich-Peterson, Hill and Unilan isotherm models and the pseudo-first-order, the pseudo-second order, Intra-particle diffusion model, Elovich and Avrami kinetic models apply to the experimental adsorption data. The maximum Cu (II) adsorption capacity estimated with Langmuir isotherm modelling was 44.60 mg g−1, for CA, 41.74 mg g−1 for CA-RHB1, 42.62 mg g−1 for CA-RHB2, 35.45 mg g−1 for CA-RHB3, and 31.52 mg g−1 for CA-RHB4, and 10.56 mg g−1 for BMB. The maximum Zn (II) adsorption capacity estimated with Langmuir isotherm modelling was 43.32 mg g−1, for RHB, 25.07 mg g−1 for CA, 22.23 mg g−1 for CA-RHB1, 23.68 mg g−1 for CA-RHB2, 22.03 mg g−1 for CA-RHB3, and 34.41 mg g−1 for CA-RHB4,