**3. Results and discussion**

#### **3.1 Silicon dioxide processing**

High-purity silicon dioxide (SiO2 content over 99.999%) is used in the production of optical glasses, optical fiber for Internet networks, silicon for solar energy, and electronics. The market for silicon dioxide is constantly growing and the demand for high-purity grades of silicon dioxide is especially high.

The raw material for the production of silicon dioxide is SiO2-mineral and concentrate or quartz sand. The existing technologies for the production of synthetic silicon oxide are energy-consuming, multi-stage, and do not meet modern environmental requirements. We consider that the most promising direction is the fluoride technology for processing quartz raw materials using ammonium fluoride.

The advantages of NH4F and NH4HF2 are the vigorous (energetic) interaction of the melt with silicon oxide, thus forming solid (NH4)2SiF6 [7]. When heated, (NH4)2SiF6 sublimes without decomposition, and when cooled, it desublimes. Multiple sublimation-desublimation is used for deep purification of quartz concentrate from impurities [8].

Ammonium fluoride reacts with the original mineral quartz sand according to the reaction:

$$\text{SiO}\_2 + \text{6NH}\_4\text{F} \rightarrow (\text{NH}\_4)\_2\text{SiF}\_6 + 2\text{H}\_2\text{O} + 4\text{NH}\_3\tag{1}$$

Ammonium bifluoride reacts with silicon oxide according to the reaction:

$$\text{SiO}\_2 + \text{3NH}\_4\text{HF}\_2 \to (\text{NH}\_4)\_2\text{SiF}\_6 + 2\text{H}\_2\text{O} + \text{NH}\_3 \tag{2}$$

The (NH4)2SiF6 formed as a result of the reaction turns into a gaseous state when heated. Gaseous (NH4)2SiF6 is condensed and treated with ammonia water with associated regeneration of the fluorinating agent. This process is described by the reaction:

$$\text{H}(\text{NH}\_4)\_2\text{SiF}\_6 + 4\text{NH}\_4\text{OH} \rightarrow \text{SiO}\_2 + 6\text{NH}\_4\text{F} + 2\text{H}\_2\text{O} \tag{3}$$

Next, the precipitate of hydrated silicon oxide is separated by filtration from the ammonium fluoride solution. The separated solution of ammonium fluoride is evaporated and crystallized in the form of technical ammonium fluoride of the composition 25% NH4F and 75% NH4HF2. As a result of drying and calcining the precipitate, silicon oxide is obtained in a finely dispersed form.

The process is clearly displayed so-called fluoroammonium cycle (**Figure 1**).

Quartz sand with a known impurity content was used as a raw material (**Table 1**). When the raw material interacts with NH4HF2, the compounds of impurity elements form the following fluorides:

$$\text{Al}\_2\text{O}\_3 + \text{6NH}\_4\text{HF}\_2 \to \text{2(NH}\_4)\_3\text{AlF}\_6 + \text{3H}\_2\text{O} \tag{4}$$

$$\text{Fe}\_2\text{O}\_3 + \text{6NH}\_4\text{HF}\_2 \rightarrow \text{2(NH}\_4)\_3\text{FeF}\_6 + \text{3H}\_2\text{O} \tag{5}$$

$$\text{TiO}\_2 + \text{3NH}\_4\text{HF}\_2 \to (\text{NH}\_4)\_2\text{TiF}\_6 + \text{2H}\_2\text{O} + \text{NH}\_3\tag{6}$$

$$\text{CaO} + \text{NH}\_4\text{HF}\_2 \rightarrow \text{CaF}\_2 + \text{H}\_2\text{O} + \text{NH}\_3 \tag{7}$$

$$\text{MgO} + \text{NH}\_4\text{HF}\_2 \to \text{MgF}\_2 + \text{H}\_2\text{O} + \text{NH}\_3\tag{8}$$

**Figure 1.** *Schematic diagram of fluoroammonium purification of silicon dioxide.*


**Table 1.**

*Composition of raw materials (quartz sand).*

Side reactions of the formation of nonstoichiometric silicon fluorides:

$$\text{S(NH}\_4\text{)}\_2\text{SiF}\_6 + \text{SiO}\_2 \rightarrow \text{6NH}\_4\text{SiF}\_5 + 4\text{NH}\_3 + 2\text{H}\_2\text{O} \tag{9}$$

$$\rm SiO\_2 + 4NH\_4HF\_2 \to (NH\_4)\_2SiF\_6 + 2H\_2O + NH\_3 + HF \tag{10}$$

$$\text{NH}\_4\text{SiF}\_5 + \text{H}\_2\text{O} \rightarrow \text{NH}\_4\text{SiOF}\_3 + 2\text{HF} \tag{11}$$

It is known that reaction (9) can occur only at temperatures above 180°С. Therefore, upon fluorination, in our case, reaction (9) does not proceed. This reaction takes place in the next apparatus with sublimation purification of (NH4)2SiF6 from impurities. Upon dissolution and subsequent precipitation of (NH4)2SiF6 with a 25% ammonia solution, an undesirable hard-to-filter silica gel is formed due to the presence of NH4SiOF3.

$$\text{NH}\_4\text{SiOF}\_3 + \text{H}\_2\text{O} \rightarrow \text{SiO}\_2(\text{gel}) + \text{NH}\_4\text{F} + 2\text{HF} \tag{12}$$

In the sublimator (NH4)2SiF6 evaporates and decomposes according to the reaction:

$$(\text{NH}\_4)\_2\text{SiF}\_6 \to 2\text{NH}\_3 + 2\text{HF} + \text{SiF}\_4 \tag{13}$$

In the desublimator NH3, HF, and SiF4 are cooled to form (NH4)2SiF6

$$2\text{NH}\_3 + 2\text{HF} + \text{SiF}\_4 \to (\text{NH}\_4)\_2\text{SiF}\_6 \tag{14}$$

Experimentally, we noticed that the temperature of the desublimation process strongly affects the quality of the resulting desublimate, in particular, the ratio of the amount of ammonium fluoride and (NH4)2SiF6, as well as the amount of impurities in condensed (NH4)2SiF6. A series of experiments was carried out to determine the effect of temperature.

The freeze-drying process consists of two stages:


To determine the thermal properties of the compounds formed as a result of hydrofluorination in the ammonium fluoride melt, and the temperatures of their decomposition, DTA were carried out (**Figure 2**).

The initial temperature of weight loss is equal to 100°С, the change in weight stops at a temperature of 252°С, 16% of the total weight of the sample remains not flown away. This residue is fluoride of silica sand impurities. The DTA graph shows two exothermic peaks with maximums at 152 and 243°C.

The second peak characterizes the sublimation of (NH4)2SiF6 and NH4HF2. Using TA instruments Universal V4.2E, the enthalpies of these processes were calculated in the first case Δ*Н* = 214 J/g, in the second case Δ*Н* = 1547 J/g. Heat of the sublimation process: *Q* = �1761 J/g.

The feedstock (quartz sand) and the reagent (ammonium fluoride) are mixed in the mixer screw and fed to the rotary drum kiln. In the furnace, a chemical reaction of interaction between quartz and ammonium fluoride takes place. The formation of

#### **Figure 2.**

*Thermogravimetric and differential thermal analyzes of the decomposition of a fluorinated product. Heating rate 10°С/min.*

solid primary (NH4)2SiF6, gaseous water and ammonia is observed at a temperature of 200–220°C. The formed (NH4)2SiF6 is heavily contaminated. It contains unreacted quartz and impurity fluoridation products. Impurities of Al, Fe, Ca, and many other substances are always contained in the original quartz sand. The gaseous phase containing ammonia and water vapor enters the absorption stage to produce ammonia water.

The solid phase [primary (NH4)2SiF6] goes to the stage of sublimation purification in the next furnace. In a sublimation oven at a temperature of 320–350°C, gaseous (NH4)2SiF6 evaporates. Impurities remain solid. Thus, the product is purified from impurities. The design of the sublimation oven is important. It is necessary to ensure high productivity of the process, but to prevent the ingress of impurities into the gas phase. Impurities can enter the gas phase due to the high velocity of the gas flow or due to intensive mixing of the reaction mass and the formation of dust. We suggest using a fixed bed furnace to prevent dust and impurities from entering the vaporized (NH4)2SiF6. Gaseous (NH4)2SiF6 from the sublimation furnace enters the condenser, where the gas is cooled and solid (NH4)2SiF6 condenses. Sublimation and desublimation operations allow for high purity (NH4)2SiF6. The impurity content can be reduced to 1 ppm. High purity (NH4)2SiF6 dissolves in water.

Ammonia water is added to the solution and silicon oxide is precipitated. Regeneration of ammonium fluoride occurs as a result of the reaction of interaction of (NH4)2SiF6 with ammonia water. The obtained silica precipitate is filtered to separate the ammonium fluoride solution. Silicon oxide is calcined in an oven to remove moisture. The ammonium fluoride solution is evaporated and crystallized. The regenerated ammonium fluoride again enters the stage of decomposition of a new portion of quartz sand. The hardware diagram of the experimental section consists of a number of standard and specially designed chemical devices (**Figure 3**).

As a result of studying the process of obtaining high-purity silicon oxide, the optimal conditions for the process of sublimation purification of (NH4)2SiF6 were determined. In the temperature range from 110 to 280°С NH4HF2, NH4F, NH4SiF5, and NH4SiOF3 are evaporated and excess NH3 is removed. At temperatures from 280 to 380°С—sublimation and capture of (NH4)2SiF6. It has been determined that at a desublimation temperature of 110–120°C it is possible to obtain the purest product with the highest content of (NH4)2SiF6. The studies carried out made it possible to launch a pilot production of high-purity synthetic silicon oxide with a basic substance SiO2 content of 99.999%.

#### **Figure 3.**

*Hardware diagram of fluoroammonium production of silicon dioxide. (1) Bunker for loading ammonium fluoride, (2) bunker for loading raw materials, (3) mixer screw, (4) drum rotary kiln, (5) ammonia absorber, (6) sublimation furnace, (7) condenser, (8) dissolution tank (NH4)2SiF6, (9) tank for storing ammonia water, (10) reactor for precipitation of SiO2, (11) vacuum filter, and (12) oven for drying SiO2.*

#### **3.2 Zircon processing**

A method for the autoclave decomposition of zircon with ammonium fluorides with the aim of producing zirconium oxide has been proposed and investigated.

It is known that zircon (ZrSiO4) is one of the most chemically strong compounds. The molten ammonium fluoride at atmospheric pressure weakly interacts with zircon according to the reactions [9, 10]:

ZrSiO4 þ 13NH4F ! ð Þ NH4 <sup>3</sup>ZrF7 þ ð Þ NH4 <sup>2</sup>SiF6 þ 8NH3 þ 4H2O (15)

$$2\text{ZrSiO}\_4 + 1\text{3NH}\_4\text{F} \cdot \text{HF} \to 2(\text{NH}\_4)\_3\text{ZrF}\_7 + 2(\text{NH}\_4)\_2\text{SiF}\_6 + 3\text{NH}\_3 + 8\text{H}\_2\text{O} \tag{16}$$

Our studies have shown that fluorides react well with zircon at elevated pressures, that is, in an autoclave.

Having carried out a series of experiments on the decomposition of zircon with ammonium fluorides under various conditions, it was possible to find the optimal parameters that allow for a complete opening of the mineral and the conversion of zirconium into a soluble compound. It has been proven that the decomposition of zircon is faster when using ammonium bifluoride.

From the experimental data presented, it is possible to propose the optimal parameters of the process—the degree of response of more than 95% is achieved at a temperature of 300°C in 4 hours and at a temperature of 400°C in 1 hour.

The regeneration of ammonium fluoride provides a high economic attractiveness of the process and environmental safety. The resulting ammonium hexafluorosilicate sublimes at temperatures above 320°C and is removed from the mixture. As the temperature rises, (NH4)2ZrF6 decomposes to zirconium tetrafluoride with the release of ammonia and hydrogen fluoride. The scheme of regeneration of ammonium fluoride and ammonium bifluoride is shown in **Figure 4**.

According to the proposed method, zircon, crushed to a particle size of 0.1 mm, is alloyed with ammonium bifluoride under isochoric conditions at a temperature of 300°C for 4 hours, while a pressure of up to 40 atm develops in the autoclave.

After decomposition, by the method of sublimation separation, zirconium tetrafluoride is isolated and purified. From the obtained ZrF4 with the help of ammonia, zirconyl hydroxide—ZrO(OH)2 is isolated.

#### **3.3 Titanium dioxide processing**

Titanium dioxide is one of the twenty main products of the chemical industry and is used as a white pigment in paints and varnishes. The ammonium fluoride method makes it possible to isolate titanium tetrafluoride from ilmenite FeTiO3 in one stage and convert it into the form of titanium dioxide [11]. The interaction of ilmenite with ammonium fluoride proceeds with the formation of ammonium hexafluorotitanate and ammonium pentafluoroferrate according to reaction (17).

$$\text{FeTiO}\_3 + \text{11NH}\_4\text{F} \rightarrow (\text{NH}\_4)\_2\text{TiF}\_6 + (\text{NH}\_4)\_3\text{FeF}\_5 + \text{6NH}\_3 + \text{3H}\_2\text{O} \tag{17}$$

This reaction begins at the melting temperature of ammonium fluoride—125°C, at a temperature of 280°C (NH4)2TiF6 decomposes to TiF4. At the same time, (NH4)3FeF5 undergoes oxidation by atmospheric oxygen with simultaneous pyrohydrolysis according to reaction (18).

**Figure 4.** *Scheme of the decomposition of zircon into zirconium and silicon oxides.*

$$4(\text{NH}\_4)\_2\text{TiF}\_6 + 4(\text{NH}\_4)\_3\text{FeF}\_5 + 4\text{H}\_2\text{O} + \text{O}\_2 \rightarrow 4\text{TiF}\_4 + 2\text{Fe}\_2\text{O}\_3 + 20\text{NH}\_4\text{F} + 8\text{HF} \tag{18}$$

Volatile titanium tetrafluoride, ammonia, water, ammonium fluoride at temperatures above 280°C are separated from iron(III) oxide. The kinetics of the fluorination of ilmenite with ammonium fluorides was studied experimentally.

In the temperature range 125–150°C, the activation energy of the process is 69 kJ/mol. The process takes place in the kinetic region of the reaction. The limiting stage of the process is the interaction of the reagents. The dependence of the degree of response on temperature and time is written by the Crank-Ginstling-Brounstein's equation:

$$a = \mathbf{1} - \left[\mathbf{1} - \sqrt{\mathbf{3}, \mathbf{18} \cdot \mathbf{10}^4 \cdot e^{-\frac{68968}{\mathbf{3} \cdot \mathbf{7}}} \cdot \mathbf{r}}\right]^3 \tag{19}$$

In the range 175–250°С, the activation energy of the process is 11 kJ/mol. The process takes place in the diffusion reaction region and is limited by the diffusion of the reaction products. In this interval, the degree of reaction can be determined by the Crank-Ginstling-Brounstein's equation:

$$a = \mathbf{1} - \left[\mathbf{1} - \sqrt{\mathbf{3} \cdot \mathbf{1} \mathbf{0}^{-3} \cdot \boldsymbol{\varepsilon}^{-\frac{100\mathbf{3}}{kT}} \cdot \boldsymbol{\pi}}\right]^3 \tag{20}$$

Ammonium hexafluorotitanate under the influence of temperature decomposes into gaseous titanium tetrafluoride, ammonia, hydrogen fluoride, and water. The gases are captured and interact when cooled according to reaction (21).

$$\text{TiF}\_4 + 4\text{NH}\_4\text{OH} \rightarrow \text{Ti}(\text{OH})\_4 + 4\text{NH}\_4\text{F} \tag{21}$$

Ammonium fluoride is regenerated and titanium hydroxide is precipitated. **Figure 5** is a diagram showing the chemistry of the process and clearly depicting the return of ammonium fluoride to the cycle.

The only consumable reagent in the fluoroammonium processing of ilmenite is air oxygen, which is necessary for the oxidation of iron to the trivalent state. According to stoichiometry, 5.26 kg of oxygen is required for the oxidation of iron in 100 kg of ilmenite, which corresponds to 37 m<sup>3</sup> of air.

A schematic process flow diagram for producing titanium dioxide and iron oxide from ilmenite is shown in **Figure 6**.

**Figure 5.** *Scheme of decomposition of ilmenite to titanium dioxide and iron oxide.*

#### **Figure 6.**

*Schematic diagram of fluoroammonium processing of ilmenite.*

Ilmenite concentrate undergoes hydrofluorination in a molten ammonium fluoride at 150–200°С. In this case, fluoroammonium complexes of titanium and iron are formed, which decompose into iron difluoride and titanium tetrafluoride at temperatures above 300°C. After sublimation of titanium tetrafluoride, iron difluoride undergoes oxidative pyrohydrolysis with the formation of iron (III) oxide. Titanium tetrafluoride, separated from iron fluorides and impurities, is captured and precipitated by ammonia water to form hydrated titanium dioxide and ammonium fluoride solution.

After filtration, washing, drying and calcination of the resulting precipitate, titanium dioxide is obtained.

Based on the research carried out, a technological sequence of operations was developed. The modes of obtaining pigment TiO2 and Fe2O3 from FeTiO3 shown in **Table 2** were determined on a pilot batch of ilmenite concentrate.

A technique has been developed for processing ilmenite concentrate with ammonium fluoride to pigment titanium dioxide and iron (III) oxide. The optimal technological modes of fluoroammonium processing of ilmenite to TiO2 (with the structure of rutile and anatase) and iron(III) oxide have been determined.

#### **3.4 Beryllium processing**

This chapter also describes the possibility of applying the fluorine-ammonium technology to the processing of beryllium ores—bertrandite Be4[Si2O7](OH)2 and phenakite Be2SiO4 and beryl BeO [12–14].

*Ammonium Fluorides in Mineral Processing DOI: http://dx.doi.org/10.5772/intechopen.101822*


#### **Table 2.**

*Modes of obtaining pigment titanium dioxide from ilmenite.*

The thermodynamic probability of the reactions of interaction of the components of the beryllium concentrate with ammonium fluoride was calculated (**Table 3**).

The reaction of fluorination of phenakite with ammonium fluoride at temperatures above 500 K proceeds in the forward direction with the formation of ammonium tetrafluoroberyllate and ammonium hexafluorosilicate. The reaction of phenakite fluorination with ammonium hydroditoride begins already at a temperature of 127°С, with an increase in temperature, the reaction proceeds more fully with the formation of products.

The reaction begins to proceed at room temperature with the formation of the beryllium fluoroammonium complex (NH4)2BeF4�nNH4F and with the release of gaseous ammonia and water. With further heating, the process of decomposition of the fluoroammonium complex of beryllium proceeds. At 200°С (NH4)2BeF4�NH4F is formed, which, when heated to 240°С, decomposed to (NH4)2BeF. When the temperature rises to 280°С, (NH4)2BeF4 decomposes to NH4BeF3, which, in turn, decomposes to BeF4 at 385°С.

Based on the analysis of thermogravimetric studies, it is possible to propose the following chain of chemical transformations occurring during the interaction of beryllium oxide with fluoride and ammonium hydrodifluoride (20):

$$\begin{array}{l}\text{BeO} + \text{NH}\_{4}\text{F} \cdot \text{HF200}\_{\underset{-}{\rightarrow}}^{\text{o}}\text{C}(\text{NH}\_{4})\_{2}\text{BeF}\_{4} \\\\ \cdot \text{NH}\_{4}\text{F240}\_{\underset{-}{\rightarrow}}^{\text{o}}\text{C}(\text{NH}\_{4})\_{2}\text{BeF}\_{4} 280{}^{\text{o}}\text{CNH}\_{4}\text{BeF}\_{3} 38\underbrace{\text{S}}\_{\underset{-}{\rightarrow}}^{\text{o}}\text{C}\text{BeF}\_{2} \end{array} \tag{22}$$

The decomposition kinetics of beryllium oxide is shown in **Figure 7**.


**Table 3.**

*Thermodynamics of the process of phenakite fluorination with ammonium fluorides.*

*Kinetics of interaction of beryllium oxide with ammonium fluoride. (1) 140°C, (2) 160°C, (3) 180°C, and (4) 200°C.*

The kinetic equation for describing the rate of the process is found experimentally:

$$a = \mathbf{1} - \left(\mathbf{1} - \mathbf{1}, \mathbf{8} \cdot e^{-\frac{3000}{8.31 \cdot T}} \cdot \mathbf{r}\right)^3 \tag{23}$$

The activation energy of the process was 31 kJ/mol, which indicates the occurrence of the reaction in the transition region between diffusion and kinetic. Kinetic studies have shown that in 20 minutes at a temperature of 200°C, the decomposition of beryllium oxide occurs by more than 95%.

Below is a diagram of a closed fluoroammonium cycle of decomposition of phenakite into silicon oxide and beryllium oxide with the regeneration of ammonium fluoride. The diagram in **Figure 8** clearly illustrates the closure of flows and the equality of material balance.

Thermodynamic and thermal analyzes of the considered system, which proved the theoretical and laboratory feasibility of the process, made it possible to proceed to the development of the process flow diagram (**Figure 9**).

The original fluorite-phenakite concentrate, containing 30% phenakite, was mixed with ammonium fluoride and heated to a temperature of 200°C. The interaction of phenakite with ammonium fluoride took place, with the formation of ammonium fluoroberrylate with ammonium hexafluorosilicate and the release of gaseous ammonia and water (24).

$$\text{Be}\_2\text{SiO}\_4 + \text{14NH}\_4\text{F} \to \text{2(NH}\_4)\_2\text{BeF}\_4 + (\text{NH}\_4)\_2\text{SiF}\_6 + \text{8NH}\_3 + 4\text{H}\_2\text{O} \tag{24}$$

$$\begin{array}{c} \begin{array}{c} \begin{array}{|c|c|c|} \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\texttt{H}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \end{array} \\ \begin{array}{c} \begin{array}{c} \begin{array}{c} \begin{array}{|c|c|} \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4} \\ \hline \end{array} \\ \hline \cr 0 & \mathsf{S}\texttt{T}\_{4}\texttt{O}\texttt{H}\_{4}\texttt{O}\texttt{H}\_{4} \\ \end{array} \\ \end{array} \\ \begin{array}{c} \begin{array}{c} \begin{array}{c} \begin{array}{c} \begin{array}{c} \begin{array}{c} \\ \hline \end{array} \\ \begin{array}{c} \\ \begin{array}{c} \\ \begin{array}{c} \\ \hline \end{$$

**Figure 8.** *Scheme of the decomposition of phenakite to beryllium oxide and silicon oxide.*

**Figure 9.** *Scheme of processing beryllium phenakite concentrate.*

Upon heating, silicon was sublimated in the form of gaseous ammonium hexafluorosilicate (NH4)2SiF6. The solid fraction contains ammonium tetrafluoroberrylate and non-fluorinated fluoride. Leaching of ammonium tetrafluoroberrylate with water makes it possible to completely isolate it from the support rock, since the solubility of ammonium tetrafluoroberyllate reaches 32%, and calcium fluoride is practically insoluble. After separation of the ammonium tetrafluoroberyllate solution, it was purified from aluminum and iron impurities. Cleaning is carried out by the method of ammonia raising the pH of the solution to 8.5. At pH = 8.5, aluminum and iron hydroxides precipitate from the solution.

The separation of aluminum impurities by means of ammonia precipitation makes it possible to apply the fluoroammonium method also to the processing of beryl (2BeO∙Al2O3∙6SiO2). With a further increase in pH to pH = 12, a precipitate of beryllium hydroxide precipitates. The beryllium hydroxide separated by filtration, after calcination, transforms into the oxide form.

A technological scheme of fluorine-ammonium processing of fluorite-phenakite concentrate with the return of ammonium fluoride to the process and the release of beryllium oxide, silicon oxide and calcium fluoride is proposed [15].
