A comparison of Ni-Co layered double oxides with memory effect on recovering U(VI) from wastewater to hydroxides

The utilization and development of nuclear energy has resulted in the discharge of uranium-containing wastewater. Layer double hydroxides (LDHs) and oxides (LDOs) were reported for efficient extracting U(VI) from wastewater. In this work, nickel–cobalt layered double oxide (Ni-Co LDO-X, X represents the calcination temperature) with excellent electrostatic attraction and complexation was synthesized via calcination of nickel–cobalt layered double hydroxide (Ni-Co LDH) under air atmosphere for extracting U(VI) comparing to Ni-Co LDH. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential analysis were conducted to characterize the Ni-Co LDO-X. Batch adsorption experiments were carried out to investigate the U(VI) extraction properties. The U(VI) adsorption capacity on Ni-Co LDO-500 increased over 3 times compared to that of Ni-Co LDH. The process of uranium removed by Ni-Co LDO-500 conforms to the Langmuir model, the calculated maximum adsorption capacity is 707.91 mg/g. The results suggested that the excellent U(VI) adsorption ability on Ni-Co LDO-500 mainly dominated by the memory effect, electrostatic interaction, and complexation on the outer-sphere surface. Ni-Co LDO-500 has excellent regeneration ability in five adsorption/desorption experiments. The Ni-Co LDO-500 had favorable ability in removing uranium in actual wastewater with the residual concentration being lower than 0.05 mg/L. The above results highlight that the Ni-Co LDO-500 is promising to be used for the decontamination of uranium in actual uranium-containing wastewater.