Study of impact of acids and comparison of adsorption efficiency of Pb(II) from carbon and its modified nano-nickel coated version.

Acidic content in wastewaters poses greater difficulty in lead removal from most adsorbents as their removal efficiency significantly decreases in acidic media. Nano-nickel coated carbon (Ni/C), compared with uncoated carbon (C), has shown a much enhanced (almost 80% higher) tendency of Pb(II) removal from solutions having different acid concentrations. All of the characterization results show the creation of more active sites and functional groups on Ni/C. The pertinent kinetic models and thermodynamics of Pb(II) adsorption have demonstrated much improved efficiency by Ni/C. Various isotherms subjected to the sorption data revealed significant increase in the sorption capacities for Ni/C. The adsorption (evidently chemisorption) kinetics are best represented by a pseudo-second-order equation. The adsorption rates in acidic solutions were much higher for Ni/C. The temperature-dependent study enabled thermodynamic parameters to be worked out for C and Ni/C; for C the values are ΔH: 19.4 ± 0.5 kJ·mol, ΔS: 76.1 ± 2.1 J·mol·K, ΔG: -0.37 ± 0.01 kJ·mol while for Ni/C the values are ΔH: 30 ± 1 kJ·mol, ΔS: 114 ± 4 J·mol·K, ΔG: -4.56 ± 0.02 kJ·mol. Both cases indicate endothermic, spontaneous and entropy-driven processes.