Surface complexation model for strontium sorption to amorphous silica and goethite

Table 10 Equilibrium constants (log K^θ) for alkaline earth surface complexation reactions.

Solids	ε	log K^θ_Ca	log K^θ_Mg	log K^θ_Sr	log K^θ_Ba
2>SOH + 2>SO^- + M²⁺ + OH^- = (>SOH)₂(>SO^-)₂_MOH⁺
rutile	121	32.5	31	33.3	34.5
goethite	15	31.1		^a31.2	31.7
γ-Al2O3	10.4	30.8	32.6	30.2	29.6
quartz	4.6	26.9
amorphous silica	3.8	26.9		^a27.0
2>SOH + 2>SO^- + M²⁺ = (>SOH)₂ (>SO^-)₂_M²⁺
goethite	15	27.1
goethite	15	26	25.2
γ-Al2O3	10.4	26.4	26.9	26.4	26
quartz	4.6	20
amorphous silica	3.8	19.2	19.3	^a19.2
>SO^- + M²⁺ + OH^- = >SO^-_MOH⁺
rutile	121	11.5	11	11.5	12
goethite	15	9.8	9.9	^a10.2
γ-Al2O3	10.4	9.8	10.3	9.3
quartz	4.6	6.8	7.6
amorphous silica	3.8
>SOH + M²⁺ = >SOH...Sr²⁺
quartz	4.6	7.7	4.7
amorphous silica	3.8	7.7	7.3	^a-0.4

^aValues for Sr sorption to amorphous silica and goethite are from this study. All other values are from Sverjensky [16]

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