Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction
Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction
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中国西南部四川泸州发电厂煤灰中的稀土元素和钇：浓缩、表征和优化提取
DOI：
10.1016/j.coal.2019.01.001
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发表时间：
2019-02
影响因子：
5.6
通讯作者：
Graham Ian T
中科院分区：
文献类型：
--
作者：
Wang Zhen;Dai Shifeng;Zou Jianhua;Frenc David;Graham Ian T
粉煤灰被认为是回收稀土和钇（REE + Y或REY）的有前途的替代资源。对四川泸州燃煤电厂的煤灰（飞灰和底灰）及相应的原料煤进行了化学和矿物学分析。进一步测试了粉煤灰提取稀土元素的可行性。原料煤的特征为低挥发性烟煤、中硫和高灰分煤，来源于中国西南部四川古墟煤田（晚二叠世龙潭组）。稀土元素、钇、高场强元素Zr（Hf）、Nb（Ta）、Li、F、Sc、V、Cr、Co、Cu、Zn、Ga、Ge、Se、Sr、Cd、In、Sn、Hg、Th、U等均在原料煤中富集。原料煤的矿物组成以高岭石和伊利石/蒙皂石（I/S）混合层为主，其次是碳酸盐矿物，包括方解石、菱铁矿、铁白云石和少量的方解石和黄钾铁矾。底灰在成分上类似于飞灰，除了它更富含高密度元素（Fe和Mn），并且更缺乏挥发性元素。REY在飞灰和底灰中都富集，尽管重REY（HREY）在飞灰中明显更富集。矿物学分析表明，粉煤灰由>70%的非晶玻璃和<30%的莫来石、石英和氧化铁等矿物相组成。底灰由~60%的无定形玻璃组成，但具有比飞灰更复杂的矿物组成。用4%的氢氟酸（HF）溶解飞灰和底灰表明，约90%的所有REY与飞灰中的无定形玻璃相关联，而底灰中小于50%的REY包含在玻璃组分中。采用碱-酸-盐酸（NaOH-HCl）顺序浸出法对泸州粉煤灰中稀土Y的浸出性能进行了研究。采用正交试验设计对萃取剂浓度、液固比、浸出温度和浸出时间进行了优化。在最佳碱浸条件下，粉煤灰中活性二氧化硅的去除率为41.10%，稀土Y的富集率为39.43%。在最佳条件下，脱硅粉煤灰的盐酸浸出率达到88.15%，与相同浸出率的原料粉煤灰相比，有了显著的提高。尽管不同来源的煤灰的提取效率可能不同，但建议将来使用一个完整的从粉煤灰中提取REY的程序。
Coal ash is considered as a promising alternative resource for rare earth elements and yttrium (REE + Y or REY) recovery. Coal ash samples (fly ash and bottom ash), as well as corresponding feed coals, collected from the Luzhou coal-fired power plant in Sichuan, southwestern China were analyzed for their chemical and mineralogical characteristics. The fly ash was further tested for its feasibility of REE extraction. The feed coals are characterized as a low-volatile bituminous, medium‑sulfur, and high-ash coal, sourced from the Guxu coalfield (Late Permian Longtan Formation) in Sichuan, SW China. REE and Y, along with high-field-strength elements Zr(Hf) and Nb(Ta), and Li, F, Sc, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Sr, Cd, In, Sn, Hg, Th, U, are all enriched in the feed coal. The mineralogical compositions of the feed coals are dominated by kaolinite and illite/smectite (I/S) mixed layers, followed by the carbonate minerals including calcite, siderite, ankerite, and minor amounts of anatase and jarosite.The combustion of the feed coals produces a Class F fly ash, characterized by an aluminosilicate composition with a low CaO content. The bottom ash is compositionally similar to the fly ash, except that it is more enriched in high-density elements (Fe and Mn), and more depleted in volatile elements. REY are enriched in both the fly ash and bottom ash, although heavy REY (HREY) are notably more enriched in the fly ash. Mineralogical analysis shows that the fly ash consists of >70% amorphous glass and <30% mineral phases such as mullite, quartz and iron oxides. The bottom ash is composed of ~60% amorphous glass but with a more complex mineralogical composition than the fly ash. Dissolution of the fly ash and bottom ash with 4% hydrofluoric acid (HF) showed that ~90% of all the REY are associated with the amorphous glass in the fly ash, whereas <50% of REY in the bottom ash is contained in the glassy component. An alkaline-acid-combined (NaOH-HCl) sequential leaching process was employed to test the extractability of REY in the Luzhou fly ash. The experimental variables, including extractant concentration, liquid-to-solid ratio, leaching temperature and leaching time, were optimized by an orthogonal array design. The optimal NaOH leaching conditions results in 41.10% of active silica removal from the fly ash and 39.43% of REY enrichment. The HCl leaching of desilicated fly ash achieves 88.15% of REY extraction efficiency under the optimal conditions, which is a dramatic increase as compared to the same leaching of raw fly ash. Even though the extraction efficiency may vary between different coal ashes from various sources, a complete REY extraction procedure from fly ash is suggested for future use.
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