黄河甘宁蒙段表层沉积物中稀土元素形态和分馏作用研究

Study on Speciation and Fractionation of Rare Earth Elements in Surface Sediments in Gansu,Ningxia and Inner Mongolia Sections of Yellow River

应用BCR连续提取法和高分辨电感耦合等离子体质谱(HR-ICP-MS)对黄河甘宁蒙段12个采样点(S1～S12)水体表层沉积物中14种稀土元素进行了含量测定及形态分析,并对稀土元素的分馏作用进行了研究。结果表明:各采样点表层沉积物中稀土元素的含量顺序均相同,且12个采样点14种稀土元素的平均含量(mg.kg-1)依次为铈(Ce,66.4)>镧(La,35.8)>钕(Nd,28.6)>镨(Pr,7.88)>钐(Sm,5.87)>钆(Gd,5.01)>镝(Dy,4.53)>镱(Yb,2.86)>铒(Er,2.51)>铕(Eu,1.31)>钬(Ho,0.856)>铽(Tb,0.760)>铥(Tm,0.428)>镥(Lu,0.404),与中国土壤背景含量相近;各稀土元素残渣态含量最高,约为71.9%～93.9%,表明生物有效性较低,对环境影响较小;可还原态含量较低,分布于0.20%～3.87%之间,均值为0.83%;弱酸提取态与可氧化态平均含量相近(7.69%和7.61%),玛曲采样点(S12)可氧化态含量(16.1%)明显高于弱酸提取态(1.73%),相关性分析结果表明总有机碳(TOC)含量与可氧化态含量之间有显著正相关关系,相关系数在0.763～0.914之间。稀土元素分馏作用研究结果表明:黄河甘宁蒙段表层沉积物中稀土元素主要来源于土壤风化,表现为轻稀土元素富集,Eu中度亏损。球粒陨石标准化图解曲线显示金沙湾(S8)和包头磴口(S1)二个采样点中La和Ce可能有外源稀土元素进入,且各采样点重稀土元素均有一定程度的外源影响。

In the present paper,BCR sequential extraction and high resolution inductively coupled plasma-mass spectrometry（HR-ICP-MS） were performed to analyze the speciation contents of 14 kinds of rare earth elements（REE） in the surface sediments from 12 sampling sites（S1-S12） in Gansu,Ningxia and Inner Mongolia Sections of Yellow River,and REE fractionation were also studied.The results indicated that the contents of REE in 12 sediment samples were the same order.The average contents of 14 rare earth elements were in this order： Ce（66.4）La（35.8）Nd（28.6）Pr（7.88）Sm（5.87） Gd（5.01）Dy（4.53）Yb（2.86）Er（2.51）Eu（1.31）Ho（0.856）Tb（0.760）Tm（0.428）Lu（0.404）,which were similar to the Chinese soil background.The residual fractions of all elements were present at the highest percentages（71.9%~93.9%）,which indicated that the bioavailability or environmental impact was low.The percentage of reducible fraction was the lowest,ranged from 0.20% to 3.87% with the mean value of 0.83%,while the oxidizable fraction percentage（7.61%） was close to acid-soluble fraction（7.69%）.But in Maqu（S12）,oxidizable percentage（16.1%） was significantly higher than the acid-soluble fraction（1.73%）.Correlation analysis showed that there was a significant positive correlation between total organic carbon（TOC） content and oxidizable percentage,and the correlation coefficients were between 0.763 and 0.914.REE fractionation results showed that： the contents of REE in surface sediments of Gansu,Ningxia and Inner Mongolia Sections of Yellow River were mainly from soil weathering,with light-REE enrichment and Eu depletion.The chondrite-normalized curve implied that La and Ce in Jinshawan（S8） and Baotou-Dengkou（S1） and heavy REE at all the sampling points might have external REE sources.