Defluoridation by fluorapatite crystallization in a fluidized bed reactor under alkaline groundwater condition

Deng, Linyu; Wang, Ying; Zhang, Xiao; Zhou, Jing

doi:10.1016/j.jclepro.2020.122805

Cited by 20 publications

(6 citation statements)

References 41 publications

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“…The fluoride removal of the n-HAp by ion exchange could be expressed by the following reactions (Equations (10)and(11)) [ 146 ]: Ca 10 (PO 4 ) 6 (OH) 2 + F − →Ca 10 (PO 4 ) 6 FOH + OH − Ca 10 (PO 4 ) 6 (OH) 2 +2F − →Ca 10 (PO 4 ) 6 F 2 + 2OH − …”

Section: Adsorption Of Fluoride Ions From Aqueous Solutionsmentioning

confidence: 99%

Applications of Nano Hydroxyapatite as Adsorbents: A Review

et al. 2022

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Nano hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has aroused widespread attention as a green and environmentally friendly adsorbent due to its outstanding ability in removing heavy metal ions, radio nuclides, organic pollutants and fluoride ions for wastewater treatment. The hexagonal crystal structure of HAp supports the adsorption mechanisms including ionic exchange reaction, surface complexation, the co-precipitation of new partially soluble phases and physical adsorption such as electrostatic interaction and hydrogen bonding. However, nano HAp has some drawbacks such as agglomeration and a significant pressure drop during filtration when used in powder form. Therefore, instead of using nano HAp alone, researchers have worked on modificationsand composites of nano HAp to overcome these issues and enhance the adsorption capacity. The modification of cationic doping and organic molecule grafting for nano HAp can promote the immobilization of ions and then increase adsorption capacity. Developing nano HAp composite with biopolymers such as gelatin, chitosan and chitin has proven to obtain a synergetic effect for improving the adsorption capacity of composites, in which nano HAp fixed and dispersed in polymers can playmuch more of a role for adsorption. This review summarizes the adsorption properties and adsorbent applications of nano HAp as well as the methods to enhance the adsorption capacity of nano HAp.

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Section: Adsorption Of Fluoride Ions From Aqueous Solutionsmentioning

confidence: 99%

Applications of Nano Hydroxyapatite as Adsorbents: A Review

et al. 2022

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“…The XRD characterization of the CaF2 crystals also revealed the absence of calcium carbonate (CaCO3), calcium sulfate (CaSO4) or fluorapatite (Ca5(PO4)3F) in the resulting crystals. These compounds are known to precipitate during fluorine removal through fluidized bed crystallization and even some cases are the main product instead of CaF2 [14,17]. The possibility of any of these compounds' formation in this study is completely eliminated through this XRD analysis which also in turn highlight the high purity of CaF2 formed.…”

Section: Characterization Of Calcium Fluoride Crystalsmentioning

confidence: 67%

Process Intensification for Enhanced Fluoride Removal and Recovery As Calcium Fluoride Using Fluidized Bed Reactor

Sinharoy,

Lee,

Chung

2024

Preprint

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This study explored the feasibility of fluoride removal from simulated semiconductor industry wastewater and its recovery as calcium fluoride using fluidized bed crystallization. The continuous reactor showed best performance (>90% fluoride removal and >95% crystallization efficiency) at a calcium to fluoride ratio of 0.6 within first 40 days of continuous operation. The resulting particle size increased by more than double during this time along with a 36% increase in the seed bed height indicating deposition of CaF2 onto the silica seed. The SEM-EDX analysis showed the size and shape of the crystals formed along with high amount of Ca-F ions presence. The purity of the CaF2 crystals were determined to be 91.1% though ICP-OES analysis. Following the continuous experiment, different process improvement strategies are explored. The addition of excess amount of calcium resulted in an additional 6% fluoride removal, however, compared to this single stage process, a two-stage approach was found to be better strategy to achieve a low effluent fluoride concentration. The fluoride removal reached 94% with this two-stage approach under optimum condition of 4 + 1 h HRT combinations and a [Ca2+]/[F-] ratio of 0.55 and 0.7 for the two reactors, respectively. CFD simulation showed the impact of inlet diameter, bottom-angle shape and width and height ratio of the reactor on mixing inside reactor and possibility of further improvement in reactor performance by optimizing the FBR configuration.

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“…This is because, at higher upflow velocity, the fines formed inside the reactor escape from the reactor, causing an increase in fluoride concentration in the effluent [7]. Also, upflow velocity is inversely proportional to the empty bed residence time, which is the reaction time available for the reactants to adhere to the seed particles [32]. Hence, at an elevated upflow velocity, this contact time reduces significantly enough to hinder effective fluoride removal in the FBR system.…”

Section: Optimization Of Process Parameters Using Rsmmentioning

confidence: 99%

“…The XRD characterization of the CaF 2 crystals also revealed the absence of calcium carbonate (CaCO 3 ), calcium sulfate (CaSO 4 ) or fluorapatite (Ca 5 (PO 4 ) 3 F) in the resulting crystals. These compounds are known to precipitate during fluoride removal through fluidized bed crystallization and, even in some cases, are the main product instead of CaF 2 [22,32]. The possibility of any of these compounds' formations during FBR operation was completely eliminated through the XRD analysis, which also, in turn, highlighted the purity of CaF 2 formed.…”

Section: Characterization Of Calcium Fluoride Crystalsmentioning

confidence: 99%

Optimization of Calcium Fluoride Crystallization Process for Treatment of High-Concentration Fluoride-Containing Semiconductor Industry Wastewater

Sinharoy,

Lee,

Chung

2024

IJMS

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This study utilized a fluidized bed reactor (FBR) for fluoride removal from high-concentration fluoride-ion-containing simulated semiconductor industry wastewater and recovered high-purity CaF2 crystals. The effects of hydraulic retention time (HRT), pH, Ca2+ to F− ratio, upflow velocity, seed size and seed bed height were investigated by performing lab-scale batch experiments. Considering fluoride removal and CaF2 crystallization efficiency, 5 h HRT, pH 6, seed height of 50 cm and [Ca2+]/[F−] ratio of 0.55 (mol/mol) were found to be optimum. The effect of the interaction between the important process parameters on fluoride removal was further analyzed using response surface methodology (RSM) experimental design. The results showed that all the individual parameters have a significant impact (p = 0.0001) on fluoride removal. SEM-EDX and FTIR analysis showed the composition of the crystals formed inside FBR. HR-XRD analysis confirmed that the crystalline structure of samples was mainly CaF2. The results clearly demonstrated the feasibility of silica seed material containing FBR for efficient removal and recovery of fluoride as high-purity calcium fluoride crystals.

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Defluoridation by fluorapatite crystallization in a fluidized bed reactor under alkaline groundwater condition

Cited by 20 publications

References 41 publications

Applications of Nano Hydroxyapatite as Adsorbents: A Review

Applications of Nano Hydroxyapatite as Adsorbents: A Review

Process Intensification for Enhanced Fluoride Removal and Recovery As Calcium Fluoride Using Fluidized Bed Reactor

Optimization of Calcium Fluoride Crystallization Process for Treatment of High-Concentration Fluoride-Containing Semiconductor Industry Wastewater

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