阅读说明：本技术 一种铬酸铵晶体的制备方法 (Preparation method of ammonium chromate crystals ) 是由 冯海涛 田森 梁建 董亚萍 李波 张波 李武 郑竹林 于 2019-11-28 设计创作，主要内容包括：本发明公开了一种铬酸铵晶体的制备方法。所述制备方法包括：以碳素铬铁作为工作电极,并至少与对电极、电解液共同构建电化学反应体系,所述电解液包括氨水或氨水与铬酸铵溶液的混合溶液；将所述工作电极、对电极分别与电源的正极、负极电连接,从而使电化学反应体系内发生电化学反应,获得混合料浆后进行固液分离,再对分离出的液相体系进行冷冻处理,获得固形物；对所述固形物进行升华干燥,获得铬酸铵晶体。本发明首度利用升华原理获得铬酸铵晶体,并采用冷冻干燥的方式制备出具有一定孔结构的铬酸铵,且铬酸铵表现出亮黄色,且本发明只需经过电解、压滤及冷冻干燥的方法即得到高纯度的铬酸铵晶体,铬酸铵晶体的纯度可以达到99.6％以上。(The invention discloses a preparation method of ammonium chromate crystals, which comprises the steps of taking carbon ferrochrome as a working electrode, at least constructing an electrochemical reaction system together with a counter electrode and electrolyte, wherein the electrolyte comprises ammonia water or a mixed solution of ammonia water and an ammonium chromate solution, electrically connecting the working electrode and the counter electrode with a positive electrode and a negative electrode of a power supply respectively, so that an electrochemical reaction is generated in the electrochemical reaction system, carrying out solid-liquid separation after mixed slurry is obtained, freezing the separated liquid phase system to obtain a solid, and carrying out sublimation drying on the solid to obtain the ammonium chromate crystals.)

A process for producing ammonium chromate crystals of kinds, characterized by comprising:

the method comprises the following steps of (1) taking carbon ferrochrome as a working electrode, and at least constructing an electrochemical reaction system together with a counter electrode and electrolyte, wherein the electrolyte comprises ammonia water or a mixed solution of the ammonia water and ammonium chromate;

electrically connecting the working electrode and the counter electrode with the anode and the cathode of a power supply respectively, so that an electrochemical reaction is generated in the electrochemical reaction system, and mixed slurry is obtained;

carrying out solid-liquid separation on the mixed slurry, and then freezing the separated liquid phase system to obtain a solid matter;

and carrying out sublimation drying on the solid matter to obtain ammonium chromate crystals.

2. The method according to claim 1, comprising:

freezing the liquid phase system at-20 to-10 ℃ for 5 to 12 hours to obtain a solid matter;

and then, carrying out sublimation drying on the solid at-50 to-40 ℃ for 6 to 24 hours under the condition that the pressure is 5 to 20Pa to obtain ammonium chromate crystals.

3. The method of claim 1, including disposing the carbon ferrochrome in an anode frame and disposing a counter electrode as a cathode on at least the side of the anode frame without contact with the anode frame, or disposing the counter electrode in the anode frame without contact with the anode frame.

4. The production method according to claim 3, characterized in that: the anode frame is made of titanium or nickel.

5. The production method according to claim 3, characterized in that: the cathode is made of nickel or stainless steel.

6. The production method according to claim 3, characterized in that: and the surface of the cathode is coated with an insulating material.

7. The production method according to claim 3, characterized in that: the shape of the cathode or anode frame comprises a plate shape, a hole shape, a net shape or a rod shape.

8. The method of claim 1, further comprising: and controlling the temperature of the electrolyte to be 20-80 ℃ during the electrochemical reaction.

9. The production method according to claim 1, characterized by comprising: and controlling the circulation flow of the electrolyte to be 0-72L/h during the electrochemical reaction.

10. The method of claim 1, wherein: the molar ratio of ammonia water to ammonium chromate in the mixed solution is 1: 10-10: 1.

11. The method of claim 1, wherein: the ammonium chromate crystal has a loose porous structure and is bright yellow.

12. The method of claim 1, further comprising: and carrying out solid-liquid separation on the mixed slurry to obtain a precipitate, wherein the precipitate comprises ferric hydroxide.

13. The method according to claim 1, comprising: and carrying out solid-liquid separation on the mixed slurry by adopting a vacuum filtration method.

14. The method of manufacturing according to claim 13, wherein: the vacuum degree adopted by the vacuum filtration method is below-0.07 Mpa, and the aperture of the adopted filter paper is 30-50 mu m.

Technical Field

The invention relates to a preparation method of inorganic salts, in particular to a preparation method of ammonium chromate crystals.

Background

The ammonium chromate is yellow crystal with ammonia smell and molecular formula of (NH)₄)₂CrO₄The relative molecular mass is 152.08, the ammonium chromate starts to decompose at 180 ℃, is soluble in water and insoluble in ethanol, has unstable chemical property, and is easy to decompose by heating to generate sodium dichromate; in addition, long-term standing also decomposes to release ammonia, and is partially converted to ammonium dichromate, so that ammonium chromate is often prepared as needed.

Ammonium chromate is mainly used in mordants, photographic coating sensitizers, catalysts, corrosion inhibitors and chemical reagents. And because of the characteristic that the chromium salt is easy to decompose when heated, the chromium salt can be used as a raw material for cleanly producing sodium bichromate, chromium oxide, chromic anhydride and other chromium salt products.

At present, the following four conventional methods for producing ammonium chromate are available:

1. ammonia water neutralization process

Ammonium dichromate is neutralized by ammonia water to prepare ammonium chromate, and the chemical reaction formula is as follows:

(NH₄)₂Cr₂O₇+2NH₄OH＝2(NH₄)₂CrO₄+H₂O

dissolving ammonium dichromate in water, controlling the concentration at about 600g/L, neutralizing with 15-20 wt% ammonium hydroxide until the orange red color turns into yellow, cooling to 5 deg.C for crystallization, centrifuging, separating, washing, and drying at room temperature to obtain ammonium dichromate crystal.

The method uses ammonium dichromate as raw material, and the ammonium dichromate is prepared by double decomposition reaction of sodium bichromate (crystal of sodium dichromate dihydrate) and ammonium chloride at 105-110 deg.C, or ammonium dichromate can be prepared by reaction of ammonium dichromate and ammonia water instead of ammonium dichromate, the process is somewhat simplified, however, no matter the ammonium dichromate or the chromic anhydride, the production process flow of the ammonium dichromate and the chromic anhydride is too long, the sodium chromate must be prepared first and then the sodium dichromate is prepared, and finally the ammonium dichromate and the chromic anhydride can be obtained, the whole process has various steps, large energy consumption, serious equipment corrosion and high cost.

2. Ammonium sulfate double decomposition method

Generally, the double decomposition reaction of potassium chromate and ammonium sulfate is used to obtain ammonium chromate, and the reaction equation is as follows:

K₂CrO₄+(NH₄)₂SO₄＝(NH₄)₂CrO₄+K₂SO₄

according to the mutual solubility relationship of quaternary phase diagram, under the condition of different temp. crystallization can respectively obtain ammonium chromate and potassium sulfate.

The method has the disadvantages that the potassium chromate raw material is not easy to obtain, the cost is high, and the hexavalent chromium contained in the by-product potassium sulfate cannot be sold.

3. Ammonium bicarbonate double decomposition method

There are kinds of technology for preparing ammonium chromate by double decomposition of alkali metal chromate and ammonium bicarbonate, which includes adding 2.0-3.5 mol/L sodium chromate solution into reactor, the ratio of ammonium bicarbonate to sodium chromate being 1:2.2, controlling the temperature of reactor at 25-65 deg.C, reacting in reactor for 0.6-2 hr, solid-liquid separating the solution, removing the precipitate of sodium bicarbonate, absorbing hydrogen in the separated ammonium chromate solution, cooling to crystallize, and filtering to obtain ammonium chromate crystal, and the said process has the reaction principle:

Na₂CrO₄+2NH₄HCO₃+2H₂O＝2NaHCO₃+(NH₄)₂CrO₄

the disadvantage of this process, like ammonium sulfate metathesis , is the recovery of by-products.

4. Cyclic carbon ammonia process

The process for producing ammonium chromate crystal by circulating carbon-ammonia method is a new process invented by process engineering research institute of Chinese academy of sciences, and is characterized by that the sodium chromate, carbon dioxide and ammonia gas are reacted to produce sodium bicarbonate precipitate and ammonium chromate solution, after the sodium bicarbonate is separated, the salting-out agent is added into the filtrate, and then the filtrate is cooled, press-filtered, washed and dried to obtain ammonium chromate crystal product, and the mother liquor is returned to dissolve sodium chromate crystal.

The reaction principle of the process is as follows:

Na₂CrO₄+2NH₃+2CO₂+2H₂O＝2NaHCO₃+(NH₄)₂CrO₄

the method has high requirements on equipment and harsh operating conditions, and the recycling of the byproduct sodium bicarbonate is also a great problem.

Although various methods for preparing ammonium chromate crystals in the prior art realize the preparation of ammonium chromate crystals, the preparation raw materials are all based on sodium chromate, the preparation process flow of the raw materials is long, the preparation cost is high, and in addition, a large amount of chromium-containing products are obtained as byproducts while the ammonium chromate is obtained, and the utilization cost is high. Furthermore, the method disclosed in chinese patent CN107585788A can only obtain ammonium dichromate crystals, but cannot obtain ammonium dichromate crystals.

Disclosure of Invention

The invention aims to provide a preparation method of ammonium chromate crystals, thereby overcoming the defects of the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:

the embodiment of the invention provides a preparation method of ammonium chromate crystals, which comprises the following steps:

the method comprises the following steps of (1) taking carbon ferrochrome as a working electrode, and at least constructing an electrochemical reaction system together with a counter electrode and electrolyte, wherein the electrolyte comprises ammonia water or a mixed solution of the ammonia water and an ammonium chromate solution;

electrically connecting the working electrode and the counter electrode with the anode and the cathode of a power supply respectively, so that an electrochemical reaction is generated in the electrochemical reaction system, and mixed slurry is obtained;

carrying out solid-liquid separation on the mixed slurry, and then freezing the separated liquid phase system to obtain a solid matter;

and carrying out sublimation drying on the solid matter to obtain ammonium chromate crystals.

In preferred embodiments, the preparation method specifically comprises:

freezing the liquid phase system at-20 to-10 ℃ for 5 to 12 hours to obtain a solid matter;

and then, carrying out sublimation drying on the solid at-50 to-40 ℃ for 6 to 24 hours under the condition that the pressure is 5 to 20Pa to obtain ammonium chromate crystals.

In preferred embodiments, the ammonium chromate crystals prepared by the present invention have a porous structure and are bright yellow in color.

Compared with the prior art, the invention has the beneficial effects that:

1) according to the method, the ammonium chromate solution can be obtained by directly using the carbon ferrochrome as a raw material through electrolysis in the step , the step of preparing ammonium chromate by sodium chromate is not needed, and the preparation process of the ammonium chromate is shortened;

2) according to the method, the ammonium chromate crystal is obtained by making ice and cooling water in a sublimation solution, the ammonium chromate crystal is obtained by firstly utilizing a sublimation principle, and the ammonium chromate with an fixed-pore structure is prepared in a freeze drying mode, so that the purity is high, the ammonium chromate content is more than 99.63%, the ammonium chromate is not easy to decompose, the ammonium chromate is bright yellow, the loose and porous crystal morphology is favorable for accelerating the dissolution, the ammonium chromate prepared by the existing method is mostly irregular blocky particles, the purity is lower than 99.5%, the ammonium chromate is easy to absorb moisture and agglomerate, and is easy to partially decompose into ammonium dichromate and the color is dark;

3) the invention electrolyzes iron in the ferrochromium to generate high-value ferric hydroxide precipitate, and the iron oxide red pigment can be prepared by calcining, thereby realizing full utilization of raw materials and products. In the traditional process, the added value of byproducts such as sodium bicarbonate, sodium sulfate or sodium chloride is low and relatively low, and the byproducts often contain hexavalent chromium, so that the byproducts are difficult to utilize, become dangerous waste and even generate serious pollution;

4) the method only needs to carry out electrolysis, filter pressing and freeze drying to obtain the high-purity ammonium chromate crystal, and the purity of the ammonium chromate crystal can reach more than 99.63 percent;

5) the ammonium chromate is crystallized by a freeze drying mode, so that a plurality of washing processes after the traditional ammonium chromate crystal is crystallized are omitted, the water consumption is greatly saved, and the wastewater discharge is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is an XRD pattern of ammonium chromate crystals prepared in an exemplary embodiment of the invention .

Fig. 2 is an SEM image of ammonium chromate crystals prepared in an exemplary embodiment of the invention .

FIG. 3 is a physical representation of ammonium chromate crystals prepared in an exemplary embodiment of the invention .

Detailed Description

In view of the defects of the prior art, the inventor of the present invention has made long-term research and extensive practice to provide a technical scheme of the present invention, in order to shorten the production process of ammonium chromate from the source, reduce the production cost, and simultaneously eliminate the generation of chromium-containing solid wastes, the inventor of the present invention provides novel techniques for preparing ammonium chromate crystals by using electrochemical techniques, and bright yellow porous ammonium chromate crystals can be prepared by using the techniques, and the technical scheme, the implementation process and the principle thereof, etc. will be explained in steps as follows.

aspects of the technical scheme of the invention relate to a method for preparing ammonium chromate crystals, which comprises the following steps:

the method comprises the following steps of (1) taking carbon ferrochrome as a working electrode, and at least constructing an electrochemical reaction system together with a counter electrode and electrolyte, wherein the electrolyte comprises ammonia water (below saturated concentration) or a mixed solution of the ammonia water and ammonium chromate;

electrically connecting the working electrode and the counter electrode with the anode and the cathode of a power supply respectively, so that an electrochemical reaction is generated in the electrochemical reaction system, and mixed slurry is obtained;

carrying out solid-liquid separation on the mixed slurry, and then freezing the separated liquid phase system to obtain a solid matter;

and carrying out sublimation drying on the solid matter to obtain ammonium chromate crystals.

In preferred embodiments, the preparation method specifically comprises:

freezing the liquid phase system at-20 to-10 ℃ for 5 to 12 hours to obtain a solid matter;

and then, carrying out sublimation drying on the solid at-50 to-40 ℃ for 6 to 24 hours under the condition that the pressure is 5 to 20Pa to obtain ammonium chromate crystals.

In preferred embodiments, the method of making includes placing the carbon ferrochrome in an anode frame and disposing a counter electrode as a cathode on at least the side of the anode frame without contact with the anode frame or disposing a counter electrode in the anode frame without contact with the anode frame.

, the cathodes are arranged at both sides of the anode frame or arranged at the middle of the anode frame.

, the anode frame includes titanium or nickel, but not limited thereto.

, the cathode is coated with insulating material, and the cathode can be made into rod shape and coated with insulating material, and then placed in the anode frame to form the counter electrode, so as to reduce the resistance.

, the cathode material includes nickel or stainless steel, but not limited thereto.

, the cathode or anode frame is in the shape of plate, hole, net or rod, but not limited to this, here, hole means punching the plate material to form the open-pore plate, and the open-pore ratio (aperture, pitch) can be set by oneself.

In preferred embodiments, the preparation method comprises controlling the temperature of the electrolyte to be 20-80 ℃ during the electrochemical reaction.

In preferred embodiments, the preparation method comprises controlling the circulation flow rate of the electrolyte to be 0-72L/h during the electrochemical reaction.

, the molar ratio of ammonia water to ammonium chromate in the mixed solution is 1: 10-10: 1.

Among the more preferred embodiments, the detailed steps of the method for preparing ammonium chromate crystals are as follows:

(1) placing a blocky carbon ferrochrome block in an anode frame, wherein the carbon ferrochrome block is connected with the positive electrode of a power supply, and a negative plate is connected with the negative electrode of the power supply, so that two negative plates can be placed on two sides of the anode, or the negative plates are placed in the anode frame, and the ferrochrome block is isolated by an insulating net, wherein the anode frame is titanium or nickel, the cathode is stainless steel or nickel, and the cathode and the anode can be plate-shaped, porous or net-shaped;

(2) filling an electrolyte solution into an electrolytic cell, controlling the temperature of the electrolyte to be 20-80 ℃ through a water bath, and controlling the circulating flow of the electrolyte to be 0-72L/h by using a peristaltic pump, wherein the electrolyte solution is ammonia water with a certain concentration or a mixed solution of the ammonia water and ammonium chromate;

(3) and (3) switching on a power supply, starting electrochemical reaction, slowly dissolving the ferrochrome in the electrolyte, wherein chromium is electrically oxidized into hexavalent chromate, iron is oxidized into trivalent iron oxide compound to be precipitated, and obtaining solid-liquid mixed slurry in the electrolytic bath. After the electrochemical reaction is finished, carrying out solid-liquid separation and washing on the obtained mixed slurry to respectively obtain an ammonium chromate solution and ferric hydroxide precipitates;

(4) putting the ammonium chromate solution into a refrigerator, freezing for 5-12 h at the temperature of-20-10 ℃, and freezing the solution into solid;

(5) and placing the obtained solid in a freeze dryer to carry out sublimation drying on the solid, wherein the sublimation temperature is-50 ℃ to-40 ℃, the pressure is 5Pa to 20Pa, and the time is 6h to 24h, and the ammonium chromate crystal powder can be obtained after the drying is finished.

, the anode in the step (1) is in a frame structure, the cathode plate can be positioned at two sides of the anode frame or in the middle of the anode frame and is provided with holes for facilitating the solution to flow, the ferrochrome is common carbon ferrochrome, the ammonium chromate solution can be obtained by directly using carbon ferrochrome as a raw material through electrolysis in the step , the ammonium chromate does not need to be prepared through sodium chromate, and the preparation process of the ammonium chromate is shortened.

, controlling the molar ratio of the ammonia water and the ammonium chromate solution in the step (2) to be 1: 10-10: 1, the temperature of the electrolytic cell to be 20-80 ℃, and the flow rate of the peristaltic pump to be 0-72L/h.

, the freezing time in step (4) is 5-12 h, the cooling temperature is-20 to-10 ℃, and the solution is ensured to be completely cooled and solidified, the ammonium chromate is crystallized by adopting a freeze drying mode, the operation temperature is-20 to-10 ℃, and is far lower than the decomposition temperature of the ammonium chromate, so that the ammonium chromate product with the purity of more than 99.63 percent can be obtained.

, the freeze-drying temperature in the step (5) is-50 to-40 ℃, the pressure is 5Pa to 20Pa, the drying time is 6h to 24h, so that the water in the solid is completely sublimated to obtain the porous ammonium chromate crystal, and in addition, no aqueous solution can be used in the vacuum drying process in the step (5) for obtaining the bright yellow ammonium chromate crystal.

In preferred embodiments, the ammonium chromate crystals prepared by the invention have a loose porous structure, are bright yellow, and have a loose porous crystalline morphology which is beneficial to accelerating dissolution.

In preferred embodiments, the preparation method further comprises the step of performing solid-liquid separation on the mixed slurry to obtain a precipitate, wherein the precipitate comprises ferric hydroxide.

, the preparation method comprises the step of carrying out solid-liquid separation on the mixed slurry by adopting a vacuum filtration method, wherein the vacuum filtration method adopts a vacuum degree below-0.07 Mpa and an air flow of 10L/min, the adopted filter paper is medium-speed qualitative filter paper, and the aperture of the filter paper is about 30-50 μm.

By the preparation process, the ammonium chromate crystal is obtained by firstly utilizing the sublimation principle, the ammonium chromate with fixed-pore structure is prepared in a freeze-drying mode, the ammonium chromate is bright yellow, and the high-purity ammonium chromate crystal can be obtained only by the methods of electrolysis, filter pressing and freeze drying, wherein the purity of the ammonium chromate can reach more than 99.63%.

For purposes of making the objects, aspects and advantages of the present invention more apparent, the following detailed description of the present invention is provided in conjunction with the drawings and several preferred embodiments, it is to be understood that the described embodiments are only a partial embodiment , rather than a full embodiment, and all other embodiments obtained by one of ordinary skill in the art without creative efforts based on the embodiments of the present invention are within the scope of the present invention.