Competitive adsorption and correlative mechanism of heavy metal ions using ploy(cellulose/humic acid/acrylic acid) in multi-element aqueous medium

A novel polymer was successfully fabricated which used to remove Pb(II), Cu(II), Cd(II) from multi-element aqueous solutions and their competed-adsorption behavior was investigated. The copolymer was characterized by FTIR spectra, TG/DTG analysis, SEM analysis and XPS analysis. The pseudo-second-order kinetic (R² > 0.99) and the Langmuir isotherm model have been fit quite well. The FTIR spectra and XPS spectra indicated that Cu(II), Pb(II) and Cd(II) were adsorbed. Maximum uptake capacities of polymer were found to be 978 mg/g, 1136 mg/g, 901 mg/g for Cu(II), Pb(II) and Cd(II), respectively. The hydrogel had the strongest affinity with Pb(II) and Cd(II) ions, but the complex for Pb(II) was instability with the adsorption going on. While adsorption promoted by presence of other ions—synergistic effects that might lead to strongly form complex of the Cd(II) ion and hydrogel, which was not affected by the initial pH in the range of 1.5–6.5. Cu(II) and Pb(II) removal was mainly achieved by ion exchange with functional groups that caused the quantity disparity of the proportion and intensity about the hydrogel surface. The sorption mean free energy E_Cu(II) = 15.1 kJ/mol, E_Pb(II) = 16 kJ/mol, E_Cd(II) = 19.2 kJ/mol were evaluated using Dubinin–Radushkevich isotherm, which suggested that was chemisorption of the adsorption mechanism. This hydrogel had large specific surface area that was as high as 140 m²/g through N₂ adsorption–desorption experiment.