Mineral Processing & Metallurgy Research Center, Resources Utilization Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-Ro, Yuesong-Gu, Daejeon, 34132, Republic of Korea.
Department of Resources Recycling, University of Science and Technology (UST), 217 Gajeong-Ro Yuseong-Gu, Daejeon, 34113, Republic of Korea.
Environ Sci Pollut Res Int. 2024 Nov;31(54):63210-63224. doi: 10.1007/s11356-024-34943-x. Epub 2024 Oct 30.
The effects of alkaline extraction on the behavior of rare earth elements in coal ashes were investigated in the present study. Independent variables are the concentration of extractant and particle size of coal ashes. Sodium hydroxide was used as an extractant, and the molarity of the solvents varied from 1.0 to 7.0 M. The coal ashes used here were fly and bottom ashes. Fly and bottom ashes were classified into four samples by particle size, with each categorized at both 45 and 300 µm. The particle size distribution and crystalline characteristics of coal ashes, leaching, and the contents of rare earth elements in coal ashes after alkaline extraction were investigated, and the effects of independent variables on the content of rare earth elements in coal ashes were discussed. The test results showed that the dissolution of amorphous phase in coal ashes mainly occurred when the molarity was not more than 3 M, while dissolution and precipitation such as geopolymerization and the formation of zeolite occurred simultaneously when the molarity was more than 5 M. The dissolution and formation of precipitates such as geopolymer in the present study affected the variation of the rare earth element contents in the ashes. Besides, the ashes being smaller in size was more favorable for an increase in the rare earth elements in coal ashes.
本研究考察了堿浸提对煤灰中稀土元素行为的影响。自变量是萃取剂浓度和煤灰粒径。选用氢氧化钠作为萃取剂，溶剂的摩尔浓度从 1.0 到 7.0 M 不等。所用煤灰为飞灰和底灰。飞灰和底灰按粒径分为四组，每组在 45 和 300 μm 处均有分类。研究了煤灰的粒径分布和结晶特性、浸出以及堿浸提后煤灰中稀土元素的含量，并讨论了自变量对煤灰中稀土元素含量的影响。试验结果表明，当摩尔浓度不超过 3 M 时，煤灰中无定形相的溶解主要发生，而当摩尔浓度超过 5 M 时，同时发生聚合和沸石形成等溶解和沉淀反应。本研究中聚合和沉淀物的溶解和形成影响了灰中稀土元素含量的变化。此外，较小粒径的煤灰更有利于煤灰中稀土元素的增加。
