海水中天然溶解有机物在针铁矿上的吸附

ADSORPITION OF NATURAL DISSOLVED ORGANIC MATTER ONTO GOETHITE IN SEAWATER

于１９９６年３月在青岛小麦岛采得天然海水样品，在实验室合成针铁矿样品。用振荡 平衡实验和紫外／过硫酸钾法测定了海水中溶解有机物在针铁矿上吸附的等温线和交换率 ──ｐＨ曲线，并讨论了天然溶解有机物的吸附对海水中溶解有机碳分布的可能影响。测定结 果表明，溶解有机物在针铁矿上的吸附等温线为Ｌａｎｇｍｕｉｒ型，当吸附达到最大值时，在针铁矿 表面能够形成有机物单覆盖层。ｐＨ能影响溶解有机碳（ＤＯＣ）在针铁矿上的吸附，在ｐＨ值为 ５－６时，ＤＯＣ的吸附百分率最大。在海水ｐＨ为 ８．１下，ＤＯＣ在针铁矿上的吸附百分率超过 ５０％，因此这种吸附作用将对海水中ＤＯＣ的分布产生一定的影响。ＤＯＣ在针铁矿上的吸附是 静电作用和特性吸附共同作用的结果。

The adsorption of dissolved organic matter onto goethite in seawater and its possible affects on distribution of dissolved organic carbon (DOC) were investigated. The seawater was collected at Xiaomaidao in Qingdao in March, 1996. Goethite was synthesized at the same time. Adsorption equilibrium was achieved by shaking and UV/persulphate method was used to determine adsorption percentage-pH curves and isotherm of DOC on goethite. Sorption of DOC onto goedrite occurred very rapidly, implying that mineral surfaces in seawater would not remain uncoated by natural organic matter for long. The isotherm of DOC on goethite showed Langmuir-type. The saturated adsorption amount is 1245.3μmol·g-1 goethute. It was calculated that an area of around 12.8A is available to each organic carbon atom over the goethite surface. On the basis of the radius of carbon atom, the amount of area actually required for each carbon atom would be approximately 22A. Therefore, a monolayer of sorbed natural organic matter exists over the goethite surface as adsorption maximum values are achieved. The adsorption of DOC on goethite were affected by solution pH. Adsorption percentage was high at pH5-6 and decreased with an increasing pH value. The adsorptions percentage of natural organic matter also appears to decrease as initial the DOC concentration increases. Over 50% of DOC was adsorbed by goethite at pH of natural seawater (pH8.1). This indicated that adsorption of DOC would affect the distribution of DOC in seawater. The mechanism of DOC adsorption on goethite is a combination of special adsorption and electrostatic interaction.