Resource utilization method of iron-aluminum-chromium waste acid

Abstract

The invention provides a resource utilization method of iron-aluminum-chromium waste acid, and belongs to the field of waste acid resource treatment. According to the hydrochloric acid type iron-aluminum-chromium waste acid, firstly, high-valence metal in the waste acid is reduced through iron powder, the acidity of a system is reduced, and the iron content is increased; secondly, high-efficiency separation of iron, aluminum and chromium is realized by accurately controlling the sodium phosphate amount, the pH value, the reaction temperature and the stirring rotating speed; and then, oxidizing an iron solution obtained by solid-liquid separation to prepare ferric chloride, and carrying out hydrothermal crystallization on aluminum phosphate and chromium phosphate precipitates to prepare chromium-containing aluminum phosphate which can be used as a catalyst. The method realizes thorough step-by-step separation of metals in the iron-chromium-aluminum hydrochloric acid type waste acid, realizes resource utilization, is free of waste gas and waste residues in the process, meets the green and environment-friendly requirements, and has remarkable environmental and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of waste acid treatment, and more specifically, to a resource utilization method of iron, aluminum and chromium waste acid. Background Art

[0002] Waste iron, aluminum and chromium acid is a common acidic waste liquid in the surface treatment, hydrometallurgy, electroplating and other industries, and is a potential secondary resource. At present, the harmless treatment methods of waste iron, aluminum and chromium acid include neutralization precipitation, ion exchange, solvent extraction, crystallization and the like. The neutralization precipitation method has high alkali consumption costs, and the precipitation effects of various metals are different, and multi-component waste acids cannot be recovered in a targeted manner. The ion exchange method and solvent extraction method are simple to operate, easy to automate, and have high production efficiency, but the operating cost is expensive. The crystallization method uses solubility differences to separate metals. It is widely used in sulfuric acid system solutions, but has the problems of narrow application range and strict operating requirements.

[0003] The prior art discloses a method for separating chromium and iron and aluminum in a sulfuric acid system solution containing chromium, iron and aluminum. The method mainly adopts an oxidant pretreatment, pH adjustment and phosphate step-by-step precipitation method to achieve the separation of chromium and aluminum and iron. The method finally obtains an iron-aluminum phosphate composite precipitate and a chromium sulfate solution, but the solution needs to adjust the pH value twice, the steps are complicated, and a large amount of alkali is added; the separated product is difficult to be used industrially; the separation of chromium and iron and aluminum is limited to a sulfuric acid system, and the application scope is small.

[0004] However, there are relatively few studies on the treatment of iron, aluminum and chromium waste acid in the hydrochloric acid system, and methods for efficient metal separation also need further research.

[0005] Therefore, developing a resource utilization method for iron, aluminum and chromium waste acid in a hydrochloric acid system with a small amount of alkali has important research significance and application value. Summary of the invention

[0006] The present invention aims to overcome the deficiencies of the above prior art, provide a method for resource utilization of iron, aluminum and chromium waste acid in a hydrochloric acid system with little alkali addition, and prepare ferric chloride and chromium-containing aluminum phosphate with industrial value.

[0007] Therefore, the object of the present invention is to provide a method for resource utilization of waste iron, aluminum and chromium acid.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for resource utilization of waste iron, aluminum and chromium acid, comprising the following steps:

[0010] S1. Add iron powder to the waste acid of iron, aluminum and chromium to 3+ ,Cr 6+ Reduction to Fe 2+ ,Cr 3+ ;

[0011] S2. Add sodium phosphate, adjust the pH value to 3.0-3.5, and separate the solid and liquid;

[0012] S3. hydrochloric acid and sodium chlorate are added to the solution obtained in S2 to obtain a ferric chloride solution;

[0013] S4. adding phosphoric acid, triethylamine and water to the precipitate obtained in S2. and hydrothermally crystallizing at 150-200° C. for 20-28 h to obtain chromium-containing aluminum phosphate;

[0014] Wherein, the iron-aluminum-chromium waste acid in step S1 is a hydrochloric acid type iron-aluminum-chromium solution;

[0015] In step S4, the molar ratio of phosphoric acid (in terms of P2O5): triethylamine: water is 1.0:0.3-0.5:0.5-1.0:20-50.

[0016] The present invention provides a step-by-step separation and resource utilization method for waste iron, aluminum and chromium acid, which not only realizes the complete separation of metals in the hydrochloric acid system, but also prepares ferric chloride with resource utilization value, which can be used as a water treatment flocculant and chromium-containing aluminum phosphate after further processing, and has no waste gas and waste residue emissions, thus realizing the resource utilization of waste iron, aluminum and chromium acid. The present invention first uses iron powder to reduce the high-valent metals in the waste acid, ensuring that the iron and chromium elements are Fe 2+ Cr 3+ The present invention is a kind of ferrous phosphate ion ...

[0017] In step S2, the pH value is adjusted to 3.0-3.5. Compared with the prior art which requires adjusting the pH value to be close to neutral or alkaline, the amount of additional alkali added is reduced, thereby reducing the processing cost.

[0018] The addition of phosphoric acid in step S4 helps to adjust the pH of the solution and promote the nucleation and growth of crystals; triethylamine, as an organic base, can react with the acidic substances in the solution to further optimize the crystal growth environment; and water, as a solvent, ensures the uniform mixing of the reactants and the medium conditions for crystal growth. Phosphoric acid, triethylamine and water are added to the reaction system. By accurately controlling the ratio of these components, as well as the temperature and time during the crystallization process, the present invention can induce the formation of a lamellar crystal structure with a diameter of about 20 microns under specific conditions. This chromium-containing aluminum phosphate with a lamellar crystal structure has excellent catalytic performance and improves catalyst activity and selectivity.

[0019] Preferably, the mass fraction of iron in the iron-aluminum-chromium waste acid is 8.0-13.0%.

[0020] Preferably, the aluminum mass fraction of the iron-aluminum-chromium waste acid is 3.0-6.0%.

[0021] Preferably, the chromium mass fraction of the iron-aluminum-chromium waste acid is 0.1-0.5%.

[0022] Preferably, the dosage of iron powder in step S1 is 2.0-10.0% of the mass of the iron-aluminum-chromium waste acid.

[0023] Preferably, the step S2 further includes the following steps:

[0024] Sodium phosphate was added to the solution obtained in step S1. After the solid was stirred and dissolved, a pH adjuster was added to a pH of 3.0 to 3.5, and the reaction was stirred for 1 hour to separate the solid and liquid.

[0025] Preferably, the addition ratio of sodium phosphate in step S2 is Cr 3+ / PO4 3- The molar ratio is 1 to 1.5:1.

[0026] Preferably, the reaction temperature in step S2 is 50-70°C.

[0027] Preferably, the reaction time in step S2 is 30 to 120 minutes.

[0028] Preferably, the stirring speed in step S2 is 100-300 rpm.

[0029] Preferably, the pH regulator in step S2 is at least one of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

[0030] Preferably, the acidity of the hydrochloric acid in step S3 is 30-36%.

[0031] Preferably, the amount of hydrochloric acid added in step S3 is 75-104 g.

[0032] Preferably, the molar ratio of the amount of sodium chlorate added in step S3 to the amount of ferrous ions in the solution obtained in S2 is 1:2.

[0033] Specifically, the step S4 is: adding phosphoric acid, triethylamine and water to the precipitate, mixing and stirring, hydrothermally crystallizing at 150-200° C. for 20-28 hours, mixing and stirring, hydrothermally crystallizing at 180° C. for 24 hours, washing and drying to obtain chromium-containing aluminum phosphate.

[0034] Preferably, the stirring time in step S4 is 30 to 120 minutes.

[0035] Preferably, the product of hydrothermal crystallization in step S4 is washed with deionized water until it becomes neutral.

[0036] Preferably, in step S4, the drying temperature is 60-120° C., and the drying time is 2-12 hours.

[0037] Preferably, the mass fraction of iron in the ferric chloride solution in step S3 is 9% to 14%.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention optimizes the pH adjustment range, significantly reduces the amount of alkali agent used, and reduces costs;

[0040] 2. The efficient separation of iron and aluminum chromium in the hydrochloric acid system was achieved, and the ferric chloride solution that can be used as a water treatment flocculant was prepared for resource utilization;

[0041] 3. The chromium-containing aluminum phosphate catalyst prepared by the method of the present invention has a purity of up to 99.3%, which meets the purity requirements of high-efficiency catalysts;

[0042] 4. The method provided by the present invention does not produce waste gas or waste residue, meets the requirements of green environmental protection, and has significant environmental and social benefits. DETAILED DESCRIPTION

[0043] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0044] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0045] 1. Experimental methods

[0046] Example 1 A method for resource utilization of iron, aluminum and chromium waste acid

[0047] S1. Reduction:

[0048] Specifically, 70 g of iron powder was added to 1000 g of iron-aluminum-chromium waste acid (HCl acidity 6.0%, iron mass fraction as Fe2O3 8.0%, aluminum mass fraction as Al2O3 4.0%, chromium mass fraction as Cr 0.2%), stirred for reaction for 24 hours and then filtered;

[0049] S2. Precipitation:

[0050] Specifically, 800 g of the filtrate was heated to 50°C, and 14 g of Na3PO4 was slowly added at 200 rpm. After the solid was dissolved, the pH of the solution was adjusted to 3.3 with ammonia water, and the solution was kept warm for 1 hour before solid-liquid separation.

[0051] S3. Preparation of ferric chloride;

[0052] Specifically, 85 g of hydrochloric acid with an acidity of 33% and 159.7 g of sodium chlorate were added to the filtrate obtained after the above separation to prepare a ferric chloride solution.

[0053] S4. Preparation of chromium-containing aluminum phosphate;

[0054] Specifically, phosphoric acid, triethylamine and water are added to the filter cake obtained after the above separation, and the mixture is mixed in a molar ratio of 1.0:0.4:0.7:30 of precipitation complex (calculated as Al2O3): phosphoric acid (calculated as P2O5): triethylamine: deionized water. After stirring for 2 hours, the mixture is transferred into a hydrothermal reactor and crystallized at 180°C for 24 hours. After the crystallization, the reactor is cooled, and the chromium-containing aluminum phosphate is washed, dried and collected.

[0055] Example 2 A method for resource utilization of iron, aluminum and chromium waste acid

[0056] The solution is the same as that of Example 1, except that the mass fraction of iron in the iron-aluminum-chromium waste acid is 13%.

[0057] Example 3 A method for resource utilization of iron, aluminum and chromium waste acid

[0058] The same scheme as in Example 1, except that:

[0059] S2. Adjust pH;

[0060] Specifically, after the solid is dissolved, the pH of the solution is adjusted to 3 with ammonia water, and the solution is kept warm for 1 hour before solid-liquid separation;

[0061] S4. Preparation of chromium-containing aluminum phosphate:

[0062] Specifically, phosphoric acid, triethylamine and water are added to the filter cake obtained after the above separation, and the mixture is mixed in a molar ratio of 1.0:0.3:0.5:20 of precipitation complex (calculated as Al2O3): phosphoric acid (calculated as P2O5): triethylamine: deionized water. After stirring for 2 hours, the mixture is transferred into a hydrothermal reactor and crystallized at 150°C for 20 hours. After the crystallization, the reactor is cooled, and the chromium-containing aluminum phosphate is washed, dried and collected.

[0063] Example 4 A method for resource utilization of iron, aluminum and chromium waste acid

[0064] The same scheme as in Example 1 is different in that:

[0065] S1. Reduction:

[0066] Specifically, 70 g of iron powder was added to 1000 g of iron-aluminum-chromium waste acid (HCl acidity 6.0%, iron mass fraction as Fe2O3 8.0%, aluminum mass fraction as Al2O3 4.0%, chromium mass fraction as Cr 0.2%), stirred for reaction for 24 hours and then filtered;

[0067] S2. Precipitation:

[0068] Specifically, 800 g of the filtrate was heated to 50°C, and 14 g of Na3PO4 was slowly added at 200 rpm. After the solid was dissolved, the pH of the solution was adjusted to 3.5 with ammonia water, and the solution was kept warm for 1 hour before solid-liquid separation.

[0069] S3. Preparation of ferric chloride:

[0070] Specifically, the filtrate obtained after the above separation was added with 78 g of 33% hydrochloric acid and 153 g of sodium chlorate to prepare a ferric chloride solution;

[0071] The hydrothermal crystallization temperature of S4 is 200°C.

[0072] Specifically, phosphoric acid, triethylamine and water are added to the filter cake obtained after the above separation, and the mixture is mixed in a molar ratio of 1.0:0.5:1:50 of precipitation complex (calculated as Al2O3): phosphoric acid (calculated as P2O5): triethylamine: deionized water. After stirring for 2 hours, the mixture is transferred into a hydrothermal reactor and crystallized at 200°C for 26 hours. After the crystallization, the reactor is cooled, and the chromium-containing aluminum phosphate is washed, dried and collected.

[0073] Comparative Example 1 A method for resource utilization of iron, aluminum and chromium waste acid

[0074] The same scheme as in Example 1, except that the pH value in S2 is 2.

[0075] Comparative Example 2 A method for resource utilization of iron, aluminum and chromium waste acid

[0076] The same scheme as in Example 1, except that the pH value in S2 is 6.

[0077] Comparative Example 3: A method for resource utilization of iron, aluminum and chromium waste acid

[0078] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:0.1:0.5:30.

[0079] Comparative Example 4: A method for recycling waste iron, aluminum and chromium acid

[0080] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:0.3:0.1:30.

[0081] Comparative Example 5: A method for recycling waste iron, aluminum and chromium acid

[0082] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:0.3:0.1:10.

[0083] Comparative Example 6: A method for resource utilization of iron, aluminum and chromium waste acid

[0084] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:1.0:0.5:30.

[0085] Comparative Example 7 A method for resource utilization of iron, aluminum and chromium waste acid

[0086] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:0.3:1.0:30.

[0087] Comparative Example 8: A method for recycling waste iron, aluminum and chromium acid

[0088] The same scheme as Example 1 is different in that the molar ratio of precipitate (in terms of Al2O3): phosphoric acid (in terms of P2O5): triethylamine: water in S4 is 1.0:0.3:0.1:70.

[0089] Comparative Example 9: A method for recycling waste iron, aluminum and chromium acid

[0090] The same scheme as in Example 1, except that the hydrothermal crystallization temperature in S4 is 50°C.

[0091] Comparative Example 10 A method for resource utilization of iron, aluminum and chromium waste acid

[0092] The solution is the same as that of Example 1, except that the hydrothermal crystallization temperature in S4 is 300°C.

[0093] Comparative Example 11 A method for resource utilization of iron, aluminum and chromium waste acid

[0094] The same scheme as in Example 1, except that the hydrothermal crystallization time in S4 is 10 h.

[0095] Comparative Example 12: A method for recycling waste iron, aluminum and chromium acid

[0096] The same scheme as in Example 1, except that the hydrothermal crystallization time in S4 is 30 hours.

[0097] The performance test indicators of the embodiments and comparative examples of the present invention are as follows:

[0098] Purity of chromium-containing aluminum phosphate: tested according to national standard GB / T 20975.25-2008, inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0099] Chromium-containing aluminum phosphate yield: the percentage of the mass of chromium-containing aluminum phosphate actually measured to the mass of chromium-containing aluminum phosphate theoretically calculated based on the original waste acid, that is, the ratio of the actually prepared chromium-containing aluminum phosphate to the theoretically obtained one.

[0100] The evaluation standard and detection method of chromium impurities in ferric chloride refer to GB / T 4482-2018 Water Treatment Agent Ferric Chloride. The electric heating atomic absorption spectrometry is used to measure the absorbance of chromium atoms at a wavelength of 429.0nm to calculate the chromium content. For specific test parameters, see standard 6.12.

[0101] 2. Experimental results

[0102] The performance test results of each embodiment and comparative example according to the above-mentioned method of the present invention are shown in Table 1.

[0103] Table 1 Test results of various embodiments and comparative examples

[0104]

[0105]

[0106] From the data in Table 1, it can be seen that the purity of the chromium-containing aluminum phosphate in Examples 1 to 4 is above 99%, the yield of the chromium-containing aluminum phosphate is above 80%, and the chromium impurity in the ferric chloride is controlled below 0.0008%, which proves that the separation effect of the chromium-containing aluminum phosphate and ferric chloride obtained by the present invention is good.

[0107] In Comparative Example 1, the pH value of the precipitate is adjusted to 2, which is relatively small, resulting in the incomplete separation of iron, aluminum and chromium, and some aluminum and chromium ions enter the solution, reducing the purity of ferric chloride; in Comparative Example 2, the pH value of the precipitate is relatively large, and part of chromium and aluminum form hydroxide precipitation, which reduces the content of chromium phosphate and aluminum phosphate, and has a relatively large adverse effect on the purity and yield of chromium-containing aluminum phosphate. In Comparative Example 3, when preparing chromium-containing aluminum phosphate by hydrothermal crystallization, a small amount of phosphoric acid is added, resulting in the obstruction of crystal nucleation and growth, reducing the purity and yield of chromium-containing aluminum phosphate; in Comparative Example 6, more phosphoric acid is added, which will increase the acidity of the system and is not conducive to the crystallization process; in Comparative Example 4, a small amount of triethylamine is added, which is difficult to coordinate with phosphoric acid regulation, affecting the environment for crystal growth; in Comparative Example 7, a large amount of triethylamine is added, the alkalinity of the system is relatively large, and the effect is poor; Comparative Examples 5 and 8 prove that water as a solvent in hydrothermal crystallization will also affect the experimental results of chromium-containing aluminum phosphate; Comparative Examples 9 to 12 prove the importance of the range of crystallization temperature and time to the yield and purity of chromium-containing aluminum phosphate.

[0108] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for resource utilization of iron, aluminum and chromium waste acid, characterized in that: The following steps are involved: S1. Add iron powder to the waste acid of iron, aluminum and chromium to 3+ ,Cr 6+ Reduction to Fe 2+ ,Cr 3+ ; S2. Add sodium phosphate, adjust the pH value to 3.0-3.5, and separate the solid and liquid; S3. hydrochloric acid and sodium chlorate are added to the solution obtained in S2 to obtain a ferric chloride solution; S4. adding phosphoric acid, triethylamine and water to the precipitate obtained in S2. and hydrothermally crystallizing at 150-200° C. for 20-28 h to obtain chromium-containing aluminum phosphate; Wherein, the iron-aluminum-chromium waste acid in step S1 is a hydrochloric acid type iron-aluminum-chromium solution; In step S4, the molar ratio of phosphoric acid (in terms of P2O5): triethylamine: water is 1.0:0.3-0.5:0.5-1.0:20-50.

2. The iron-aluminum-chromium waste acid according to claim 1, characterized in that: The mass fraction of iron in the iron-aluminum-chromium waste acid is 8.0-13.0%.

3. The iron-aluminum-chromium waste acid according to claim 1, characterized in that: The aluminum mass fraction of the iron-aluminum-chromium waste acid is 3.0-6.0%.

4. The iron-aluminum-chromium waste acid according to claim 1, characterized in that: The chromium mass fraction of the iron-aluminum-chromium waste acid is 0.1-0.5%.

5. The method according to claim 1, characterized in that The dosage of the iron powder in step S1 is 2.0-10.0% of the mass of the iron-aluminum-chromium waste acid.

6. The method according to claim 1, characterized in that The step S2 also includes the following steps: Sodium phosphate was added to the solution obtained in step S1. After the solid was stirred and dissolved, a pH adjuster was added to a pH of 3.0 to 3.5, and the reaction was stirred for 1 hour to separate the solid and liquid.

7. The method according to claim 1, characterized in that The addition ratio of sodium phosphate in step S2 is Cr 3+ / PO4 3 The molar ratio is 1 to 1.5:

1.

8. The method according to claim 6, characterized in that The pH regulator is at least one of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

9. The method according to claim 1, characterized in that: The acidity of the hydrochloric acid in step S3 is 2-6%.

10. The method according to claim 1, characterized in that The mass fraction of iron in the ferric chloride solution in step S3 is 9% to 14%.

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