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Carbonate adsorption behavior on alpha-iron oxyhydroxide (Goethite): An equilibrium study.

机译：碳酸盐在α-羟基氧化铁（针铁矿）上的吸附行为：一项平衡研究。

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The purpose of this study was to elucidate reactions involving carbonate at the goethite-aqueous interface, under conditions applicable to those found in natural settings. Increased understanding of the goethite-carbonate interactions will provide insight to the range of effects on adsorption of trace elements.; The goals of this investigation were: (i) to study the effects of the following chemical variables on the quantitative sorption of aqueous carbonate onto goethite: a pH interval between 3 and 9, ionic strengths of 0.1 M and 0.01 M NaCl and NaNO3, and equilibrium aqueous carbonate concentrations between 10 muM and 5 mM; (ii) to gain insight into the bonding mechanisms of aqueous carbonate species to goethite using a triple layer surface complexation modeling approach (TLM), as well as Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR); and (iii) to establish predictive capabilities of its interaction and effects on the adsorption of chromium(VI) and lead(II) onto goethite, using the TLM.; It was found that carbonate adsorption is strongly affected by pH and ionic strength. A thorough modeling, as well as ATR-FTIR spectroscopic, analyses, revealed that complexation to the surface occurs most likely in an inner-sphere monodentate fashion. One single complex on the goethite surface was found to explain most of the quantitative carbonate sorption occurring in the range of conditions investigated. The concept of "inner-sphere complex", in the realm of triple-layer surface complexation modeling, was expanded from the conventional notions. Allocating charge beyond the surface (0-) plane for inner-sphere complexes, allowed a complexation behavior that is more strongly influenced by electrostatic conditions at the solid-water interface.; Projections for situations under natural conditions yielded a potential for coverage by carbonate of more than half the total number of sites on goethite-like particles. Available data on the effects of natural concentration levels of carbonate on the adsorption of two representative trace-metal systems, were adequately predicted by the TLM. Reduction of anionic Cr(VI) sorption to goethite was successfully simulated, through competitive and electrostatic effects. Formation of a ternary Pb(II) carbonato surface complex on goethite, was proposed to explain adsorption behavior in the mixed aqueous Pb(II)-carbonate system.
机译：这项研究的目的是阐明在适用于自然环境下的条件下，针铁矿-水界面处涉及碳酸盐的反应。对针铁矿-碳酸盐相互作用的加深了解将提供对微量元素吸附的影响范围的见解。这项研究的目标是：（i）研究以下化学变量对碳酸盐水溶液在针铁矿上定量吸附的影响：pH值介于3和9之间，离子强度分别为0.1 M和0.01 M NaCl和NaNO3，以及碳酸盐平衡水的浓度在10到5毫米之间; （ii）使用三层表面络合建模方法（TLM）以及衰减全反射傅立叶变换红外光谱（ATR-FTIR）来深入了解碳酸盐水溶液物种与针铁矿的结合机理； （iii）使用TLM建立预测其相互作用以及对铬（VI）和铅（II）吸附在针铁矿上的影响的预测能力；已经发现，碳酸盐的吸附受pH和离子强度的强烈影响。全面的建模以及ATR-FTIR光谱分析表明，与表面的络合最有可能以内球单齿方式发生。发现在针铁矿表面上存在一种单一的络合物，可以解释在所研究条件范围内发生的大多数定量碳酸盐吸附。在三层表面络合建模领域中，“内层络合物”的概念是从传统概念扩展而来的。对于内球络合物，将电荷分配到表面（0-）平面以外，从而允许络合物行为受到固体-水界面处的静电条件的强烈影响。对自然条件下的情况进行的预测表明，碳酸盐可能覆盖针铁矿状颗粒上的位点总数的一半以上。 TLM充分预测了碳酸盐自然浓度水平对两种代表性痕量金属系统吸附的影响的可用数据。通过竞争和静电作用，成功地模拟了阴离子对Cr（VI）的吸附减少到针铁矿中。有人提出在针铁矿上形成三元Pb（II）碳酸盐表面配合物，以解释在Pb（II）-碳酸盐混合水体系中的吸附行为。

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