Continuous production method of low Cr < 6 + > chromium oxide green

Abstract

The invention discloses a continuous production method of low Cr < 6 + > chromium oxide green, which comprises the following steps: uniformly adding chromic anhydride into a rotary kiln, and decomposing at high temperature to generate chromium oxide green; performing high-temperature water quenching on the chromium oxide green material at the discharge end of the rotary kiln, and pulping to obtain chromium oxide green slurry; introducing a reducing substance into the chromium oxide green slurry to reduce unreduced Cr < 6 + > in the slurry; washing and filter-pressing the chromium oxide green slurry to remove soluble salt; and carrying out low-temperature drying, crushing and bagging on the obtained filter cake to realize continuous production of the low Cr < 6 + > chromium oxide green. The invention discloses a continuous production method of low Cr < 6 + > chromium oxide green, which comprises the following steps: calcining raw materials in a rotary kiln, and carrying out high-temperature water quenching, pulping, efficient reduction treatment, washing, drying, crushing and bagging on the material at a discharge end to realize low-hexavalent chromium production of all chromium green, thereby improving the current situations of large dust, material color difference and non-uniform granularity in the existing reduction treatment process. The quality of the chromium oxide green product and the production continuity are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of chromium oxide green production, and more specifically, the present invention relates to a low Cr 6+ A process for the continuous production of chromium oxide green. Background Art

[0002] With the improvement of environmental awareness in the current society, chromium products need to further develop green and environmentally friendly products with zero hexavalent chromium and low soluble chromium. The chromium oxide green produced by the traditional chromium anhydride thermal decomposition method is to put chromic anhydride into a rotary kiln and thermally decompose it at a temperature of 800-1350℃ to produce chromium trioxide. However, because chromium anhydride itself is a hexavalent chromium salt product, there is some hexavalent chromium that is not completely decomposed. Therefore, the hexavalent chromium of the product produced is generally between 200-1000ppm, and the soluble chromium is higher (soluble chromium is the sum of soluble hexavalent chromium and soluble trivalent chromium). The traditional method uses the chromium trioxide produced by the thermal method to add a reducing agent to reduce the hexavalent chromium in the product. However, this reduction process requires the chromium trioxide and the reducing agent to be fully mixed. During the mixing period, the dust is slightly larger and the on-site environment is not good. After adding the reducing agent, the physical properties of the product such as fluidity, water absorption and dispersibility have a certain impact.

[0003] CN103253709A (publication date: 2013.08.21) discloses a method for producing chromium trioxide by thermal method, which records a technical solution that achieves the effect of less than 1ppm hexavalent chromium in chromium oxide green product by thermal treatment, mixing 0.2-3% thiourea into the kiln tail material. However, it is found in the actual production process that the above method can generally treat hexavalent chromium to less than 10ppm, and further treatment to reduce hexavalent chromium is still difficult. The biggest problem is that the chromium sulfate generated after the sulfur element in thiourea reduces the hexavalent chromium is a soluble trivalent chromium salt, and the soluble chromium is still greater than 100ppm, which cannot meet the standard requirements of chromium oxide green products with low soluble chromium.

[0004] CN108793252A (publication date: 2018.11.13) discloses a method for reducing hexavalent chromium in chromium oxide green, and records a method for reducing the hexavalent chromium of the product by thermal decomposition using reducing agents such as ammonium salts, ammonia water, alcohols and aldehydes. The principle of the method is basically the same as that of CN103253709A. The purpose of reducing the hexavalent chromium of the product is achieved through thermal treatment, but the effect of completely reducing the soluble chromium of the product to below 20 ppm cannot be achieved. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these objects and other advantages according to the present invention, a low Cr 6+The continuous production method of chromium oxide green comprises the following steps:

[0007] Step 1: uniformly add chromic anhydride into a rotary kiln and decompose it under high temperature to generate chromium oxide green;

[0008] Step 2, high-temperature water quenching and pulping of the chromium oxide green material at the discharge end of the rotary kiln to obtain chromium oxide green slurry;

[0009] Step 3: Add a reducing substance into the chromium oxide green slurry prepared in step 2 to reduce the unreduced Cr in the slurry. 6+ ;

[0010] Step 4: washing and filtering the chromium oxide green slurry treated in step 3 to remove soluble salts to obtain a filter cake;

[0011] Step 5: Dry, crush and package the filter cake obtained in step 4 at low temperature to achieve low Cr 6+ Continuous production of chromium oxide green.

[0012] Preferably, in step 1, the high temperature condition is 700°C to 1400°C.

[0013] Preferably, in the step 2, pulping is performed by directly pulping the material discharged from the kiln, and the pulping time is 10 to 60 minutes.

[0014] Preferably, in the step 2, the mass ratio of the chromium oxide green material to water is 1:2-4.

[0015] Preferably, in step three, the reducing substance is any one or more of alcohol, methanol, sulfur dioxide, formaldehyde, and hydrazine hydrate.

[0016] Preferably, in step three, the dosage ratio of chromium oxide green slurry to reducing substance is 1:0.003-0.01.

[0017] Preferably, in step 5, the low-temperature drying requires a temperature not higher than 300°C.

[0018] Preferably, the device used in the continuous production method comprises:

[0019] Rotary kiln;

[0020] A pulping tank, which is arranged at the discharge end of the rotary kiln;

[0021] A transfer tank connected to the pulping tank via a pipeline;

[0022] a storage tank connected to the transfer tank via a pipeline;

[0023] a first plate and frame filter press connected to the storage tank via a pipeline;

[0024] A washing tank, which is arranged at the outlet of the first plate and frame filter press;

[0025] a second plate and frame filter press connected to the washing tank via a pipeline;

[0026] A low-temperature dryer, whose feed port faces the outlet of the second plate-and-frame filter press;

[0027] A conveyor belt, the transmission start end of which is arranged at the discharge port of the low-temperature dryer;

[0028] A multi-roll mill is arranged at the conveying end of the conveyor belt.

[0029] Preferably, in the step 2, the chromium oxide green material is subjected to high-temperature water quenching and pulping in a pulping tank;

[0030] In the step 3, the slurry of chromium oxide green is introduced into a transfer tank, and a reducing substance is introduced to reduce the unreduced Cr in the slurry. 6+ .

[0031] Preferably, in the step 4, the chromium oxide green slurry treated in step 3 is introduced into a storage tank for standby; the chromium oxide green slurry in the storage tank is filtered by a first plate and frame filter press to remove soluble salts; the filter cake obtained by the filtration is put into a washing tank for slurrying again; the chromium oxide green slurry in the washing tank is filtered again by a second plate and frame filter press to obtain a filter cake.

[0032] Among them, in step 5, after the filter cake is dried at low temperature, the chromium oxide green is crushed by a multi-roll mill, crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using a composite modified dispersant; wherein the preparation method of the composite modified dispersant includes:

[0033] S1. Mix sodium polyacrylate, polyvinyl pyrrolidone and sodium tripolyphosphate in a ratio of 3:1:1, add deionized water in an amount of 20 to 50 times the mass of sodium polyacrylate, and stir evenly to obtain a mixed solution;

[0034] S2, add sodium dodecyl sulfate and polyethylene glycol octyl phenyl ether to the mixed solution, continue stirring until completely dissolved, then raise the temperature to 60-80° C., keep warm for 20-40 min, and obtain dispersion A; wherein the mass ratio of sodium polyacrylate, sodium dodecyl sulfate and polyethylene glycol octyl phenyl ether is 3:0.2-0.5:1-3;

[0035] S3, let the dispersion A stand at room temperature, add ethanol and polypropylene glycol PPG-2000, stir again to obtain dispersion B, evaporate and concentrate the dispersion B, and freeze-dry it at -40 to -20°C to obtain a composite modified dispersant. The mass volume ratio of sodium polyacrylate, ethanol and polypropylene glycol PPG-2000 is 3g:50 to 80mL:0.1 to 0.4g.

[0036] The chromium oxide green powder and the prepared compound modified dispersant are added into water, wherein the mass of the water is 2 to 3 times the mass of the chromium oxide green powder, and the compound modified dispersant accounts for 1% to 5% of the mass of the chromium oxide green powder. The mixture is stirred at a speed of 300 to 1200 rpm for 30 to 60 minutes, and then allowed to stand for 6 to 8 hours. After filtering and washing, the chromium oxide green powder is dried at a temperature of 200 to 300° C. to obtain slurry-dispersed chromium oxide green powder.

[0037] The present invention has at least the following beneficial effects:

[0038] The invention discloses a low Cr 6+ A continuous production method for chromium oxide green (chromium oxide), wherein the raw materials are calcined in a rotary kiln, and the materials at the discharge end are subjected to high-temperature water quenching and pulping, and then subjected to efficient reduction treatment, washing, drying, crushing and packaging, so as to achieve the production of all chromium green low hexavalent chromium, improve the existing reduction treatment process with high dust, material color difference and uneven particle size, and further improve the quality of chromium green products and the continuity of production.

[0039] The invention adds a compound modified dispersant during the chromium oxide green pulping process, thereby improving the dispersibility and particle size distribution uniformity of the chromium oxide green powder during pulping, reducing the agglomeration of the chromium oxide green powder, and thus improving the quality of the chromium oxide green product.

[0040] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of the continuous production device used in Example 1. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0043] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0044] Example 1

[0045] This embodiment provides a low Cr 6+ Continuous production method of chromium oxide green, such as Figure 1 As shown, the structure of the continuous production device used includes:

[0046] Rotary kiln 1;

[0047] A pulping tank 2, which is arranged at the discharge end of the rotary kiln 1;

[0048] A transfer tank 3, which is connected to the pulping tank 2 through a pipeline;

[0049] A storage tank 5, which is connected to the transfer tank 3 through a pipeline;

[0050] A first plate-frame filter press 6, which is connected to the storage tank 5 via a pipeline;

[0051] A washing tank 7, which is arranged at the outlet of the first plate and frame filter press 6;

[0052] A second plate-frame filter press 8, which is connected to the washing tank 7 via a pipeline;

[0053] A low-temperature dryer 9, whose feed port faces the outlet of the second plate-frame filter press 8;

[0054] A conveyor belt 10, the conveying start end of which is arranged at the discharge port of the low-temperature dryer 9;

[0055] The multi-roller mill 11 is arranged at the conveying end of the conveyor belt 10 .

[0056] Among them, the continuous production device is used to produce low Cr 6+ The method for continuous production of chromium oxide green comprises the following steps:

[0057] Step 1, adding chromic anhydride evenly into the rotary kiln 1, calcining and decomposing at 900° C. to generate chromium oxide green;

[0058] Step 2: Pour the chromium oxide green material calcined at the discharge end of the rotary kiln directly into the pulping tank 2 for high-temperature water quenching and pulping to obtain chromium oxide green slurry. The mass of water is twice that of the chromium oxide green material, and the pulping time is 30 minutes;

[0059] Step 3: The slurried chromium oxide green slurry is introduced into the transfer tank 3, and alcohol is added to reduce the Cr in the chromium oxide green slurry. 6+ During the addition of alcohol, sulfuric acid and phosphoric acid (700 mL of an equal volume of 98% concentrated sulfuric acid and phosphoric acid mixed solution) were used to detect the presence of Cr in the slurry. 6+ , stop adding alcohol until there is no color reaction in the sulfur-phosphorus mixed acid test slurry, and the final amount of alcohol is 0.6% of the mass of the chromium oxide green slurry;

[0060] Step 4, introducing the treated chromium oxide green slurry into a storage tank 5 for standby use; filtering the chromium oxide green slurry in the storage tank 5 with a first plate-frame filter press 6 to remove soluble salts; putting the filter cake obtained by filtering into a washing tank 7 for re-slurrying; filtering the chromium oxide green slurry in the washing tank 7 again with a second plate-frame filter press 8 to obtain a filter cake;

[0061] Step 5: Put the filter cake obtained by the second plate-frame filter press 8 into a low-temperature dryer 9 for low-temperature drying, and the drying temperature is not higher than 300°C; the dried chromium oxide green material is transported to a multi-roll mill 11 through a conveyor belt 10 for crushing, and then packaged to achieve low Cr 6+ The continuous production of chromium oxide green was measured to determine the soluble chromium (Cr 6+ ) content is 10ppm, achieving low Cr 6+ Purpose of chromium oxide green product production.

[0062] Example 2

[0063] This embodiment provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 1 in that the reducing agent used in step 3 is methanol, and sulfuric acid and phosphoric acid mixed acid are used to detect whether the slurry contains Cr during the addition of methanol. 6+ , until the sulfur-phosphorus mixed acid slurry has no color reaction, the addition of methanol is stopped. The process parameters of the remaining steps of this embodiment are the same as those of Example 1.

[0064] Example 3

[0065] This embodiment provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 1 in that the reducing agent used in step 3 is sulfur dioxide, and sulfur-phosphorus mixed acid is used to detect whether the slurry contains Cr in the process of introducing sulfur dioxide. 6+ , until the sulfur-phosphorus mixed acid slurry has no color reaction, the introduction of sulfur dioxide is stopped. The process parameters of the remaining steps of this embodiment are the same as those of Example 1.

[0066] Example 4

[0067] This embodiment provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 1 in that the reducing agent used in step 3 is formaldehyde, and sulfuric acid and phosphoric acid mixed acid are used to detect whether the slurry contains Cr in the process of adding formaldehyde. 6+ , until the sulfur-phosphorus mixed acid slurry has no color reaction, the addition of formaldehyde is stopped. The process parameters of the remaining steps of this embodiment are the same as those of Example 1.

[0068] Example 5

[0069] This embodiment provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 1 in that the reducing agent used in step 3 is hydrazine hydrate, and sulfuric acid and phosphoric acid are used to detect whether the slurry contains Cr during the addition of hydrazine hydrate. 6+ , until the sulfur-phosphorus mixed acid detection slurry has no color reaction, stop adding hydrazine hydrate. The process parameters of the remaining steps of this embodiment are the same as those of Example 1.

[0070] Example 6

[0071] This embodiment provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 1, wherein, in step 5, after the filter cake is dried at low temperature, the chromium oxide green is crushed with a multi-roll mill, the crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using a composite modified dispersant; wherein the preparation method of the composite modified dispersant comprises:

[0072] S1, 30g sodium polyacrylate, 10g polyvinyl pyrrolidone and 10g sodium tripolyphosphate were mixed, and 1200mL deionized water (the mass of sodium polyacrylate) was added, and stirred evenly to obtain a mixed solution;

[0073] S2, add 4g of sodium dodecyl sulfate and 30g of polyethylene glycol octylphenyl ether to the mixed solution, continue stirring until completely dissolved, then raise the temperature to 80°C and keep warm for 40min to obtain dispersion A;

[0074] S3. Allow the dispersion A to stand at room temperature, add 500 mL of ethanol and 4 g of polypropylene glycol PPG-2000, and stir evenly again to obtain a dispersion B. Evaporate and concentrate the dispersion B, and freeze-dry it at -20°C to obtain a composite modified dispersant.

[0075] The chromium oxide green powder and the prepared compound modified dispersant are added into water, wherein the mass of the water is twice that of the chromium oxide green powder and the compound modified dispersant accounts for 5% of the mass of the chromium oxide green powder. The mixture is stirred at a speed of 600 rpm for 40 minutes, and then allowed to stand for 6 hours. After filtering and washing, the chromium oxide green powder is dried at 200°C to obtain slurry-dispersed chromium oxide green powder.

[0076] The methods and process parameters of the remaining steps of this embodiment are the same as those of Embodiment 1.

[0077] Example 7

[0078] This embodiment provides a low Cr 6+The continuous production method of chromium oxide green is different from that of Example 1, wherein, in step 5, after the filter cake is dried at low temperature, the chromium oxide green is crushed with a multi-roll mill, the crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using a composite modified dispersant; wherein the preparation method of the composite modified dispersant comprises:

[0079] S1. Mix 30 g of sodium polyacrylate, 10 g of polyvinyl pyrrolidone and 10 g of sodium tripolyphosphate, add 1500 mL of deionized water times the mass of sodium polyacrylate, stir well to obtain a mixed solution;

[0080] S2, add 5g of sodium dodecyl sulfate and 20g of polyethylene glycol octylphenyl ether to the mixed solution, continue stirring until completely dissolved, then raise the temperature to 80°C and keep warm for 40min to obtain dispersion A;

[0081] S3. Allow the dispersion A to stand at room temperature, add 500 mL of ethanol and 2 g of polypropylene glycol PPG-2000, and stir evenly again to obtain a dispersion B. Evaporate and concentrate the dispersion B, and freeze-dry it at -20°C to obtain a composite modified dispersant.

[0082] The chromium oxide green powder and the prepared compound modified dispersant are added into water, wherein the mass of the water is twice that of the chromium oxide green powder and the compound modified dispersant accounts for 5% of the mass of the chromium oxide green powder. The mixture is stirred at a speed of 600 rpm for 40 minutes, and then allowed to stand for 6 hours. After filtering and washing, the chromium oxide green powder is dried at 200°C to obtain slurry-dispersed chromium oxide green powder.

[0083] The methods and process parameters of the remaining steps of this embodiment are the same as those of Embodiment 1.

[0084] Comparative Example 1

[0085] This comparative example provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 6 in that, after the filter cake is dried at low temperature in step five, the chromium oxide green is crushed with a multi-roll mill, the crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using sodium polyacrylate, and the mass of the sodium polyacrylate is the same as the mass of the compound modified dispersant in Example 6.

[0086] The methods and process parameters of the remaining steps of this comparative example are the same as those of Example 6.

[0087] Comparative Example 2

[0088] This comparative example provides a low Cr 6+The continuous production method of chromium oxide green is different from that of Example 6 in that, after the filter cake is dried at low temperature in step five, the chromium oxide green is crushed with a multi-roll mill, the crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using polyethylene glycol octylphenyl ether, and the mass of the sodium polyacrylate is the same as the mass of the compound modified dispersant in Example 6.

[0089] The methods and process parameters of the remaining steps of this comparative example are the same as those of Example 6.

[0090] Comparative Example 3

[0091] This comparative example provides a low Cr 6+ The continuous production method of chromium oxide green is different from that of Example 6 in that, after the filter cake is dried at low temperature in step five, the chromium oxide green is crushed with a multi-roll mill, the crushed and sieved through 80 mesh, and then the sieved chromium oxide green powder is slurried and dispersed using a mixed dispersant, and the quality of the mixed dispersant is the same as that of the compound modified dispersant in Example 6. The mixed dispersant is prepared by directly mixing sodium polyacrylate, polyvinyl pyrrolidone, sodium tripolyphosphate, sodium dodecyl sulfate, polyethylene glycol octyl phenyl ether, ethanol and polypropylene glycol PPG-2000, and the amount ratio of sodium polyacrylate, polyvinyl pyrrolidone, sodium tripolyphosphate, sodium dodecyl sulfate, polyethylene glycol octyl phenyl ether, ethanol and polypropylene glycol PPG-2000 is 15g:5g:5g:2g:15g:250mL:2g, that is, the amount ratio of each raw material is the same as that in Example 6; the preparation method of the mixed dispersant is to add sodium polyacrylate, polyvinyl pyrrolidone, sodium tripolyphosphate, sodium dodecyl sulfate, polyethylene glycol octyl phenyl ether and polypropylene glycol PPG-2000 into ethanol at the same time, stir and mix evenly, and evaporate and concentrate to remove ethanol to obtain a mixed dispersant.

[0092] The methods and process parameters of the remaining steps of this comparative example are the same as those of Example 6.

[0093] The particle size distribution of the chromium oxide green powder prepared in Example 1, Example 6, Example 7 and Comparative Examples 1 to 3 was measured respectively, and the following table was obtained:

[0094] D10(μm) D90(μm) Example 1 127.2 355.9 Example 6 25.0 80.4 Example 7 29.3 95.7 Comparative Example 1 68.5 161.0 Comparative Example 2 77.6 169.1 Comparative Example 3 50.7 145.8 In Example 6, the sieving was not followed by slurry dispersion. 98.5 174.2

[0095] As can be seen from the above table, Example 6 and Example 7 use a compound modified dispersant for slurry dispersion, and the particle size distribution of the chromium oxide green powder obtained is more concentrated, more uniform, and smaller in size, which is significantly better than Example 1 and Example 6 Comparative Examples 1 to Comparative Examples 3.

[0096] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0097] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A low Cr 6+ A method for the continuous production of chromium oxide green, characterized in that: The following steps are involved: Step 1: uniformly add chromic anhydride into a rotary kiln and decompose it under high temperature to generate chromium oxide green; Step 2, high-temperature water quenching and pulping of the chromium oxide green material at the discharge end of the rotary kiln to obtain chromium oxide green slurry; Step 3: Add a reducing substance into the chromium oxide green slurry prepared in step 2 to reduce the unreduced Cr in the slurry. 6+ ; Step 4: washing and filtering the chromium oxide green slurry treated in step 3 to remove soluble salts to obtain a filter cake; Step 5: Dry, crush and package the filter cake obtained in step 4 at low temperature to achieve low Cr 6+ Continuous production of chromium oxide green.

2. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 1, the high temperature condition is 700°C to 1400°C.

3. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 2, the pulping is performed by directly pulping the material discharged from the kiln tail, and the pulping time is 10 to 60 minutes.

4. The low Cr as claimed in claim 3 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 2, the ratio of the chromium oxide green material to water is 1:2-4.

5. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 3, the reducing substance is any one or more of alcohol, methanol, sulfur dioxide, formaldehyde, and hydrazine hydrate.

6. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step three, the mass ratio of the chromium oxide green slurry to the reducing substance is 1:0.003-0.

01.

7. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 5, the low temperature drying requires the temperature to be no higher than 300°C.

8. The low Cr as claimed in claim 1 6+ A method for the continuous production of chromium oxide green, characterized in that: The continuous production device used in the continuous production method includes: Rotary kiln; A pulping tank, which is arranged at the discharge end of the rotary kiln; A transfer tank connected to the pulping tank via a pipeline; a storage tank connected to the transfer tank via a pipeline; a first plate and frame filter press connected to the storage tank via a pipeline; A washing tank, which is arranged at the outlet of the first plate and frame filter press; a second plate and frame filter press connected to the washing tank via a pipeline; A low-temperature dryer, whose feed port faces the outlet of the second plate-and-frame filter press; A conveyor belt, the transmission start end of which is arranged at the discharge port of the low-temperature dryer; A multi-roll mill is arranged at the conveying end of the conveyor belt.

9. The low Cr as claimed in claim 8 6+ A method for the continuous production of chromium oxide green, characterized in that: In the step 2, the chromium oxide green material is subjected to high-temperature water quenching and pulping in a pulping tank; In the step 3, the slurry of chromium oxide green is introduced into a transfer tank, and a reducing substance is introduced to reduce the unreduced Cr in the slurry. 6+ .

10. The low Cr as claimed in claim 9 6+ A method for the continuous production of chromium oxide green, characterized in that: Also includes: In the step 4, the chromium oxide green slurry treated in step 3 is introduced into a storage tank for standby; the chromium oxide green slurry in the storage tank is filtered by a first plate and frame filter press to remove soluble salts; the filter cake obtained by the filtration is put into a washing tank for slurrying again; the chromium oxide green slurry in the washing tank is filtered again by a second plate and frame filter press to obtain a filter cake.

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