阅读说明：本技术 生产水合磷酸氢锌的方法 (Method for producing hydrated zinc hydrogen phosphate ) 是由 K·哈利斯 D·迪巴 R·布利夫 于 2019-09-12 设计创作，主要内容包括：本发明涉及一种由氧化锌ZnO和磷酸H-3PO-4生产水合磷酸氢锌(Zn-3(HPO-4)-3,3H-2O)的方法,其主要特征在于包括以下步骤：将磷酸放入反应器中,将确定量的氧化锌溶解在磷酸中以形成反应混合物,选择所述确定量的氧化锌以使磷酸和氧化锌之间的重量比H-3PO-4/ZnO大于或等于1,机械混合反应混合物以形成水合磷酸氢锌。(The invention relates to a zinc oxide-phosphoric acid H 3 PO 4 Production of hydrated zinc hydrogen phosphate (Zn) 3 (HPO 4 ) 3 ,3H 2 O), which is characterized by comprising the following steps: placing phosphoric acid in a reactor, dissolving a determined amount of zinc oxide in the phosphoric acid to form a reaction mixture, said determined amount of zinc oxide being selected such that the weight ratio between phosphoric acid and zinc oxide is H 3 PO 4 (ii)/ZnO is greater than or equal to 1, and mechanically mixing the reaction mixture to form hydrated zinc hydrogen phosphate.)

1. A composite material prepared from zinc oxide ZnO and phosphoric acid H₃PO₄Production of hydrated zinc hydrogen phosphate (Zn)₃(HPO₄)₃,3H₂O), characterized in that it comprises the following steps:

-placing phosphoric acid in a reactor,

-dissolving a determined quantity of zinc oxide in phosphoric acid to form a reaction mixture, said determined quantity of zinc oxide being selected so that the weight ratio between phosphoric acid and zinc oxide is H₃PO₄The ratio of/ZnO is greater than or equal to 1,

-mechanically kneading the reaction mixture to form zinc hydrogen phosphate hydrate.

2. The process according to claim 1, further comprising drying of the reaction mixture obtained at the end of the mechanical kneading.

3. The process according to claim 2, wherein the drying of the reaction mixture is carried out at a temperature between 40 ℃ and 100 ℃, preferably between 50 ℃ and 60 ℃.

4. A process according to any one of the preceding claims, wherein phosphoric acid and zinc oxide are placed in the reactor at room temperature and the reaction mixture is kneaded at room temperature.

5. The method according to any one of the preceding claims, wherein the mixing time is between 5 and 90 minutes, preferably between 15 and 45 minutes.

6. A process according to any one of the preceding claims, wherein zinc oxide is added to the phosphoric acid gradually.

7. The process according to any one of the preceding claims, wherein the volume ratio of liquid phase to solid phase of the mixture of phosphoric acid and zinc oxide is comprised between 0.3 and 2, preferably between 0.5 and 2, more preferably between 0.8 and 1.5.

8. The method according to any one of the preceding claims, wherein the phosphoric acid has phosphorus pentoxide P₂O₅Is between 10% and 65%, preferably between 45% and 65%, more preferably between 55% and 61%.

9. The method according to any of the preceding claims, wherein the zinc oxide is preconditioned by grinding and refining.

10. The process according to any one of the preceding claims, wherein the phosphoric acid is derived from the action of a strong acid on natural phosphates.

11. A method according to any one of the preceding claims, wherein the zinc oxide is derived from the extraction of ore or industrial waste.

12. A process according to any one of the preceding claims, wherein the reaction mixture is formed by adding zinc oxide only to phosphoric acid.

13. An apparatus (10) for carrying out the method for producing zinc hydrogen phosphate hydrate according to any one of the preceding claims, the apparatus (10) comprising a reactor (17), a roller mill (12) suitable for grinding zinc oxide and a sieve (13) provided with openings; the reactor (17) is provided with a zinc oxide injection path, and a phosphoric acid injection path different from the zinc oxide injection path; and the roller mill (12) and the screen (13) are upstream of the zinc oxide injection path, the openings of the screen (13) being calibrated to enable selective passage of zinc oxide abrasive particles of a predetermined size.

14. The apparatus according to claim 13, wherein the reactor (17) comprises a rotating hook kneader (18) suitable for mechanically kneading a mixture of zinc oxide and phosphoric acid.

15. The apparatus of one of claims 13 or 14, further comprising a programmable solenoid valve (15) on at least one of the zinc oxide injection path and the phosphoric acid injection path, the programmable solenoid valve (15) configured to selectively allow or prevent injection of zinc oxide or phosphoric acid into the reactor (17).

Technical Field

The invention relates to a method for producing hydrated zinc hydrogen phosphate and to a device for carrying out said method.

Background

Zinc phosphate is a rare mineral in its natural form, in which the main chemical component is Zn₃(PO₄)·4H₂Hopeite of O, and two other forms relatively close to hopeite in structure, i.e. chemical composition of Zn₂(PO₄) (OH) and Zn₄(PO₄)₂(OH)₂·3H₂O's triclopyr and monoclinic hopeite.

Synthetic zinc phosphates are, as such, produced under controlled conditions to ensure satisfactory reproducibility of the technical reaction characteristics, in particular good quality of the end product and high reaction yields. Of particular importance in the synthesis of different forms of zinc phosphate is the hydration of zinc hydrogen phosphate Zn₃(HPO₄)₃·3H₂O。

P₂O₅-ZnO-H₂The phase diagram of O is relatively complex, since the solid phase (polyhydrated hydrogenphosphates, in particular Zn) is variable in many constituents₃(PO₄)₂·4H₂O、ZnHPO₄·3H₂O、ZnHPO₄·H₂O、Zn(H₂PO₄)₂·2H₂O and Zn (H)₂PO₄)₂·1.5H₂O) depends mainly on the initial concentrations of zinc (Zn) and phosphate (P), the reaction pH and the temperature.

Eberly et al [1 ]]Plotting P at room temperature₂O₅-ZnO-H₂Phase diagram of O, then Goloshchapov and Filatovto [1]Phase diagrams are drawn at different temperatures in the range of 0 to 60 ℃. Phase diagrams of Goloshhcapov and Filatovto [1]Shown in fig. 1. It shows the presence area of the different phases as a function of reaction temperature and zinc oxide (ZnO) mole fraction:

(1) the liquid is a mixture of a liquid and a gas,

(2)β-Zn₃(PO₄)₂+ a liquid (a liquid) and (b),

(3)β-Zn₃(PO₄)₂+β-Zn₂P₂O₇，

(4)α-Zn₃(PO₄)₂+β-Zn₂P₂O₇，

(5)β-Zn₂P₂O₇+ a liquid (a liquid) and (b),

(6)β-Zn₂P₂O₇+β-Zn(PO₃)₂。

thermodynamically, zinc phosphate Zn tetrahydrate₃(PO₄)₂·4H₂O is the most stable in the phase diagram.

In contrast, zinc hydrogen phosphate trihydrate Zn₃(HPO₄)₃·3H₂Production of zinc phosphate tetrahydrate Zn by O (recorded as ZHPT)₃(PO₄)₂·4H₂O is an unstable and transient product in the reaction and is therefore difficult to obtain and isolate.

Up to now, with respect to ZHPT and Zinc phosphate tetrahydrate Zn₃(PO₄)₂·4H₂O is rarely studied. Young et al [2]The first study was conducted and the results showed that the two phosphate products share common characteristics such as synthesis mechanism and purity.

According to this study, ZHPT was used to synthesize zinc phosphate tetrahydrate, Zn, with slight modification₃(PO₄)₂·4H₂O operating procedure. The ZHPT is obtained by: concentrated phosphoric acid was placed in the reactor and then neutralized with ammonia solution. Next, zinc acetate is added followed by nitric acid. Sodium hydroxide was added dropwise over two days. Finally, triethanolamine is added.

The main disadvantage of this reaction is that it is extremely slow, since it takes more than two days.

Riou et al [3 ]]Another study was carried out and the results showed that the ZHPT crystals were at 353K and contained 30 wt% P₂O₅17% by weight of ZnO and 53% by weight of water, by very slow evaporation. These crystals were precipitated in the form of transparent needles.

Disclosure of Invention

Accordingly, the inventionAims to provide a method for producing zinc hydrogen phosphate trihydrate Zn₃(HPO₄)₃·3H₂The O (abbreviated ZHPT) method overcomes the disadvantages of the prior art, wherein the reaction time is greatly reduced compared to the prior art method.

The proposed method also aims at reducing the production costs of the ZHPT.

The reduction in time and cost makes the process more suitable for high industrial throughput.

It is also an object of the present invention to provide a process which enables to obtain ZHPT as a final stable product, not as an unstable reaction intermediate, and with high purity.

Another object of the present invention is to provide an apparatus for implementing said method for producing ZHPT.

For this purpose, the invention relates to a process for the preparation of a zinc oxide coating from zinc oxide ZnO and phosphoric acid H₃PO₄Production of hydrated zinc hydrogen phosphate (Zn)₃(HPO₄)₃,3H₂O), which is characterized by comprising the following steps:

-placing phosphoric acid in a reactor,

-dissolving a determined quantity of zinc oxide in phosphoric acid to form a reaction mixture, said determined quantity of zinc oxide being selected so that the weight ratio between phosphoric acid and zinc oxide is H₃PO₄The ratio of/ZnO is greater than or equal to 1,

-mechanically kneading the reaction mixture to form zinc hydrogen phosphate hydrate.

Adding zinc oxide into phosphoric acid which is placed in a reactor in advance, wherein the weight ratio H of the phosphoric acid to the zinc oxide₃PO₄the/ZnO is 1 or more and then the reaction mixture is mechanically kneaded, so that ZHPT as a final stable reaction product can be formed with excellent yield.

In fact, the addition of zinc oxide to phosphoric acid consists in incorporating a powder (zinc oxide) into a liquid (phosphoric acid), which enhances the mixing of these two reagents and therefore favours the reaction, compared to the addition of liquid phosphoric acid to zinc oxide powder.

Furthermore, the weight ratio H of phosphoric acid to zinc oxide₃PO₄ZnO is greater than or equal to 1 and is capable of rendering all of the compounds HPO₄ ^2-The phosphoric acid in the form reacts with the zinc oxide and at the same time contributes to obtaining pure ZHPT, i.e. a single phase consisting of ZHPT at the end of the reaction.

The term "mechanical agitation" means that phosphoric acid and zinc oxide are intimately mixed due to the mechanical mixing process so that the zinc oxide powder can be incorporated well into the phosphoric acid solution and a homogeneous reaction mixture in the form of a gel is obtained.

According to other aspects, the proposed method has the following different features, alone or according to all technically possible combinations:

the process further comprises drying of the reaction mixture obtained at the end of the mechanical kneading;

-the drying of the reaction mixture is carried out at a temperature comprised between 40 ℃ and 100 ℃, preferably between 50 ℃ and 60 ℃;

-placing phosphoric acid and zinc oxide in a reactor at room temperature and kneading the reaction mixture at room temperature;

-kneading time comprised between 5 minutes and 90 minutes, preferably comprised between 15 minutes and 45 minutes;

-adding zinc oxide gradually to phosphoric acid;

-the volume ratio of the liquid phase to the solid phase of the mixture of phosphoric acid and zinc oxide is comprised between 0.3 and 2, preferably between 0.5 and 2, more preferably between 0.8 and 1.5;

phosphorus pentoxide P possessed by phosphoric acid₂O₅Is between 10% and 65%, preferably between 45% and 65%, more preferably between 55% and 61%;

-pre-conditioning the zinc oxide by grinding and refining;

the phosphoric acid originates from the action of strong acids on natural phosphates;

zinc oxide is derived from the extraction of ores or industrial waste;

the reaction mixture is formed by adding only zinc oxide to phosphoric acid.

The invention further relates to a device for carrying out the method for producing zinc hydrogen phosphate hydrate as described above. The apparatus comprises a reactor having a zinc oxide injection path and a phosphoric acid injection path different from the zinc oxide injection path and upstream of the zinc oxide injection path, the apparatus comprising a roller mill adapted to mill zinc oxide and a screen provided with openings calibrated to enable selective passage of zinc oxide milling particles of a predetermined size.

According to one embodiment, the reactor comprises a rotating hook kneader suitable for mechanically kneading a mixture of zinc oxide and phosphoric acid.

According to one embodiment, the apparatus further comprises a programmable solenoid valve on at least one of the zinc oxide injection path and the phosphoric acid injection path, the programmable solenoid valve configured to selectively allow or prevent injection of zinc oxide or phosphoric acid into the reactor.

Drawings

Other advantages and characteristics of the invention will become clear from reading the following description, given for illustrative purposes and without limitation, with reference to the accompanying drawings, in which:

FIG. 1, in Golloshchapov and Filatovto [1 ]]P produced in the study of (1)₂O₅-ZnO-H₂A phase diagram of O;

figure 2, a schematic view of an apparatus for implementing a process for producing ZHPT according to one embodiment;

-figure 3, X-ray diffraction pattern of ZHPT produced by the process of the invention;

4A and 4B, Scanning Electron Microscope (SEM) views of the ZHPT produced by the method of the invention, and 4C, 4D, 4E, 4F and 4G, which show X-ray dispersion analysis diffractograms of the different regions of the ZHPT represented in FIG. 4B;

FIGS. 5A and 5B, Compound Zn₃(PO₄)₂A Scanning Electron Microscope (SEM) view of (a);

figure 6, X-ray diffraction diagram of the final product obtained in example 2 of the description;

figure 7, X-ray diffraction diagram of the final product obtained in example 3 of the description.

Detailed Description

The first subject of the invention relates to a composition consisting of zinc oxide ZnO and phosphoric acid H₃PO₄Method for producing ZHPT by mixing by a mechanical kneading method, which does not require additives, i.e. ZnO and H₃PO₄Chemical species other than the chemical species.

When the ZHPT is formed by a conventional method for producing zinc phosphate tetrahydrate, the ZHPT is generally considered to be an unstable intermediate product. Thermodynamically, zinc phosphate tetrahydrate is considered to be the most stable in the phase diagram.

The process of the invention enables to obtain the ZHPT, preferably at room temperature, as a final stable and pure product.

Firstly, phosphoric acid H₃PO₄Placing into a reactor. The reactor is preferably at room temperature.

Next, zinc oxide was added to the reactor until it was completely dissolved in phosphoric acid, and then the resulting mixture was mechanically kneaded at room temperature.

At the end of the reaction, the reaction mixture is dried, so that a ZHPT can be obtained.

The first parameter of the process studied by the applicant is the weight ratio between phosphoric acid and zinc oxide, denoted as H₃PO₄/ZnO。

In a manner known per se, zinc oxide is insoluble in water, but soluble in acidic and strongly basic solutions. The zinc oxide is formed by Zn²⁺Ions and O^2-Ionic compounds formed by ions.

In acidic solution, zinc oxide reacts with H according to reaction (1)₃O⁺Ion reaction:

ZnO (solid) +2H₃O⁺(aqueous solution) ═ Zn₂+ (aqueous solution) +3H₂O (1)

In alkaline solution, zinc oxide reacts with H according to reaction (2)₃O⁺Ion reaction:

ZnO (solid) +2OH^-(aqueous solution) + H₂O＝Zn(OH)₄ ^2-(aqueous solution) (2)

The applicant has shown that the addition of ZnO (1 gram) to pure phosphoric acid (0.1M, initial pH equal to 1.68) increases the pH of the mixture. The dissolution of zinc oxide is actually reflected by the consumption of acid and thus by the increase in pH. The tests performed are shown in table 1 below.

Table 1: addition of ZnO to 0.1M H₃PO₄Influence of solution pH value according to stirring time

In a concentrated medium (61% by weight of P)₂O₅) Neutralization at room temperature, the dissolution of ZnO is slow, requiring between 20 minutes and 45 minutes under mechanical kneading, which weakens the Zn — O bond of zinc oxide. The zinc oxide goes into solution according to the following reaction (3):

ZnO+2H₃O⁺→Zn²⁺+3H₂O (3)

during dissolution of ZnO, phosphoric acid (61% P)₂O₅) Becomes rich in H₂PO₄ ^-/HPO₄ ^2-A compound is provided. Ionic compound HPO₄ ^2-Is amphoteric, acts as a base in an acidic medium and reacts with Zn according to the following reaction (4)²⁺Reaction:

3HPO₄ ^2-+3Zn²⁺+3H₂O→Zn₃(HPO₄)₃,3H₂O(＝ZHPT) (4)

the addition of zinc oxide to the phosphoric acid enhances the mixing of the two chemicals and favors Zn²⁺Formation of cations and ionic compound HPO in the reaction medium₄ ^2-So that reaction (4) for the synthesis of ZHPT is dominant in the reaction medium.

Preferably zinc oxideGradually, i.e. by continuous or discontinuous addition of zinc oxide to the phosphoric acid. This gradual addition of powder (zinc oxide) to the liquid (phosphoric acid) allows the zinc oxide to dissolve regularly, forming Zn regularly²⁺Ions, which can then be used more easily. This favors Zn²⁺Ion and ionic compound HPO₄ ^2-Interaction between them, thus favoring the reaction for the synthesis of ZHPT (4).

The kneading of the reaction mixture is preferably carried out during the addition of the zinc oxide and then optionally continued after said addition.

Alternatively, the kneading of the reaction mixture is carried out only after the addition of zinc oxide.

Further, in reaction (4) for synthesizing ZHPT, ionic compound HPO₄ ^2-And Zn²⁺The ions react in a stoichiometric manner. 3 moles of HPO₄ ^2-With 3 moles of Zn²⁺The reaction formed 1 mole of ZHPT.

To make HPO₄ ^2-Complete reaction, the amount of zinc oxide added to the reactor being selected so that the weight ratio H of phosphoric acid to zinc oxide₃PO₄the/ZnO is greater than or equal to 1 in the initial state, and preferably approximately equal to 1. H₃PO₄This choice of a/ZnO weight ratio greater than or equal to 1 also makes it possible to avoid ZnO in the reaction medium with respect to H₃PO₄Supersaturation of (c).

More generally, the applicant has noted that H₃PO₄The weight ratio of/ZnO directly influences the pH of the reaction medium during formation of the ZHPT. For measuring pH, for different H₃PO₄Different ZHPT samples were obtained in the/ZnO weight ratio, applicants diluted about 5 grams of ZHPT in about 100mL of distilled water. H₃PO₄The influence of the/ZnO weight ratio on the pH of the reaction medium means that this weight ratio also has an influence on Zn²⁺Ion and ionic compound HPO₄ ^2-The interaction between them and thus the synthesis of ZHPT.

The Applicant has thus observed that for H₃PO₄The weight ratio of ZnO is less than 1, the pH value is increased, then H₃PO₄The pH value of the/ZnO weight ratio of about 1 was stabilized. These results are consistent with the previous results detailed in table 1.

The second parameter of the process studied by the applicant is the concentration of phosphoric acid in the reaction mixture.

In a manner known per se, phosphoric acid behaves as a triacid, the dissociation of which depends on the following acid-base equilibrium:

from these chemical equilibria it can be deduced that phosphoric acid is not its first dissociation constant Ka₁And pKa₁The suggested strong acids. Phosphoric acid is actually stronger than acetic acid, but weaker than sulfuric and hydrochloric acids.

The Applicant has shown that for phosphoric acid H₃PO₄Initial concentration C of (neutral form)₀From 5.5mol/L to 1mol/L and further to 0.1mol/L, H₂PO₄ ^-/H₃PO₄The molar ratio of (A) was increased from 3.7% to 8.4% and then to 29%, respectively.

It was observed that 29% molar H was obtained from dilute phosphoric acid (0.1mol/L)₂PO₄ ^-(Compound H)₂PO₄ ^-Commonly referred to as "monovalent anions"). At this concentration, the ionic force is low. In contrast, 3.7 mol% H was obtained from concentrated phosphoric acid (5.5mol/L)₂PO₄ ^-. At this concentration, the ionic force is high.

Generally, the ionic force is denoted as I, and the activity of the ions in solution is taken into account. It is calculated with the following formula:

I＝∑₁CiZi² (8)

wherein: i is the ion, Ci is the molar concentration of the ion i, and Zi is the charge of the ion i.

Neutral H is given in Table 2 below₃PO₄And a monovalent anion H₂PO₄ ^-The distribution of the forms varies with the molar concentration of phosphoric acid. pK according to reaction (5)₁And calculating an indicated value by the ion force equation (8).

Table 2: h₃PO₄And H₂PO₄ ^-The distribution of (A) is varied according to the concentration of phosphoric acid in the solution

From these results it is concluded that preferably the intermediate concentration of phosphoric acid is between 0.5 and 1.5mol/L, in particular close to 1.2mol/L, since it represents the monovalent anion H in the reaction medium₂PO₄ ^-A good compromise between the presence of (a) and the ionic force. In fact, at this concentration, H is indeed present in the solution₂PO₄ ^-And the ionic force is relatively high. Such a phosphoric acid concentration can thus improve the yield of reaction (4) for synthesizing ZHPT.

A third parameter of the process studied by the applicant is the mechanical mixing or kneading time of the zinc oxide and the phosphoric acid.

For this reason, the applicant has studied ZnO and Zn₃(PO₄)₂And ZnSO₄At 61% pure phosphoric acid P₂O₅The solubility of (b) changes with time.

The results are shown in Table 3 below.

Table 3: ZnO, Zn₃(PO₄)₂、ZnSO₄And Zn₃(HPO₄)₃,3H₂Solubility of O in phosphoric acid (61% P)₂O₅，V＝50ml)

Table 3 shows that the solubility of the crystals increases when stirred for a determined time.

For a stirring time of 60 minutes or more, the ZHPT is greater than the Zn zinc phosphate₃(PO₄)₂Zinc oxide ZnO and zinc sulfate ZnSO₄The solubility in phosphoric acid is higher.

Thus, a mixing time of zinc oxide and phosphoric acid of greater than or equal to 5 minutes will preferably be selected, preferably greater than or equal to 15 minutes, and in a more preferred manner greater than or equal to 60 minutes.

In particular, the mixing time is preferably between 5 minutes and 90 minutes, and more preferably between 15 minutes and 45 minutes.

An embodiment will now be described which illustrates the use of a suitable reaction apparatus 10 for carrying out the process. The reaction apparatus is shown in FIG. 2.

As a description of the following, zinc oxide is indicated in the form of a water-insoluble white powder. The zinc oxide may be derived from the extraction of ore or industrial waste.

The zinc oxide powder forms a solid phase.

Phosphoric acid is phosphorus pentoxide P in a given concentration₂O₅(also known as phosphoric anhydride) in the form of an aqueous solution. Preferably, the concentration of phosphoric acid is between 10 and 65 wt.% of P₂O₅More preferably between 45 and 65% by weight of P₂O₅. The phosphoric acid may be derived from the action of strong acids on natural phosphates.

Phosphoric acid forms a liquid phase.

The liquid phase comprising the aqueous phosphoric acid solution is first fed into a reactor 16 provided with a kneading chamber 17, which kneading chamber 17 is represented in fig. 2 by a rotating hook kneader 18.

Preferably, the liquid phase is conveyed to the reactor 16 by means of a programmable solenoid valve 15, the programmable solenoid valve 15 being configured to selectively allow or prevent the injection of the liquid phase into the reactor (17). Such a programmable solenoid valve may also be used to deliver the solid phase to the reactor.

The solid phase comprising zinc oxide powder is loaded into the feed hopper 11 of the reaction apparatus 10. The bottom of the hopper is connected to a roller mill 12, the rollers 13 of the roller mill 12 allowing the solid phase to be classified to obtain fine zinc oxide powder.

The solid phase is then passed through a sieve 14 in order to obtain powder particles of small diameter at the output. The small particle size makes it possible to increase the surface area for solid-liquid contact, i.e. in ZnO and H₃PO₄The surface area in between. For reference, the following distribution of particle diameters was measured by a laser particle size analyzer, where D (0, x) ═ y denotes that x% of the particles are equal to or less than y in size: d (0,10) ═ 1.44 μm; d (0,20) ═ 2.43 μm; d (0,50) ═ 8.86 μm; d (0,80) ═ 38.69 μm; d (0,90) ═ 82.27 μm.

The solid phase is subsequently conveyed into a rotating hook kneader 17, in which the solid phase is poured into the liquid phase. Next, the solid phase and the liquid phase are kneaded using the rotating hook 18 to complete the reaction and formation of the ZHPT.

The reaction mixture obtained at the end of the reaction, which has a high viscosity and even a pasty appearance, is then passed through a roller mill 19.

The final reaction mixture is a powder, the particles of which are bound together by acid molecules. The volume ratio of liquid phase/solid phase is between 0.3 and 2, preferably between 0.8 and 1.5, and in a more preferred manner between 0.5 and 2, so that the amount of phosphoric acid present can be both sufficient to hydrate all the powder particles (without caking) and not so much as to be excessive (excess phosphoric acid does not react). Under these conditions, upon sufficient kneading, the final reaction mixture had a single phase, being a hydrated powder. In addition, the mixture appears homogeneous to the naked eye, but under a microscope it consists of individual particles or crystals that are visible.

The final reaction mixture was dried in an oven. The temperature is preferably adjusted so that drying is as fast as possible in order to comply with industrial production volumes while maintaining the quality of the crystals, i.e. while avoiding melting of the crystals. Therefore, the drying temperature is advantageously lower by tens of degrees celsius than the melting temperature of the crystals. The drying is preferably carried out at a temperature between 40 ℃ and 100 ℃ and, in a more preferred manner, between 50 ℃ and 60 ℃. In addition, the temperature may be varied during drying, so that, for example, the temperature may be increased between the start and the end of drying.

At the end of drying, a grey solid was obtained, identified by X-ray diffraction and observed by scanning optical microscopy in the examples below.

Examples of Synthesis of Zinc Hydrogen phosphate hydrate

₃Example 1: from ZnO and HPO _{4 3 4 3 3 4}The stoichiometric mixture of (2) gives Zn (HPO) in a ZnO/HPO weight ratio of 1.

2g of 61% phosphoric acid P are added to a mechanical kneader₂O₅And 2g of zinc oxide was added thereto. The zinc oxide and the phosphoric acid are in a stoichiometric ratio, i.e. a weight ratio of 1: 1. The mixture was kneaded for 20 minutes and then fed to a roll mill. At the outlet of the roller mill, a very viscous paste-like fluid is obtained.

The viscous fluid is dried in an oven at a temperature of about 80 c for 4 hours. After drying, the product was obtained as a grey solid.

The product was then subjected to several analyses, the operating steps and the results of which are detailed below.

a)Chemical analysis

The obtained product was subjected to ICP-AOES optical analysis. ICP-AOES, referred to as "inductively coupled plasma-atomic emission spectroscopy", is an analytical technique that can measure the content of an element or compound in a solid sample that has been previously dissolved in a strong acid or mixture of strong acids.

For this purpose, the sample to be analyzed is prepared by introducing the solid product into a container. 65% perchloric acid is added and the container is then covered, for example with a glass.

The mixture was heated until the white smoke disappeared and was clear, and then the mixture was cooled to room temperature.

Distilled water was added to the vessel at the mark and the mixture was completed.

The mixture was homogenized and then filtered.

The first few milliliters of solution were discarded and the filtrate was collected for analysis.

Chemical analysis showed that the product obtained consisted of 38.50% by weight of Zn and 33.50% by weight of P₂O₅And (4) forming. These results are shown in table 4 below.

Table 4: product Zn₃(HPO₄)₃,3H₂Composition of O

Composition (I)	By weight%
		Zn	38.50
P2O5	33.50

b)Diffraction by X-ray

The product was analyzed by X-ray diffraction. The X-ray diffraction pattern obtained is shown in figure 3 and shows the intensity I (per unit area) of the received radiation as a function of the diffraction angle theta (2 theta).

The diffraction pattern shows that the final product contains a single phase, i.e., zinc hydrogen phosphate hydrate (Zn)₃(HPO₄)₃,3H₂O). The final product is therefore pure.

The reaction yield was 100%.

c)Structure and form

Observations by Scanning Electron Microscopy (SEM) combined with energy dispersive X-ray analysis (EDAX) showed that ZHPT was composed mainly of phosphate particles in a regular shape of a stem, as shown in fig. 4A and 4B.

These stems are open at the tip and exhibit many branches. They are dome-shaped, similar to the shape of wild fennel (latin for "Ammi visnaga").

Referring to fig. 4B, ZHPT is homogeneous such that the morphology and composition of the crystals varies only slightly with the crystal region. Reference numerals (1), (2), (3), (4) and (5) denote five regions at the level of which the crystal has been analysed by X-ray dispersion. The results obtained are represented by the diffraction diagrams of fig. 4C, 4D, 4E, 4F and 4G, which correspond to the reference signs (1), (2), (3), (4) and (5), respectively, and represent the variation of the radiation intensity (in electrons per second and electron volts) (counts per second per eV, Cps/eV) with the energy E (in kilo-electron volts (keV)).

P phosphorus P, zinc Zn and oxygen O₂The measurement of the weight percentage of (a) confirms a very slight variation of the crystal structure between the five measurement areas, thus confirming the crystal homogeneity of the ZHPT obtained by the method of the present invention.

Zn₃(HPO₄)₃,3H₂SEM micrograph of O is different from Zn₃(PO₄)₂As shown in fig. 5A and 5B. It can be seen that Zn₃(PO₄)₂The particles have a regular morphology, with particles of different sizes. A high degree of particle agglomeration was also observed. The reaction system produces the product Zn in a square and rectangular form₃(PO₄)₂,4H₂O, and Zn in the form of irregularly shaped leaves with a crystal shape₃(PO₄)₂,4H₂O。

_{3 4 3 4 3 3 4}Example 2: zn (HPO) is synthesized by a mixture of ZnO and HPO, and the weight ratio of ZnO/HPO is more than 1.

The method of example 1 was carried out under similar experimental conditionsThe only difference being ZnO and H₃PO₄In such a ratio that ZnO/H is introduced₃PO₄The weight ratio is more than 1.

At the end of the reaction, a two-phase precipitate is obtained, starting from the complex Zn (HPO)₄)₃,3H₂O (═ ZHPT) and the complex Zn₁₁(HPO₃)₈(OH)₆And (4) forming. The presence of these two phases was observed visually and by X-ray diffraction, the diffractogram of which is shown in FIG. 6, in which ZHPT refers to (a), Zn₁₁(HPO₃)₈(OH)₆Reference (b). Noise reference brt.

In addition, it was experimentally observed that when ZnO/H was used₃PO₄Zn is present at a weight ratio of 1 or more and close to 1₁₁(HPO₃)₈(OH)₆The phase difference of the complex is reduced until the complex disappears, and ZnO/H in example 1 is finally formed₃PO₄A single-phase system with a weight ratio substantially equal to 1.

Example 3: the order of introduction of the reagents into the kneader.

The process of example 1 was carried out under similar experimental conditions, the only difference being that the zinc oxide was first placed in a mechanical kneader, to which phosphoric acid was then added.

At the end of the reaction, a precipitate consisting of four phases is obtained, consisting of the complex Zn₃(HPO₄)₃,3H₂O (═ ZHPT, large number), the complex Zn (OH)₂(minor amount), complex Zn₃(PO₄)₂,2H₂O (in small amount) and complex Zn₃(PO₄)₂(minor) formation.

The presence of these four phases was observed visually and by X-ray diffraction, the diffraction pattern of which is shown in FIG. 7, wherein ZHPT is referred to as (a), Zn (OH)₂Reference (c), Zn₃(PO₄)₂,2H₂O reference (d), Zn₃(PO₄)₂Reference (e). Noise reference brt.

Therefore, when phosphoric acid is added to zinc oxide, the resulting product is not pure, since the formation reaction (4) of ZHPT does not dominate in solution. In addition, purification of ZHPT from such heterogeneous mixtures is very difficult in practice.

Example 4: the effect of mixing time.

Taking ZnO/H₃PO₄The process of example 1 was repeated several times with a weight ratio equal to 1, with mixing times of 5 minutes, 10 minutes, 20 minutes, 45 minutes and 60 minutes, respectively.

The obtained reaction product was analyzed by X-ray diffraction. The results obtained are shown in table 5 below.

Table 5: phase obtained by X-ray diffraction (XRD)

Time	Formed phase
		5 minutes	ZnHPO4,3H2O***；Zn(OH)2 *；Zn3(PO4)2,2H2O；
10 minutes	ZnHPO4,3H2O***；Zn(OH)2 *；Zn3(PO4)2,2H2O；Zn3(PO4)2 *
		20 minutes	Zn3(HPO4)3,3H2O＝ZHPT
45 minutes	Zn3(HPO4)3,3H2O
		60 minutes	Zn3(HPO4)3,3H2O

^***: main phase of

^*: minor phase

These results show that a kneading time of at least 20 minutes makes it possible to obtain a single-phase system in which a single phase corresponds to the hydration of the zinc hydrogen phosphate and which persists for more than 20 minutes.

Therefore, a mixing time of between 20 minutes and 45 minutes is necessary and sufficient to obtain pure zinc hydrogen phosphate hydrate (single phase system).

Reference to the literature

[1]F.Lemont,“Procédés hautes températures；de la réactivitédes systèmes au developpement et l’optimisation de technologies sensibles”,Habilitationàdiriger des recherches,Institut National polytechnique de Grenoble.

[2] J.r.young, j.m.didymus, p.r.brown, s.mann et al, Nature 356(1992) 516; (b) k.henriksen, s.l.s.stipp, j.r.young, p.r.brown, am.mineral 88(2003)2040.

[3]A.Riou,R.Cudennec,Y.Gernault,“Hydrogénophosphate de zinc hydrate”,Acta cryst,(1987),C43,194-197.