Process Development for Rare Earth Elements Recovery and Struvite Production from Biocrudes

IF 2.5 3区 材料科学 Q3 GREEN & SUSTAINABLE SCIENCE & TECHNOLOGY
Shiyu Li, Wencai Zhang
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Abstract

Phytomining emerges as an innovative technique for extracting rare earth elements (REEs) from soil by employing hyperaccumulators. REE hyperaccumulators were treated using microwave-assisted hydrothermal carbonization (MHTC) in acid-mediated systems to efficiently transfer REEs and other elements into biocrudes and produce high purity and value-added hydrochar. However, the subsequent treatment of biocrudes to recover valuable elements still presents a significant challenge. In this study, a process that combines solvent extraction and struvite precipitation was first developed to address this challenge. In the extraction step, 95.6% of REEs were extracted using 0.05 mol/L di(2-ethylhexyl)phosphoric acid (D2EHPA) with an aqueous to organic (A/O) ratio of 1:1 at pH 3.0. However, 75.1% of Al, 81.2% of Ca, 54.5% of Fe, 61.5% of Mn, and 81.3% of Zn were co-extracted into the organic phase with the REEs. To solve this issue, a subsequent scrubbing step using deionized water was applied, with the removal of over 98% of these impurities, while incurring negligible loss of REEs. After the scrubbing step, over 97% of REEs were ultimately stripped out from the organic phase as REE oxalates using 0.01 mol/L oxalic acid as the stripping agent. Furthermore, phosphorous (P) was found to be retained in the raffinate after the solvent extraction process. 94.4% of the P was recovered by forming struvite precipitate at pH 9.0 and a Mg/P molar ratio of 1.5. In general, high purity and value-added REE products and struvite precipitate were eventually achieved from biocrudes in environmentally friendly and economically viable ways.

Graphical Abstract

Abstract Image

从生物原油中回收稀土元素和生产白云石的工艺开发
植物采矿是通过利用超积累器从土壤中提取稀土元素(REEs)的一种创新技术。在酸介导系统中使用微波辅助水热碳化(MHTC)处理稀土超积累器,可有效地将稀土元素和其他元素转移到生物泥中,并产生高纯度和高附加值的水碳。然而,如何对生物原油进行后续处理以回收有价值的元素仍是一项重大挑战。本研究首先开发了一种结合溶剂萃取和硬石膏沉淀的工艺来应对这一挑战。在萃取步骤中,使用 0.05 摩尔/升二(2-乙基己基)磷酸(D2EHPA),在 pH 值为 3.0、水与有机物(A/O)之比为 1:1 的条件下,萃取出了 95.6% 的稀土元素。然而,75.1% 的铝、81.2% 的钙、54.5% 的铁、61.5% 的锰和 81.3% 的锌与稀土元素一起被萃取到有机相中。为了解决这个问题,随后使用去离子水进行了洗涤步骤,这些杂质的去除率超过 98%,而 REEs 的损失几乎可以忽略不计。在洗涤步骤之后,使用 0.01 摩尔/升草酸作为剥离剂,97% 以上的 REE 最终以 REE 草酸盐的形式从有机相中剥离出来。此外,还发现在溶剂萃取过程后,磷(P)被保留在糠酸中。在 pH 值为 9.0、Mg/P 摩尔比为 1.5 的条件下,94.4% 的磷通过形成石英沉淀被回收。总之,最终以环境友好且经济可行的方式从生物萃取液中获得了高纯度、高附加值的稀土元素产品和硬石膏沉淀。
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来源期刊
Journal of Sustainable Metallurgy
Journal of Sustainable Metallurgy Materials Science-Metals and Alloys
CiteScore
4.00
自引率
12.50%
发文量
151
期刊介绍: Journal of Sustainable Metallurgy is dedicated to presenting metallurgical processes and related research aimed at improving the sustainability of metal-producing industries, with a particular emphasis on materials recovery, reuse, and recycling. Its editorial scope encompasses new techniques, as well as optimization of existing processes, including utilization, treatment, and management of metallurgically generated residues. Articles on non-technical barriers and drivers that can affect sustainability will also be considered.
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