Advances in research on the activation and recovery of strategic and critical valuable metals from coal fly ash

Authors

WANG Yuhao, School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, ChinaFollow
DONG Zhongbing, School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China

Abstract

Background Coal fly ash, a bulk solid waste byproduct from coal-fired power generation, has a global annual output exceeding 0.75 billion tons. Its disordered piling poses severe environmental risks, such as the generation of heavy metal leachate and PM_2.5 emissions. However, coal fly ash is rich in aluminum (Al 100‒200 mg/g), gallium (Ga 10‒300 μg/g), lithium (Li 1 300‒3 700 μg/g), and rare earth elements (REEs 200‒800 μg/g), establishing it as a potential alternative resource of strategic metals. Methods By analyzing the current domestic and international technologies for metal recovery from coal fly ash, this study expatiates on the mechanisms behind the occurrence of various valuable metals in coal fly ash. Specifically, Li occurs in aluminosilicates through isomorphous replacement of Al³⁺ or Si⁴⁺; Ga occurs in aluminosilicates in the form of Ga³⁺ by replacing Al³⁺; germanium (Ge) is dispersed in the glass phase as GeO₂, and REEs are mainly trapped in the aluminosilicate glass phase by the Si-O-Al network structure.Advances This study focuses on advances in the activation, recovery, and separation techniques for strategic and critical valuable metals such as Li, Ga, and REEs. Li is recovered through acid/alkaline leaching, adsorption by adsorbents, and elution, with Li₂CO₃ crystals being obtained. Ga can be recovered through acid leaching, solvent extraction, and back-extraction. REEs can be recovered through acid/alkaline leaching, separation and enrichment, and precipitation and calcination. In combination with experimental data and industrial cases, the study reveals that key factors controlling the techniques’ efficiency include calcination temperature, promoter type, and concentration of acids/alkalis. This helps reduce the dissolution rates of impurities. Prospects This study proposes the development directions of multi-metal synergistic recovery and low-carbon techniques, including (1) establishing the technique of phased pleaching and selective separation of multiple metals, (2) developing activation and selective enhancement based on mixed promoters, (3) replacing high-energy consumption steps with green techniques such as microwave/ultrasonic waves to reduce calcination temperature and energy consumption, and (4) developing waste heat recovery and renewable energy technologies including preheating leaching solution and preparing zeolite molecular sieves using residues. In response to the complexity and secondary pollution associated with the activation and extraction techniques of strategic and critical metals, it is advisable to develop reusable leaching solvents using green, low-carbon techniques and smart material design. This will promote the large-scale application of the technologies for reutilization of coal fly ash.

Keywords

coal fly ash, strategic metal, activation, recovery, green, low-carbon, reutilization, advances

DOI

10.12363/issn.1001-1986.25.04.0240

Recommended Citation

W D. (2025) "Advances in research on the activation and recovery of strategic and critical valuable metals from coal fly ash," Coal Geology & Exploration: Vol. 53: Iss. 8, Article 11.
DOI: 10.12363/issn.1001-1986.25.04.0240
Available at: https://cge.researchcommons.org/journal/vol53/iss8/11

Reference

[1] SAHOO P K，KIM K，POWELL M A，et al. Recovery of metals and other beneficial products from coal fly ash：A sustainable approach for fly ash management[J]. International Journal of Coal Science & Technology，2016，3(3)：267−283.

[2] SU Haifeng，TAN Furong，LIN Jiafu. An integrated approach combines hydrothermal chemical and biological treatment to enhance recycle of rare metals from coal fly ash[J]. Chemical Engineering Journal，2020，395：124640.

[3] 张伟伟，曹素改，顾春雷，等. 低等级粉煤灰活化及在蒸压砖生产中的应用[J]. 砖瓦，2012(8)：9−12.

ZHANG Weiwei，CAO Sugai，GU Chunlei，et al. Poor quality fly ash activation and application in autoclaved brick[J]. Brick–Tile，2012(8)：9−12.

[4] 吴笑笑，郭彦霞，燕可洲，等. Na₂SO₄对粉煤灰活化提取氧化铝的影响[J]. 煤炭科学技术，2018，46(增刊1)：235−238.

WU Xiaoxiao，GUO Yanxia，YAN Kezhou，et al. Effect of Na₂SO₄ on activation of fly ash for alumina extraction[J]. Coal Science and Technology，2018，46(Sup.1)：235−238.

[5] 赵泽森，崔莉，郭彦霞，等. 粉煤灰中战略金属镓的提取与回收研究进展[J]. 化工学报，2021，72(6)：3239−3251.

ZHAO Zesen，CUI Li，GUO Yanxia，et al. Research progress on extraction and recovery of strategic metal gallium from coal fly ash[J]. CIESC Journal，2021，72(6)：3239−3251.

[6] 刘大锐，许立军，李世春，等. 粉煤灰中战略金属锂的回收研究进展[J]. 无机盐工业，2023，55(1)：56−63.

LIU Darui，XU Lijun，LI Shichun，et al. Research progress of recovery of strategic metal lithium from fly ash[J]. Inorganic Chemicals Industry，2023，55(1)：56−63.

[7] STOY L，XU Jiale，KULKARNI Y，et al. Ionic liquid recovery of rare–earth elements from coal fly ash：Process efficiency and sustainability evaluations[J]. ACS Sustainable Chemistry & Engineering，2022，10(36)：11824−11834.

[8] 缪应菊，钱育林，杨兴敏，等. 粉煤灰浸提活性激发实验研究[J]. 煤炭转化，2017，40(4)：69−73.

MIAO Yingju，QIAN Yulin，YANG Xingmin，et al. Experimental study on activation of fly ash extraction activity[J]. Coal Conversion，2017，40(4)：69−73.

[9] 王震，黄珍丽，王培根，等. 电厂粉煤灰活化工艺参数的研究[J]. 应用化工，2016，45(6)：1100−1102.

WANG Zhen，HUANG Zhenli，WANG Peigen，et al. Study on process parameters for activating power plant fly ash[J]. Applied Chemical Industry，2016，45(6)：1100−1102.

[10] ZHAO Zesen，CUI Li，GUO Yanxia，et al. Recovery of gallium from sulfuric acid leach liquor of coal fly ash by stepwise separation using P507 and Cyanex 272[J]. Chemical Engineering Journal，2020，381：122699.

[11] 李婷，辛志峰，徐梦，等. 复合助剂活化粉煤灰对镓酸浸效果的研究[J]. 化学工程，2016，44(7)：55−57.

LI Ting，XIN Zhifeng，XU Meng，et al. Acid leaching of gallium from fly ash activated by compound additive[J]. Chemical Engineering (China)，2016，44(7)：55−57.

[12] LIU Pan，ZHAO Simin，XIE Nan，et al. Green approach for rare earth element (REE) recovery from coal fly ash[J]. Environmental Science & Technology，2023，57(13)：5414−5423.

[13] PAN Jinhe，HASSAS B V，REZAEE M，et al. Recovery of rare earth elements from coal fly ash through sequential chemical roasting，water leaching，and acid leaching processes[J]. Journal of Cleaner Production，2021，284：124725.

[14] FAN Xiaolu，LYU Shaoqing，XIA Jinlan，et al. Extraction of Al and Ce from coal fly ash by biogenic Fe³⁺ and H₂SO₄[J]. Chemical Engineering Journal，2019，370：1407−1424.

[15] AHMARUZZAMAN M. A review on the utilization of fly ash[J]. Progress in Energy and Combustion Science，2010，36(3)：327−363.

[16] 刘汇东，田和明，邹建华. 粉煤灰中稀有金属镓–铌–稀土的联合提取[J]. 科技导报，2015，33(11)：39−43.

LIU Huidong，TIAN Heming，ZOU Jianhua. Combined extraction of rare metals Ga–Nb–REE from the fly ash[J]. Science & Technology Review，2015，33(11)：39−43.

[17] 刘冲，何天松，王渝榕，等. 粉煤灰活化及其胶凝性能研究[J]. 山东化工，2022，51(21)：11−13.

LIU Chong，HE Tiansong，WANG Yurong，et al. Study on activation of fly ash and its cementitious properties[J]. Shandong Chemical Industry，2022，51(21)：11−13.

[18] 屈磊，吴随，王春芳，等. 粉煤灰活化技术研究[J]. 粉煤灰，2014，26(4)：4−5.

QU Lei，WU Sui，WANG Chunfang，et al. Study of activation technology of fly ash[J]. Coal Ash，2014，26(4)：4−5.

[19] ZHAO Zesen，CUI Li，GUO Yanxia，et al. A stepwise separation process for selective recovery of gallium from hydrochloric acid leach liquor of coal fly ash[J]. Separation and Purification Technology，2021，265：118455.

[20] 王苗，郭彦霞，程芳琴. 粉煤灰活化提取铝铁的研究[J]. 科技创新与生产力，2012(1)：91−94.

WANG Miao，GUO Yanxia，CHENG Fangqin. Research on drawing Al and Fe from pulverized fuel ash[J]. Sci–Tech Innovation and Productivity，2012(1)：91−94.

[21] 刘艳玲，任映奇. 循环流化床粉煤灰中金属元素的溶出[J]. 河北大学学报(自然科学版)，2022，42(1)：38−43.

LIU Yanling，REN Yingqi. Dissolution of metal elements in the circulating fluidized bed fly ash[J]. Journal of Hebei University (Natural Science Edition)，2022，42(1)：38−43.

[22] 薄朋慧，吴士豪，王炎，等. 粉煤灰中有价金属元素铝、镓、锂活化浸出提取研究进展[J]. 应用化工，2019，48(8)：1924−1929.

BO Penghui，WU Shihao，WANG Yan，et al. Research progress of activated leaching and extraction of valuable aluminum，gallium and lithium metal elements from fly ash[J]. Applied Chemical Industry，2019，48(8)：1924−1929.

[23] 袁福龙，王淑霞. 粉煤灰的综合利用：金属元素的提取[J]. 化学工程师，1995，9(1)：41−42.

YUAN Fulong，WANG Shuxia. Comprehensive uses of the ash：Extract of the metals[J]. Chemical Engineer，1995，9(1)：41−42.

[24] LI Shenyong，QIN Shenjun，KANG Lianwei，et al. An efficient approach for lithium and aluminum recovery from coal fly ash by pre–desilication and intensified acid leaching processes[J]. Metals，2017，7(7)：272.

[25] MOSTAJERAN M，BONDY J M，REYNIER N，et al. Mining value from waste：Scandium and rare earth elements selective recovery from coal fly ash leach solutions[J]. Minerals Engineering，2021，173：107091.

[26] 王丽萍，李超，李世春. 粉煤灰中稀散金属锗的富集回收技术研究进展[J]. 稀有金属与硬质合金，2022，50(6)：27−32.

WANG Liping，LI Chao，LI Shichun. Research progress of enrichment and recovery technology of scattered metal germanium in coal fly ash[J]. Rare Metals and Cemented Carbides，2022，50(6)：27−32.

[27] REZAEI H，SHAFAEI S Z，ABDOLLAHI H，et al. A sustainable method for germanium，vanadium and lithium extraction from coal fly ash：Sodium salts roasting and organic acids leaching[J]. Fuel，2022，312：122844.

[28] STOY L，DIAZ V，HUANG C H. Preferential recovery of rare–earth elements from coal fly ash using a recyclable ionic liquid[J]. Environmental Science & Technology，2021，55(13)：9209−9220.

[29] RYBAK A，RYBAK A. Characteristics of some selected methods of rare earth elements recovery from coal fly ashes[J]. Metals，2021，11(1)：142.

[30] PAN Jinhe，NIE Tiancheng，HASSAS B V，et al. Recovery of rare earth elements from coal fly ash by integrated physical separation and acid leaching[J]. Chemosphere，2020，248：126112.

[31] MOKOENA B. K，MOKHAHLANE L S，CLARKE S. Effects of acid concentration on the recovery of rare earth elements from coal fly ash[J]. International Journal of Coal Geology，2022，259：104037.