Adsorption of lead, zinc and cadmium ions on polyphosphate-modified kaolinite clay

Abstract

The aim of this research work is to determine the potential of application of sodium polyphosphate-modified kaolinite clay as an adsorbent for the removal of lead (II), zinc (II) and cadmium (II) ions from aqueous solutions. The adsorbent dosage, pH, temperature and contact time were investigated. The adsorption isotherms of all three metal ions followed well Langmuir equation. Modified sodium polyphosphate-kaolinite clay was found to remove heavy metal ions efficiently from aqueous solutions with selectivity in the order of Pb2+ > Zn2+ > Cd2+. The maximum heavy metal ions adsorbed by modified kaolinite clay was found to be 92.10, 74.26 and 55.12% and the sorption capacity for Pb2+ was 40.00 mg/g, for Zn2+ 27.78 mg/g, and for Cd2+ 13.23 mg/g, respectively. The thermodynamic parameters, standard Gibb's free energy (∆Go), standard enthalpy (∆Ho) and standard entropy (∆So) calculated using the Langmuir constants for metal ions sorption on the sodium polyphosphate-kaolinite clay showed that the adsorption process is spontaneous and endothermic in nature. The results of this study showed that the sodium polyphosphate-kaolinite clay powder can be efficiently used as a low-cost adsorbent for the removal of divalent lead, zinc and cadmium from aqueous solution.    Key words: Adsorption, heavy metals, sodium polyphosphate, kaolinite clay, Langmuir isotherms.