粤北大宝山酸性矿山废水的稀土元素地球化学特征

Geochemical Characteristics of Rare Earth Elements in Dabaoshan Acid Mine Drainages,Guangdong Province,China

在粤北大宝山多金属矿槽对坑和铁龙尾矿库酸性矿山废水,选取不同p H水体的9个采样点,进行水样和底泥的稀土元素以及水样的重金属元素分析,探讨酸性矿山废水的稀土元素地球化学特征以及p H值对酸性水的稀土元素含量和分布的影响。结果表明：（1）该矿山酸性矿山废水的稀土总量及轻重稀土比值较高：槽对坑水样稀土总量为115.71~1 307.68μg/L,LREE/HREE比值为7.45~13.59;铁龙水样稀土总量为6.86~2 498.83μg/L,LREE/HREE比值为6.32~10.98。稀土元素北美页岩标准化分布模式呈略为右倾的重稀土元素亏损模式,Gd为正异常,与底泥的稀土元素分布模式相似,但水样中Ce呈正异常。（2）酸性水的稀土总量明显受p H值控制,p H值越低,水样的稀土总量越高;在p H〈3时,水样的稀土总量显著增高,达812μg/L以上。（3）影响酸性水稀土元素地球化学行为的关键p H值为3;p H〈3不仅有利于稀土在水体富集,而且会使水体发生富含Ce和中稀土元素（MREE）的稀土分异作用。（4）在p H〈4时,水体同时富集稀土元素和Cu、Pb、Zn、Mn、Cd等重金属元素。

Water and precipitation samples were collected from 9 sampling positions under various p H conditions in acid mine drainages（ AMD） at Caoduikeng and Tielong tailing ponds of Dabaoshan polymetallic mine,north Guangdong Province,China. Rare earth elements（ REE） of the samples and some heavy metallic elements of water samples were measured to study REE geochemical characteristics of AMD and effects of p H value on REE concentration and distribution in AMD. It was investigated that REE is enriched with high ratios of LREE / HREE in acid water samples. Total REE contents of the water samples from Caoduikeng tailing pond lie in between 115.71 and 1 307.68 μg / L with ratios of LREE / HREE between 7.45 and 13.59. Total REE contents of water samples from Tielong tailing pond lie in between 6.86 and 2 498.83 μg / L,with ratios of LREE / HREE in the range of 6.32 ~ 10.98. The REE in the water samples,distributed in a slightly right-leaning NASC-normalized pattern with positive Gd anomaly,is similar to REE chondritenormalized pattern of the precipitations,but with a positive anomaly of Ce. Concentration of REE in water is affected obviously by the p H value. The lower the p H value is,the higher the concentration of REE will be. The REE content increases apparently to higher than 812 μg / L under the condition of p H 3. The critical p H value that affects REE behavior in the AMD would be 3. It is not only beneficial for REE enrichments in water but also make the differentiation of REE enriched in Ce and middle rare earth elements（ MREE）,for acidic condition of p H 3. Both REE and measured heavy metallic elements such as Cu,Pb,Zn,Mn and Cd enrich in waters with p H4,indicating that a stronger acidic environment is beneficial for the enrichments of REE and heavy metallic elements.