Kinetics and isotherms for aqueous lead adsorption by natural minerals

The low grade (<15% P2O5) carbonatic rock phosphate and hydroxy aluminosilicate based mineral (pyrophyllite) of Madhya Pradesh (India) were investigated as adsorbents for their possible application for the removal of aqueous lead under static system. The kinetics and effect of temperature on adsorption of lead ions on the above two natural minerals have been studied. The adsorption process follows first-order kinetics and the rate of adsorption and film transfer coefficients are observed to decrease with increase in initial concentration of lead ions in solutions. It has been found that these natural minerals are effective in removing 65-99% of lead ions from 5.0 to 500 mg/L lead solutions. The Langmuir adsorption isotherm was used to represent experimental data for carbonatic rock phosphate whereas the Freundlich adsorption isotherm was found suitable to represent data for pyrophyllite. The adsorption process is found to be endothermic in the case of pyrophyllite and exothermic in the case of carbonatic rock phosphate.