Cation exchange properties of low rank Turkish coals: removal of Hg, Cd and Pb from waste water

The removal of contaminant heavy-metal ions from spiked aqueous samples containing low-to-moderate levels of contamination using Turkish Beypazari low rank coal was investigated. Carboxylic acid and phenolic hydroxyl functional groups present on the coals surface were the adsorption site to remove cations from solution via ion exchange. The equilibrium pH of the coal/solution mixture has been shown to be the principal factor controlling the extent of removal of Hg(II), Cd(II), and Pb(II) ions from aqueous solutions. The optimum pH was measured to be 4.0 for Hg and Cd, and 5.0 for Pb and it was found that the system reached equilibrium in 20 min. The maximum adsorption capacities of the metal ions from their single solutions were 0.039 mmol for Hg(II), 0.008 mmol for Cd(II) and 0.041 mmol for Pb(II) per gram of coal. The order of affinity on a mole basis was as follows: Pb(II)>Hg(II)>Cd(II). The same behavior was observed during the competitive adsorption, that is in the case of adsorption from their ternary solutions. Waste water samples were obtained from a mining industry plant located within Aegean Region, Turkey. It was observed that the use of low rank coal was considerably effective in removing Hg, Cd and Pb cations from water.