Ion exchange properties of a Western Kentucky low-rank coal

The ion exchange properties of a low-rank coal were evaluated to explore its viability as an inexpensive material for removing radionuclides and heavy metals from solution. Cobalt was used as a model metal to investigate the kinetics and thermodynamics of the exchange process and the effect that solution pH has on the exchange capacity. Maximum metal adsorption was found to occur at pH greater than or equal to 3.5. The exchange was found to follow first-order kinetics and to proceed rapidly; over the temperature range investigated (-15 to 50 degrees C) equilibrium was reached within 10-20 min. The exchange was well described by the Langmuir adsorption isotherm with a Gibbs free energy of -8.85+/-0.24 kJ/mol. Additional studies with environmentally significant metals and radionuclides demonstrated that cations with higher charge density were preferentially adsorbed.