Surface complexation modeling of Fe₃O₄-H⁺ and Mg(II) sorption onto maghemite and magnetite

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• 作者：Rickard Jolster? ; Lars Gunneriusson ; Allan Holmgren
• 关键词：Potentiometric titration ; Magnetite ; Maghemite ; Acid/base properties ; Active surface sites ; Sorption ; Magnesium ion adsorption ; Surface complexation modeling ; Constant capacitance
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 出版时间：15 November, 2012
• 年：2012
• 卷：386
• 期：1
• 页码：260-267
• 全文大小：459 K

文摘

The surface acid/base properties of magnetite (Fe₃O₄) particles and the sorption of Mg²⁺ onto magnetite and maghemite (¦Ã-Fe₂O₃) have been studied using high precision potentiometric titrations, batch experiments, and zeta potential measurements. The acid/base properties of magnetite were found to be very similar to maghemite except for the difference in surface site density, N_s (sites nm^?2), 1.50 ¡À 0.08 for magnetite, and 0.99 ¡À 0.05 for maghemite. The experimental proton exchange of the magnetite surface increased from pH 10 and above, indicating dissolution/transformation reactions of magnetite at alkaline conditions. Thus, magnetite with its Fe(II) content proved to be less stable toward dissolution in comparison with pure Fe(III) oxides also at high pH values.

Three different ratios between surface sites and added Mg²⁺ were used in the sorption experiments viz. 0.5, 1, and 2 Mg²⁺ site^?1. Surface complexation modeling of the Mg²⁺ sorption onto maghemite and magnetite was restricted to pH conditions where the interference from Mg(OH)₂(s) precipitation could be ruled out. The model calculations showed that Mg²⁺ sorb onto the magnetite and maghemite surfaces as a mixture of mono- or bidentate surface complexes at 0.5 Mg²⁺ site^?1 and as monodentate complexes at 1 and 2 Mg²⁺ site^?1 conditions. Mg²⁺ was also found to adsorb more readily at the maghemite surfaces in comparison with magnetite surfaces. For experiments with excess Mg²⁺ relative to the number of surface sites, the calculations suggested the formation of polynuclear surface complexes on maghemite.