Sorption studies of heavy metal ions by salicylic acid–formaldehyde–catechol terpolymeric resin: Isotherm, kinetic and thermodynamics

Terpolymeric resin has been synthesized by condensing salicylic acid with catechol employing formaldehyde as a cross linking agent at 80 ± 5 °C using DMF as a solvent. The resin was characterized by elemental analysis, FTIR, XRD and thermal analysis (TGA, DTA and DTG). The morphology of the resin was studied by optical photographs and scanning electron micrographs (SEM) at different magnifications. The physico-chemical properties have been studied. The uptake behavior of various metal ions viz. Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) towards synthesized resin has been studied depending on contact time, pH and temperature. The selectivity order found is: Cu(II) > Zn(II) > Pb(II) > Ni(II) > Cd(II). The sorption data obtained at optimized conditions were analyzed by six two parameter isotherm models like Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), Halsey and Harkins–Jura. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms were found better to describe the sorption data with high correlation for the adsorption with a low SSE value for all the metals under study. The adsorption capacities of the SFC resin for removal of Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) were determined with the Langmuir equation and found to be 0.815, 1.104, 1.215, 0.498, and 0.931 mmol/g respectively. The adsorption process follows first order kinetics and specific rate constant Kr was obtained by the application of Lagergren equation. Thermodynamic parameters viz. ΔGads, ΔSads and ΔHads have also been calculated for the metal-resin systems. The external diffusion rate constant (Ks) and intra-particle diffusion rate constant (Kid) were calculated by Spahn–Schlunder and Weber–Morris models respectively. Desorption studies were done using various desorbing agents viz. de-ionized water, boiled water, various concentrations of HCl, ammonia, thiourea, citric acid and tartaric acid.