碱提取法分析海洋沉积物生物硅方法中碎屑组分污染的评估及校正

Evaluation and calibration on the detrital contamination to biogenic opal of marine sediments by alkali leachate methods

利用电感耦合等离子体质谱(ICP-MS)和电感耦合等离子体原子发射光谱(ICP-AES)方法分析了常规碱液提取海洋沉积物中的生物硅所获取的溶液中的Si、Al和Ti含量。分析结果显示,碱液提取法获取的溶液中Si和Al明显地由两种来源混合而成,其中,Si有较大比例的陆源碎屑成分的贡献,并不能直接代表沉积物中的生物硅含量,而需要对其中的陆源碎屑贡献进行扣除。通常使用Al来代表陆源碎屑进行扣除的方法无法给出正确结果,因为碱提取液中Al存在明显的非碎屑组分。对数个土壤及水系沉积物标准样品物质的试验发现,碱提取可以优先溶解其中的Si和Al,而提取液中的SiO2/TiO2比值相对于土壤和沉积物全样的SiO2/TiO2比值有一个比较固定的富集系数(约14左右)。对南海沉积物而言,根据这个富集系数和区域的碎屑物质的化学组成算得碱提取液中碎屑组分SiO2/TiO2比值约为748,这与根据二端员混合估计的比值相当。这样,根据提取液中的Ti含量可以较好地扣除出碎屑组分对生物硅的污染,对于更准确测定海洋沉积物中低含量的生物硅具有重要意义。

Al, Si and Ti contents of the alkali leachates of the sediments from the South China Sea for biogenic opal analysis were measured by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results indicate that the Si and Al in the alkali leachates of the marine sediments are mixed by authigenic component anddetrital dissolved component. Especially, a great part of leached Si is contributed from the dissolved detrital materials. Therefore, the Si in alkali leachatecould not be used as biogenic opal estimates before the detrital contribution is correctly subtracted. Generally, Al is used to estimate the contribution of the detrital materials in marine sediments. However, Al could not be used to subtract the contribution of the detrital materials because there are significant non-detrital Al components in alkali leachates. The alkali leach test on several soils and stream deposits reveals that Si and Al could be preferentially leachedby alkali relative to Ti. The SiO2/TiO2 ratios in alkali leachates are generally about 11～15 times of those in the bulk soils and deposits, giving an averageabout 14. Estimated from this enriched coefficient and the chemical compositions of the detrital materials in the South China Sea, the SiO2/TiO2 ratio of the detrital contribution in the alkali leachates of the sediments from the South China Sea may be about 748, which agrees with the value generated by two end-mixture estimation. Therefore, using this SiO2/TiO2 ratio, the detrital contributionto biogenic opal could be subtracted by the Ti contents in the alkali leachates. This is helpful to obtain precise results of those marine sediments in which biogenic opal content is low.