Removal of lead from aqueous solutions by activated phosphate

The potential of using activated phosphate as a new adsorbent for the removal of Pb from aqueous solutions was investigated. The kinetic of lead adsorption and the adsorption process were compared for natural phosphate (NP) and activated phosphate (AP). The results indicate that equilibrium was established in about 1 h for NP and 3 h for AP. The effect of the pH was examined in the range 2-6. The maximum removal obtained is between two and three for NP and between three and four for AP. The maximum adsorption capacities at 25 °C are 155.04 and 115.34 mg/g for AP and NP, respectively. The effect of temperature has been carried out at 25, 35 and 45 °C. The data obtained from adsorption isotherms of lead at different temperatures fit to linear form of Langmuir adsorption equation. The thermodynamic parameters such as enthalpy (ΔH), free energy (ΔG) and entropy (ΔS) were calculated. They show that adsorption of lead on NP and AP is an endothermic process more effective at high temperatures. These results show that AP is a good adsorbent for heavy metals from aqueous solutions and could be used as a purifier for water and wastewater.