Bäckström Mattias, Dario Mårten, Karlsson Stefan, Allard Bert
Man-Technology-Environmental Research Centre, Orebro University, 701 82 Orebro, Sweden.
Sci Total Environ. 2003 Mar 20;304(1-3):257-68. doi: 10.1016/S0048-9697(02)00573-9.
The effects of an aquatic fulvic acid on the pH-dependent adsorption of Hg(II) and Cd(II) to particulate goethite (alpha-FeOOH) were studied in batch systems. The ionic medium consisted of 0.01 M HClO(4) and the total concentrations of mercury and cadmium were maintained at 10(-8) M with 203Hg and 109Cd as tracers. pH In the systems was varied in the range 3-10 by addition of HClO(4) and NaOH. All commercial chemicals were of analytical grade or better. An aquatic fulvic acid (20 ppm), previously isolated and characterised in detail, was used as a model for humic substances and its adsorption to goethite is included in this study. The adsorption of the fulvic acid (20 ppm) onto goethite decreased slowly from 90% at pH 3-7.5 to 10% at pH 10. In systems without fulvic acid the adsorption of mercury increased in a linear fashion from 10% at pH 3 to 70% at pH 10. In the presence of fulvic acid (20 ppm), the adsorption was almost quantitative in the intermediate pH range (pH 5-7), and exceeded 92% over the entire pH range. Thus, association between mercury and the fulvic acid enhanced adsorption in general although the largest impact was found at low pH. Adsorption of cadmium increased from nearly 0 to almost 100% at approximately pH 6. In the presence of fulvic acid, the adsorption increased below pH 7 and decreased above pH 7. The adsorption isotherm for mercury when the concentration was increased from 10(-8) to 1.8 x 10(-4) M showed a corresponding increase of K(d) (l/g) up to a total concentration at 10(-6) M. At higher mercury concentrations K(d) was lowered. In the presence of fulvic acid the corresponding relationship of K(d) was bi-modal, i.e. high values at low and intermediate concentrations of mercury. This behaviour suggests that in the absence of fulvic acid the adsorption follow the expected behaviour, i.e. adsorption sites with similar affinity for mercury. In the presence of fulvic acid, additional adsorption sites are available by the organic molecule (possibly sulfur groups) when it is associated to the goethite. The adsorption isotherm for cadmium indicates a lowering of K(d) at 10(-4) M. Cadmium had no competitive effect on mercury and vice versa. Zinc, however, affected the adsorption of cadmium but not the adsorption of mercury.
在间歇系统中研究了一种水生富里酸对汞（II）和镉（II）在颗粒针铁矿（α-FeOOH）上pH依赖性吸附的影响。离子介质由0.01 M高氯酸组成，汞和镉的总浓度以203Hg和109Cd作为示踪剂维持在10^(-8) M。通过添加高氯酸和氢氧化钠将系统中的pH值在3 - 10范围内变化。所有市售化学试剂均为分析纯或更高纯度。一种先前已详细分离和表征的水生富里酸（20 ppm）被用作腐殖质的模型，本研究包括其对针铁矿的吸附。富里酸（20 ppm）在针铁矿上的吸附从pH 3时的90%缓慢下降至pH 10时的10%。在没有富里酸的系统中，汞的吸附从pH 3时的10%以线性方式增加到pH 10时的70%。在存在富里酸（20 ppm）的情况下，在中间pH范围（pH 5 - 7）吸附几乎是定量的，并且在整个pH范围内超过92%。因此，汞与富里酸之间的缔合总体上增强了吸附，尽管在低pH时影响最大。镉的吸附在大约pH 6时从几乎0增加到几乎100%。在存在富里酸的情况下，吸附在pH 7以下增加而在pH 7以上减少。当汞的浓度从10^(-8) M增加到1.8×10^(-4) M时，汞的吸附等温线显示K(d)（l/g）相应增加，直至总浓度达到10^(-6) M。在更高的汞浓度下K(d)降低。在存在富里酸的情况下，K(d)的相应关系是双峰的，即在低和中等汞浓度下值较高。这种行为表明，在没有富里酸的情况下，吸附遵循预期行为，即对汞具有相似亲和力的吸附位点。在存在富里酸的情况下，当有机分子（可能是硫基团）与针铁矿缔合时会有额外的吸附位点。镉的吸附等温线表明在10^(-4) M时K(d)降低。镉对汞的吸附没有竞争作用，反之亦然。然而，锌影响镉的吸附但不影响汞的吸附。
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