Adsorption of Cr(III) ions by Turkish brown coals

The equilibrium and kinetic properties of Cr(III) ion adsorption by two brown coals from Anatolia, Turkey, have been investigated in batch stirred-tank experiments. The effects of adsorbent dose, initial sorbate concentration and contact time on the adsorption of Cr(III) by Isparta-Yalvaç-Yarikkaya (YK) and Kasikara (KK) brown coals were evaluated. The Cr(III) ions are able to form complex compounds with carboxylic and phenolic groups of brown coals and they were also bounded with phenolic groups even at low pH reaction of the solution (<3). Mechanisms including ion exchange, complexation and adsorption to the surface are possible in the sorption process. Our batch adsorption studies show the equilibrium adsorption data fit the linear Langmuir adsorption isotherm. Adsorption equilibrium was achieved in about 15–20 min for chromium(III). The Langmuir adsorption isotherm was used to describe the observed sorption phenomena. The maximum equilibrium uptake was 0.05 mmol of Cr(III)/g for KK, and 0.26 mmol of Cr(III)/g for YK, respectively, at a pH of 4.5. More than 90% of chromium(III) was removed by KK and YK from an aqueous solution after 60 min. In every experiment, the maximum Cr(III) was sequestered from the solution within 60 min. It is proposed that KK and YK brown coals can be used as potential sorbents for Cr(III) removal from aqueous solutions.