Protano G, Riccobono F
Dipartimento di Scienze Ambientali, Sezione di Geochimica Ambientale e Conservazione del Patrimonio Culturale Lapideo, University of Siena, Italy.
Environ Pollut. 2002;117(3):499-514. doi: 10.1016/s0269-7491(01)00173-7.
Stream waters draining an old mining area present very high rare earth element (REE) contents, reaching 928 microg/l as the maximum total value (sigmaREE). The middle rare earth elements (MREEs) are usually enriched with respect to both the light (LREEs) and heavy (HREEs) elements of this group, producing a characteristic "roof-shaped" pattern of the shale Post-Archean Australian Shales-normalized concentrations. At the Fenice Capanne Mine (FCM), the most important base metal mine of the study area, the REE source coincides with the mine tailings, mostly the oldest ones composed of iron-rich materials. The geochemical history of the REEs released into Noni stream from wastes in the FCM area is strictly determined by the pH, which controls the REE speciation and in-stream processes. The formation of Al-rich and mainly Fe-rich flocs effectively scavenges the REEs, which are readily and drastically removed from the solution when the pH approaches neutrality. Leaching experiments performed on flocs and waste materials demonstrate that Fe-oxides/oxyhydroxides play a key role in the release of lanthanide elements into stream waters. The origin of the "roof-shaped" REE distribution pattern as well as the peculiar geochemical behavior of some lanthanide elements in the aqueous system are discussed.
流经一个旧矿区的溪水呈现出非常高的稀土元素（REE）含量，总含量最大值（∑REE）达到928微克/升。相对于该组稀土元素中的轻稀土元素（LREEs）和重稀土元素（HREEs），中稀土元素（MREEs）通常会富集，从而在澳大利亚后太古代页岩标准化浓度中产生特征性的“屋顶状”模式。在该研究区域最重要的贱金属矿——费尼塞卡潘内矿（FCM），稀土元素的来源与矿尾矿一致，主要是由富铁材料构成的最古老尾矿。从FCM区域的废弃物释放到诺尼溪中的稀土元素的地球化学历史严格受pH值控制，pH值控制着稀土元素的形态和溪流中的过程。富含铝且主要富含铁的絮凝物的形成有效地清除了稀土元素，当pH值接近中性时，稀土元素很容易从溶液中被大量去除。对絮凝物和废料进行的浸出实验表明，铁氧化物/羟基氧化物在镧系元素释放到溪水中的过程中起关键作用。本文讨论了“屋顶状”稀土元素分布模式的成因以及一些镧系元素在水体系中的特殊地球化学行为。
