Selective recovery of La3+ from rare earth mine tailwater by titanium phosphate adsorbents with different crystal forms

Titanium phosphate (TiP) materials in different crystalline forms—amorphous TiP (am-TiP), scaly TiP (s-TiP), platy TiP (p-TiP) and alpha-type TiP (α-TiP) were synthesized by using titanium source of TiOSO4 and phosphorus source of H3PO4. The structures and properties of the four TiP materials and their adsorption selectivity for rare earth La3+ ions were studied. The results showed that the ion exchangeability of TiP was related to the phosphate groups in the structures. The -HPO4 groups dominated the phosphate groups of am- and p-TiP, while -H2PO4 and-HPO4 groups were the only phosphate groups of s- and α-TiP, respectively. La3+ ions were mainly adsorbed through ion exchange with H+ of P-OH groups of TiP. However, the adsorption was not only related to the cation exchange capacity, but also to the structure features of the materials. The adsorption capacity for La3+ was negatively correlated with the crystallinity of TiP, which decreased in the order of 102.25 (am-TiP) >56.08 (s-TiP) > 22.77 (p-TiP) > 6.79 mg⋅g−1 (α-TiP). The adsorption of La3+ by TiP was basically unaffected by the mono- and di-valent impurity ions except for the tri-valent ions, such as Al3+. Additionally, the semi-crystalline s-TiP had the best desorption and regeneration performance among the four TiP. [Display omitted] •The higher the crystallinity of TiPs, the lower the adsorption capacity for La3+.•The adsorption quantity of TiPs for La3+ reaches maximum at pH of 4 and above.•The adsorption of La3+ is not affected by the mono- and di-valent impurity ions.•P-OH groups in TiPs play a key role in adsorption of La3+.•s-TiP is the most suitable for the adsorption of rare earth elements in tailwater.