Batch removal of copper(II) and zinc(II) from aqueous solutions with low-rank Turkish coals

The 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 present on the coal surface were the adsorption site to remove metal ions 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 Cu(II) and Zn(II) ions from aqueous solutions. The optimum pH was measured to be 4.0 and it was found that the adsorption reached equilibrium in 20 min. The maximum adsorption capacities of the metal ions from their single solutions were 1.62 mg for Cu(II) and 1.20 mg for Zn(II) per g of coal. The order of affinity based on a weight uptake by coal was as follows: Cu(II) > Zn(II). The same behavior was observed during the competitive adsorption, that is in the case of adsorption from their binary solutions. The adsorption phenomena appeared to follow a typical Langmuir isotherm. It was observed that use of low-rank coal was considerably effective in removing Cu(II) and Zn(II) ions from aqueous solutions. Higher amounts of adsorbed metal ions could be desorbed (up to 80%) using 25 mM EDTA. Low-rank Turkish coals are suitable for consecutive use for more than three cycles without significant loss of adsorption capacity. (C) 2000 Elsevier Science B.V. All rights reserved.