Removal of Cu(II) from aqueous solutions using dolomite-palygorskite clay: Performance and mechanisms

Dolomite-palygorskite clay (DPC) generally exists in palygorskite ore deposits. The morphological and mineralogical properties of a DPC sample were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), and its performance on the removal of Cu(II) from an aqueous solution was evaluated by batch experiments. The effects of various parameters, viz., contact time (0-6 h), initial pH (2-6), initial Cu(II) concentration (50-300 mg L− 1), temperature (288-308 K), and ion strength ([Na+]: 0.001-0.5 mol L− 1), on copper removal were investigated. The majority of copper ions were removed within an equilibrium time of 4 h, and kinetic data were expressed using a pseudo-second-order model. Maximum copper removal was achieved at pH 5 with a removal efficiency of 99.6%. The Freundlich model provided a better fit to equilibrium data, and the maximum removal capacity was estimated to be 225.7 mg g− 1 (308 K), which was nearly three times as high as that of dolomite (DO) and seven times that of palygorskite (PG). The thermodynamic results revealed the endothermic nature of the removal process and the strong chemical bonding between Cu(II) and DPC. Ion strength studies and TEM analyses indicated that the major mechanisms for removal of Cu(II) by DPC were surface precipitation and dissolution reactions by the formation of basic copper carbonate [CuCO3·Cu(OH)2], surface complexation, and electrostatic attraction.