Properties and Mechanism of U(VI) Removal by Calcium Orthovanadate

doi:10.15541/jim20250009

Abstract

Abstract:

Mining process of natural uranium ore generates uranium-containing wastewater, while removal of uranium(VI) from such wastewater has emerged as a critical challenge, requiring urgent resolution in the nuclear industry. Guided by the principle of "from uranium mines, back to uranium mines," this study selected calcium orthovanadate (Ca₃(VO₄)₂) as an adsorbent for U(VI) removal. Adsorption performance of Ca₃(VO₄)₂ powder under varying conditions and its underlying mechanism were investigated. Results demonstrated that under optimal conditions (pH 6, adsorption for 2 h, adsorbent dosage at 0.1 g·L^-1, initial U(VI) mass concentration at 120 mg·L^-1, temperature at 308 K), Ca₃(VO₄)₂ powder exhibited a high adsorption capacity (1179.92 mg·g^-1) and removal efficiency (98.33%) for U(VI). Removal mechanism was attributed to dissolution and mineralization processes, forming metatyuyamunite (Ca(UO₂)₂(VO₄)₂·3H₂O) on the powder surface after adsorption. Even in the environment of six coexisting ions (Zn²⁺, Cr³⁺, Cu²⁺, Ni²⁺, Co²⁺, and Ba²⁺), Ca₃(VO₄)₂ maintained high adsorption performance, reducing U(VI) mass concentration from 121.49 to 0.1 mg·L^-1, which is below the limit specified by the national discharge standard (GB 23727-2020). These findings highlight Ca₃(VO₄)₂ as a promising adsorbent for efficient treatment of U(VI)-containing wastewater.

Key words: calcium orthovanadate, U(VI), adsorption capacity, removal rate, mineralization

CLC Number:

X591

WANG Hongqin, DENG Hao, LIANG Hua, TIAN Qiang, YAN Minhao, HUANG Yi. Properties and Mechanism of U(VI) Removal by Calcium Orthovanadate[J]. Journal of Inorganic Materials, 2025, 40(11): 1268-1276.

Figures/Tables 14

Table 1 Initial mass concentrations of several metal ions in coexisting ionic solution

Metal ion	ρ₀/(mg·L^-1)	Metal ion	ρ₀/(mg·L^-1)
Zn²⁺	648.63	Co²⁺	67.12
Cr³⁺	101.22	Ba²⁺	64.22
Cu²⁺	72.55	U(VI)	121.49
Ni²⁺	133.04

Fig. 1 Characterization results of Ca3(VO4)2 powder (a) XRD patterns of Ca3(VO4)2 prepared at different temperatures for 4 h; (b-h) FT-IR spectrum (b), particle size distribution (c), nitrogen adsorption-desorption curves (d), SEM image (e) and EDS mappings (f-h) of Ca3(VO4)2 prepared at 1100 ℃ for 4 h

Fig. 2 Effect of pH and adsorption time on removal of U(VI) by Ca3(VO4)2 (a) Species distribution of U(VI) with different pH (U(VI) at mass concentration of 120 mg·L-1 under 308 K); (b, c) Adsorption capacity and removal rate of U(VI) with different pH (b) and durations (c); (d-f) Pseudo-first-order (d), pseudo-second-order (e) and Weber-Morris (f) models fitting (temperature at 308 K, initial U(VI) mass concentration at 120 mg·L-1, adsorbent dosage at 0.1 g·L-1)

Table 2 Fitting parameters of pseudo-first-order and pseudo-second-order kinetic models

Material	Pseudo-first-order		Pseudo-second-order
Material	k₁/min^-1	R²	k₂/(g·mg^-1·min^-1)	R²
Ca₃(VO₄)₂	0.01	0.447	2.62×10^-4	0.999

Table 3 Fitting parameters of Weber-Morris dynamic model

Material	Weber-Morris
Material	k_p,1/(mg·g^-1·min^-1/2)	R₁²	k_p,2/(mg·g^-1·min^-1/2)	R₂²
Ca₃(VO₄)₂	312.25	0.956	7.65	0.400

Fig. 3 Effects of adsorbent dosage, initial U(VI) mass concentration, and temperature on removal of U(VI) by Ca3(VO4)2 (a, b) Adsorption capacity and removal rate of U(VI) with different adsorbent dosages (a) and initial U(VI) mass concentrations (b);(c, d) Langmuir (c) and Freundlich (d) isothermal adsorption models fitting; (e) Adsorption capacity and removal rate of U(VI) at different temperatures; (f) Relationship between lnK and 1/T (temperature at 308 K, pH 6, adsorption time at 2 h)

Table 4 Fitting parameters of Freundlich and Langmuir isothermal adsorption models

Material	Freundlich		Langmuir
Material	k_F/(mg·g^-1)·(mg·L^-1)^-1/ⁿ	R²	k_L/(L·mg^-1)	R²
Ca₃(VO₄)₂	623.24	0.969	0.09	0.975

Table 5 Thermodynamic fitting parameters

Material	∆H/(kJ·mol^-1)	∆S/(J·mol^-1·K^-1)	∆G/(kJ·mol^-1)
Material	∆H/(kJ·mol^-1)	∆S/(J·mol^-1·K^-1)	303 K	308 K	313 K	318 K	323 K
Ca₃(VO₄)₂	28.55	140.74	-14.09	-14.79	-15.50	-16.20	-16.91

Fig. 4 SEM images and surface element distributions of Ca3(VO4)2 before and after adsorption of U(VI) (a, b) SEM images of Ca3(VO4)2 before (a) and after (b) adsorption of U(VI); (c-f) EDS mappings of Ca3(VO4)2 after adsorption of U(VI)

Fig. 5 Characterization results of Ca3(VO4)2 before and after adsorption of U(VI) (a) XPS spectra of Ca3(VO4)2 and UO2(NO3)2·6H2O; (b) U4f XPS spectrum of Ca3(VO4)2 after adsorption of U(VI); (c, d) XRD patterns (c) and FT-IR spectra (d) of Ca3(VO4)2

Table 6 Mass concentrations of several metal ions in coexisting ionic solution after adsorption

Metal ion	ρ₀/(mg·L^-1)	Metal ion	ρ₀/(mg·L^-1)
Zn²⁺	588.55	Co²⁺	63.66
Cr³⁺	0.01	Ba²⁺	60.51
Cu²⁺	0.90	U(VI)	0.10
Ni²⁺	126.60

Fig. 6 Adsorption capacity and removal rate of Ca3(VO4)2 for several metal ions in coexisting ionic solution pH 6; Adsorption time: 2 h; Adsorbent dosage: 0.1 g·L-1; Temperature: 308 K

Table 7 Selective adsorption parameters of Ca3(VO4)2 for several metal ions in coexisting ionic solution

Metal ion	K_d/(L·g^-1)	k	Metal ion	K_d/(L·g^-1)	k
U(VI)	12039.43	1.00	Ni²⁺	0.51	23673.64
Zn²⁺	1.02	11793.32	Co²⁺	0.54	22142.30
Cr³⁺	168687.73	0.07	Ba²⁺	0.61	19636.28
Cu²⁺	791.97	15.20

Table 8 Adsorption capacity of Ca3(VO4)2 and other adsorbents for uranium (VI) removal[11-12,15,33-37]

Material	Adsorption capacity/(mg·g^-1)	pH	Ref.
Mg₂CO₃(OH)₂	370.00	5.0	[33]
Crab carapace	1.38	8.0	[11]
PG/SFA	84.60	6.0	[12]
HAP	130.08	5.0	[34]
Kaolinite	9.17	4.5	[35]
ZSM-12 zeolite	12.00	3.0	[36]
H₁₁Al₂V₆O_23.2	917.00	5.0	[37]
EuVO₄	276.16	4.5	[15]
Ca₃(VO₄)₂	1179.92	6.0	This study

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