CN111620380A - Method for preparing scorodite by hydrothermally treating trivalent arsenic and application thereof - Google Patents

Abstract

The invention discloses a method for preparing scorodite by hydrothermal treatment of trivalent arsenic and its application. The method comprises: using nitric acid and alkaline solution to adjust the pH value of a mixed aqueous solution containing ferric nitrate and trivalent arsenic to 1.1-1.6; It is placed in a closed reaction kettle, and hydrothermally reacts at a temperature of 120°C or higher to obtain scorodite crystals. The method for preparing scorodite by hydrothermal treatment of trivalent arsenic provided by the invention directly oxidizes trivalent arsenic and fixes it into scorodite crystals, does not need to pre-oxidize trivalent arsenic to pentavalent arsenic, and can directly act on trivalent arsenic in wastewater Arsenic removal and direct stabilization.

Description

A method for preparing scorodite by hydrothermal treatment of trivalent arsenic and its application

technical field

The invention belongs to the technical field of wastewater treatment, and more particularly relates to a method for preparing scorodite by hydrothermal treatment of trivalent arsenic and its application.

Background technique

With the continuous development of my country's non-ferrous metal smelting industry, the wastewater containing trivalent arsenic has the characteristics of high acidity, high trivalent arsenic content and complex composition, which seriously threatens environmental safety and residents' health, and gradually attracts widespread attention. With the frequent occurrence of arsenic pollution incidents in water bodies at home and abroad, all sectors of society have paid increasing attention to the major harm of arsenic pollution (especially trivalent arsenic pollution) to human beings and the environment.

Minerals that are widely present in nature have a good fixation effect on arsenic in natural water environment. The existence of arsenic in some crystal structures provides a feasible idea for the removal of arsenic in water systems, that is, the formation of arsenic-containing crystals can be promoted by controlling the reaction conditions. , compared with traditional methods, its products are stable and small in volume, and have better environmental friendliness. Among them, scorodite (FeAsO ₄ ·2H ₂ O) is the most studied.

The arsenic content in scorodite crystals is very high (32%), which has the advantages of stable storage and easy solid-liquid separation. The synthesis methods of scorodite are divided into hydrothermal method, normal pressure method and improved normal pressure method. All the above three methods need to use pentavalent arsenic as the arsenic source; When scorodite is used for the treatment of trivalent arsenic-containing wastewater, it is necessary to pre-oxidize trivalent arsenic to pentavalent.

To sum up, developing a short-flow, one-step method for treating trivalent arsenic-containing wastewater is a technical problem to be solved urgently in the art.

In view of this, the present invention is proposed.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the present invention provides a method for preparing scorodite by hydrothermal treatment of trivalent arsenic and its application.

To achieve the above object, the present invention adopts the following technical solutions:

A method for preparing scorodite by hydrothermal treatment of trivalent arsenic, comprising: using nitric acid and lye to adjust the pH value of a mixed aqueous solution containing ferric nitrate and trivalent arsenic to 1.1-1.6, then placing it in a closed reaction kettle, It is equal to the hydrothermal reaction under the condition of 120 ℃, that is, scorodite crystals are obtained.

Specifically, in the above technical solution, temperature and pressure in the hydrothermal reaction affect the solubility of substances, and for the same solvent, the temperature determines the pressure, so most of the hydrothermal reactions only regulate the formation of crystals by adjusting the temperature.

In the above technical solution, in the mixed aqueous solution, the molar ratio of Fe/As is 0.5-1.5, preferably 1.0.

Specifically, in the above technical solution, when Fe/As is too high, iron ions are easily hydrolyzed to form amorphous substances; when Fe/As is too low, excess arsenic will adhere to the surface of the crystal nucleus and inhibit growth. Only when Fe/As is 0.5-1.5, can scorodite crystals be formed.

In the above technical solution, the content of trivalent arsenic in the mixed aqueous solution is 4-12 g/L, preferably 8 g/L.

Specifically, in the above technical solution, the initial arsenic concentration of the hydrothermal reaction needs to be greater than or equal to 4 g/L, because the hydrothermal acid system requires a higher degree of supersaturation, so a higher concentration is required for nucleation; in addition, when the concentration If it is too high, the crystallinity of the synthesized product will decrease.

Further, in the above technical solution, the pH value is adjusted to 1.3-1.5.

Specifically, in the above technical solution, the high temperature and high acid environment will increase the solubility of scorodite, resulting in its back-dissolution. When the pH is lower than 1.3, most of the arsenic cannot be fixed in the form of scorodite; as the pH rises to 1.5. Ferric iron begins to hydrolyze, and the hydrolyzate adsorbs a large amount of trivalent arsenic in the solution, thereby inhibiting the transformation of trivalent arsenic into pentavalent arsenic, resulting in the prominent advantages of precipitation of trivalent arsenic and ferric iron, so the product is derived from scorodite. Converted to figure water arsenite. Therefore, it can be concluded that the process of preparing scorodite from trivalent arsenic requires precise pH control, and the pH of the reaction system is 1.3-1.5 comprehensively.

Further, in the above technical solution, the reaction temperature of the hydrothermal reaction is 120-150°C, preferably 120°C.

Specifically, in the above technical solution, high temperature can increase the potential of the reaction system, which can be obtained by combining the Fe-As-H ₂ O system potential-pH diagram, and the pentavalent arsenic component is relatively stable under high potential conditions; At ℃, the system cannot oxidize trivalent arsenic, resulting in the formation of non-solid products; when the reaction temperature reaches 120℃, oxidation products appear, and at 150℃, 99.99% of arsenic can be converted into scorodite , the effect is already very good, and higher temperature has little effect.

Still further, in the above technical solution, the trivalent arsenic is sodium arsenite.

Still further, in the above-mentioned technical scheme, the lye solution is an aqueous sodium hydroxide solution or an aqueous sodium carbonate solution.

Specifically, in the above technical solution, the reaction time of the hydrothermal reaction is 8-24h, preferably 8h.

Another aspect of the present invention also provides scorodite crystals prepared by the above-mentioned method for preparing scorodite by hydrothermal treatment of trivalent arsenic.

Another aspect of the present invention also provides the application of the above-mentioned method for preparing scorodite by hydrothermal treatment of trivalent arsenic in treating wastewater containing trivalent arsenic.

Advantages of the present invention:

The method for preparing scorodite by hydrothermal treatment of trivalent arsenic provided by the invention directly oxidizes trivalent arsenic and fixes it into scorodite crystals, does not need to pre-oxidize trivalent arsenic to pentavalent arsenic, and can directly act on trivalent arsenic in wastewater Arsenic removal and direct stabilization.

Description of drawings

Fig. 1 is the XRD pattern of the obtained solid sample in the embodiment of the present invention 1;

Fig. 2 is the Raman diagram of the solid sample obtained in the embodiment of the present invention 1;

Fig. 3 is the XRD pattern of the obtained solid sample in the embodiment of the present invention 2;

Fig. 4 is the relation diagram of the removal rate of arsenic and iron and reaction temperature in the embodiment of the present invention 2;

5 is a graph showing the relationship between the removal rate of arsenic and iron and the reaction time in Example 2 of the present invention;

FIG. 6 is the XRD pattern of the solid sample obtained in Example 3 of the present invention.

Detailed ways

The specific embodiments of the present invention will be described in further detail below with reference to specific embodiments.

The following examples are used to illustrate the present invention, but are not intended to limit the protection scope of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified.

In the embodiment of the present invention, sodium arsenite, ferric nitrate, concentrated nitric acid, sodium hydroxide and sodium sulfate are all commercially available products.

Example 1

The present embodiment provides a method for preparing scorodite by hydrothermal treatment of trivalent arsenic, and the specific process is as follows:

Weigh the ferric nitrate and sodium arsenite solids, make them into a mixed solution with deionized water and concentrated nitric acid, control the As concentration to be 8g/L (in terms of arsenic), and the mol ratio of ^Fe /As to be 1; Control the amount of nitric acid added to change the pH of the mixed solution (respectively 1.1, 1.3, 1.5, 1.6, 1.7, 1.9, 2.1, 2.3, 2.5, 2.8 and 3.0); add 45 mL of this mixed solution to a 50 mL autoclave; react The kettle was placed in a 120°C oven for 8 hours and then cooled naturally; the reacted solution was filtered, washed and dried to obtain a solid sample.

Figure 1 shows the XRD patterns of the solid samples obtained at different pH values in Example 1. It can be seen from the analysis of the results in Figure 1 that when the pH of the mixed solution is 1.6-2.5, the resulting product is arsenic oxyhydroxide. For jarosite crystals, when the pH of the mixed solution is 1.1-1.6, the resulting product is scorodite crystals, wherein, when the pH of the mixed solution is between 1.3-1.5, the scorodite crystals have the best crystallinity.

Figure 2 is the Raman diagram of the solid samples obtained at different pH values in Example 1. It can be seen from the analysis of the results in Figure 2 that the arsenic valences in the two substances are completely different, indicating that trivalent arsenic can be Direct oxidation forms scorodite crystals.

Example 2

The present embodiment provides a method for preparing scorodite by hydrothermal treatment of trivalent arsenic, and the specific process is as follows:

Weigh the ferric nitrate and sodium arsenite solid, make it into a mixed solution with deionized water, control the As concentration to be 8g/L (as arsenic), and the mol ratio of ^Fe /As to be 1; by adding concentrated nitric acid Adjust the pH of the mixed solution to 1.3; add 45 mL of the mixed solution to a 50 mL autoclave; place the reaction still in an oven at 90°C, 105°C, 120°C, 135°C, and 150°C for 8 hours of reaction, then cool naturally; After the solution is filtered, washed and dried, a solid sample is obtained.

The solid samples were characterized and detected, and the XRD results were shown in Figure 3, indicating that scorodite crystals can be formed at 120°C-150°C; when the temperature is lower than 120°C, solid phase products cannot be formed. Considering the reaction cost, 120°C is more reasonable. temperature reflex.

Figure 4 shows that the method of oxidizing trivalent arsenic to form scorodite can effectively remove pollutants in water, and the arsenic removal rate is close to 100%. Specifically, when the temperature is lower than 120 °C, no scorodite crystals are formed, so most of the arsenic and iron remain in the reaction solution; as the temperature reaches 120 °C, the solid-phase product scorodite appears, and the removal rate of arsenic and iron increases with the increase of the temperature. When the reaction reaches 120 °C, most of the trivalent arsenic in the solution can be converted into scorodite, and the high temperature enhances the potential value of the system to promote the oxidation of trivalent arsenic to pentavalent arsenic. match.

Figure 5 shows that the arsenic and iron in the water were almost completely removed when the hydrothermal reaction was carried out for 8 h. Specifically, within 6 hours of the reaction, no solid-phase product was formed in the system, indicating that both arsenic and iron remained in the solution, so the removal rate of arsenic and iron did not change significantly in the figure. After 6 hours, with the formation of scorodite, the removal of arsenic and iron The rate of arsenic in the solution began to rise, and reached a good removal effect of nearly 100% at 8h, indicating that the trivalent arsenic in the solution had been basically transformed into scorodite.

According to the above examples, the temperature for directly oxidizing trivalent arsenic to form scorodite is 120°C-150°C, and the reaction time is greater than or equal to 8h.

Example 3

The present embodiment provides a method for preparing scorodite by hydrothermal treatment of trivalent arsenic, and the specific process is as follows:

Weigh ferric nitrate, sodium arsenite, and sodium sulfate solids, and prepare a mixed solution. The arsenic concentration is 8 g/L, the iron-arsenic molar ratio is 1, and the sulfate concentration is 0, 0.025 mol/L, and 0.05 mol/L, respectively. , 0.1mol/L, 0.2mol/L, 0.3mol/L, adjust the pH to 1.3 with nitric acid and sodium hydroxide; add the mixed solution to a 50mL autoclave; the reactor is placed in a 120°C oven and reacted for 8 hours , natural cooling; the reacted solution is filtered, washed and dried to obtain the sample.

The solid was characterized and detected, and it can be seen from Figure 6 that the presence of excess sulfur inhibits the formation of scorodite. When the concentration of sodium sulfate is higher than 0.025mol/L, the purity of scorodite and the arsenic removal rate are significantly decreased; this is because trivalent arsenic needs to be oxidized to pentavalent before it can combine with iron ions to form scorodite crystals. The presence of sulfate radicals will promote its combination with trivalent arsenic and trivalent iron, thereby inhibiting the oxidation of trivalent arsenic.

Finally, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. A method for preparing scorodite by hydrothermally treating trivalent arsenic,

comprises adjusting the pH value of a mixed aqueous solution containing ferric nitrate and trivalent arsenic to 1.1-1.6 by using nitric acid and alkali liquor, then placing the mixed aqueous solution in a closed reaction kettle, and carrying out hydrothermal reaction at the temperature of more than or equal to 120 ℃ to obtain scorodite crystals.

2. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to claim 1,

the molar ratio of Fe/As in the mixed aqueous solution is 0.5 to 1.5, preferably 1.0.

3. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to claim 1,

the content of the trivalent arsenic in the mixed aqueous solution is 4-12g/L, and 8g/L is preferred.

4. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to any one of claims 1 to 3,

the pH value is adjusted to 1.3-1.5.

5. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to any one of claims 1 to 3,

the reaction temperature of the hydrothermal reaction is 120-150 ℃, and preferably 120 ℃.

6. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to any one of claims 1 to 5,

the trivalent arsenic is sodium arsenite;

and/or the alkali liquor is a sodium hydroxide aqueous solution or a sodium carbonate aqueous solution.

7. The method for preparing scorodite by hydrothermally treating trivalent arsenic according to any one of claims 1 to 6,

the reaction time of the hydrothermal reaction is 8-24h, and 8h is preferred.

8. A scorodite crystal produced by the method of hydrothermally treating trivalent arsenic according to any one of claims 1 to 7 to produce scorodite.

9. Use of the method for the hydrothermal treatment of trivalent arsenic as defined in any one of claims 1-7 for the treatment of wastewater containing trivalent arsenic for the preparation of scorodite.

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