Preparation of emulsion hydrogels encapsulating extractant by the Pickering emulsion template method to recover lanthanum ions in aqueous solutions

To solve the problem of liquid-liquid extraction of La(III), Pickering emulsion hydrogels (PEHGs) were prepared to realize liquid-solid extraction to better remove La(III) in aqueous solutions. The oil-in-water Pickering emulsions were prepared by utilizing the aqueous solution of sodium alginate as the continuous phase, kerosene-diluted extractant di-(2-ethylhexyl) phosphate (P204) as the dispersed phase, and modified silica as an emulsifier. The emulsions were added to a calcium chloride solution to prepare the PEHGs. The PEHGs were characterized using Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy. The adsorption properties of PEHGs for La(III) in the aqueous solution were investigated using a UV-vis spectrophotometer. The study found that P204 was successfully coated by hydrogels and reached the highest adsorption capacity of 48 mg/g at pH 4. The amount of adsorption increased with the rise in temperature from 298 to 318 K. La(III) adsorption experimental data were more consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model. Thermodynamic parameters showed that the adsorption of La(III) by PEHGs was a spontaneous endothermic process. The internal diffusion model revealed a linear relationship, indicating that internal diffusion played a role in the adsorption process. The encapsulating property of PEHGs indicated its potential usefulness in industrial wastewater for treating La(III).