Synthesis of Mg(II) doped goethite and its cation sorption behaviour

Modified goethite samples were prepared with Mg(II) content varying in the range of 0-1.36%. A typical TEM of Mg(II) doped sample showed needle shaped goethite particles having 10-30 nm width and 100-400 nm length. Sorption studies of cations namely Pb(II), Cu(II), Cd(II), Zn(II) and Fe(III) were conducted onto the Mg(II) doped modified goethite surface. Goethite doping with 0.18 M Mg (GMg(2)) showed better sorption capacity for Pb(II), Cu(II) and Cd(II). Therefore, the effect of contact time, solution pH, sorbate and sorbent concentrations on the sorption of various metal ions was studied on this sample in batch experiments. The time data fitted to pseudo-second-order kinetics for all the metal ions. Sorption on GMg(2) sample for the metal ions increased with the increase in pH from 2 to 4. The isothermic data showed good fit to both Langmuir and Freundlich isotherms except for Cd(II) which followed only the later model. The sorption capacities with respect to Pb(II), Cd(II), Zn(II), Cu(II) and Fe(III) were found to be 87.7, 153.25, 86.25, 33.4 and 72.5mg/g respectively. The results of sorption studies on GMg(2) from binary and ternary solutions have also been presented. The XRD patterns of metal ion loaded GMg(2) samples confirmed that metal ion adsorption resulted in shifting of d-values/altering of relative intensity (RI) of major planes of goethite.