Organo-functional modified pyrophyllite: preparation, characterisation and Pb(II) ion adsorption property

Surface modification of clay minerals has become increasingly important for improving the practical applications of clays such as fillers and adsorbents. In this study, the surface of pyrophyllite mineral was modified by coating with 3-(2-aminoethylamino) propyl-methyldimethoxysilane (APMDS) coupling agent and utility of the APMDS-modified pyrophyllite was investigated as an adsorbent for removal of Pb(II) ions from aqueous solutions. XRD, FT-IR and SEM analysis were used to characterise the surface modification and it was suggested that hydrogen bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of pyrophyllite and hydroxyl groups of APMDS. The APMDS-modified pyrophyllite adsorbed approximately 93% of Pb(II) ions at an initial concentration of 20 mg/l, while natural pyrophyllite did only 35% under the same conditions. The adsorption of Pb(II) increased with increasing pH and reached a maximum value in the pH range 6.5–7. The effects of various factors on the adsorption, such as pH of the solution, contact time, amount of adsorbent and initial Pb(II) concentration, were studied. The adsorption isotherm has been determined and data have been analysed according to the Langmuir model and found to be favourable, i.e., the separation parameter is less than unity (RL<1).