Removal of lead ions from aqueous solutions by low-rank Pakistani coal.

Low-rank Pakistani coal was studied as an adsorbent for the removal of lead ions (Pb²⁺) from aqueous solutions. Adsorption efficiency was studied as a function of contact time, pH, amount of adsorbent, temperature, concentration of adsorbate and concentration of different acids using batch method and atomic absorption spectrometric technique. Maximum removal of lead ions was achieved at 5 pH, using 0.5 g of adsorbent for 10 mL of 4.826 × 10^-5 mol L^–1 lead concentration with equilibration time of 50 min. The adsorption of lead followed pseudo-second-order kinetics with rate constant “K₂ ” of 1.261 g mg^–1 min^–1. The adsorption data obeyed the Freundlich, Langmuir and Dubinin–Radushkevich isotherms over the lead concentration range of 4.826 × 10^-5 to 3.378 × 10^-4 mol L^–1. The characteristic Freundlich constants, that is, 1/n = 0.609 ± 0.016 and K = 2.164 ± 0.063 m mol g^–1 have been computed for the adsorption system. Thermodynamic parameters for the adsorption process were determined and discussed. The adsorption of lead by the presence of high concentration of foreign ions has also been studied. The proposed method was successfully applied for the removal of lead from spiked tap water sample. [ABSTRACT FROM AUTHOR]