{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,14]],"date-time":"2026-10-14T13:32:06Z","timestamp":1791984726908,"version":"4.4.0"},"reference-count":34,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T00:00:00Z","timestamp":1776902400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>The presence of impurities directly affects the properties of \u03b1-hemihydrate gypsum (\u03b1-HH) prepared from phosphogypsum (PG) as a raw material. However, the effect of soluble fluorine impurities on the properties of \u03b1-HH by autoclaving remains insufficiently understood. This study investigated the influence of sodium fluoride on the morphology, hydration, and hardening properties of \u03b1-HH, using XRD, XPS, SEM, MIP, and tests of setting time, evolution of hydration temperature increase, and strength. The results showed that during the preparation of \u03b1-HH, some F\u2212 reacted with Ca2+ to form CaF2, which adhered to the surface of the \u03b1-HH crystal, hindering the growth and development of the crystal and resulting in small crystals with rough surfaces. When \u03b1-HH hydrated, sodium fluoride caused the early, rapid nucleation of dihydrate gypsum (DH) crystals, accelerating the crystallization process of DH. The introduction of sodium fluoride inhibited the early hydration of \u03b1-HH and promoted its later hydration. The increase in sodium fluoride content caused the initial setting time of \u03b1-HH hydration to first increase and then decrease, while the final setting time continued to decrease. In the absence of sodium fluoride, the average pore diameter of the hardened paste was approximately 617.99 nm. When the NaF content was 0.2%, the DH crystals were prismatic and densely packed, which resulted in a decrease in the average pore diameter to 449.35 nm. When the NaF content was 0.6%, the DH crystals exhibited a plate-like morphology and were loosely interlocked, leading to an increase in the average pore diameter to 1169.58 nm. Based on these results, the sodium fluoride content in PG should be controlled below 0.2%.<\/jats:p>","DOI":"10.3390\/ma19091706","type":"journal-article","created":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T12:04:42Z","timestamp":1776945882000},"page":"1706","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Effect of Sodium Fluoride on the Properties of \u03b1-Hemihydrate Gypsum from Phosphogypsum"],"prefix":"10.3390","volume":"19","author":[{"given":"Wanqing","family":"Zhou","sequence":"first","affiliation":[{"name":"Hubei Key Laboratory of Disaster Prevention and Mitigation, Yichang 443002, China"},{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jiayi","family":"Huang","sequence":"additional","affiliation":[{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rui","family":"Zou","sequence":"additional","affiliation":[{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dongmei","family":"Liu","sequence":"additional","affiliation":[{"name":"Hubei Key Laboratory of Disaster Prevention and Mitigation, Yichang 443002, China"},{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jian","family":"Yang","sequence":"additional","affiliation":[{"name":"Hubei Key Laboratory of Disaster Prevention and Mitigation, Yichang 443002, China"},{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"},{"name":"Hubei Engineering Research Center for Disaster Prevention and Mitigation (China Three Gorges University), Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi","family":"Qin","sequence":"additional","affiliation":[{"name":"College of Civil Engineering & Architecture, Guangxi Eco-Engineering Vocational and Technical College, Liuzhou 545004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yanzhou","family":"Peng","sequence":"additional","affiliation":[{"name":"Hubei Key Laboratory of Disaster Prevention and Mitigation, Yichang 443002, China"},{"name":"College of Civil Engineering & Architecture, China Three Gorges University, Yichang 443002, China"},{"name":"Hubei Engineering Research Center for Disaster Prevention and Mitigation (China Three Gorges University), Yichang 443002, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"106172","DOI":"10.1016\/j.cemconres.2020.106172","article-title":"Durability of phosphogypsum-based supersulfated cement mortar against external attack by sodium and magnesium sulfate","volume":"136","author":"Pinto","year":"2020","journal-title":"Cem. Concr. Res."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1016\/j.conbuildmat.2018.02.022","article-title":"Low cost and high efficiency utilization of hemihydrate phosphogypsum: Used as binder to prepare filling material","volume":"167","author":"Jiang","year":"2018","journal-title":"Constr. Build. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"129244","DOI":"10.1016\/j.seppur.2024.129244","article-title":"Research Advances in Phosphogypsum Flotation Purification: Current Status and Prospects","volume":"354","author":"Jia","year":"2025","journal-title":"Sep. Purif. Technol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"418","DOI":"10.1016\/j.jclepro.2018.03.131","article-title":"Recycling phosphogypsum and construction demolition waste for cemented paste backfill and its environmental impact","volume":"186","author":"Chen","year":"2018","journal-title":"J. Clean. Prod."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"142032","DOI":"10.1016\/j.conbuildmat.2025.142032","article-title":"Insight into Mechanical Properties and Damaging Evolution of Base Materials Incorporating 80% Phosphogypsum for Pavement Application","volume":"488","author":"Wang","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"116777","DOI":"10.1016\/j.conbuildmat.2019.116777","article-title":"Compressive strength and hydration process of ground granulated blast furnace slag-waste gypsum system managed by wet grinding","volume":"228","author":"Zhang","year":"2019","journal-title":"Constr. Build. Mater."},{"key":"ref_7","first-page":"1","article-title":"Current situation of comprehensive utilization of phosphogypsum and its development trend of 14th Five-Year Plan","volume":"54","author":"Cui","year":"2022","journal-title":"Inorg. Chem. Ind."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Chernysh, Y., Yakhnenko, O., Chubur, V., and Roub\u00edk, H. (2021). Phosphogypsum recycling: A review of environmental issues, current trends, and prospects. Appl. Sci., 11.","DOI":"10.3390\/app11041575"},{"key":"ref_9","first-page":"1212649","article-title":"Effect of soluble P2O5 form on the hydration and hardening of hemihydrate phosphogypsum","volume":"2022","author":"Zhang","year":"2022","journal-title":"Adv. Mater. Sci. Eng."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1016\/j.fuel.2016.01.073","article-title":"Preparation of alpha-calcium sulfate hemihydrate from FGD gypsum in chloride-free Ca(NO3)2 solution under mild conditions","volume":"174","author":"Jiang","year":"2016","journal-title":"Fuel"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"95","DOI":"10.1038\/s41598-021-04122-w","article-title":"The study on the effect of flotation purification on the performance of \u03b1-hemihydrate gypsum prepared from phosphogypsum","volume":"12","author":"Du","year":"2022","journal-title":"Sci. Rep."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"130114","DOI":"10.1016\/j.conbuildmat.2022.130114","article-title":"Effect of modifiers on crystalizing habit and mechanical strength of \u03b1-hemihydrate gypsum prepared from PG by an autoclaved method","volume":"366","author":"Liu","year":"2023","journal-title":"Constr. Build. Mater."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2631","DOI":"10.1039\/C9CE00140A","article-title":"Effects of phosphorus impurities on the preparation of \u03b1-calcium sulfate hemihydrate from waste phosphogypsum with the salt solution method under atmospheric pressure","volume":"21","author":"Mi","year":"2019","journal-title":"CrystEngComm"},{"key":"ref_14","first-page":"e04170","article-title":"Effect of modified phosphogypsum on the dimensional stability of supersulfated cement-based materials","volume":"22","author":"Jin","year":"2025","journal-title":"Case Stud. Constr. Mater."},{"key":"ref_15","first-page":"1983","article-title":"Effect of soluble phosphorus on high-strength \u03b1-hemihydrate gypsum prepared by atmospheric hydrothermal method","volume":"66","author":"Ru","year":"2015","journal-title":"CIESC J."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"126021","DOI":"10.1016\/j.conbuildmat.2021.126021","article-title":"Preparation of anhydrite from phosphogypsum: Influence of phosphorus and fluorine impurities on the performances","volume":"318","author":"Cao","year":"2022","journal-title":"Constr. Build. Mater."},{"key":"ref_17","first-page":"137","article-title":"Study on influence of phosphorus and fluorine impurities on properties of building-purpose gypsum","volume":"44","author":"Song","year":"2024","journal-title":"Mode. Chem. Ind"},{"key":"ref_18","first-page":"1076","article-title":"Study on the effect of different forms of water-soluble fluoride on performance of gypsum","volume":"31","author":"Zhang","year":"2012","journal-title":"Bull. Chin. Silic. Soc"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"113106","DOI":"10.1016\/j.mtcomm.2025.113106","article-title":"Effect of Different Retarding Agents on the Hydration-Crystallization Process of \u03b2-Hemihydrate Gypsum","volume":"47","author":"Ding","year":"2025","journal-title":"Mater. Today Commun."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"62815","DOI":"10.1007\/s11356-023-26484-6","article-title":"Effect of phosphate rock acid insoluble residue on hydration process and mechanical properties of \u03b1-hemihydrate gypsum","volume":"30","author":"Wang","year":"2023","journal-title":"Environ. Sci. Pollut. Res."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"2304","DOI":"10.1007\/s10163-024-01972-0","article-title":"Effect of sodium fluoride on the crystal regulation of high-strength \u03b1-hemihydrate gypsum from calcium sulphate dihydrate and phosphogypsum","volume":"26","author":"Ru","year":"2024","journal-title":"J. Mater. Cycles Waste Manag."},{"key":"ref_22","unstructured":"(2018). phosphogypsum (Standard No. GB\/T 23456:2018)."},{"key":"ref_23","unstructured":"(2010). \u03b1 Type High-Strength Gypsum (Standard No. JC\/T 2038:2010)."},{"key":"ref_24","unstructured":"(1999). Gypum Plasters-Determination of Physical Properties of Pure Paste (Standard No. GB\/T 17669.4:1999)."},{"key":"ref_25","unstructured":"(1999). Gypum Plasters-Determination of Water of Crystalline Content (Standard No. GB\/T 17669.2:1999)."},{"key":"ref_26","unstructured":"(1999). Gypum Plasters-Determination of Mechanical Properties (Standard No. GB\/T 17669.3:1999)."},{"key":"ref_27","unstructured":"Shui, Z. (2019). Cementitious Material Science, Wuhan University of Technology Press. [2nd ed.]."},{"key":"ref_28","unstructured":"Li, Y. (2023). Preparation of \u03b1-Type High-Strength Gypsum by Autoclaved Microcrystalline Method of Industrial By-Product Gypsum and Its Mechanism. [Ph.D. Thesis, University of Science and Technology Beijing]."},{"key":"ref_29","first-page":"3248","article-title":"Effect of fluoride on the structure and properties of gypsum-based cementitious materials","volume":"42","author":"Guo","year":"2023","journal-title":"Bull. Chin. Silic. Soc"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"104725","DOI":"10.1016\/j.jobe.2022.104725","article-title":"Role of NaF on the performances of \u03b2-hemihydrate gypsum plaster","volume":"55","author":"Jia","year":"2022","journal-title":"J. Build. Eng."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"704","DOI":"10.1016\/S0022-0248(98)01206-8","article-title":"Crystallization of gypsum from hemihydrate in presence of additives","volume":"198","author":"Badens","year":"1999","journal-title":"J. Cryst. Growth"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"179","DOI":"10.1016\/j.cemconres.2009.10.008","article-title":"Changes in C3S hydration in the presence of cellulose ethers","volume":"40","author":"Pourchez","year":"2010","journal-title":"Cem. Concr. Res."},{"key":"ref_33","first-page":"1504","article-title":"A review of impurity types and impurity removal methods in phosphogypsum","volume":"35","author":"Huang","year":"2016","journal-title":"Bull. Chin. Silic. Soc"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"17141","DOI":"10.1021\/jacs.8b09907","article-title":"Interaction of water with the gypsum (010) surface: Structure and dynamics from nonlinear vibrational spectroscopy and ab initio molecular dynamics","volume":"140","author":"Santos","year":"2018","journal-title":"J. Am. Chem. Soc."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/9\/1706\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T12:09:55Z","timestamp":1776946195000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/9\/1706"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,23]]},"references-count":34,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,5]]}},"alternative-id":["ma19091706"],"URL":"https:\/\/doi.org\/10.3390\/ma19091706","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,23]]}}}