Ni²⁺ and H₂PO₄^- uptake properties of compounds in the CaTiO₃-CaFeO_2.5 system

A batch method was used to investigate the uptake of heavy metal cations and anions by the compounds in the CaTiO₃-CaFeO_2.5 system, in which a series of oxygen vacancies was systematically introduced into a perovskite structure as the x-value of Ca(Fe_xTi_1-x)O_3-x/2 was increased. Samples of CaTiO₃, CaFe_0.1Ti_0.9O_2.95, CaFe_0.5Ti_0.5O_2.75, CaFe_0.67Ti_0.33O_2.67 and CaFeO_2.5 were prepared by solid mixing (SM), co-precipitation (CP) and gel evaporation (GE) methods. The resulting samples were calcined at temperatures between 400 and 1000°C. The target crystalline phases differed according to the preparation method, but in most cases were formed at 700-800°C. The Ni²⁺ sorption isotherms of all the samples were fitted better by the Langmuir model than by the Freundlich model, while in the case of H₂PO₄^- sorption isotherms, these were better fitted by the latter model. The uptake ability increased with increasing x value of the samples. The maximum values for the saturated sorption of Ni²⁺ (Q₀(Ni²⁺)=2.83mmol/g) and H₂PO₄^- (K_F(H₂PO₄^-)=2.95mmol/g) were achieved for x=1 (i.e. CaFeO_2.5) sample.