The development of middle rare earth element enrichments in freshwaters: weathering of phosphate minerals
The development of middle rare earth element enrichments in freshwaters: weathering of phosphate minerals
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DOI：
10.1016/s0009-2541(00)00355-7
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发表时间：
2001-06-01
期刊：
影响因子：
3.9
通讯作者：
Sholkovitz, ER
中科院分区：
文献类型：
--
作者：
Hannigan, RE;Sholkovitz, ER
许多生物成因、自生成因和成岩成因的磷矿物以稀土元素(REE)组成来区分，它们具有发育良好的中稀土元素(MREE)富集度，其特征是稀土元素的页岩归一化比值逐渐向REE系列的中间(La-Lu)靠拢。此外，亚马逊河、苍蝇河和赛皮克河(以及其他河流、湖泊和地下水)水域中溶解物质的稀土元素组成具有良好的MREE丰度。利用亚马逊河岸沉积物进行了一系列淋溶实验，研究了MREE富集物的开发。塞皮克河和密西西比河。为了更好地评估磷酸盐矿物风化与富含MREE溶液的形成之间的关系，还对富含MREE的特征良好的页岩进行了淋滤，其主体成分中含有明显的MREE。每个沉积物的两个淋洗液由pH为5的过滤湖水和相同的调至pH 2的湖水组成。通过对四条河流沉积物的淋洗实验，发现溶液中的REE成分发生了广泛的分馏，从初始沉积物中产生了MREE富集物，而初始沉积物没有显示MREE富集物。与pH为5的渗滤液相比，pH为2的渗滤液具有更高的REE浓度和更充分的MREE富集度。在pH值为2的情况下，MREE通常在实验开始后一小时内形成富集物。磷酸盐页岩的研究结果表明，在pH值为5时和在pH值为2时，均有大量MREE优先释放，表明磷酸盐矿物在天然淡水PHS中具有良好的耐候性。Sepik River pH 5实验还表明，在近中性条件下，MREE显著富集。在浸出液中MREE富集物的形成和保留伴随着溶解磷酸盐浓度的增加。虽然MREE的富集量与释放的磷酸盐百分比没有直接关系，但实验数据表明，风化过程中磷酸盐矿物的优先溶解可以导致大量河流沉积物与水之间的REE分馏，从而导致淡水中MREE的富集性。(C)2001 Elsevier Science B.V.保留所有权利。
Many phosphatic minerals of biogenic, authigenic and diagenetic origin are distinguished by rare-earth element (REE) compositions, which have a well-developed middle rare-earth element (MREE) enrichment defined by a gradual increase in the shale-normalized ratios of REE toward the middle of the REE series (La to Lu). Also, the REE composition of dissolved matter in the waters of the Amazon, Fly and Sepik Rivers las well as other river, lake and ground waters) have well-developed MREE enrichments. The development of MREE enrichments was studied through a series of leaching experiments using river-bank sediments from the Amazon, Fly. Sepik and Mississippi Rivers. A well-characterized phosphate mineral-rich shale with a pronounced MREE enrichment in its bulk composition was also leached in order to better assess the relationship between the weathering of phosphate minerals and the formation of MREE-enriched solutions. The two leaching solutions per sediment consisted of filtered lake water at pH 5 and the same water adjusted to pH 2.Leaching experiments with the four river sediments result in extensive fractionation whereby the REE compositions of the solutions develop MREE enrichments from starting sediments that show no MREE enrichments. The pH 2 leachates have much higher concentrations of the REE and more fully developed MREE enrichments than do the pH 5 leachates. The MREE enrichments at pH 2 usually form within an hour of starting the experiments. The phosphatic shale results show that there is preferential release of large amounts of MREE at pH 5, as well as at pH 2, demonstrating the weather ability of the phosphatic minerals at pHs of natural freshwaters. The Sepik River pH 5 experiment also shows significant MREE enrichment under near-neutral conditions.The development and retention of the MREE enrichments in the leaching solutions is accompanied by an increase in dissolved phosphate concentrations. Although the magnitudes of the MREE enrichment do not directly correlate with the percent of phosphate released, the experimental data suggest that the preferential dissolution of phosphatic minerals during weathering can result in extensive REE fractionation between bulk river sediment and water, leading to freshwaters with MREE enrichments. (C) 2001 Elsevier Science B.V. All rights reserved.