Thermal and hydrothermal alkaline modification of kaolin for the adsorptive removal of lead(II) ions from aqueous solution

The properties of Enugu kaolin were modified by thermal and alkaline hydrothermal means. The raw and modified kaolin samples were characterized using Brunauer-Emmett-Teller nitrogen adsorption surface area analysis, X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy and Scanning electron microscopy techniques. The effectiveness of the modified kaolin for the removal of lead(II) ions from aqueous solution was studied and compared to that of the raw kaolin sample. The results showed that the surface area of the modified samples increased from 19.170 m(2)/g to 247.889 m(2)/g, 208.745 m(2)/g and 221.608 m(2)/g, followed by an increase in the pore volume for the modified samples. However, the modification led to a weak alteration to the kaolin structure. Residual ions detected by atomic absorption spectroscopy showed that the modified kaolin samples have improved removal efficiency for Pb(II) (83%, 88%, 85%) when compared to the raw sample (33%). The adsorption capacities of the raw kaolin and modified kaolin (sample C) were observed to increase with increase in contact time, initial metal ion concentration and adsorbent dose. The adsorption of Pb(II) unto the raw and modified kaolin followed Freundlich (R-2 =0.9937) and Langmuir (R-2 = 0.9837) adsorption isotherm models respectively. The modified kaolin efficiently eliminated Pb(II) from aqueous solution. Enugu kaolin has the potential to be a catalyst-type material based on the surface analysis and adsorption experiments.