Preliminary study on removing Cs⁺/Sr²⁺ by activated porous calcium silicate—A by-product from high-alumina fly ash recycling industry

Figures & data

Figure 1. XRD pattern of activated porous calcium silicate.

Figure 2. SEM image of activated porous calcium silicate.

Figure 3. Effect of pH on K_d of Cs⁺/Sr²⁺ (50 mg/L Cs⁺/Sr²⁺ 20 mL, adsorbent: 100 mg activated porous calcium silicate, 2 hr).

Figure 4. Effect of activated porous calcium silicate amount on Cs⁺/Sr²⁺ adsorption (50 mg/L Cs⁺/Sr²⁺ 20 mL, pH = 7.0, 2 hr).

Figure 5. Effect of contact time on Cs⁺/Sr²⁺ adsorption (50 mg/L Cs⁺/Sr²⁺ 20 mL, pH = 7.0, 100 mg activated porous calcium silicate).

Figure 6. Effect of Cs⁺ /Sr²⁺ initial concentration on Cs⁺/Sr²⁺ adsorption (pH = 7.0, 100 mg activated porous calcium silicate, 2 hr).

Table 1. Adsorption equilibrium data using Langmuir and Freundlich isotherm models

				Constants
Model	Sample	Temperature	Equation	KL (L/mol)	qm (mg/g)	R^2
Langmuir	Cs^+	15°C	Ce/qe = 0.0061Ce + 0.273	0.022	163.9	0.913
		45°C	Ce/qe = 0.0023Ce + 0.313	0.0073	134.78	0.902
	Sr^2+	15°C	Ce/qe = 0.0076Ce + 0.0714	0.1018	131.57	0.963
		45°C	Ce/qe = 0.007Ce + 0.0745	0.0943	142.32	0.882
				KF (mol/g)	1/n	R^2
Freundlich	Cs^+	15°C	lnqe = 0.878lnCe + 1.319	3.731	0.878	0.997
		45°C	lnqe = 0.756lnCe + 1.686	5.397	0.756	0.979
	Sr^2+	15°C	lnqe = 0.616lnCe + 2.632	13.87	0.616	0.995
		45°C	lnqe = 0.596lnCe + 2.664	14.35	0.596	0.971

Table 2. Comparison of sorption capacity for Cs⁺ /Sr²⁺ by using various adsorbents

Adsorbent	Sample	Capacity (mg/g)	Reference
AMP-PAN	Cs^+	81.31	Park et al., 2010
Ferrite	Cs^+	108.6	Sheha and Metwally, 2007
NiHCF/PTCF	Cs^+	41.61	Sun et al., 2012
CA	Cs^+	50.23	Awual et al., 2014
CMC	Sr^2+	108.71	Wang et al., 2009
CMCts	Sr^2+	99.00	Wang et al., 2009
Carbon nanotubes	Sr^2+	27.40	Ji et al., 2010
AMP-PAN	Sr^2+	6.62	Park et al., 2010
This study	Cs^+	163.9
This study	Sr^2+	131.57

Table 3. Thermodynamic parameters for the adsorption Cs⁺/Sr²⁺ by activated porous calcium silicate

	−ΔG° (kJ/mol)
Sample	15°C	45°C	ΔH° (kJ/mol)	ΔS° (kJ/mol·K)
Cs^+	9.13	13.007	27.99	0.1289
Sr^2+	5.47	5.263	1.942	25.739

Figure 7. Modeling of the kinetic data using pseudo-second-order kinetics model.

Figure 8. Modeling of the kinetic data using intraparticle diffusion model.

Table 4. The kinetic parameters of intraparticle diffusion model

Sample	First Equation	Second Equation	ki (g/mg·min^0.5)
Cs^+	qt = 1.4765t^0.5 + 3.873	qt = 0.1787t^0.5 + 9.5876	1.4765 (first) 0.1787 (second)
Sr^2+	qt = 7.7572t^0.5 + 3.873	qt = 0.0657t^0.5 + 15.775	7.7572 (first) 0.657 (second)

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