Sorption behavior of thorium onto granite and its constituent minerals

Figures & data

Table 1. Thermodynamic data for Th species [2,3].

Species	Reaction	log K
Th(OH)^3+	Th^4+ + H2O = Th(OH)^3+ + H^+	−2.500 ± 0.500
Th(OH)2^2+	Th^4+ + 2H2O = Th(OH)2^2+ + 2H^+	−6.200 ± 0.500
Th(OH)4(aq)	Th^4+ + 4H2O = Th(OH)4(aq) + 4H^+	−17.400 ± 0.700
Th2(OH)2^6+	2Th^4+ + 2H2O = Th2(OH)2^6+ + 2H^+	−5.900 ± 0.500
Th2(OH)3^5+	2Th^4+ + 3H2O = Th2(OH)3^5+ + 3H^+	−6.800 ± 0.200
Th4(OH)8^8+	4Th^4+ + 8H2O = Th4(OH)8^8+ + 8H^+	−20.400 ± 0.400
Th4(OH)12^4+	4Th^4+ + 12H2O = Th4(OH)12^4+ + 12H^+	−26.600 ± 0.200
Th6(OH)14^10+	6Th^4+ + 14H2O = Th6(OH)14^10+ + 14H^+	−36.800 ± 1.200
Th6(OH)15^9+	6Th^4+ + 15H2O = Th6(OH)15^9+ + 15H^+	−36.800 ± 1.500
Th(CO3)5^6−	Th^4+ + 5CO3^2− = Th(CO3)5^6−	31.000 ± 0.700
Th(OH)2(CO3)2^2−	Th^4+ + 2H2O + 2CO3^2− = Th(OH)2(CO3)2^2− + 2H^+	8.798 ± 0.501
ThOH(CO3)4^5−	Th^4+ + H2O + 4CO3^2− = ThOH(CO3)4^5− + H^+	21.599 ± 0.500
Th(OH)4CO3^2−	Th^4+ + 4H2O + CO3^2− = Th(OH)4CO3^2− + 4H^+	−15.605 ± 0.603
ThO2(am, aged)	Th^4+ + 2H2O = ThO2(am, aged) + 4H^+	−8.504 ± 0.900

Figure 1. Solubility of Th in 0.01 mol dm⁻³ NaHCO₃ solution (a) and 0.1 mol dm⁻³ NaHCO₃ solution (b) calculated with existing thermodynamic data [2,3].

Figure 2. Scanning electron microscope images of the employed solids (×100 magnification).

Table 2. Experimental variables and data for Th sorption on albite.

NaHCO3
0.01 mol dm^−3		0.05 mol dm^−3		0.1 mol dm^−3
pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)
8.70	>9.9 × 10^0	8.71	(3.0 ± 0.3) × 10^0	8.67	(7.3 ± 0.4) × 10^−1
8.80	>9.9 × 10^0	8.95	(1.9 ± 0.1) × 10^0	8.77	(4.8 ± 0.1) × 10^−1
9.21	>9.9 × 10^0	9.24	(1.2 ± 0.1) × 10^0	8.89	(3.3 ± 0.1) × 10^−1
9.50	>9.9 × 10^0	9.64	(7.6 ± 0.8) × 10^−1	9.00	(2.9 ± 0.1) × 10^−1
10.16	>9.9 × 10^0	9.95	(5.6 ± 0.3) × 10^−1	9.10	(2.2 ± 0.1) × 10^−1
10.82	>9.9 × 10^0	10.05	(4.6 ± 0.3) × 10^−1	9.20	(1.9 ± 0.1) × 10^−1
		10.59	(1.1 ± 0.1) × 10^0	9.45	(1.2 ± 0.1) × 10^−1
				9.74	(8.7 ± 0.3) × 10^−2
				10.39	(1.7 ± 0.1) × 10^−1

Table 3. Experimental variables and data for Th sorption on quartz.

NaHCO3
0.01 mol dm^−3		0.05 mol dm^−3		0.1 mol dm^−3
pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)
8.63	(9.5 ± 1.2) × 10^0	8.68	(1.3 ± 0.1) × 10^−1	8.53	(5.1 ± 1.2) × 10^−2
8.85	(8.0 ± 0.8) × 10^0	9.01	(1.3 ± 0.1) × 10^−1	8.82	(4.2 ± 0.2) × 10^−2
8.99	(2.9 ± 0.3) × 10^0	9.24	(1.1 ± 0.1) × 10^−1	8.96	(3.0 ± 0.3) × 10^−2
9.19	(4.4 ± 0.7) × 10^0	9.56	(1.0 ± 0.1) × 10^−1	9.07	(2.1 ± 0.2) × 10^−2
9.51	(3.6 ± 0.5) × 10^0	9.96	(1.4 ± 0.1) × 10^−1	9.18	(2.4 ± 0.2) × 10^−2
10.18	(7.8 ± 1.3) × 10^0	10.31	(1.6 ± 0.1) × 10^−1	9.21	(3.2 ± 0.2) × 10^−2
10.67	>9.9 × 10^0	10.82	(2.1 ± 0.4) × 10^0	9.71	(2.5 ± 0.2) × 10^−2
				10.39	(5.5 ± 0.3) × 10^−2

Table 4. Experimental variables and data for Th sorption on biotite.

NaHCO3
0.01 mol dm^−3		0.05 mol dm^−3		0.1 mol dm^−3
pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)
8.96	>9.9 × 10^0	8.70	>2.1 × 10^1	8.76	(2.8 ± 0.4) × 10^1
9.07	>9.9 × 10^0	8.98	>2.1 × 10^1	8.90	(1.9 ± 0.1) × 10^1
9.30	>9.9 × 10^0	9.25	(2.1 ± 0.8) × 10^1	8.96	(9.6 ± 0.9) × 10^0
9.54	>9.9 × 10^0	9.39	(1.2 ± 0.2) × 10^1	9.06	(1.5 ± 0.1) × 10^1
10.16	>9.9 × 10^0	9.55	(1.0 ± 0.1) × 10^1	9.21	(8.6 ± 0.7) × 10^0
10.67	>9.9 × 10^0	9.93	(1.0 ± 0.2) × 10^1	9.48	(5.9 ± 0.2) × 10^0
		10.13	(2.0 ± 0.9) × 10^1	9.76	(3.9 ± 0.3) × 10^0
		10.46	(2.1 ± 0.5) × 10^1	10.26	(3.3 ± 0.3) × 10^0
		10.52	>2.1 × 10^1	10.37	(7.1 ± 0.6) × 10^0

Table 5. Experimental variables and data for Th sorption on granite.

NaHCO3
0.01 mol dm^−3		0.05 mol dm^−3		0.1 mol dm^−3
pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)	pH	Kd (m^3 kg^−1)
8.61	(4.3 ± 0.5) × 10^0	8.84	(1.9 ± 0.1) × 10^−1	8.70	(6.9 ± 0.3) × 10^−2
8.81	(5.9 ± 0.9) × 10^0	8.99	(7.2 ± 0.4) × 10^−2	8.77	(4.6 ± 0.2) × 10^−2
9.21	(4.7 ± 0.5) × 10^0	9.07	(1.4 ± 0.1) × 10^−1	8.90	(7.0 ± 0.3) × 10^−2
9.32	(8.9 ± 0.1) × 10^0	9.25	(6.7 ± 0.4) × 10^−2	9.00	(4.2 ± 0.2) × 10^−2
9.57	(3.9 ± 0.6) × 10^0	9.31	(1.2 ± 0.1) × 10^−1	9.03	(3.9 ± 0.2) × 10^−2
9.59	(7.9 ± 0.5) × 10^0	9.47	(1.1 ± 0.1) × 10^−1	9.11	(3.9 ± 0.2) × 10^−2
9.78	(7.6 ± 1.4) × 10^0	9.56	(5.3 ± 0.4) × 10^−2	9.17	(9.2 ± 0.3) × 10^−2
10.17	(7.2 ± 1.6) × 10^0	9.59	(8.9 ± 0.4) × 10^−2	9.20	(4.2 ± 0.3) × 10^−2
10.23	(9.4 ± 0.9) × 10^0	9.80	(8.5 ± 0.3) × 10^−2	9.22	(1.7 ± 0.2) × 10^−2
10.55	>9.9 × 10^0	9.96	(5.2 ± 0.3) × 10^−2	9.59	(1.7 ± 0.2) × 10^−2
10.63	>9.9 × 10^0	9.97	(9.2 ± 0.4) × 10^−2	9.75	(3.4 ± 0.2) × 10^−2
		10.08	(6.9 ± 0.4) × 10^−2	9.81	(1.5 ± 0.2) × 10^−2
		10.55	(2.5 ± 0.1) × 10^−1	10.06	(1.5 ± 0.3) × 10^−2
		10.56	(2.0 ± 0.1) × 10^−1	10.30	(1.9 ± 0.2) × 10^−2
				10.59	(4.3 ± 0.2) × 10^−2

Figure 3. Comparison of K_d values for Th obtained in this study and previously reported ones: (a) albite, (b) quartz [12,14], (c) biotite, and (d) granite [11]. ‘0.01 M’ represents the 0.01 mol dm⁻³ NaHCO₃ concentration. Previous data for albite and biotite are not available.

Table 6. Existing literature values of equilibrium constants for surface complexation of Th.

Reaction	log K
	NEM					DLM	TLM
	Kaolinite	Montmorillonite	Illite	Illite	Hematite	Hematite	Kaolinite	Quartz	Goetite	Goetite
≡SOH + H^+ = ≡SOH2^+	4.55	4.5	4	4.0	5.9	7.43	1.75	−0.8	–	5.57
≡SOH = ≡SO^− + H^+	−9.01	−7.9	−6.2	−6.2	−8.5	−8.17	−6.25	−6.8	–	−9.52
≡SOH + Th^4+ = ≡SOTh^3+ + H^+	–	7.2	–	7.4	5.6	–	–	–	1.0	3.5
≡SOH + Th^4+ + H2O = ≡SOThOH^2+ + 2H^+	–	2.7	–	2.3	–	–	0.2	0.6	−0.75	0.2
≡SOH + Th^4+ + 2H2O = ≡SOTh(OH)2^+ + 3H^+	−4.5	−2.6	−3.0	−2.4	−3.5	−2	−4.6	−3.7	−2.38	−6.38
≡SOH + Th^4+ + 3H2O = ≡SOTh(OH)3^0 + 4H^+	−9.8	−9.1	−8.0	−8.8	−9.2	–	−10.1	−9.8	−9.85	−10.6
≡SOH + Th^4+ + 4H2O = ≡SOTh(OH)4^− + 5H^+	−17.8	−16.9	−13.4	−15.3	−17.3	−16.7	–	−15.5	−16.75	−16.3
≡SOH + Th^4+ + 2H2O + CO3^2^−
= ≡SOTh(OH)2CO3^2^− + 3H^+	5.1	–	5.3	–	–	–	–	–	–	–
References	[30]	[27]	[30]	[28]	[19]	[19]	[22]	[22]	[21]	[23]

Figure 4. Correlation of surface complexation constants of metal species sorbing on the mineral surface with the corresponding aqueous hydrolysis constants (blue and green marks) summarized in Bradbury and Baeyens [27,28]. The blue line shows LFER for montmorillonite and the green dotted line for illite. Red marks are the data reported by Ervanne et al. [30].

Figure 5. Comparison of K_d values of Th predicted using the NEM (lines) with experimentally measured ones (marks).

Table 7. Model parameters and equilibrium constants for the NEM calculation.

			Albite	Quartz	Biotite
Surface area	S	m^2 g^−1	1	0.7	4.3
Site density	ns	sites nm^−2	4.05	5.67	3.81
Surface acidity constant	log Ka1		4.13	−1.26	4.6
	log Ka2		−8.46	−7.28	−6.4
Formation constant	log K1		−9.8	–	−8.8
	log K2		−17.8	−17.5	−15.3
	log K3		16.0	15.5	18.5
	log K4		27.5	–	–

Figure 6. Calculated mole fraction of Th species under 0.05 mol dm⁻³ NaHCO₃ condition. (a) Albite, (b) quartz, (c) biotite, (d) granite and (e) granite calculated using one order of magnitude lower K₁–K₇ values for feldspar. (F), feldspar; (Q), quartz; (B), biotite.

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