CN106673069A - Black ferric arsenate crystal and synthesis method thereof - Google Patents

Abstract

The invention discloses a black iron arsenate crystal. The black iron arsenate crystal is a micron-sized petal-shaped particle, the particle size is 10-20 μm, and the appearance feature is black powder; its chemical formula is Fe ₆ (AsO ₄ ) ₅ ; its The diffraction peaks are 2θ=~13.9, 16.0, 21.2, 24.9, 25.2, 27.8, 28.4, 29.1, 30.5, 32.3, 34, 34.2. The invention also discloses a method for synthesizing the black iron arsenate crystal. The synthesis method includes the following steps: using ferric nitrate, sodium arsenate, nitric acid and deionized water to prepare a synthesis solution; mixing the alcohol and the synthesis solution in proportion by volume, The mixed solution is obtained; the mixed solution is put into a high-pressure reactor for reaction, the reaction temperature is 160-200 DEG C, and the reaction time is 8-24 hours; after the reaction is completed, it is centrifuged, the solid is washed with ethanol and water, and dried to obtain the product. The synthesis of the black iron arsenate crystal makes the removal rates of Fe and As greater than 97%, so it has great application potential in the removal of As.

Description

A kind of black iron arsenate crystal and its synthesis method

technical field

The invention relates to the technical field of crystal synthesis, in particular to a black iron arsenate crystal and a synthesis method thereof.

Background technique

As a common environmental pollutant, arsenic has received extensive attention in recent years. In the arsenic removal process, the iron salt method has more advantages than the sulfidation method and the lime neutralization method, which is shown in 1) for high-concentration arsenic-containing wastewater, it can form iron arsenate compound to remove arsenic by co-precipitation; 2) for low-concentration arsenic-containing wastewater Arsenic wastewater can be adsorbed to remove arsenic by using iron oxides and hydroxides. Therefore, iron arsenate compound is a common waste residue in the treatment of arsenic-containing wastewater. In addition to the amorphous phase, ferric arsenate also includes a variety of crystals with different crystal water contents, such as FeAsO ₄ ·0.75H ₂ O (Ferric orthoarsenate or ferric arsenate sub-hydrate), FeAsO ₄ ·2H ₂ O (Scrorodite and parascorodite), FeAsO ₄ ·3.5H ₂ O (Kaňkite), etc. Scoorite FeAsO ₄ ·2H ₂ O is recognized as the best arsenic-fixing mineral due to its high stability, high arsenic content (~32%), easy liquid-solid separation, and low water content. Scoorite is a kind of orthorhombic crystal. Researchers have proposed two different microstructure models, namely the double-dentate double-core structure and the double-dentate single-core model [Geochimica et Cosmochimica Acta,2008,72:2649-2672. & Geochimica et Cosmochimica Acta, 2010, 74:4597-4602.]. However, thermodynamic studies have found that FeAsO ₄ ·2H ₂ O is a metastable substance, which can be obtained from FeAsO ₄ or further transformed into FeAsO ₄ ·3.5H ₂ O. FeAsO ₄ ·3.5H ₂ O is more stable than FeAsO ₄ ·2H ₂ O, but the microstructure of FeAsO ₄ ·3.5H ₂ O is not yet clear, it is speculated that it has the same properties as Fe ₂ (SO ₄ )(AsO ₄ )(OH)· 9H ₂ O (Bukovskyite) similar chain structure [Hydrometallurgy117–118(2012)47–56]. Recently, researchers suggested that FeAsO ₄ ·0.75H ₂ O also has lower solubility than scorodite [Hydrometallurgy 164(2016) 136–140.]. The synthesis and structural study of ferric arsenate compounds are conducive to exploring new treatment technologies for arsenic-containing wastewater and improving the long-term stability of existing ferric arsenate slag.

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the invention is how to improve the removal rate of As, and provide a black iron arsenate crystal and a synthesis method thereof.

(2) Technical solutions

In order to solve the above-mentioned technical problems, the present invention provides a black iron arsenate crystal, the black iron arsenate crystal is micron-sized petal-shaped particles, the particle size is 10-20 μm, and the appearance feature is black powder; its chemical formula is Fe ₆ ( AsO ₄ ) ₅ ; its diffraction peaks are 2θ=~13.9, 16.0, 21.2, 24.9, 25.2, 27.8, 28.4, 29.1, 30.5, 32.3, 34, 34.2.

The present invention also provides a synthesis method of the black iron arsenate crystal, the synthesis method comprising the following steps:

Step 1: Use ferric nitrate, sodium arsenate, nitric acid and deionized water to prepare a synthesis solution, wherein the molar ratio of Fe/As is 1.0-2.0, the concentration of As is 0.02-0.21mol/L, and the concentration of nitric acid is 0.26-2.6mol/L L;

Step 2: Mixing the alcohol with the synthetic solution obtained in Step 1 according to the volume ratio to obtain a mixed solution, wherein the volume of the alcohol is controlled at 10% to 50% to obtain a mixed solution;

Step 3: Put the mixed solution obtained in Step 2 into a high-pressure reactor according to the filling capacity of 50-80%, seal it and heat it for reaction. The reaction temperature is 160-200°C, and the reaction time is 8-24 hours;

Step 4: After the reaction is completed, cool down to room temperature naturally, open the reaction kettle and transfer the solid and liquid products into a centrifuge tube at a speed of 4000-6000rpm for 10-20min. The supernatant is used to analyze the concentration of residual Fe and As, and ethanol is used for the solid Rinse with water for 3 to 4 times and dry under vacuum at 35 to 45°C.

Preferably, in step 1, the molar ratio of Fe/As is 1.5, the concentration of As is 0.21 mol/L, and the concentration of nitric acid is 2.6 mol/L.

Preferably, in step 2, the alcohol includes methanol, ethanol, isopropanol or tert-butanol.

Preferably, in step 2, the alcohol is isopropanol; the volume of isopropanol in the mixed solution is controlled at 50%.

Preferably, in Step 3, the mixed solution is loaded into a stainless steel autoclave with a filling capacity of 80%; the reaction temperature is 200° C., and the reaction time is 8 hours.

Preferably, in step 4, the centrifugation speed is 5000rpm, and the centrifugation time is 10min.

Preferably, the synthesis method comprises the steps of:

Step 1: using ferric nitrate, sodium arsenate, nitric acid and deionized water to prepare a synthetic solution, wherein the molar ratio of Fe/As is 1.5, the concentration of As is 0.21mol/L, and the concentration of nitric acid is 2.6mol/L;

Step 2: mixing isopropanol with the synthetic solution obtained in step 1 in volume ratio to obtain a mixed solution, wherein the volume of isopropanol is controlled at 50% to obtain a mixed solution;

Step 3: Put the mixed solution obtained in Step 2 into a stainless steel autoclave with a filling capacity of 80%, the reaction temperature is 200°C, and the reaction time is 8 hours;

Step 4: After the reaction is completed, cool down to room temperature naturally, open the reaction kettle, transfer the solid and liquid products into a centrifuge tube and centrifuge at a speed of 5000rpm for 10min, the supernatant is used to analyze the concentration of residual Fe and As, and the solid is washed with ethanol and water respectively 3 times and dried under vacuum at 40°C.

(3) Beneficial effects

According to the synthesis method of the invention, the synthesis solution of scorodite is mixed with alcohol according to the volume ratio, and a new type of iron arsenate crystal is obtained under the same high-pressure hydrothermal condition. The new type of ferric arsenate is black petal-shaped crystal particles with almost no crystal water. Therefore, its appearance and microstructure are different from the light green biconical scorodite crystals containing two crystal waters. In addition, the removal rates of Fe and As in the synthesis of the new iron arsenate crystals are greater than 97%, while the removal rates of Fe and As in the synthesis of scorodite are only 89-90%. Therefore, the new black iron arsenate crystal phase Compared with scorodite, it has better application potential for arsenic removal.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

In the examples of the present invention, the appearance and color of synthetic products such as black crystals and scorodite have obvious differences: the NO ₃ -scorodite synthesized by the nitric acid system is a blue-green powder, and the SO ₄ -sorodite synthesized by the sulfuric acid system is a green powder , the black iron arsenate crystal Fe ₆ (AsO ₄ ) ₅ synthesized in nitric acid-isopropanol mixed system was black powder, and the iron oxide Fe ₂ O ₃ synthesized in nitric acid-isopropanol mixed system without arsenic was red powder. The microstructure characterization of the crystals described above is as shown in the accompanying drawings:

Fig. 1 is the XRD result of NO ₃ -sororite, SO ₄ -sororite, black iron arsenate crystal Fe ₆ (AsO ₄ ) ₅ and iron oxide Fe ₂ O ₃ in the examples of the present invention;

Fig. 2 is the electron diffraction spot of black iron arsenate crystal Fe ₆ (AsO ₄ ) ₅ in the embodiment of the present invention;

Figure 3 is black iron arsenate crystals synthesized by using different alcohols in the examples of the present invention (methanol-Fe ₆ (AsO ₄ ) ₅ , ethanol-Fe ₆ (AsO ₄ ) ₅ , isopropanol-Fe ₆ (AsO ₄ ) ₅ , tert-butanol-Fe ₆ (AsO ₄ ) ₅ ) and NO ₃ -scorrodite surface XPS (a) Fe2p, (b) As3d;

Figure 4 is black iron arsenate crystals synthesized by using different alcohols in the examples of the present invention (methanol-Fe ₆ (AsO ₄ ) ₅ , ethanol-Fe ₆ (AsO ₄ ) ₅ , isopropanol-Fe ₆ (AsO ₄ ) ₅ , tert-butanol-Fe ₆ (AsO ₄ ) ₅ ) XRD results;

Fig. 5 is the XRD result of black iron arsenate crystal obtained at different reaction temperatures and reaction times in the embodiment of the present invention;

Figure 6 shows (a) NO ₃ -sororite, (b) SO ₄ -sororite and black iron arsenate crystals obtained at different synthesis temperatures ((c) 160°C-Fe ₆ (AsO ₄ ) ₅ , (d) 180℃-Fe ₆ (AsO ₄ ) ₅ , (e) 200℃-Fe ₆ (AsO ₄ ) ₅ , (f) 200℃-Fe ₆ (AsO ₄ ) ₅ ) SEM results;

Fig. 7 is the thermogravimetric results of NO ₃ -sororite and black iron arsenate crystals obtained at different synthesis temperatures in the examples of the present invention.

detailed description

Embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

Iron arsenate has similar properties to iron phosphate. The synthesis and structure study of iron phosphate [Journal of Guizhou University: Natural Science Edition, 2011, 28(6):48-51.] shows that the medium can affect the thermal stability of iron phosphate crystal and the purity of the product. In addition, the solvent has a very important influence on the crystallization process, product morphology and other physical properties of iron phosphate crystals [patent document: CN102838102A]. Inspired by this, we investigated the effect of solvents on the hydrothermal synthesis of scorodite. Unexpectedly, we obtained a black crystal in the mixed system of organic alcohol and nitric acid, with the appearance of regular scorodite (green, blue-green, off-white, gray-green, blue, tan, violet) The characteristics are distinctly different. The XRD results of the crystal show that its microstructure is also different from that of scorodite, iron oxide, tussorite and other arsenic and iron crystals; XPS shows that the chemical valence and binding environment of Fe and As in the black crystal are similar to those of scorodite. It is very similar to scorodite; EDS shows that the content of iron and arsenic in the crystal is more than 32%, and the atomic ratio of iron to arsenic is 1.2; thermogravimetry shows that the content of crystallization water in the crystal is much lower than that of scorodite; SEM shows that it is consistent with biconical The crystal grains of scorodite are different, the crystals are petal-shaped, and the particle size is 10-20 microns. Therefore, the black crystal is a new structure of iron arsenate crystal, which has potential application in arsenic removal.

Example 1

Sodium arsenate and ferric nitrate are used as As(V) source and Fe(III) source respectively to configure scorodite synthesis solution, the molar ratio of As(V)/Fe(III) in the solution is 1.5, and the concentration of arsenic is 0.21mol/ L, nitric acid concentration is 2.6mol/L. The solution was directly reacted at 200° C. for 8 hours to form blue-green scorodite (NO ₃ -scorodite in FIG. 1 and FIG. 6 a ), so this solution was called scorodite synthesis solution (synthetic solution). Mix isopropyl alcohol and scorodite synthetic solution in proportion, control the alcohol volume in the mixed solution to be 50%, the mol ratio of Fe/As is 1.5, the As concentration is 0.10mol/L, and the nitric acid concentration is 1.3mol/L, and then Put it into a stainless steel reaction kettle with a filling degree greater than 50%, and obtain a black solid after reacting at 200° C. for 8 hours. A black powder can be obtained after the solid is subjected to centrifugation, repeated washing, drying and other treatments. SEM showed that the black powder was petal-shaped particles of 10-20 μm (Fig. 6c-f). XRD results show that the powder is not scorodite, nor iron oxide or arsenic oxide (Fe ₆ (AsO ₄ ) ₅ in Figure 1), but it has hexagonal crystal diffraction spots (Figure 2), indicating that the black The crystal faces of the crystals have the same orientation and crystallization is good. In addition, the Fe and As on the surface of the black crystal obtained under various synthesis conditions were analyzed by XPS, and the results showed that the chemical valence state of Fe and As of the black powder was the same as that of scorodite (Figure 3), so the black crystal was iron arsenate Crystalline Fe ₆ (AsO ₄ ) ₅ .

The above typical system for synthesizing black iron arsenate is "As(V)-Fe(III)-HNO ₃ -IPA (isopropanol)", and the components of the system were changed for comparative experiments. The results show that: (a) if the When the synthesis system does not contain sodium arsenate, the hydrothermal product is red iron oxide (Fe ₂ O ₃ in Figure 1); (b) if the hydrothermal synthesis system does not contain iron nitrate, no solid matter is produced; ( C) if the nitric acid in this system is replaced by sulfuric acid, when ferric nitrate is replaced by ferric sulfate, without any solid matter produces; (d) when nitric acid is replaced by sulfuric acid, ferric nitrate is replaced by ferric sulfate, does not introduce Virahol simultaneously, The resulting solid is green scorodite (SO ₄ - scorodite in Figure 1 and Figure 6b); (e) When other substances remain unchanged, only isopropanol is replaced by methanol, ethanol, and tert-butanol, and the solid product It is still a black powder, but its microscopic morphology is slightly different. The XRD results show that the peak positions are consistent and the peak intensities are slightly different. Therefore, nitric acid, As(V), Fe(III) and alcohol (methanol, ethanol, isopropanol or tert-butanol) are necessary combinations for the synthesis of new black iron arsenate crystals, and the type of alcohol will affect the crystal plane orientation and microscopic Morphology has an effect (Figure 4).

In a typical system for the synthesis of black ferric arsenate, black ferric arsenate crystals can be formed when the hydrothermal temperature is above 160°C (Figure 5), and scorodite will be produced when the hydrothermal temperature is below 160°C. The higher the temperature, the rougher the surface of the product particles (Fig. 6c–f). The amount of alcohol added should not be too much, and the experimental results show that the volume of alcohol should be 10% to 50%. If the amount of alcohol added is too large, the pH value will increase, and the product will change from black iron arsenate crystals to iron oxide. A 10-fold reduction in the concentration of arsenic and iron does not affect the formation of black iron arsenate crystals. The removal rates of As and Fe were higher than 97% before and after the synthesis of black iron arsenate crystals, while the removal rates of As and Fe were only 90.4% and 88.8% when scorodite was synthesized by nitric acid system. Therefore, the black iron arsenate crystal has potential for arsenic removal. The thermogravimetric results of black iron arsenate crystals synthesized at different temperatures show that the crystal water content in the crystal is very small, which is much smaller than that in scorodite.

The black substance obtained in this example is a new type of iron arsenate crystal, which has completely different crystal diffraction peaks from arsenic and iron crystals such as scorodite, iron oxide, and arsenite. The crystals are petal-shaped particles of 10-20 μm, with regular regular hexagonal crystal diffraction spots, which are completely different from the microstructure of scorodite crystals. The crystal contains almost no crystal water, and the molar ratio of Fe/As analyzed by EDS is 1.2. XPS shows that the chemical states of As and Fe are very close, and its chemical formula is Fe ₆ (AsO ₄ ) ₅ . During the synthesis process of the crystal, the removal rates of As and Fe are both higher than 97%, so it has good arsenic removal potential.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should cover Within the scope of the claims of the present invention.

Claims (8)

1. a kind of black ferric arsenate crystal, it is characterised in that the black ferric arsenate crystal is micron order petal-shaped granule, granule chi Very little is 10~20 μm, and external appearance characteristic is black powder；Its chemical formula is Fe₆(AsO₄)₅；Its diffraction maximum be 2 θ=~13.9, 16.0,21.2,24.9,25.2,27.8,28.4,29.1,30.5,32.3,34,34.2.

2. the synthetic method of the black ferric arsenate crystal described in claim 1, it is characterised in that the synthetic method includes following step Suddenly：

Step one：Synthetic solvent is configured using ferric nitrate, natrium arsenicum, nitric acid and deionized water, the wherein mol ratio of Fe/As is 1.0~2.0, As concentration is 0.02~0.21mol/L, and concentration of nitric acid is 0.26~2.6mol/L；

Step 2：By volume example is mixed to get mixed solution to the synthetic solvent that alcohol and step one are obtained, and wherein alcohol volume is 10%~50%, obtain mixed solution；

Step 3：The mixed solution that step 2 is obtained loads autoclave by loading 50-80%, and sealing post-heating is carried out Reaction, reaction temperature is 160~200 DEG C, and the response time is 8~24 hours；

Step 4：Room temperature is naturally cooled to after the completion of reaction, reactor is opened and is proceeded to centrifuge tube to turn by solid, liquid product therein 4000~6000rpm of speed is centrifuged 10~20min, and supernatant is used to analyze residual Fe, As concentration, and solid second alcohol and water is respectively rinsed 3~4 times and the drying under 35-45 DEG C of vacuum condition, obtain final product.

3. the synthetic method of black ferric arsenate crystal according to claim 2, it is characterised in that described in step one Fe/As mol ratio be 1.5, As concentration be 0.21mol/L, concentration of nitric acid is 2.6mol/L.

4. the synthetic method of black ferric arsenate crystal according to claim 2, it is characterised in that described in step 2 Alcohol include methanol, ethanol, isopropanol or the tert-butyl alcohol.

5. the synthetic method of black ferric arsenate crystal according to claim 4, it is characterised in that described in step 2 Alcohol be isopropanol；The fixing fabric structure of isopropanol is 50% in the mixed solution.

6. the synthetic method of black ferric arsenate crystal according to claim 2, it is characterised in that described in step 3 Mixed solution press loading 80% load rustless steel autoclave；The reaction temperature is 200 DEG C, and the response time is 8 little When.

7. the synthetic method of black ferric arsenate crystal according to claim 2, it is characterised in that described in step 4 Centrifugal rotational speed be 5000rpm, centrifugation time is 10min.

8. the synthetic method of black ferric arsenate crystal according to claim 2, it is characterised in that the synthetic method include as Lower step：

Step one：Synthetic solvent is configured using ferric nitrate, natrium arsenicum, nitric acid and deionized water, the wherein mol ratio of Fe/As is 1.5, As concentration are 0.21mol/L, and concentration of nitric acid is 2.6mol/L；

Step 2：By volume example is mixed to get mixed solution, wherein isopropyl to the synthetic solvent that isopropanol and step one are obtained The fixing fabric structure of alcohol obtains mixed solution 50%；

Step 3：The mixed solution that step 2 is obtained loads rustless steel autoclave, the reaction temperature by loading 80% Spend for 200 DEG C, the response time is 8 hours；

Step 4：Room temperature is naturally cooled to after the completion of reaction, reactor is opened and is proceeded to centrifuge tube to turn by solid, liquid product therein Fast 5000rpm is centrifuged 10min, and supernatant is used to analyze residual Fe, As concentration, and solid second alcohol and water is respectively rinsed 3 times and in 40 Dry under DEG C vacuum condition, obtain final product.