Adsorption of low concentration humic acid from water by palygorskite

Humic acid (HA) is a common contaminant in groundwater and surface water. Many efforts were made to use high efficiency low cost materials to remove HA from water. In this study, the effectiveness of using palygorskite to adsorb low concentrations of HA was investigated as a function of the initial HA concentration, equilibrium time, solution pH and ionic strength, temperature, and palygorskite dose. With a particle size of 0.074–0.025 mm, the maximum adsorption of HA on palygorskite was 17 mg/g at 20 °C. The adsorption equilibrium reached in 2 h at pH 6–7 and the data fitted well to the pseudo-second-order adsorption model. Higher HA adsorption was found at low pH and high ionic strength, indicating that electrostatic interaction played an important role between HA and palygorksite. The X-ray diffraction of raw mineral and spent palygorksite showed no difference in d-spacing, suggesting surface adsorption. Fourier transform infrared spectra revealed the presence of CH2 vibrations at 2850 and 2923 cm− 1, indicating direct uptake of HA by palygorskite.