Precipitation Of Calcium Fluoride Research Articles

Sulfate Doping Promotes Agglomeration of Calcium Fluoride Crystals.

Calcium salt precipitation is an effective solution to wastewater fluoride pollution. The purity and precipitation efficiency of calcium fluoride is critical for its removal and recovery. This study aimed to reveal the role of coexisting sulfates in the precipitation of calcium fluoride. A low sulfate concentration promoted calcium fluoride precipitation. The size of calcium fluoride-aggregated particle clusters increased from 750 to 2000 nm when the molar ratio of sulfate to fluoride was increased from 0 to 3:100. Sulfate doped in the calcium fluoride crystals neutralized the positive charge of the calcium fluoride. Online atomic force microscopy measurements showed that sulfate reduced the repulsive force between calcium fluoride crystals and increased the adhesion force from 1.62 to 2.46 nN, promoting the agglomeration of calcium fluoride crystals. Sulfate improved the precipitation efficiency of calcium fluoride by promoting agglomeration; however, the purity of calcium fluoride was reduced by doping. Sulfate reduced the induction time of calcium fluoride crystallization and improved the nucleation rate of calcium fluoride. Sulfate should be retained to improve the precipitation of calcium fluoride and to avoid its loss from the effluents. However, it is necessary to separate sulfate from fluoride to obtain high-purity calcium fluoride. Therefore, sulfate concentration regulation in high-fluoride wastewater is key to achieving the efficient removal and recovery of fluoride ions.

Simultaneous removal of fluoride and phosphate from semiconductor wastewater via chemical precipitation of calcium fluoride and hydroxyapatite using byproduct of recycled aggregate

Semiconductor wastewater with high concentrations of fluoride and phosphate is an environmental issue that cannot be ignored. Moreover, the byproduct of recycled aggregates, concrete fines, cannot be reused in concrete manufacturing, which is a key issue to address for the sustainable development of the concrete industry. The objective of this study was to tackle the crucial environmental issues of these two industries by developing concrete fines as an alternative material to treat semiconductor wastewater. The chemical precipitation of calcium fluoride and hydroxyapatite in the presence of concrete fines was determined as the mechanism underpinning the removal of fluoride and phosphate in wastewater. Owing to the wide range of contaminant concentration and solution pH and the possibility of multi-stage treatment, the effects of the initial contaminant concentration (F: 100–1000 mg/L; P: 20–200 mg/L) and solution pH (pH: 2–7) on the removal reactions were determined. The highest F and P removal percentages were more than 99%, and the final F and P concentrations met the effluent standard (F: 15 mg/L, P: 1.3 mg/L). The removal reactions of F and P are generally in competition, and the removal of F has priority over the removal of P. The pseudo-second-order model can describe the kinetics of the removal reactions well. The formation of fluorapatite can reduce the F concentration below the concentration achievable by CaF2 precipitation alone. Furthermore, using the byproduct of recycled aggregates instead of conventional chemicals to treat semiconductor wastewater is promising in terms of reducing CO2 emissions, and prospective applications are discussed. This study can lead to the development of a sustainable and clean process for semiconductor wastewater treatment using byproducts from the concrete industry.

Solid Features Modification by the Reactor Selection and US Support during Reactive Crystallization.

The use of materials requires adjusting their features to current applications/needs. In crystallization, the production methods leading directly to the product with pre-determined characteristics are being sought. The research focuses on the abilities of "shaping" the solid product (CSD, shape, form, etc.) and is based on experimental work carried out in the ultrasound (US)-assisted Koflo static mixer (STM). As the model reaction calcium fluoride precipitation has been used as a "common denominator" that complements the previous authors' studies, providing comprehensive knowledge and a more general look at the mentioned problem. It has been shown that it is possible to obtain crystals with the desired characteristics; however, one should be aware of the used reactors' limitations. The conscious selection of operating conditions, as well as US parameters (if they are used), is also essential. It has been revealed that the introduction of US to the STM only affects the turbulence intensity, but it doesn't change the mixing profile. The kinetics of crystallization remain unchanged, but crystals are subjected to greater attrition. In the stirred tank reactors, one might significantly improve the homogeneity of the unit mixing distribution by the selection of the relative input power εrel and, thus, affect the kinetics of crystallization.

Development of Chemical Procedures for Isotope Harvesting: Separation of Trace Hafnium from Tungsten

ABSTRACT The separation of trace hafnium from bulk tungsten alloys is of interest for isotope harvesting at the National Superconducting Cyclotron Laboratory and the Facility for Rare Ion Beams because 172Hf, the parent of 172Lu, accumulates in tungsten alloy beam blockers at these facilities. In this work, a procedure for the separation of trace hafnium from a bulk tungsten alloy (454 g) was established using tracer isotopes (175Hf, 88Zr, 173Lu, and 88Y). The procedure employed dissolution in an HF–HNO3 solution followed by a calcium fluoride precipitation, and then extraction chromatography was used for more selective separation steps. Two stages of column separations using LN resin (HDEHP based) and TRU resin (CMPO based) were performed. Gamma-ray spectroscopy and mass spectrometry were used to analyze the final hafnium sample and follow the steps in the chemical processing. The final recovery of hafnium was high (90 ± 8)%, and the mass of tungsten and other transition metals was reduced to near background levels (as determined by ICP-MS of the blank acid solutions). Zirconium follows hafnium quantitatively in this procedure; there was no detectable 173Lu in the final hafnium sample.

Removal of fluoride ions from aqueous solution by metaettringite.

Fluoride contamination is a major problem in wastewater treatment. Metaettringite (which has previously shown enhanced anion adsorption) was investigated as a possible adsorbent to remove fluoride from low-concentration solution (25 mg-F/L). The fluoride removal properties of ettringite and metaettringite were first compared at pH 10, and metaettringite was found to be more effective. The dominant reaction mechanism for fluoride adsorption in metaettringite was found to be recrystallization of metaettringite by rehydration; this was accompanied by precipitation of calcium fluoride. The adsorption kinetics followed the pseudo-second order model. Metaettringite was also able to remove fluoride effectively in low pH environment (i.e., at pH 3.5). The influence of coexistence of sulfate ions in solution on the fluoride removal performance was investigated, and a small decrease in performance was noted. The residual fluoride concentrations obtained with higher doses of metaettringite were lower than those specified by the Japanese effluent standard (non-coastal areas: 8 mg-F/L; coastal areas: 15 mg-F/L). The fluoride removal capacity of metaettringite was compared with those of other solid materials. The observed maximum capacity was 174.7 mg-F/g-metaettringite. In the case of high fluoride concentration solution, the main removal mechanism will be changed to calcium fluoride precipitation. In general, metaettringite is regarded as promising material for fluoride removal in wastewater treatment.

Biogas and calcite handling in calcium fluoride precipitation from aqueous solution guided by thermodynamic simulation with PHREEQC

In this innovative study, biogas has been associated with calcium carbonate [CaCO3] to promote the precipitation of fluorite, aiming at the treatment of wastewater with high content of fluoride. The work associates distinct sources of calcium and CO2 for the precipitation of fluorite according to previous simulation with the free software PHREEQC. Considering the reaction at equilibrium, the minimal predicted Ca dosage was 215 mg/L, lower than the 430 mg/L that was experimentally determined, independent of Ca source. The simultaneous use of CaCO3 and CO2 from distinct gas sources (pure CO2, 1:1 CO2:N2, and biogas) exhibited high performance permitting the reduction of fluoride content from 134 to 10 mg/L, with low gas consumption. The biogas consumption of 66.0 mmol/L, equivalent to 33.4 mmol/L of CO2 (1.47 kgCO2/m3 treated wastewater) was predicted, indicating that the biogas storage bag of 700 L would be able to treat 469 L of wastewater. Furthermore, the inert fraction of biogas (CH4) did not impact the reaction and it may be used after the reaction as an alternative source of power, equivalent to 8.25 kWh/m3 treated wastewater. Final solids were composed by fluorite and non-dissolved calcite, confirming the predictions obtained by PHREEQC.

Nano-imaging confirms improved apatite precipitation for high phosphate/silicate ratio bioactive glasses

Bioactive glasses convert to a biomimetic apatite when in contact with physiological solutions; however, the number and type of phases precipitating depends on glass composition and reactivity. This process is typically followed by X-ray diffraction and infrared spectroscopy. Here, we visualise surface mineralisation in a series of sodium-free bioactive glasses, using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) and X-ray nano-computed tomography (nano-CT). In the glasses, the phosphate content was increased while adding stoichiometric amounts of calcium to maintain phosphate in an orthophosphate environment in the glass. Calcium fluoride was added to keep the melting temperature low. TEM brought to light the presence of phosphate clustering and nearly crystalline calcium fluoride environments in the glasses. A combination of analytical methods, including solid-state NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation. Nano-CT gives insight into bioactive glass particle morphology after immersion, while TEM illustrates how compositional changes in the glass affect microstructure at a sub-micron to nanometre-level.

Bivalve shells (Corbula trigona) as a new adsorbent for the defluoridation of groundwater by adsorption-precipitation

Defluoridation of groundwater was performed in a batch reactor using bivalve shell powder (BSP) as adsorbent. The physicochemical characteristics of BSP, studied by Fourier Transform Infrared, X-ray Diffraction and Inductively Coupled Plasma-Optical Emission Spectrometry after dissolution, have shown that BSP was mainly composed of crystalline CaCO3 (∼97.8%). The effects of pH, initial fluoride concentration, adsorbent dose and contact time on the adsorption capacity of BSP were investigated. For an initial fluoride concentration of 2.2 mg/L and with 16 g/L of BSP, after 8 hours of treatment, 27.3% were eliminated at pH 7.5 versus 68% at pH 3, highlighting the efficiency of the adsorption process. The difference in adsorption capacity as a function of pH was correlated to the pHpzc of the BSP, which was equal to 8.2. Thus, at pH below pHpzc, electrostatic attraction between the fluoride anions and the positively charged adsorbent could justify the adsorption mechanism. Fittings of experimental data have evidenced that the adsorption kinetics were of pseudo-second order whereas the adsorption isotherms were of Langmuir type. The chemical precipitation of calcium fluoride was also revealed to occur upon release of Ca2+ from partial dissolution of CaCO3 in acidic conditions.

Synthesis and characterization of hydrocalumite for removal of fluoride from aqueous solutions.

Fluoride can cause some diseases to humans when ingested in large quantities and for a long time. Due to this, it is necessary to remove or reduce the amount of fluoride in effluents before release into the water bodies. This work aimed to evaluate the ability of hydrocalumites synthesized by two different methodologies and calcined hydrocalumite in reducing the content of fluoride in aqueous solutions. The materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 physisorption, thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The removal capacity of fluoride ions ranged from 14.9 to 189.6mgF- g-1. The removal mechanisms by hydrocalumites were ion exchange and adsorption at low concentrations, while at high concentrations were adsorption and precipitation of calcium fluoride. In relation to the use of calcined hydrocalumite, the removal mechanisms were ion exchange and reconstruction of structure (memory effect) in low concentrations. By the adsorption tests, it was observed that the results fit better the Langmuir isotherm model.

Effect of biocides and anionic homopolymeric inhibitors on the precipitation behavior of calcium fluoride

This paper describes the effect of biocides and of the anionic homopolymeric inhibitors on the precipitation behavior of calcium fluoride (CaF2).The efficiency of inhibitors in the presence and absence of biocides was calculated using the half-life (t1/2) approach, where 50% of the concentration has been precipitated. Conductometric and X-ray diffraction (XRD) analysis have been performed for the calcium fluoride scale minerals using three polymeric inhibitors and three biocides, which are commonly used in industrial processes. The main aim of the study was to investigate the role of anionic homopolymerspoly(acrylic acid) PAA, and of the oxidizing and non-oxidizing biocides such as; sodium hypochlorite, gluteraldehyde, tris(hydroxymethyl) nitromethane). It was found that addition of low concentration (1-10 mg/L) of the polymers (K-752, K-732 and K-702) have great inhibitory effect on the precipitation of calcium fluoride (CaF2). Their inhibition efficiency was in the order, K-752 > K-732 > K-702. The observed behaviour can be attributed to the effect of molecular weight of the polymer. The polymer having higher molecular weight shows weaker inhibiting ability. However, the oxidizing and non-oxidizing biocides have no appreciable effect on their performance and hence on the overall inhibition process. KEY WORDS: Calcium fluoride, Precipitation, Inhibition, Homopolymeric inhibitors, Biocides Bull. Chem. Soc. Ethiop. 2017, 31(1), 115-126.DOI: http://dx.doi.org/10.4314/bcse.v31i1.10

Effect of biocides on the precipitation of calcium fluoride in the presence of anionic copolymeric inhibitors

ABSTRACTThe inhibitory efficiency of anionic copolymers and the effect of the biocides sodium hypochlorite, glutaraldehyde, and tris(hydroxymethyl)nitromethane on the precipitation behavior of calcium fluoride (CaF2) were studied. The efficiency of polymeric inhibitors was traced from conductivity measurements by using half-life (t1/2) method. X-ray diffraction parameters have been measured for calcium fluoride scale minerals. An anionic copolymer (K-798) acts as one of the best inhibitors for the precipitation process of the calcium fluoride in water as compared to K-775. It is assigned to the fact that the copolymer (K-798) contains both sulfonic acid and sulfonated styrene groups while the polymer (K-775) having only the sulfonic acid group. It was further observed that the biocides have no appreciable effect on the performance of the anionic polymeric inhibitors.

DEVELOPMENT ACID COMPOSITION FOR THE HIGH TEMPERATURE CONDITIONS OF TERRIGENOUS ROCKS-RESERVOIRS

The trend of development of the oil and gas industry in recent years leads to the fact that such methods of stimulation, like hydraulic fracturing or acid treatments are used during the development and commissioning of wells in operation. Acid treatment is often used when entering producing wells after drilling or choke during repair works. Despite the fact that the acid treatment used in oil and gas industry for a very long time, all the problems arising from their implementation, have not been fully solved. This article is devoted to the development of acidic composition for use in low-permeability terrigenous rocks-reservoirs with high carbonate content. In the process of treatments collectors of this type of mud acid is important to prevent the deposition of insoluble precipitation of calcium fluoride (CaF 2 ). Thus, you should very carefully approach the issue of selecting the concentration of fluorine-containing agents in the composition of the developed acids. In the process of conducting laboratory studies of the dependences of the dissolution rate and the proportion of dissolution of quartz and marble from time to time. A comparison of the data dependencies for standard glyoxylate and acid compositions on the basis of formic acid and ammonium bifluoride. Based on changes sadkovaya ability of acid solutions of concentration in their composition of formic acid and ammonium bifluoride. It is established that the introduction of formic acid in the composition allows to increase the time of neutralization of the acid, and this, in turn, will contribute to increasing the depth of processing bottom-hole formation zone, unlike the standard acid.

Adsorption and precipitation of fluoride on calcite nanoparticles: A spectroscopic study

Adsorption and precipitation of fluoride on the surface of calcite (CaCO3) nanoparticles was investigated. Results from X-ray photoelectron spectroscopy (XPS) showed that calcium fluoride (fluorite, CaF2) precipitated on the surface of calcite nanoparticles at pH 7.2±0.1 and fluoride concentration of 100mg/L, while no precipitate was found at 10mg/L. Analysis by high resolution transmission electron microscopy (HRTEM) of calcite nanoparticles reacted with 40mg/L of fluoride showed a thin layer of fluorite on the surfaces. Interaction of calcite nanoparticles with 100mg/L of fluoride resulted in damage of single calcite nanoparticle, and more grains of precipitate were observed. Transition from adsorption to precipitation was confirmed by zeta potential of calcite nanoparticles that shifted to negative values when at fluoride concentration of 5mg/L, and then increased with fluoride concentration. Fluoride at low concentration is mainly removed by surface adsorption via electrostatic interactions, while surface precipitation of calcium fluoride begins at higher fluoride concentration (ca. ≧10mg/L), and surface precipitation becomes dominant at higher concentration (ca. ≧40mg/L).

Combined Influence of Fluoride and Biofilms on the Biotribocorrosion Behavior of Titanium Used for Dental Applications

Dental implant failures occur mainly due to biofilm infections and mastication micro-movements or load stresses that may induce wear degradation. Dental implants' microgaps are highly susceptible areas for bio- film formation and fluoride retention. Although fluoride is an antimicrobial agent widely used in caries prevention, its influence on biofilms under sliding wear remains unknown. The main aim of this work was to assess the effect of mixed biofilms and fluoride on the tribocorrosion behavior of titanium. Streptococcus mutans and Candida albicans mixed biofilms were cultured for 8 days on ground and polished commercially pure titanium. Biofilms' formation was influenced by topography: higher roughness surfaces presented higher levels of biomass. Reciprocating sliding tests were performed on both surfaces, with and without biofilms, immersed in artificial saliva in the absence or presence of fluoride (30 and 227 ppm F - ). The low friction coefficient registered indicated the lubricating effect of biofilms on titanium surfaces. Fluoride was also found to have lubricating properties on titanium during sliding, probably due to the precipitation of calcium fluoride (or like) salts. The presence of fluoride influenced the biotri- bological behavior of titanium surfaces covered with biofilms, facilitating their structural disruption and detachment. Nevertheless, open circuit potential tests reduced the corrosion of titanium in the presence of fluo- ride (227 ppm F - ) and biofilms. In conclusion, it is

Fluoride recovery from spent fluoride etching solution through crystallization of Na3AlF6 (synthetic cryolite)

Fluoride removal by precipitation of calcium fluoride is the most common practice in Taiwan to treat fluoride-containing wastewater in semiconductor or optoelectronic industries. Due to very fine CaF2 precipitates (∼0.1μm), coagulants/flocculants are needed to facilitate sedimentation of CaF2. In turn, large amount of sludge is produced by CaF2 precipitation/sedimentation process. In this study, removal of fluoride from spent fluoride etching solution by cryolite crystallization was investigated. Experimental and chemical equilibrium modeling results show that a good control of reaction pH and Al:F molar ratio is the key to form cryolite successfully. Formation of cryolite is exothermic reaction and formation of cryolite is less favor under elevated temperature. The highest residual fluoride concentration is found at reaction temperature of 90°C while those at 20 and 55°C are similar. Under Al/F molar ratios of 1:3 and 1:6 and pH of 5.5, the precipitates produced at room temperature are very similar to the commercial cryolite according to XRD, SEM, and EDX analysis. Particle size of cryolite precipitates ranges from 3μm to 15μm and is much larger than CaF2 precipitates of 0.1μm, resulting in rapid sedimentation. Cryolite crystallization process produces much less sludge volume than does by CaF2 precipitation.

Oral hygiene products, medications and drugs - hidden aetiological factors for dental erosion.

Acidic or EDTA-containing oral hygiene products and acidic medicines have the potential to soften dental hard tissues. The low pH of oral care products increases the chemical stability of some fluoride compounds and favours the incorporation of fluoride ions in the lattice of hydroxyapatite and the precipitation of calcium fluoride on the tooth surface. This layer has some protective effect against an erosive attack. However, when the pH is too low or when no fluoride is present these protecting effects are replaced by direct softening of the tooth surface. Oral dryness can occur as a consequence of medication such as tranquilizers, antihistamines, antiemetics and antiparkinsonian medicaments or of salivary gland dysfunction. Above all, patients should be aware of the potential demineralization effects of oral hygiene products with low pH. Acetyl salicylic acid taken regularly in the form of multiple chewable tablets or in the form of headache powder, as well as chewing hydrochloric acids tablets for the treatment of stomach disorders, can cause erosion. There is most probably no direct association between asthmatic drugs and erosion on the population level. Consumers and health professionals should be aware of the potential of tooth damage not only by oral hygiene products and salivary substitutes but also by chewable and effervescent tablets. Several paediatric medications show a direct erosive potential in vitro. Clinical proof of the occurrence of erosion after use of these medicaments is still lacking. However, regular and prolonged use of these medicaments might bear the risk of causing erosion. Additionally, it can be assumed that patients suffering from xerostomia should be aware of the potential effects of oral hygiene products with low pH and high titratable acidity.

Rapid determination of radiostrontium in large soil samples

A new method for the determination of radiostrontium in large soil samples has been developed at the Savannah River Environmental Laboratory (Aiken, SC, USA) that allows rapid preconcentration and separation of strontium in large soil samples for the measurement of strontium isotopes by gas flow proportional counting. The need for rapid analyses in the event of a radiological dispersive device or improvised nuclear device event is well-known. In addition, the recent accident at Fukushima Nuclear Power Plant in March, 2011 reinforces the need to have rapid analyses for radionuclides in environmental samples in the event of a nuclear accident. The method employs a novel pre-concentration step that utilizes an iron hydroxide precipitation (enhanced with calcium phosphate) followed by a final calcium fluoride precipitation to remove silicates and other matrix components. The pre-concentration steps, in combination with a rapid Sr Resin separation using vacuum box technology, allow very large soil samples to be analyzed for 89,90Sr using gas flow proportional counting with a lower method detection limit. The calcium fluoride precipitation eliminates column flow problems typically associated with large amounts of silicates in large soil samples.

Acid-enhanced limestone defluoridation in column reactor using oxalic acid

Acid enhanced limestone defluoridation of water has been studied in a crushed limestone column reactor using oxalic acid (OA). The defluoridation has been studied with varying initial fluoride concentrations of 5, 10, 15 and 20 mg/L and acid concentrations of 0.01, 0.05 and 0.1 M. The fluoride removal was found to increase with increase in the concentration of the acid, removing fluoride up to 95% with 0.1 M OA. The observed good fluoride removal has been attributed to a combination of two mechanisms of fluoride removal, viz., precipitation of calcium fluoride and adsorption of fluoride ions on limestone surfaces. While the removal by precipitation remains same on repeated use of the same limestone column, the adsorption is more with the fresh limestone and decreases gradually on repeated use of the same limestone column. The precipitate has been characterized using various analytical tools, viz., X-ray diffraction, IR spectroscopy, thermogravimetric analysis, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The Ca 2+ ions, formed due to dissolution of limestone by the acid, precipitate calcium fluoride along with precipitation of calcium oxalate. A good fluoride removal ability, low residual oxalate, acceptable final pH, low-cost and simplicity of the process make the present acid-enhanced limestone defluoridation process with OA a potential method for defluoridation of groundwater.

Selective separation of phosphate and fluoride from semiconductor wastewater

Hydrofluoric acid (HF) and phosphoric acid (H(3)PO(4)) are widely used in semiconductor industry for etching and rinsing purposes. Consequently, significant amount of wastewater containing phosphate and fluoride is generated. Selective separation of phosphate and fluoride from the semiconductor wastewater, containing 936 mg/L of fluoride, 118 mg/L of phosphate, 640 mg/L of sulfate, and 26.7 mg/L of ammonia, was studied. Chemical precipitation and flotation reactions were utilized in the two-stage treatment processes. The first-stage reaction involved the addition of magnesium chloride (MgCl(2)) to induce selective precipitation of magnesium phosphate. The optimal condition was pH 10 and molar ratio, [Mg(2 + )]/[(PO(4) (3-))], of 3:1, and 66.2% of phosphate was removed and recovered as bobierrite (Mg(3)(PO(4))(2).8H(2)O). No reaction was found between MgCl(2) and fluoride. Calcium chloride (CaCl(2)) was used in the second-stage reaction to induce precipitation of calcium fluoride and calcium phosphate. The optimum molar ratio, [Ca(2 + )]/[F(-)], was 0.7 at pH 10, and residual fluoride concentration of 10.7 mg/L and phosphate concentration of lower than 0.5 mg/L was obtained. Thermodynamic equilibrium was modeled with PHREEQC and compared with experimental results. Sodium dodecylsulfate (SDS) was an effective collector for subsequent solid-liquid removal via dispersed air flotation (DiAF). The study demonstrated that phosphate can be selectively recovered from the wastewater. Potential benefits include recovery of phosphate for reuse, lower required dosage of calcium for fluoride removal, and less amount of CaF(2) sludge.

Fluidized bed reactor for fluoride removal

The common methods for fluoride removal from industrial wastewater involve chemical precipitation. This process generates large amounts of a water rich sludge requiring disposal with increasing costs. Due to the high water content and the low quality of the sludge, reuse of fluoride is not an economical option. The crystallization in a fluidized bed reactor offers an alternative to the conventional precipitation. The influence of the supersaturation and recycling conditions in order to control the efficiency of the process was studied. A high supersaturation level decreases the fluoride removal efficiency due to the formation of small particles (fines). The main mechanism concerning the precipitation of calcium fluoride in a fluidized bed was established. Fines were produced by nucleation in liquid phase (homogeneous and secondary nucleation) in the reactor and the dilute fluoride tank, in order to decrease the amount of fines it is very important the control of the supersaturation.