Preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid

Abstract

The invention belongs to the technical field of catalyst precursor preparation, and discloses a rhodium nitrate crystal preparation method based on rhodium-containing waste liquid. The method comprises the following steps: taking rhodium-containing waste liquid obtained in a rhodium waste recovery process as an initial raw material, performing ultrasonic-assisted direct reduction by utilizing a formic acid solution to obtain active rhodium black, dissolving the active rhodium black by adopting a chlorination method to obtain a relatively pure chlororhodate solution, adding hydroxide to obtain rhodium hydroxide, washing, and adding nitric acid to obtain a rhodium nitrate solution; and finally drying by distillation and removing acid to obtain crystal rhodium nitrate. According to the preparation scheme, a formic acid method is improved, powder wrapping is reduced through liquid-liquid reduction, and the content of base metal impurities is reduced by controlling the pH value, so that the rhodium black with relatively high purity is obtained. Moreover, the ultrasonic-assisted reduction can shorten the reduction reaction time and increase the specific surface area of the rhodium black, so that the rhodium black is better in activity and easier to react with chlorine, and the overall production cycle is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst precursor preparation, and in particular to a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid. Background Art

[0002] Rhodium nitrate is an important catalyst precursor, mainly used in the production of automobile exhaust catalysts. At present, the main supply form of rhodium nitrate is rhodium nitrate solution, which usually contains 5% or 10%. Compared with solution, solid rhodium nitrate can be prepared by the user to obtain the required concentration and pH, which is more conducive to experimental improvement. In addition, solid transportation is more convenient than liquid transportation, and the freight of solid rhodium nitrate with the same rhodium content is cheaper than that of liquid rhodium nitrate.

[0003] Generally, rhodium nitrate is prepared by dissolving rhodium hydroxide in nitric acid.

[0004] For example, a method for synthesizing rhodium nitrate solution using rhodium-containing waste liquid is mentioned in a Chinese patent application with publication number CN112537808A, wherein the method is as follows: a precipitant is added to a rhodium leaching solution and boiled for 12 to 24 hours to precipitate rhodium, then cooled and filtered, dissolved, filtered, washed, dissolved to obtain a rhodium-containing solution, exchanged with a resin to obtain a rhodium solution, then potassium hydroxide is added to obtain rhodium hydroxide, and washed and dissolved in nitric acid to obtain a rhodium nitrate solution. However, the above preparation process is somewhat lengthy.

[0005] A Chinese patent application with publication number CN108264100A mentions an efficient synthesis method of rhodium nitrate solution, wherein rhodium powder and barium peroxide are fully mixed and dissolved to obtain rhodium hydroxide, which is then washed and dissolved in nitric acid to obtain rhodium nitrate solution. However, barium peroxide is an explosive substance and is highly dangerous, and barium needs to be removed with sulfuric acid to prepare the rhodium solution.

[0006] In addition to using hydroxide, the Chinese patent application with publication number CN115537833A also mentions directly using activated metal rhodium and nitric acid to prepare rhodium nitrate solution in an electrolytic cell, and then using rotary evaporation below 40° C. to obtain rhodium nitrate dihydrate. However, the speed of rotary evaporation below 40° C. is slow, and once the temperature is out of control, rhodium nitrate may decompose explosively, leading to accidents. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, so as to overcome the technical difficulties in preparing solid rhodium nitrate in the existing scheme.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The invention provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, comprising the following steps:

[0010] (1) mixing rhodium-containing waste liquid, formic acid, alkaline substances and water, and performing a reduction reaction under the assistance of ultrasound to obtain rhodium black;

[0011] (2) mixing the rhodium black, chloride and chlorine to carry out a chlorination reaction; dissolving and filtering the product of the chlorination reaction to obtain a chlororhodium salt solution;

[0012] (3) mixing the chlororhodium salt solution with a hydroxide to obtain rhodium hydroxide;

[0013] (4) mixing the rhodium hydroxide with a nitric acid solution, performing a neutralization reaction, and obtaining a rhodium nitrate solution; evaporating the rhodium nitrate solution to dryness, washing, and obtaining rhodium nitrate crystals;

[0014] Wherein, the rhodium-containing waste liquid in step (1) includes potassium chlororhodate or sodium chlororhodate.

[0015] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (1), the molar ratio of the rhodium element in the rhodium-containing waste liquid to the formic acid is 1:1.5~4.5; and the pH value after mixing the rhodium-containing waste liquid, formic acid, alkaline substance and water is 3~5.

[0016] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (1), the temperature of the reduction reaction is 60-100°C, the time of the reduction reaction is 2-5h, and the ultrasonic power of the reduction reaction is 200-1200W.

[0017] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, step (1) further comprises the following steps after the reduction reaction: under a protective atmosphere, the product after the reduction reaction is filtered, washed, and then vacuum dried in sequence; the protective atmosphere comprises nitrogen, argon or helium.

[0018] Preferably, in the preparation method of rhodium nitrate crystals based on rhodium-containing waste liquid, the specific process of step (2) comprises the following steps:

[0019] The rhodium black, chloride and chlorine are mixed to carry out a chlorination reaction; the product of the chlorination reaction is dissolved and filtered to obtain a filtrate and a filter residue;

[0020] Replace the rhodium black with the obtained filter residue, and repeat the chlorination reaction, dissolution, and filtration process 1 to 4 times;

[0021] All the obtained filtrates were mixed to obtain a chlororhodium salt solution.

[0022] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (2), the mass ratio of the rhodium black to the chloride is 1:2-5; and the introduction rate of the chlorine gas is 0.1-3 L / min.

[0023] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (2), the temperature of the chlorination reaction is 550-750° C., and the time of the chlorination reaction is 1-2.5 h.

[0024] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (2), the rhodium chloride solution further comprises: passing the rhodium chloride solution through a cation exchange resin before carrying out subsequent steps.

[0025] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (3), the pH value of the chlororhodium salt solution after mixing with the hydroxide is 7 to 8.

[0026] Preferably, in the method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, in step (4), the temperature of the neutralization reaction is 60 to 95° C., and the time of the neutralization reaction is 0.5 to 2 h.

[0027] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Formic acid reduction is usually to obtain rhodium black (rhodium powder containing partially oxidized rhodium) from a purified rhodium solution. The preparation scheme of the present invention improves the formic acid method, reduces powder coating by using liquid-liquid reduction, and reduces the content of base metal impurities by controlling pH, thereby obtaining rhodium black with higher purity.

[0029] (2) The present invention utilizes ultrasound-assisted reduction to shorten the reduction reaction time and increase the specific surface area of ​​rhodium black, thereby making the rhodium black more active and easier to react with chlorine, thereby shortening the overall production cycle.

[0030] (3) The present invention utilizes an evaporator to evaporate the rhodium nitrate solution, which is fast and easier to industrialize, and can avoid the explosive decomposition of rhodium nitrate due to temperature runaway. DETAILED DESCRIPTION

[0031] The invention provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, comprising the following steps:

[0032] (1) mixing rhodium-containing waste liquid, formic acid, alkaline substances and water, and performing a reduction reaction under the assistance of ultrasound to obtain rhodium black;

[0033] (2) mixing the rhodium black, chloride and chlorine to carry out a chlorination reaction; dissolving and filtering the product of the chlorination reaction to obtain a chlororhodium salt solution;

[0034] (3) mixing the chlororhodium salt solution with a hydroxide to obtain rhodium hydroxide;

[0035] (4) mixing the rhodium hydroxide with a nitric acid solution, performing a neutralization reaction, and obtaining a rhodium nitrate solution; evaporating the rhodium nitrate solution to dryness, washing, and obtaining rhodium nitrate crystals;

[0036] Wherein, the rhodium-containing waste liquid in step (1) includes potassium chlororhodate or sodium chlororhodate.

[0037] In the present invention, the main chemical reaction occurring in the preparation method (the alkaline substance in step (1) is potassium hydroxide as an example, the chloride in step (2) is potassium chloride as an example, and the hydroxide in step (3) is potassium hydroxide as an example) is as follows:

[0038] 2K3RhCl6+3HCOOH+6KOH=2Rh+3CO2+12KCl+6H2O;

[0039] 2Rh+6KCl+3Cl2=2K3RhCl6;

[0040] K3RhCl6+3KOH=Rh(OH)3+6KCl;

[0041] Rh(OH)3+3HNO3=Rh(NO3)3+3H2O.

[0042] Rh(NO3)3+2H2O=Rh(NO3)3·2H2O

[0043] In the present invention, in step (1), the alkaline substance preferably includes potassium hydroxide or sodium hydroxide, and more preferably includes potassium hydroxide.

[0044] In the present invention, in step (1), the method of mixing the rhodium-containing waste liquid, formic acid, alkaline substance and water is preferably: mixing formic acid with water to obtain a formic acid solution; mixing the alkaline substance with water to obtain an alkaline solution; adding the formic acid solution dropwise to the rhodium-containing waste liquid to carry out a first reaction; and adding the alkaline solution dropwise to the solution obtained by the first reaction to carry out a second reaction.

[0045] In the present invention, the mass concentration of rhodium element in the rhodium-containing waste liquid is preferably 0.1-10%, more preferably 0.4-5%, and even more preferably 0.5-2%.

[0046] In the present invention, the mass concentration of the formic acid solution is preferably 80 to 98%, more preferably 80 to 90%, and even more preferably 85%.

[0047] In the present invention, when the formic acid solution is added dropwise to the rhodium-containing waste liquid, the temperature of the rhodium-containing waste liquid is preferably 60 to 100°C, more preferably 75 to 95°C, and even more preferably 85 to 90°C.

[0048] In the present invention, the rate of dripping the formic acid solution is preferably 2 to 50 mL / min, more preferably 2 to 20 mL / min, and more preferably 2 to 10 mL / min.

[0049] In the present invention, the time of the first reaction is preferably 0.5 to 2 hours, more preferably 40 minutes to 1.5 hours, and more preferably 40 minutes to 1 hour.

[0050] In the present invention, the mass concentration of the alkaline solution is preferably 5 to 20%, more preferably 10 to 20%, and even more preferably 10 to 15%.

[0051] In the present invention, the rate of adding the alkaline solution dropwise is preferably 10 to 100 mL / min, more preferably 10 to 50 mL / min, and even more preferably 10 to 20 mL / min.

[0052] In the present invention, the time of the second reaction is preferably 0.5 to 2 hours, more preferably 0.5 to 1 hour, and more preferably 0.5 hour to 40 minutes.

[0053] In the present invention, in step (1), the molar ratio of the rhodium element in the rhodium-containing waste liquid to the formic acid is preferably 1:1.5-4.5, more preferably 1:2-4, and more preferably 1:3-3.6.

[0054] In the present invention, in step (1), the pH value of the mixture of the rhodium-containing waste liquid, formic acid, alkaline substance and water is preferably 3 to 5, more preferably 3 to 4.5, and more preferably 3 to 4.

[0055] In the present invention, in step (1), the temperature of the reduction reaction is preferably 60-100°C, more preferably 75-95°C, more preferably 85-90°C; the time of the reduction reaction is preferably 2-5h, more preferably 2-4h, more preferably 2-3h; the ultrasonic power of the reduction reaction is preferably 200-1200W, more preferably 600-1100W, more preferably 800-1000W.

[0056] In the present invention, step (1) preferably further comprises the following steps after the reduction reaction: under a protective atmosphere, the product after the reduction reaction is filtered, washed, and then vacuum dried in sequence.

[0057] In the present invention, the protective atmosphere preferably includes nitrogen, argon or helium.

[0058] In the present invention, the method of suction filtration is not limited, as long as solid-liquid separation is achieved.

[0059] In the present invention, the washing agent is preferably water. The washing conditions are not limited, and washing until neutrality is sufficient.

[0060] In the present invention, the vacuum drying temperature is preferably 60-90°C, more preferably 75-90°C, and more preferably 85-90°C; the vacuum drying time is preferably 2-8h, more preferably 3-6h, and more preferably 4-5h.

[0061] In the present invention, the chloride in step (2) preferably includes potassium chloride or sodium chloride, and more preferably includes potassium chloride.

[0062] In the present invention, the specific process of step (2) preferably includes the following steps:

[0063] The rhodium black, chloride and chlorine are mixed to carry out a chlorination reaction; the product of the chlorination reaction is dissolved and filtered to obtain a filtrate and a filter residue;

[0064] The obtained filter residue is used to replace the rhodium black, and the process of chlorination reaction, dissolution and filtration is repeated 1 to 4 times (more preferably 1 to 3 times, more preferably 1 time);

[0065] All the obtained filtrates were mixed to obtain a chlororhodium salt solution.

[0066] In the present invention, the filter residue is dried before the repeated operation. The drying conditions are not limited and can be carried out according to the schemes known to those skilled in the art.

[0067] In the present invention, in step (2), the mass ratio of the rhodium black to the chloride is preferably 1:2-5, more preferably 1:2-3.5, and more preferably 1:2.02-2.2.

[0068] In the present invention, in step (2), the introduction rate of the chlorine gas is preferably 0.1 to 3 L / min, more preferably 0.5 to 2.5 L / min, and more preferably 1 to 2 L / min.

[0069] In the present invention, in step (2), the temperature of the chlorination reaction is preferably 550-750°C, more preferably 580-680°C, and more preferably 600-650°C; the time of the chlorination reaction is preferably 1-2.5h, more preferably 1.5-2.5h, and more preferably 2-2.5h.

[0070] In the present invention, in step (2), the chlororhodium salt solution further comprises: passing the chlororhodium salt solution through a cation exchange resin before carrying out subsequent steps.

[0071] In the present invention, the cation exchange resin is preferably 001×7 strong acid styrene cation exchange resin.

[0072] In the present invention, in step (3), the hydroxide is preferably a hydroxide solution.

[0073] In the present invention, in step (3), the hydroxide preferably includes potassium hydroxide or sodium hydroxide, and more preferably includes potassium hydroxide.

[0074] In the present invention, the mass concentration of the hydroxide solution is preferably 5 to 20%, more preferably 10 to 20%, and even more preferably 10 to 15%.

[0075] In the present invention, in step (3), the pH value of the chlororhodium salt solution after mixing with the hydroxide is preferably 7 to 8, more preferably 7.2 to 8, and more preferably 7.5 to 8.

[0076] In the present invention, in step (3), after the chlororhodium salt solution is mixed with the hydroxide, the process further comprises: filtering and washing the obtained precipitate.

[0077] In the present invention, the filtering conditions are not limited, and any method known to those skilled in the art may be used.

[0078] In the present invention, the cleaning method is preferably: cleaning with water multiple times.

[0079] In the present invention, the total mass of the water is preferably 200 to 1000 times the mass of the rhodium hydroxide, more preferably 200 to 500 times, and more preferably 300 to 400 times.

[0080] In the present invention, the number of times of the multiple washing is preferably 3 to 4 times, and more preferably 3 times.

[0081] In the present invention, in step (4), the nitric acid is preferably a nitric acid solution.

[0082] In the present invention, the mass concentration of the nitric acid solution is preferably 65-68%.

[0083] In the present invention, in step (4), the mass ratio of the rhodium hydroxide to the nitric acid is 1:2-5, more preferably 1:2-3.5, and more preferably 1:2.5-3.

[0084] In the present invention, in step (4), the temperature of the neutralization reaction is preferably 60 to 95°C, more preferably 75 to 95°C, and more preferably 85 to 90°C; the time of the neutralization reaction is preferably 0.5 to 2h, more preferably 1 to 2h, and more preferably 1 to 1.5h.

[0085] In the present invention, in step (4), the evaporation to dryness is preferably carried out in a water bath, and the temperature of the evaporation to dryness is preferably 80 to 96°C, more preferably 85 to 96°C, and more preferably 90 to 95°C.

[0086] In the present invention, in step (4), the washing method is preferably: washing with water multiple times.

[0087] In the present invention, the total mass of the water is preferably 2 to 20 times the mass of the rhodium hydroxide, more preferably 5 to 15 times, and more preferably 8 to 12 times.

[0088] In the present invention, the number of times of the multiple washing is preferably 3 to 5 times, and more preferably 4 to 5 times.

[0089] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0090] Example 1

[0091] The present embodiment provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, comprising the following steps:

[0092] (1) Weigh 2000.0 g of a rhodium-containing waste liquid (the rhodium element exists in the form of potassium chlororhodate, and the impurity metals in the solution are Cu: 1000 ppm, Fe: 2000 ppm, and Ni: 3200 ppm) with a rhodium mass fraction of 2.00%, and heat to 90° C. with stirring and an ultrasonic power of 800 W; add 74.2 g of an 85 wt % formic acid solution to the above-mentioned rhodium-containing waste liquid at a rate of 3 mL / min, and react for 40 min after the addition is complete; then add 10 wt % potassium hydroxide solution to the above-mentioned reaction solution at a rate of 20 mL / min until the pH is 4.0, and react for 30 min after the addition is complete; filter the product obtained by the reaction by suction with nitrogen, wash the precipitate with water until it is neutral, and then vacuum dry it at 85° C. for 4 h to obtain 44.5 g of rhodium black (rhodium content 88.12 wt %, Cu: 100 ppm, Fe: 300 ppm, Ni: 280 ppm), with a yield of 98.0%;

[0093] (2) 44.5 g of rhodium black and 90.0 g of potassium chloride powder were mixed evenly, placed in a quartz boat, the quartz boat was placed in a reactor, chlorine gas was introduced at 600° C., the chlorine introduction rate was 1.5 L / min, and the reaction was carried out for 2.5 h; the product was dissolved in 500.0 g of water and filtered; the filtrate was collected, and the filter residue was dried to obtain 8.9 g of filter residue; 8.9 g of the filter residue was mixed with 20.0 g of potassium chloride and the above reaction, dissolution, and filtering steps were repeated to obtain 5.3 g of filter residue; all the filtrates were collected and combined, the total amount of the filtrate was 800.0 g, and the filtrate was potassium chlororhodate solution;

[0094] (3) passing the potassium chlororhodate solution through a cation exchange resin (manufactured by Zhejiang Zhengguang Industrial Co., Ltd., model 001×7), adding 10 wt % potassium hydroxide solution to the potassium chlororhodate solution after ion exchange to adjust the pH to 7.2, and precipitating; after the precipitation is complete, filtering the precipitate, and washing the rhodium hydroxide precipitate with 12 kg of deionized water three times to obtain 290.13 g of rhodium hydroxide (water content 80.1%);

[0095] (4) Add 166.0 g of 65 wt% concentrated nitric acid to 290.13 g of rhodium hydroxide, reflux at 90° C. for 1 h, and filter to obtain a rhodium nitrate solution; evaporate to dryness in a water bath at 90° C., wash with 600.0 g of deionized water three times to remove the nitric acid, and obtain 123.2 g of rhodium nitrate crystals (rhodium content 31.5 wt%, Cu: 15 ppm, Fe: 20 ppm, Ni: 18 ppm), with a yield of 97.02%.

[0096] Example 2

[0097] The present embodiment provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, comprising the following steps:

[0098] (1) Weigh 6000.0 g of a rhodium-containing waste liquid (rhodium is present in the form of potassium chlororhodate, and the impurity metals in the solution are Cu: 1230 ppm, Fe: 1890 ppm, and Ni: 3560 ppm) with a rhodium mass fraction of 0.50%, and heat to 85° C. with an ultrasonic power of 1000 W; add 50.0 g of an 85 wt % formic acid solution to the rhodium-containing waste liquid at a rate of 2 mL / min, and react for 60 min after the addition is complete; then add 15 wt % potassium hydroxide solution to the reaction solution at a rate of 10 mL / min until the pH is 3.0, and react for 40 min after the addition is complete; filter the product obtained by the reaction by suction under nitrogen, wash the precipitate with water until it is neutral, and then vacuum dry at 85° C. for 4 h to obtain 32.0 g of rhodium black (rhodium content 89.2 wt %, Cu: 80 ppm, Fe: 270 ppm, Ni: 240 ppm), with a yield of 95.1%;

[0099] (2) 32.0 g of rhodium black and 70.0 g of potassium chloride powder were mixed evenly, placed in a quartz boat, the quartz boat was placed in a reactor, chlorine gas was introduced at 600° C., the chlorine introduction rate was 2.0 L / min, and the reaction was carried out for 2.0 h; the product was dissolved in 500.0 g of water and filtered; the filtrate was collected, and the filter residue was dried to obtain 4.5 g of filter residue; 4.5 g of the filter residue was mixed with 10.0 g of potassium chloride and the above reaction, dissolution, and filtering steps were repeated to obtain 3.5 g of filter residue; all the filtrates were collected and combined, the total amount of the filtrate was 800.0 g, and the filtrate was potassium chlororhodate solution;

[0100] (3) passing the potassium chlororhodate solution through a cation exchange resin (manufactured by Zhejiang Zhengguang Industrial Co., Ltd., model 001×7), adding 10 wt % potassium hydroxide solution to the potassium chlororhodate solution after ion exchange to adjust the pH to 8.0, and precipitating; after the precipitation is complete, filtering the precipitate, and washing the rhodium hydroxide precipitate with 10 kg of deionized water 4 times to obtain 234.80 g of rhodium hydroxide (water content 82.0%);

[0101] (4) Add 160.0 g of 65 wt% concentrated nitric acid to 234.80 g of rhodium hydroxide, reflux at 85° C. for 1.5 h, and filter to obtain a rhodium nitrate solution; evaporate to dryness in a water bath at 95° C., wash with 600.0 g of deionized water for 5 times to remove the nitric acid, and obtain 90.6 g of rhodium nitrate crystals (rhodium content 31.2 wt%, Cu: 12 ppm, Fe: 15 ppm, Ni: 14 ppm), with a yield of 94.22%.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, which is different from Example 1 in that: the ultrasonic wave in step (1) is removed to obtain 44.3 g of rhodium black (rhodium content 82.1 wt%, Cu: 300 ppm, Fe: 600 ppm, Ni: 590 ppm), with a yield of 90.9%; in step (2), the rhodium black and the filter residue obtained after the reaction need to be subjected to chlorination reactions for a total of 3 times, and the proportions and reaction conditions of the other steps are the same as those in Example 1, to obtain 116.1 g of rhodium nitrate crystals (rhodium content 31.0 wt%, Cu: 50 ppm, Fe: 70 ppm, Ni: 38 ppm), with a yield of 90.0%.

[0104] Comparative Example 2

[0105] This comparative example provides a method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, which is different from Example 2 in that: the nitrogen in step (1) is removed to obtain 35.6 g of rhodium black (rhodium content 80.0 wt%, Cu: 100 ppm, Fe: 290 ppm, Ni: 250 ppm), with a yield of 94.9%; in step (2), the rhodium black and the filter residue obtained after the reaction need to undergo chlorination reactions for a total of 4 times, and the proportions and reaction conditions of the other steps are the same as those in Example 2, to obtain 90.6 g of rhodium nitrate crystals (rhodium content 31.1 wt%, Cu: 10 ppm, Fe: 25 ppm, Ni: 15 ppm), with a yield of 93.9%.

[0106] In summary, the present invention recycles the intermediate product rhodium-containing waste liquid of rhodium waste as the starting raw material, utilizes formic acid solution and ultrasonic wave assisted direct reduction to obtain active rhodium powder, adopts medium temperature chlorination method to dissolve active rhodium powder to obtain relatively pure chlororhodate solution, removes trace impurity metal by cation exchange resin, adds hydroxide to obtain rhodium hydroxide, adds nitric acid to obtain rhodium nitrate solution after washing, then evaporates in evaporator to obtain syrupy rhodium nitrate solid, then adds appropriate amount of deionized water to drive away excess nitric acid to obtain crystalline rhodium nitrate. The production cycle of the present invention is short, the purity of the obtained rhodium nitrate is higher, and it is conducive to realizing industrial production.

[0107] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid, characterized in that, The following steps are involved: (1) mixing rhodium-containing waste liquid, formic acid, alkaline substances and water, and performing a reduction reaction under the assistance of ultrasound to obtain rhodium black; (2) mixing the rhodium black, chloride and chlorine to carry out a chlorination reaction; dissolving and filtering the product of the chlorination reaction to obtain a chlororhodium salt solution; (3) mixing the chlororhodium salt solution with a hydroxide to obtain rhodium hydroxide; (4) mixing the rhodium hydroxide with a nitric acid solution, performing a neutralization reaction, and obtaining a rhodium nitrate solution; evaporating the rhodium nitrate solution to dryness, washing, and obtaining rhodium nitrate crystals; Wherein, the rhodium-containing waste liquid in step (1) includes potassium chlororhodate or sodium chlororhodate.

2. a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid according to claim 1, is characterized in that, In step (1), the molar ratio of the rhodium element in the rhodium-containing waste liquid to the formic acid is 1:1.5-4.5; and the pH value of the mixture of the rhodium-containing waste liquid, formic acid, alkaline substance and water is 3-5.

3. according to claim 1 or 2 a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid, it is characterized in that, In step (1), the temperature of the reduction reaction is 60-100° C., the time of the reduction reaction is 2-5 hours, and the ultrasonic power of the reduction reaction is 200-1200W.

4. a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid according to claim 3, is characterized in that, Step (1) further comprises the following steps after the reduction reaction: filtering, washing and vacuum drying the product after the reduction reaction in sequence under a protective atmosphere; the protective atmosphere comprises nitrogen, argon or helium.

5. a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid according to claim 1, is characterized in that, The specific process of step (2) comprises the following steps: The rhodium black, chloride and chlorine are mixed to carry out a chlorination reaction; the product of the chlorination reaction is dissolved and filtered to obtain a filtrate and a filter residue; Replace the rhodium black with the obtained filter residue, and repeat the chlorination reaction, dissolution, and filtration process 1 to 4 times; All the obtained filtrates were mixed to obtain a chlororhodium salt solution.

6. according to claim 1 or 5 a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid, it is characterized in that, In step (2), the mass ratio of the rhodium black to the chloride is 1:2-5; and the introduction rate of the chlorine gas is 0.1-3 L / min.

7. a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid according to claim 6, is characterized in that, In step (2), the temperature of the chlorination reaction is 550-750° C., and the time of the chlorination reaction is 1-2.5 h.

8. according to claim 1 or 7 a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid, it is characterized in that, In step (2), the chlororhodate solution further comprises, before the subsequent steps are performed, passing the chlororhodate solution through a cation exchange resin.

9. a kind of preparation method of rhodium nitrate crystal based on rhodium-containing waste liquid according to claim 1, is characterized in that, In step (3), the pH value of the chlororhodium salt solution after mixing with the hydroxide is 7 to 8.

10. A method for preparing rhodium nitrate crystals based on rhodium-containing waste liquid according to claim 1, characterized in that, In step (4), the temperature of the neutralization reaction is 60 to 95° C., and the time of the neutralization reaction is 0.5 to 2 h.