Adsorption of Cd(II), Pb(II) and Ni(II) onto natural sediments from the Gulf of Aqaba Jordan

Abstract

ABSTRACT Carbonate and silicate natural sediments from the gulf of Aqaba-Jordan have been used to study adsorption of nickel(II), lead(II) and cadmium(II) ions, separately, from aqueous solutions. Both sediment types were characterised by FTIR, XRD and SEM. Adsorption of these metal ions were investigated using batch technique as a function of initial concentration of metal cations, adsorbent dosage, initial pH, contact time and temperature. The metal uptake enhanced with increasing pH until a maximum removal at pH 8.0 for Ni, 5.0 for Pb and 6.0 for Cd. Kinetic study shows that the adsorption obeys a pseudo-second-order kinetic model. The adsorption isothermal behaviour of the metal ions uptake onto carbonate and silicate sediments were examined using Langmuir, Freundlich and Dubinin–Radushkevich (D-R) adsorption isotherms. The maximum adsorption capacity obtained by Langmuir isotherm model (25°C) onto carbonate sediments was 2.64, 4.41 and 4.15 mg/g for Ni(II), Pb(II) and Cd(II), respectively. While the adsorption onto silicate sediments was 2.57, 3.56 and 3.15 mg/g, respectively. These adsorption values on carbonate sediments comparing to silicate sediments were attributed to some physical and chemical properties of both sediments, especially the higher permeability and porosity for carbonate sediments. Thermodynamic functions, ΔG*, ΔH* and ΔS* were determined. Negative ΔG* values show that the adsorption process of these metal ions onto both sediments is spontaneous. While the positive ΔH* values indicate that adsorptions are endothermic, and the positive values of entropy ΔS* suggest that the adsorption is driven by increasing of randomness. Conservative calculations using the data in this study and some other from the literature shows that the shallow sediments would adsorb roughly 7 × 10 16 kg of heavy metals that may be introduced into the sea through different anthropogenic activities.