Surface complexation model for strontium sorption to amorphous silica and goethite

Carroll, Susan A; Roberts, Sarah K; Criscenti, Louise J; O'Day, Peggy A

doi:10.1186/1467-4866-9-2

Geochemical Transactions

Table 9 Equilibrium constants for alkaline earth sorption, where Log K⁰ is the equilibrium constant referenced to a 1 M standard state, Log K^θ is the equilibrium constant referenced to a site-occupancy standard state, N_s is the site density (# nm^-2), A_s is the surface area (m²g^-1), and C_s is the solid concentration (g L^-1). The site-occupancy standard state assumes reference N_s = 10 sites nm^-2 and A_s = 10 m²g^-1.

From: Surface complexation model for strontium sorption to amorphous silica and goethite

Solid	Log K⁰	Surface Complexation Reaction	N_s	A_s	C_s	Log K^θ
^aAmorphous silca	-2.5	>SOH + H⁺ = >SOH₂⁺	4.6	277	40	-1.4
	-5.9	>SOH = >SO^- + H⁺	4.6	277	40	^d7.0
	-1.4	>SOH + H⁺ + Cl^- = >SOH₂⁺_Cl^-	4.6	277	40	1.1
	-7.2	>SOH + Na⁺ = >SO^-_Na⁺ + H⁺	4.6	277	40	^d0.9
	-1.5	>SOH + Sr²⁺ = >SOH...Sr²⁺	4.6	277	40	-0.4
	-10.0	4>SOH + Sr²⁺ = (>SOH)₂(>SO^-)₂_Sr²⁺ + 2H⁺	4.6	277	40	^d19.2
	-16.2	4>SOH + Sr²⁺ + H₂O = (>SOH)₂(>SO^-)₂_SrOH⁺ + 3H⁺	4.6	277	40	^d 27.0
^bGoethite	5.6	>SOH + H⁺ = >SOH₂⁺	16.4	37.7	40	6.4
	-11.2	>SOH = >SO^- + H⁺	16.4	37.7	40	^d 12.0
	8.9	>SOH + H⁺ + Cl^- = >SOH₂⁺_Cl^-	16.4	37.7	40	3.3
	-9.3	>SOH + Na⁺ = >SO^-_Na⁺ + H⁺	16.4	37.7	40	^d3.5
	-16.6	>SOH + Sr²⁺ + H₂O = >SO^-_SrOH⁺ + 2H⁺	16.4	37.7	40	^d10.2
	-20.7	4>SOH + Sr²⁺ + H2O = (>SOH)₂(>SO^-)₂_SrOH⁺ + 3H⁺	16.4	37.7	40	^d31.2
	-10.0	4>SOH + 2Sr²⁺ = (>SOH)₂(>SO^-)₂_Sr₂⁴⁺ + 2H⁺	16.4	37.7	40	^d15.9
	13.8	>SOH + H⁺ + CO₃^2- = >SO^-2_COO^-8 + H₂O	16.4	37.7	40	13.0
	13.2	>SOH + H⁺ + Na⁺ + CO₃^2- = >SOCOONa + H₂O	16.4	37.7	40	12.4
	18.6	>SOH + 2H⁺ + CO₃^2- = >SOCOOH + H₂O	16.4	37.7	40	17.8
	6.5	>SOH + CO₃^2- + Sr²⁺ = >SO^0.2-_COOSrOH^0.2+	16.4	37.7	40	5.8
	12.8	>SOH + H⁺ + CO₃^2- + Sr²⁺ = >SO^0.2-_COOSr^1.2+ + H₂O	16.4	37.7	40	12.0
^cGoethite	5.7	>SOH + H⁺ = >SOH₂⁺	16.4	27.7	10	6.4
	-11.3	>SOH = >SO^- + H⁺	16.4	27.7	10	^d 12.0
	9.1	>SOH + H⁺ + Cl^- = >SOH₂⁺_NO₃^-	16.4	27.7	10	3.3
	-9.1	>SOH + Na⁺ = >SO^-_Na⁺ + H⁺	16.4	27.7	10	^d3.5
	-16.5	>SOH + Sr²⁺ + H₂O = >SO^-_SrOH⁺ + 2H⁺	16.4	27.7	10	^d10.4
	-18.4	4>SOH + Sr²⁺ + H₂O = (>SOH)₂(>SO^-)₂_SrOH⁺ + 3H⁺	16.4	27.7	10	^d31.3
	13.6	>SOH + H⁺ + CO₃^2- = >SO^-.2_COO^-.8 + H₂O	16.4	27.7	10	13.0
	13.0	>SOH + H⁺ + Na⁺ + CO₃^2- = >SOCOONa + H₂O	16.4	27.7	10	12.4
	18.4	>SOH + 2H⁺ + CO₃^2- = >SOCOOH + H₂O	16.4	27.7	10	17.8
	6.4	>SOH + CO₃^2- + Sr²⁺ = >SO^0.2-_COOSrOH^0.2+	16.4	27.7	10	5.8
	12.7	>SOH + H⁺ + CO₃^2- + Sr²⁺ = >SO^0.2-_COOSr^1.2 + H₂O	16.4	27.7	10	12.0

a. Experiments conducted with and without dissolved carbonate in NaCl solutions, C₁ = 105 μF cm^-2 and C₂ = 0.2 μF cm^-2, C₁ was predicted for amorphous silica from Equation 82 in Sverjensky [16].
b. Experiments conducted with dissolved carbonate in 0.1 M NaCl solutions, C₁ = 97 μF cm^-2 and C₂ = 0.2 μF cm^-2. Mid-range value for C₁ was used in goethite because there is no clear explanation for the wide range of reported values [16].
c. Experiments conducted with dissolved carbonate in 0.1 M NaNO₃ solutions, C₁ = 97 μF cm^-2 and C₂ = 0.2 μF cm^-2. Mid-range value for C₁ was used in goethite because there is no clear explanation for the wide range of reported values [16].
d. Mass balance reactions for log K^θ after Sverjensky [16]. All other mass balance reactions are the same for log K^θ and log K⁰.

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ISSN: 1467-4866

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