Extraction and separation of rare earth elements from hydrothermal metalliferous sediments
Extraction and separation of rare earth elements from hydrothermal metalliferous sediments
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DOI：
10.1016/j.mineng.2017.12.014
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发表时间：
2018-03-15
影响因子：
4.8
通讯作者：
Albarran, Carlos Ponce de Leon
中科院分区：
文献类型：
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作者：
Josso, Pierre;Roberts, Steve;Albarran, Carlos Ponce de Leon
通过简单的浸出和选择性沉淀，可以有效地从塞浦路斯特罗多斯蛇绿岩中的稀土、铁锰金属沉积物中提取稀土元素（REE），而不产生放射性副产物。翁山主要由无定形铁和锰氧化物和少量针铁矿、石英和沸石组成，含有350-500 mg kg（-1）的稀土元素和钇（REY），比许多主要REY源矿石低200倍。为了补偿相对较低的等级，开发了一种具有成本效益的提取工艺，该工艺利用弱浸出剂浓度（0.1-1.5 N）和短反应时间（5分钟至11小时）。即使在20 ℃下，酸溶液也能回收初始样品REY含量的70-85%。相比之下，使用NaCl和硫酸铵的离子溶液的提取被证明是无效的。REY的酸回收率在70 ℃时增加近10%，并且使用不同的酸（HCl，HNO 3，H2SO 4）产生相当的结果。浸出液中的主要杂质包括Ca和Na，即使在最弱的酸浓度（0.1 N）下。然而，两步浸出法大大降低了富REY液中杂质的浓度，尽管REY损失接近20%。通过选择性沉淀REY作为草酸盐来纯化浸出液是非常有效的，尽管pH依赖性。在pH 1和2之间发生最大REY沉淀（96-99%），精确调节pH允许将REY与其他沉淀杂质（Ca）分离。沉淀物的最大纯度在pH 1.1时达到（> 65%）。强和一致的分馏沿着在沉淀实验中观察到的镧系元素已成功地解释使用形态建模软件（PHREEQC）。实验中草酸盐对REY的吸收紧密地遵循REY-草酸盐固体络合物稳定常数的钟形分布（-log β（RE（2）Ox（3）中心点nH（2）O）），复制了在pH < 1.1时观察到的分馏趋势。模拟结果还表明，在等稀土浓度下，草酸盐沉淀破碎稀土的顺序为：中稀土>轻稀土>>重稀土。这种顺序和吸收的可变程度反映了水性REY-草酸盐复合物（log（HOx）β（1）、（Ox）β（1）和（Ox）β（2））与由固体REY-草酸盐稳定性常数分布诱导的自然分馏的相互作用。总的来说，在简单的两步工艺中，组合的浸出工艺和选择性草酸盐沉淀产生从样品到草酸盐沉淀的REY的总富集因子在1400和2400之间，形成混合REY的高纯度最终产物。
Rare earth elements (REE) can be efficiently extracted from umbers, ferromanganese metalliferous sediments of the Troodos ophiolite (Cyprus) by simple leaching and selective precipitation, without accumulation of radioactive by-products. Umbers are dominantly composed of amorphous Fe and Mn oxides with minor goethite, quartz and zeolites, and contain 350-500 mg kg(-1) of rare earth elements and yttrium (REY), 200 times lower than many of the major REY source ores. To compensate for relatively low grades, a cost-effective extraction process was developed that utilises a weak lixiviant concentration (0.1-1.5 N) and short reaction times (5 min to 11 h). Acid solutions recover 70-85% of the initial sample REY content even at 20 degrees C. By contrast, extraction using ionic solutions of NaCl and ammonium sulphate proved ineffective. Acid recoveries of REY increase by nearly 10% at 70 degrees C and the use of different acids (HCl, HNO3, H2SO4) yields comparable results. The main impurities in the leachate include Ca and Na at even the weakest acid concentration (0.1 N). However, two-step leaching method greatly reduces concentrations of impurities in the REY-rich liquor, although with REY losses approaching 20%. Purification of the leach liquor via selective precipitation of REY as an oxalate is highly efficient although pH dependent. With maximum REY precipitation (96-99%) occurring between pH 1 and 2, the precise adjustment of pH allows separation of REY from other precipitating impurities (Ca). The maximum purity of the precipitate is achieved at pH 1.1 (> 65%). Strong and consistent fractionation along the lanthanide series observed during the precipitation experiments has been successfully explained using a speciation modelling software (PHREEQC). The uptake of REY by oxalate in the experiments closely follows the bell-shape distribution of REY-oxalate solid complexes stability constant (-log beta (RE(2)Ox(3)center dot nH(2)O)) replicating the fractionation trends observed at pH < 1.1. In addition, the modelling demonstrates that at equivalent REE concentration in solution, oxalate precipitates fractionate REY in the following order: middle REE > light REE >> heavy REE. This ordering and the variable degrees of uptake reflects the interplay of aqueous REY-oxalate complexes (log (HOx)beta(1), (Ox)beta(1) and (Ox)beta(2)) with the natural fractionation induced by solid REY-oxalate stability constant distribution. Overall, the combined leaching process and selective oxalate precipitation produces a total enrichment factor ranging between 1400 and 2400 for REY from the sample to the oxalate precipitate in a simple two-step process forming a high-purity end-product of mixed REY.