Lanthanum-Modified Activated Alumina for Selective Removal of Fluoride from Phosphogypsum Leachate

Abstract

Fluoride-rich phosphogypsum leachate is a challenging industrial wastewater because of its low pH, high ionic strength, and the presence of competing anions. In this study, lanthanum-modified activated alumina (La-AA) was prepared and evaluated as a selective adsorbent for the removal of fluoride from complex phosphate-industry wastewater. The results showed that La modification improved the adsorption performance of activated alumina, and the 10% La-AA sample exhibited the best fluoride removal behavior among the tested materials. Kinetic and thermodynamic analyses indicated that fluoride adsorption on La-AA was more favorable than on pristine activated alumina and proceeded spontaneously and endothermically under the tested conditions. In competitive adsorption tests, La-AA maintained better fluoride uptake than unmodified activated alumina in the presence of chloride, sulfate, and phosphate, demonstrating improved matrix tolerance. When applied to authentic phosphogypsum leachate, the optimized La-AA reduced fluoride concentration from 9.67 mgꞏL⁻¹ to 0.58 mgꞏL⁻¹, below the WHO guideline value. These results suggest that La modification is a practical strategy to improve the selectivity and applicability of activated alumina for fluoride removal in complex industrial process water.

Keywords

Activated alumina / Lanthanum modification / Selective removal / Fluoride adsorption / Phosphogypsum leachate

References

[1] Srivastava S, Flora SJS. Fluoride in Drinking Water and Skeletal Fluorosis: A Review of the Global Impact. Curr. Environ. Health Rep. 2020, 7, 140-146. DOI:10.1007/s40572-020-00270-9

[2] Ghosh A, Mukherjee K, Ghosh SK, Saha B. Sources and Toxicity of Fluoride in the Environment. Res. Chem. Intermed. 2013, 39, 2881-2915. DOI:10.1007/s11164-012-0841-1

[3] Jha SK, Mishra VK, Sharma DK, Damodaran T. Fluoride in the Environment and Its Metabolism in Humans. In Reviews of Environmental Contamination and Toxicology ; Whitacre DM, Ed.; Springer: New York, NY, USA, 2011; Volume 211, pp. 121-142.

[4] He Y, Huang L, Song B, Wu B, Yan L, Deng H, et al. Defluorination by Ion Exchange of SO₄²⁻ on Alumina Surface: Adsorption Mechanism and Kinetics. Chemosphere 2021, 273, 129678. DOI:10.1016/j.chemosphere.2021.129678

[5] You K, Li P, Fu J, Kang N, Gao Y, Cheng X, et al. Fabrication of Manganese-Supported Activated Alumina Adsorbent for Defluoridation of Water: A Kinetics and Thermodynamics Study. Water 2021, 13, 1219. DOI:10.3390/w13091219

[6] Kumari U, Behera SK, Meikap BC. Defluoridation of Synthetic and Industrial Wastewater by Using Acidic Activated Alumina Adsorbent: Characterization and Optimization by Response Surface Methodology. J. Environ. Sci. Health Part A 2019, 54, 79-88. DOI:10.1080/10934529.2018.1521674

[7] Ekamparam ASS, Khaitan H, Nimesh V, Singh A. Relative Extents, Mechanisms, and Kinetics of Fluoride Removal from Synthetic Groundwater by Prevalent Sorbents. Chemosphere 2023, 342, 140161. DOI:10.1016/j.chemosphere.2023.140161

[8] Hiemstra T, Riemsdijk WHV. A Surface Structural Approach to Ion Adsorption: The Charge Distribution (CD) Model. J. Colloid Interface Sci. 1996, 179, 488-508. DOI:10.1006/jcis.1996.0242

[9] Yu C, Liu L, Wang X, Fu J, Wu Y, Feng C, et al. Fluoride Removal Performance of Highly Porous Activated Alumina. J. Sol-Gel Sci. Technol. 2023, 106, 471-479. DOI:10.1007/s10971-022-05722-2

[10] Lin JY, Chen YL, Hong XY, Huang C, Huang CP. The Role of Fluoroaluminate Complexes on The Adsorption of Fluoride onto Hydrous Alumina in Aqueous Solutions. J. Colloid Interface Sci. 2020, 561, 275-286. DOI:10.1016/j.jcis.2019.10.085

[11] Gai WZ, Zhang SH, Yang Y, Sun K, Jia H, Deng ZY. Defluoridation Performance Comparison of Aluminum Hydroxides with Different Crystalline Phases. Water Supply 2022, 22, 3673-3684. DOI:10.2166/ws.2022.012

[12] Xiao J, Sun W, Song Y, Li Q, Wu M, Yang Y. Removal of Fluoride Ions from Zinc Sulfate Solution by Mesoporous Alumina: Performance and Mechanism. Hydrometallurgy 2025, 234, 106471. DOI:10.1016/j.hydromet.2025.106471

[13] Gao S, Cui J, Wei Z. Study on The Fluoride Adsorption of Various Apatite Materials in Aqueous Solution. J. Fluor. Chem. 2009, 130, 1035-1041. DOI:10.1016/j.jfluchem.2009.09.004

[14] Ku Y, Chiou HM. The Adsorption of Fluoride Ion from Aqueous Solution by Activated Alumina. Water Air Soil Pollut. 2002, 133, 349-361. DOI:10.1023/A:1012929900113

[15] Dolganov AV, Balandina AV, Chugunov DB, Timonina AS, Knyazev AV. Sorption of Fluoride Ions onto Cellulose and Aluminum Oxide Composites. Russ. J. Inorg. Chem. 2020, 65, 1770-1775. DOI:10.1134/s0036023620110030

[16] Badillo-Almaraz VE, Solache-Ríos MJ, Badillo-Almaraz V, Zarate-Morales A, Flores-Moreno A. Radiotracer Techniques (¹⁸F) and Modeling of Fluoride Sorption on Alumina. J. Fluor. Chem. 2017, 199, 113-118. DOI:10.1016/j.jfluchem.2017.04.001

[17] Kundu S, Chowdhury IH, Sinha PK, Naskar MK. Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride Ions Removal from Water. J. Chem. Eng. Data 2017, 62, 2067-2074. DOI:10.1021/acs.jced.7b00129

[18] Singh PK, Saharan VK, George S. Studies on Performance Characteristics of Calcium and Magnesium Amended Alumina for Defluoridation of Drinking Water. J. Environ. Chem. Eng. 2018, 6, 1364-1377. DOI:10.1016/j.jece.2018.01.053

[19] Kumari U, Siddiqi H, Bal M, Meikap BC. Calcium and Zirconium Modified Acid Activated Alumina for Adsorptive Removal of Fluoride: Performance Evaluation, Kinetics, Isotherm, Characterization and Industrial Wastewater Treatment. Adv. Powder Technol. 2020, 31, 2045-2060. DOI:10.1016/j.apt.2020.02.035

[20] Sanini B, Leichtweis J, Silvestri S, Welter N, Emiliano C, Mancuso MA, et al. Impregnation of Activated Alumina with CeO₂ for Water Defluoridation. Mater. Chem. Phys. 2022, 291, 126648. DOI:10.1016/j.matchemphys.2022.126648

[21] Duan Y, Wang C, Li X, Xu W. Fluoride Adsorption Properties of Three Modified Forms of Activated Alumina in Drinking Water. J. Water Health 2014, 12, 715-721. DOI:10.2166/wh.2014.016

[22] Luo Z, Zhang J, Liu Z, Tang K, Zhang D, Hou Y, et al. Performance and Mechanism of Manganese-modified Activated Alumina for Cost-Effective Removal of Fluorine from Water. Mater. Today Commun. 2025, 48, 113555. DOI:10.1016/j.mtcomm.2025.113555

[23] Saraiva ÍCG, Ezaki S, Calabria GD, Shinzato MC. Groundwater Defluoridation Efficacy of Manganese-Oxide-Coated Alumina Prepared via Two-Step Heating. Environ. Technol. 2022, 43, 2684-2696. DOI:10.1080/09593330.2021.1894242

[24] Zhu X, Wen B, Fan C, Zhang L. The Discovering of Rapid Formation La(OH)₃ from LaH₃ . Green Chem. Technol. 2024, 1, 10005. DOI: 10.70322/gct.2024.10005

[25] Zhang Y, Lin X, Zhou Q, Luo X. Fluoride Adsorption from Aqueous Solution by Magnetic Core-Shell Fe₃O₄@Alginate-La Particles Fabricated via Electro-Coextrusion. Appl. Surf. Sci. 2016, 389, 34-45. DOI:10.1016/j.apsusc.2016.07.087

[26] He Y, Zhang L, An X, Wan G, Zhu W, Luo Y. Enhanced Fluoride Removal from Water by Rare Earth (La and Ce) Modified Alumina: Adsorption Isotherms, Kinetics, Thermodynamics and Mechanism. Sci. Total Environ. 2019, 688, 184-198. DOI:10.1016/j.scitotenv.2019.06.175

[27] Jiang S, Wang Z, Qin Y, Cao B, Chi R. Eco-Friendly Synthesis of Spherical Lanthanum-Doped Hydroxyapatite from Phosphogypsum Waste: A High-Efficiency Strategy for Fluoride Removal in Aqueous Solutions. Green Chem. Technol. 2026, 3, 10008. DOI: 10.70322/gct.2026.10008

[28] Zhao M, Zhou X, Li J, Li F, Li X, Yu J, et al. Efficient Removal of Phosphate and Fluoride from Phosphogypsum Leachate by Lanthanum-Modified Zeolite: Synchronous Adsorption Behavior and Mechanism. J. Environ. Chem. Eng. 2024, 12, 113294. DOI:10.1016/j.jece.2024.113294

[29] Dhawane SH, Khan AA, Singh K, Tripathi A, Hasda R, Halder G. Insight into Optimization, Isotherm, Kinetics, and Thermodynamics of Fluoride Adsorption onto Activated Alumina. Environ. Prog. Sustain. Energy 2017, 37, 766-776. DOI:10.1002/ep.12814

[30] Sing K. The Use of Nitrogen Adsorption for The Characterisation of Porous Materials. Colloid Surface A 2001, 187-188, 3-9. DOI:10.1016/S0927-7757(01)00612-4

[31] Kang D, Yu X, Ge M, Lin M, Yang X, Jing Y. Insights into adsorption mechanism for fluoride on cactus-like amorphous alumina oxide microspheres. Chem. Eng. J. 2018, 345, 252-259. DOI:10.1016/j.cej.2018.03.174

[32] Yu X, Kang D, Hu Y, Tong S, Ge M, Cao C, et al. One-pot synthesis of porous magnetic cellulose beads for the removal of metal ions. RSC Adv. 2014, 4, 31362. DOI:10.1039/c4ra05601a

[33] Ekka B, Dhaka RS, Patel RK, Dash P. Fluoride removal in waters using ionic liquid-functionalized alumina as a novel adsorbent. J. Clean. Prod. 2017, 151, 303-318. DOI:10.1016/j.jclepro.2017.03.061

[34] Sun X, Ke C, Lu Q, Liang L, Xie G. Adsorption of fluoride ion on Al/La modified acidified attapulgite composite materials. Sep. Purif. Technol. 2025, 354, 128791. DOI:10.1016/j.seppur.2024.128791

[35] Xiang B, Tang J, Feng X, Zhu Y, Li Y, Tan T. Preparation of Aluminium-Hydroxide-Modified Diatomite and Its Fluoride Adsorption Mechanism. Sci. Rep. 2023, 13, 3871. DOI:10.1038/s41598-023-30901-8

[36] Chinnakoti P, Chunduri ALA, Vankayala RK, Patnaik S, Kamisetti V. Enhanced Fluoride Adsorption by Nano Crystalline γ-Alumina: Adsorption Kinetics, Isotherm Modeling and Thermodynamic Studies. Appl. Water Sci. 2017, 7, 2413-2423. DOI:10.1007/s13201-016-0490-9

[37] Lima ÉC, Adebayo MA, Machado FM. Kinetic and Equilibrium Models of Adsorption. In Carbon Nanomaterials as Adsorbents for Environmental and Biological Applications ; Bergmann CP, Machado FM, Eds.; Springer: Cham, Switzerland, 2015; pp. 33-69.

[38] Tao W, Zhong H, Pan X, Wang P, Wang H, Huang L. Removal of Fluoride from Wastewater Solution Using Ce-AlOOH with Oxalic Acid as Modification. J. Hazard. Mater. 2020, 384, 121373. DOI:10.1016/j.jhazmat.2019.121373

[39] Xiong WL, Zhang J, Yu JX, Chi RA. Competitive Adsorption Behavior and Mechanism for Pb²⁺ Selective Removal from Aqueous Solution on Phosphoric Acid Modified Sugarcane Bagasse Fixed-Bed Column. Process Saf. Environ. 2019, 124, 75-83. DOI:10.1016/j.psep.2019.02.001