Cadmium (II) and mercury (II) removal from aquatic solutions with low-rank Turkish coal

Official URL: http://dx.doi.org/10.1081/SS-100108354

Removal of heavy metal ions from aqueous solutions containing low-to-moderate levels of contamination using Turkish Beypazari low-rank coal was investigated. Carboxylic acid and phenolic hydroxyl functional groups on the coal surface were the adsorption sites for heavy metal ions via the ion-exchange mechanism. The equilibrium pH of the coal-solution mixture was the principal factor controlling the extent of removal of Cd(II) and Hg(II) from aqueous solutions. The optimum pH was 4.0, and the adsorption reached equilibrium in 30 minutes. The maximum adsorption capacities of the metal ions from their single solutions were 1.55 mg for Hg(II) and 1.42 mg for Cd(II) per g of coal. Based on a weight uptake by coal, Hg(II) was found to have a greater affinity for the adsorption sites than does Cd(II). The same behavior was observed during competitive adsorption, that is, adsorption from binary solutions. The adsorption phenomena followed a typical Langmuir isotherm. The maximum adsorption capacities (q(m)) were calculated as 2.03 mg/g and 1.70 mg/g for Hg(II) and Cd(II), respectively. The K-d values were 8.2 mg/L for Cd(II) and 9.8 mg/L for Hg(II). The use of low-rank coal was considerably effective in removing Hg(II) and Cd(II) from aqueous solutions. High amounts of adsorbed metal ions could be desorbed (up to 90%) with 25 mmol/L EDTA. Low-rank Turkish coals are suitable for use in more than 10 cycles without experiencing significant loss of adsorption capacity.