A removing agent and a removing method for heavy metal cadmium in phosphoric acid

Abstract

The present application belongs to the technical field of phosphoric acid purification, and particularly relates to a heavy metal cadmium removal agent and a removal method for phosphoric acid. The removal agent comprises a solvent and a thiophosphoric acid type capturing agent A and a thiophosphoric acid type capturing agent B dispersed in the solvent; the thiophosphoric acid type capturing agent A and the thiophosphoric acid type capturing agent B are different types of thiophosphoric acid type capturing agents, the thiophosphoric acid type capturing agent A and the thiophosphoric acid type capturing agent B are independently selected from one of a hydrocarbyl dithiophosphoric acid or a salt thereof, a phenolic dithiophosphoric acid or a salt thereof, and an amine dithiophosphoric acid or a salt thereof, and at least one hydrocarbyl dithiophosphoric acid or a salt thereof is selected; the salt is a sodium salt or an ammonium salt; and the solvent is water or an alkaline aqueous solution. The present application uses a combination of dithiophosphoric acid type capturing agents as a cadmium removal agent for wet-process phosphoric acid, and generates a precipitate that is difficult to dissolve in a strong acidic aqueous phase after reaction, so that the cadmium in the phosphoric acid is removed after filtration. Compared with the conventional sulfide precipitation method, the present application has less cadmium residue and less pollution in the phosphoric acid.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphoric acid purification, and particularly relates to a remover and a method for removing heavy metal cadmium from phosphoric acid. Background Art

[0002] Approximately 160 million tons of phosphate rock are consumed annually worldwide for the production of phosphoric acid and phosphate fertilizers, 95% of which is produced through the wet process. Phosphate rock commonly contains the heavy metal cadmium, with concentrations ranging from 1 to 110 mg / kg, but in some cases (such as the United States), levels can reach as high as 980 mg / kg. During wet-process phosphoric acid production, approximately 50%-70% of the cadmium enters the phosphoric acid solution as ions. If this highly toxic heavy metal enters phosphate fertilizers and other products without treatment, it can cause serious soil and water pollution.

[0003] To address this issue, various cadmium removal processes have been developed during the wet production of phosphoric acid using inorganic acid hydrolysis of phosphate rock, including chemical precipitation, ion exchange, adsorption, solvent extraction, and membrane separation. Each method has its own characteristics and limitations:

[0004] (1) Chemical precipitation method: It is widely used because of its mature process, simple operation and low cost. This method mainly uses sulfides such as Na2S, NaHS, (NH4)2S as precipitants to combine with heavy metal ions in the solution to form sulfide precipitates. However, the precipitate generated by this method has poor stability, is prone to secondary pollution, and releases toxic gas H2S, which poses potential harm to the environment. In addition, although the solubility product of cadmium sulfide (CdS) is very low, it is actually affected by H2S. + Inhibits the formation of 2- It will first react with the large amount of H + The H2S gas generated by the combination will escape, causing the CdS precipitate to dissolve in reverse. The actual solubility can reach 10 at 25℃ under acidic conditions. -4 mol / L, resulting in poor cadmium removal efficiency under strong acidic solution conditions.

[0005] (2) Ion exchange method: Various ion exchange resins are used to purify solutions containing heavy metal ions, which has a high removal efficiency. However, the high investment cost of this method limits its large-scale application.

[0006] (3) Adsorption method: This method uses the porous structure of the adsorption material to adsorb heavy metal substances from the solution to achieve the purpose of impurity removal. However, the effect of this method is unstable and it is difficult to ensure a continuous and efficient cadmium removal effect.

[0007] (4) Solvent extraction method: a common method for purifying phosphoric acid by wet process, which mainly removes cadmium from wet-process phosphoric acid through solvent extraction coupled with emulsion liquid membrane. Similarly, this method also faces the problem of high investment and operating costs.

[0008] (5) Membrane separation method: with its advantages of high efficiency and easy operation, it has broad application prospects in removing heavy metals. However, the relatively high cost of this method limits its widespread adoption.

[0009] In summary, although the existing technology provides a variety of solutions to deal with the problem of cadmium pollution in phosphoric acid, the limitations of each require further research and development of more effective and economical new methods to achieve safe removal of cadmium in the wet production process of phosphoric acid. This not only helps environmental protection, but also improves the quality of phosphate fertilizer and ensures the sustainable development of agricultural production. Therefore, it is particularly important to propose new solutions for the removal of cadmium from wet-process phosphoric acid. SUMMARY

[0010] (I) Technical problems to be solved

[0011] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a removal agent and a removal method for heavy metal cadmium in phosphoric acid. A composition of dithiophosphoric acid collector (DTP) is used as a removal agent for cadmium in wet-process phosphoric acid. After reaction, a precipitate is formed which is difficult to dissolve in strong acidic aqueous phase. The solubility product (Ksp) of the precipitate is extremely low, and it is easy to achieve the purpose of removing cadmium from phosphoric acid by filtration. This method does not produce toxic gas H2S, and the removal rate of cadmium in phosphoric acid reaches more than 98%, and the absolute value of cadmium content in phosphoric acid is reduced to less than 1.99 mg / kg P2O5. It solves the problem of secondary pollution caused by sulfide and the problem that the efficiency of removing cadmium is easily affected by H + suppression in the prior art.

[0012] (II) Technical solutions

[0013] In a first aspect, the present application provides a removal agent for heavy metal cadmium in phosphoric acid, which comprises a solvent and a dithiophosphoric acid collector A and a dithiophosphoric acid collector B dispersed in the solvent; the dithiophosphoric acid collector A and the dithiophosphoric acid collector B are different types of dithiophosphoric acid collectors, and the dithiophosphoric acid collector A and the dithiophosphoric acid collector B are independently selected from one of hydrocarbyl dithiophosphoric acid or its salt, phenolic dithiophosphoric acid or its salt, and amine dithiophosphoric acid or its salt, and at least one hydrocarbyl dithiophosphoric acid or its salt is selected; the salt is sodium salt or ammonium salt; the solvent is water or alkaline aqueous solution.

[0014] Preferably, the hydrocarbyl dithiophosphoric acid or its salt is selected from the group consisting of dibutyl dithiophosphoric acid, dibutyl dithiophosphoric acid ammonium, dibutyl dithiophosphoric acid sodium, diisobutyl dithiophosphoric acid, diisobutyl dithiophosphoric acid ammonium, diisobutyl dithiophosphoric acid sodium; the phenyl dithiophosphoric acid is selected from the group consisting of dimethylphenyl dithiophosphoric acid, dimethylphenyl dithiophosphoric acid ammonium, dimethylphenyl dithiophosphoric acid sodium; the amine dithiophosphoric acid or its salt is selected from the group consisting of diphenylamine dithiophosphoric acid, diphenylamine dithiophosphoric acid ammonium, diphenylamine dithiophosphoric acid sodium.

[0015] In a second aspect, the present application provides a method for removing cadmium heavy metal from phosphoric acid, comprising the steps of:

[0016] S1, fully dissolving the dithiophosphoric acid type collector A and the dithiophosphoric acid type collector B in a solvent to obtain a cadmium removal agent;

[0017] The dithiophosphoric acid type collector A and the dithiophosphoric acid type collector B are different types of dithiophosphoric acid type collectors, and the dithiophosphoric acid type collector A and the dithiophosphoric acid type collector B are independently selected from one of hydrocarbyl dithiophosphoric acid or its salt, phenyl dithiophosphoric acid or its salt, amine dithiophosphoric acid or its salt, and at least one hydrocarbyl dithiophosphoric acid or its salt is selected; the salt is sodium salt or ammonium salt; the solvent is water or alkaline aqueous solution;

[0018] S2, detecting the content of Cd, Cu and Zn metal ions in the crude phosphoric acid to be removed, calculating the theoretical value of the dithiophosphoric acid type collector in the removal agent, the theoretical value is more than 2 times the total molar amount of Cd, Cu and Zn metal ions, and the removal agent is taken according to the theoretical value;

[0019] S3, adding the removal agent to the crude phosphoric acid to carry out precipitation reaction, after the reaction is completed, the precipitate is removed by filtration, and the filtrate is cadmium-free phosphoric acid and the filter residue is metal chelate.

[0020] Preferably, in S1, the hydrocarbyl dithiophosphoric acid or its salt is selected from the group consisting of dibutyl dithiophosphoric acid, dibutyl dithiophosphoric acid ammonium, dibutyl dithiophosphoric acid sodium, diisobutyl dithiophosphoric acid, diisobutyl dithiophosphoric acid ammonium, diisobutyl dithiophosphoric acid sodium; the phenyl dithiophosphoric acid is selected from the group consisting of dimethylphenyl dithiophosphoric acid, dimethylphenyl dithiophosphoric acid ammonium, dimethylphenyl dithiophosphoric acid sodium; the amine dithiophosphoric acid or its salt is selected from the group consisting of diphenylamine dithiophosphoric acid, diphenylamine dithiophosphoric acid ammonium, diphenylamine dithiophosphoric acid sodium.

[0021] Preferably, the basic aqueous solution is an aqueous solution containing at least one solute of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate and ammonia; the pH range of the basic aqueous solution is 10-13 (black medicine pH range). Since the thiophosphoric group contained in DTP has strong soft acid-soft base affinity for cadmium, but DTP is easy to decompose under high temperature and high acidity, therefore when preparing the removal agent, water or basic aqueous solution is preferably used to improve the stability of DTP and its availability in the process.

[0022] Preferably, in S1, the temperature of the solvent is 0-45℃, preferably 15-35℃.

[0023] Preferably, in S3, the temperature of the precipitation reaction is 0-60℃, preferably 30-40℃; the reaction time is 1-100min, preferably 30-60min. In S3, stirring is accompanied during the precipitation reaction, and the stirring speed is 200-400rpm, which can accelerate the reaction.

[0024] When the crude phosphoric acid contains Cu, Cd and Zn metal ions, the total molar amount of the thiophosphoric chelating agent contained in the removal agent to be added is more than 2 times the molar amount of the three metal ions, preferably 2 times to 2 times plus 10%, such as 2-2.2 times the total molar amount of Cd, Cu and Zn metal ions. The chelation priority is Cu>Cd>Zn.

[0025] Preferably, in S1, the thiophosphoric chelating agent A and the thiophosphoric chelating agent B in the removal agent are two different hydrocarbyl chain length dihydrocarbyl dithiophosphates. The two different hydrocarbyl chain length dihydrocarbyl dithiophosphates are compounded to inhibit Fe 3+ interference and improve the selectivity to Cd (the selectivity of dithiophosphates to Cd 2+ is higher than that of sulfidation method). In addition, the dihydrocarbyl dithiophosphates with short chain hydrocarbyl groups can quickly capture Cd 2+ , and the dihydrocarbyl dithiophosphates with long chain hydrocarbyl groups help to strengthen the precipitation. The carbon number of the hydrocarbyl group in the dihydrocarbyl dithiophosphates is C4-C12.

[0026] The hydrocarbyl dithiophosphoric acid or its salt has stronger hydrophobicity of the chelate formed with heavy metal ions than the "phenyl dithiophosphoric acid or its salt" and "amine dithiophosphoric acid or its salt", and the precipitation is more stable, can precipitate faster, and is less affected by the hydrogen ions in the crude phosphoric acid and the temperature rise; therefore, preferably, at least one hydrocarbyl dithiophosphoric acid or its salt should be selected in the removal agent.

[0027] In S3, the DTP-Cd chelate formed by the dithiophosphoric chelating agent (DTP) and Cd 2+ is a precipitate, and the typical reaction is as follows:

[0028] wherein, when R is alkyl or cycloalkyl (such as ethyl, butyl), the collector is a dihydrocarbyl dithiophosphoric acid collector. Diphenylamine dithiophosphoric acid is a dihydrocarbyl dithiophosphoric acid collector in which -O-R is replaced by -N-Ph (Ph is phenyl). The diphenylamine derivative, due to the presence of an aniline group, has significantly different hydrophilicity, steric hindrance and pH sensitivity from dihydrocarbyl dithiophosphoric acid collectors, and dihydrocarbyl dithiophosphoric acid collectors have stronger acid resistance and cadmium ion selectivity. The R in the di-cresyl dithiophosphoric acid collector is methyl phenyl. The di-cresyl dithiophosphoric acid collector contains a phenolic group, and the phenyl ring conjugated system will weaken the polarity of the P=O bond, resulting in weaker coordination ability with heavy metals (such as Cd 2+ ) and poorer dispersibility in water than dihydrocarbyl dithiophosphoric acid collectors. Therefore, dihydrocarbyl dithiophosphoric acid collectors have the best effect in removing wet-process phosphoric acid.

[0029] wherein, the long-chain hydrocarbon group (R) makes the chelate poorly soluble in strongly acidic aqueous phase, and the Ksp of the chelate in crude phosphoric acid (pH <1) is extremely low (<10 -10 ), much lower than that of Cd3(PO4)2 and other phosphates, so the chelate is precipitated and can be easily removed by filtration.

[0030] Preferably, in S1, the removal agent also contains 0.5-2% thiourea derivatives. The combination of DTP and thiourea derivatives can improve the acid resistance of DTP in crude phosphoric acid. The sulfur atom and amino nitrogen atom in thiourea ((NH2)2C=S) can selectively adsorb H + , forming a stable thiourea-proton complex, which acts as a local alkaline pH buffer, forming a slightly alkaline environment (pH 1-3) around the DTP molecule, delaying the breakage of the P=S bond in DTP. Thiourea derivatives preferentially bind to free H + , rather than competing with Cd 2+ for DTP coordination. A small amount of thiophosphoric acid collector in the removal agent can react with H + in crude phosphoric acid to generate H2S, and thiourea can capture H2S to convert it into thiocarbamate, avoiding gaseous loss, pollution and corrosion. Thiocarbamate itself is also a weak chelating agent, which can assist in the precipitation of cadmium ions. The thiourea derivative is preferably tetramethyl thiourea or tetraethyl thiourea, which has strong steric hindrance and strong acid resistance. However, an excessive amount of thiourea (such as >5%) can cause the precipitation rate of Cd-DTP to decrease.

[0031] CdS is easy to be dissolved reversely in strong acid, which leads to the increase of actual solubility; the solubility of CdS also increases in geometric progression with the increase of temperature. CdS is usually stable when pH>4. Compared with CdS, DTP-Cd chelate is more stable in acid condition (pH≤3), which makes the precipitation integrity be maintained and is not easy to be dissolved reversely; the solubility is stable in high temperature and high acidity due to the protection of hydrophobic alkyl group introduced by DTP. In addition, the particle size of DTP-Cd chelate is larger than that of CdS, which is more easy to be separated by filtration.

[0032] Preferably, when S2 detects that the concentration of cadmium ions in the crude phosphoric acid is high, the concentration of cadmium ions can be reduced by diluting the crude phosphoric acid, thereby increasing the removal rate of cadmium ions; or a flocculation aid such as 0.1‰ polyacrylamide (PAM) can be added to the crude phosphoric acid in step S3 to increase the particle size and precipitation rate of the precipitated particles, simplify the filtration operation and the removal rate of heavy metals.

[0033] Preferably, in S3, the filtration uses a plate and frame filter press or a candle filter, preferably a plate and frame filter press, with a retention accuracy of 5-10 μm, which is suitable for large-scale and high-slag high-efficiency filtration, and can reduce the purification of industrial wet-process phosphoric acid, balance the cost and efficiency. If the filtration accuracy needs to be further improved, a candle filter with a retention accuracy of 0.5-2 μm can be used, which is suitable for low-slag filtration treatment.

[0034] Preferably, the metal chelate obtained in S3 can be dechelated by nitric acid or dilute sulfuric acid to generate CdO, and CdO can be collected by filtration; the filtrate is adjusted to pH 5-6 with NaOH, and then extracted with an organic phase (such as kerosene + 10-15% TBP), and then stripped with dilute acid to recover the dihydrocarbyl dithiophosphoric acid-type capture agent DTP. The recovery method is suitable for the recovery of dihydrocarbyl dithiophosphoric acid-type capture agent, but not suitable for phenolic dithiophosphoric acid-type capture agent.

[0035] (Three) beneficial effects

[0036] (1) The composition of the dihydrocarbyl dithiophosphoric acid-type capture agent DTP is used as a cadmium removal agent for removing cadmium metal in wet-process phosphoric acid, which has a higher removal rate and less cadmium residue in phosphoric acid than the conventional sulfide (Na2S, NaHS, (NH4)2S, etc.) precipitation method, and does not produce toxic gas H2S, which pollutes the gas environment of the plant less.

[0037] (2) The composition of the dithiophosphoric acid type collector DTP as a cadmium removal agent removes heavy metal cadmium in wet-process phosphoric acid, and the generated Cd-containing chelate precipitate is more stable than sulfide precipitate, the formed chelate solid is more stable, especially in phosphoric acid solution, the Cd-containing chelate is more stable under acidic conditions (pH≤3), so that the integrity of the precipitate is maintained and reverse dissolution is not easy to occur; due to the protective effect of the hydrophobic hydrocarbon group introduced by DTP, the solubility is stable at high temperature and high acidity. In addition, the particle size of the DTP-Cd chelate precipitate is larger than that of CdS particles, and it is more easy to separate by filtration.

[0038] The CdS generated by the traditional sulfide precipitation method is easy to reverse dissolve under strong acid, which leads to the increase of the actual solubility; when the temperature increases, the solubility of CdS also increases in geometric progression. Generally, CdS needs pH>4 to maintain stability, which is not conducive to the removal of heavy metal cadmium in crude phosphoric acid.

[0039] (3) The composition of the dithiophosphoric acid type collector DTP is used to remove heavy metal cadmium in wet-process phosphoric acid, and compared with a single type of collector DTP, the composition is more thorough in removing cadmium in crude phosphoric acid. DETAILED DESCRIPTION

[0040] In order to better explain the present application, the following will describe the present application in detail in combination with specific embodiments.

[0041] The dithiophosphoric acid type collector DTP is usually used as a non-ferrous metal sulfide ore flotation collector. The sulfur group in the collector molecule has strong combination ability with metal ions, fast reaction speed, can form stable chelates and is not easy to decompose. At present, the related research and application of the dithiophosphoric acid type collector DTP are mainly limited to the fields of mineral flotation recovery and industrial wastewater environmental protection treatment, and it has not been seen to be used for removing heavy metal cadmium in wet-process phosphoric acid. The present application uses two kinds of dithiophosphoric acid type collectors (at least one is a hydrocarbyl dithiophosphoric acid or a salt thereof) for the cadmium removal process of wet-process phosphoric acid, which can obtain a higher cadmium removal rate, and the process technology method for removing cadmium in phosphoric acid has a good application prospect.

[0042] The heavy metal cadmium removal agent provided by the present application removes cadmium in crude phosphoric acid. The dithiophosphoric acid collector DTP in the removal agent exists in the form of dithiophosphoric acid in phosphoric acid. The sulfur atom in the active group thereof has small electronegativity, a large radius, is easy to lose electrons, and can polarize and deform to generate a negative electric field. When the dithiophosphoric acid collector DTP combines with heavy metal ions in the solution, the two sulfur atoms in the molecular structure of the dithiophosphoric acid collector DTP are coordinated with the heavy metal ions to form a four-membered ring chelate, and then a chelate with a larger particle size is obtained. The chelate is removed by filtration. Compared with the unstable precipitate formed by the traditional sulfide chemical precipitation method, the dithiophosphoric acid can form a spatial configuration with a smaller tension with metal ions of different valence bond orbits, so that the chelate formed by combination has high stability, the integrity of the precipitate is maintained, and reverse dissolution and toxic H2S gas (less environmental pollution in the production plant) are less likely to occur, thereby reducing secondary pollution and removing cadmium more completely. In 40% H3PO4, the solubility of the chelate Cd-DTP formed by the dithiophosphoric acid collector DTP and cadmium ions is 0.08 ppm at 25°C, and the solubility of CdS is 1.2 ppm under the same conditions. Therefore, the solubility of Cd-DTP is smaller, which is more conducive to improving the removal rate of Cd ions in phosphoric acid. In addition, due to the protection of the hydrophobic hydrocarbon group introduced by DTP, the solubility is stable at high temperature and high acidity. In addition, the particle size of the DTP-Cd chelate precipitate is larger than that of the CdS particle (the larger the particle size, the less likely the filter hole is blocked, the lower the specific resistance of the filter cake, and the higher the filtration flux), and the chelate is more easily separated by filtration.

[0043] The scheme features and technical effects of the present application are further described in combination with the preferred embodiments of the present application. In the following examples and comparative examples, the metal content in the phosphoric acid solution is detected by inductively coupled plasma spectrometry (ICP).

[0044] Example 1

[0045] The present embodiment provides a method for removing heavy metal cadmium in phosphoric acid, comprising the following steps:

[0046] (1) 50 g of water is added to a container, and the water temperature is 20°C. Under stirring, 100 g of diisobutyl sodium dithiophosphate (containing 50.10% of active ingredients by mass fraction) and 50 g of dibutyl ammonium dithiophosphate (containing 91.33% of active ingredients by mass fraction) are sequentially added to the container, and after being fully mixed and dissolved, a removal agent for heavy metal cadmium in phosphoric acid is obtained.

[0047] (2) The volume of the crude phosphoric acid solution to be treated (an aqueous solution with pH 1.5) is 100 mL, the content of Cd ions is 8.75 mg / L, the content of Cu ions is 66.25 mg / L, and the content of Zn ions is 206 mg / L. The total molar amount of the three kinds of ions is about 4.27 x 104 mol.

[0048] (3) While stirring, add 0.5 g of the removal agent to the crude phosphoric acid solution to be treated and react at 20-25°C for 1 hour. After the reaction is complete, filter to obtain a filter cake of crude phosphoric acid and metal chelates after cadmium removal. The cadmium content in the crude phosphoric acid decreases from 8.75 mg / L to 0.175 mg / L, with a removal rate of 98%.

[0049] Example 2

[0050] This embodiment provides a method for removing heavy metal cadmium from phosphoric acid, comprising the following steps:

[0051] (1) Add 50g of water to a container at a temperature of 20°C. While stirring, add 100g of sodium dibutyl dithiophosphate (containing 49.82% of the active ingredient by mass) and 50g of ammonium dibutyl dithiophosphate (containing 91.33% of the active ingredient by mass) to the container in sequence. After thorough mixing and dissolution, a heavy metal cadmium remover in phosphoric acid is obtained.

[0052] (2) The volume of the crude phosphoric acid solution to be treated (pH 1.5 aqueous solution) was 100 mL, of which the Cd ion content was 8.75 mg / L, the Cu ion content was 66.25 mg / L, and the Zn ion content was 206 mg / L. The total molar weight of the three ions was approximately 4.27×10 4 mol.

[0053] (3) While stirring, add 0.47 g of the removal agent to the crude phosphoric acid solution to be treated and react at 20-25°C for 1 hour. After the reaction is complete, filter to obtain a filter cake of crude phosphoric acid and metal chelates after cadmium removal. The cadmium content in the crude phosphoric acid decreases from 8.75 mg / L to 0.181 mg / L, with a removal rate of 97.93%.

[0054] Example 3

[0055] This embodiment provides a method for removing heavy metal cadmium from phosphoric acid, comprising the following steps:

[0056] (1) Add 50 g of sodium hydroxide aqueous solution with a pH of 9 into a container at a water temperature of 20°C. While stirring, add 100 g of sodium diisobutyl dithiophosphate (containing 50.10% by mass of active ingredient) and 50 g of diphenylamino dithiophosphoric acid (containing 49.21% by mass of active ingredient) into the container in sequence. After thorough mixing and dissolution, a heavy metal cadmium remover in phosphoric acid is obtained.

[0057] (2) The volume of the crude phosphoric acid solution to be treated (an aqueous solution with pH 1.5) is 100 mL, the content of Cd ions is 8.75 mg / L, the content of Cu ions is 66.25 mg / L, and the content of Zn ions is 206 mg / L. The total molar amount of the three kinds of ions is about 4.27 x 10 4 mol.

[0058] (3) Under stirring, 0.628 g of the removing agent is added into the crude phosphoric acid solution to be treated, and the reaction is carried out at 25-30°C for 45 min. After the reaction is completed, filtration is carried out to obtain the crude phosphoric acid after Cd removal and the metal chelate filter cake. The content of Cd in the crude phosphoric acid is reduced from 8.75 mg / L to 0.212 mg / L, and the removal rate is 97.58%.

[0059] Example 4

[0060] The embodiment provides a method for removing heavy metal Cd in phosphoric acid, which comprises the following steps:

[0061] (1) 50 g of water is added into a container, the water temperature is 20°C, and under stirring, 100 g of sodium dibutyldithiophosphate (containing 49.82% of active ingredient by mass fraction) and 50 g of sodium dimethylphenyldithiophosphate (containing 63.20% of active ingredient by mass fraction) are sequentially added into the container, and after being fully mixed and dissolved, a removing agent for heavy metal Cd in phosphoric acid is obtained.

[0062] (2) The volume of the crude phosphoric acid solution to be treated (an aqueous solution with pH 1.5) is 100 mL, the content of Cd ions is 8.75 mg / L, the content of Cu ions is 66.25 mg / L, and the content of Zn ions is 206 mg / L. The total molar amount of the three kinds of ions is about 4.27 x 10 4 mol.

[0063] (3) Under stirring, 0.60 g of the removing agent is added into the crude phosphoric acid solution to be treated, and the reaction is carried out at 25-30°C for 50 min. After the reaction is completed, filtration is carried out to obtain the crude phosphoric acid after Cd removal and the metal chelate filter cake. The content of Cd in the crude phosphoric acid is reduced from 8.75 mg / L to 0.233 mg / L, and the removal rate is 97.34%.

[0064] Example 5

[0065] The embodiment provides a method for removing heavy metal Cd in phosphoric acid, which comprises the following steps:

[0066] (1) In a container, 50 g of water is added, the water temperature is 20°C, 100 g of sodium dibutyl dithiophosphate (containing 49.82% of active ingredient by mass fraction) and 50 g of ammonium dibutyl dithiophosphate (containing 91.33% of active ingredient by mass fraction) are added into the container in turn under stirring, and after being fully mixed and dissolved, 1 wt% of tetraethyl thiourea is added to obtain a heavy metal cadmium removal agent for phosphoric acid.

[0067] (2) The solution volume of the crude phosphoric acid (pH 1.5 aqueous solution) to be treated is 100 mL, the Cd ion content is 8.75 mg / L, the Cu ion content is 66.25 mg / L, and the Zn ion content is 206 mg / L. The total molar amount of the three ions is about 4.27×10 4 mol.

[0068] (3) Under stirring, 0.475 g of the removal agent is added into the crude phosphoric acid solution to be treated, and the reaction is carried out at 25°C for 30 min; after the reaction is completed, filtration is carried out to obtain the crude phosphoric acid after cadmium removal and the metal chelate filter cake. The cadmium content in the crude phosphoric acid is reduced from 8.75 mg / L to 0.114 mg / L, and the removal rate is 98.70%.

[0069] In addition, the stability of the dithiophosphonic trapping agent DTP in Test Example 2 and Example 5 at pH 0.5 and 80°C is tested: the half-life of the dithiophosphonic trapping agent DTP in Example 2 is 4.2 hours, while the half-life of the dithiophosphonic trapping agent DTP in Example 5 reaches 12.4 hours. It can be seen that the addition of tetraethyl thiourea can improve the stability of the removal agent, so that there is more process operation time in the production process. At the same time, after shortening the precipitation reaction time in Example 5, a higher cadmium ion removal rate is still obtained compared with Example 2. This shows that the addition of 1% thiourea in the removal agent can also promote the removal rate of Cd ions.

[0070] Example 6

[0071] In this example, 0.1‰ of PAM is further added after the precipitation reaction in step (3) of Example 2 is completed, and stirring is carried out for 2 min, and then static filtration is carried out. The specific operation is as follows:

[0072] (3) Under stirring, 0.47 g of the removing agent was added into the crude phosphoric acid solution to be treated, and reacted at 20-25 °C for 35 min; after the reaction was completed, 0.1 ‰ of PAM was added, stirred for 2 min and stood for 15 min, filtered to obtain the crude phosphoric acid after removal of cadmium and the metal chelate filter cake. The cadmium content in the crude phosphoric acid was reduced from 8.75 mg / L to 0.121 mg / L, and the removal rate was 98.62%. In this embodiment, the flocculation and adsorption functions of PAM were utilized to further improve the removal rate of Cd ions and the purification degree of phosphoric acid. At the same time, PAM also simplifies the subsequent filtration operation. Especially for large-scale industrial applications, PAM can increase the particle size of the precipitated particles, reduce the difficulty of filtration, and reduce the filter membrane blockage.

[0073] Example 7

[0074] In this embodiment, the dithiophosphoric acid-type capturing agent in the metal chelate filter cake was further recovered in Example 2. The recovery method was as follows: the metal chelate filter cake was dried until the weight no longer changed, placed in a beaker, and dechelated by adding excess 1.0 M nitric acid, reacted at 25 °C for 1 h, the pH was adjusted to 10, and excess hydrogen peroxide was added at 25 °C and reacted for 30 min, filtered, and the filtrate was retained. The filtrate was adjusted to pH 5.5, and an extracting agent was added, the extracting agent was composed of kerosene + 15% TBP, after extraction, 0.5 M H2SO4 solution was added for back extraction, and dibutyl dithiophosphoric acid DTP was obtained, the recovery rate was >80%. The recovered dibutyl dithiophosphoric acid-type capturing agent can be recycled.

[0075] Comparative Example 1

[0076] In this comparative example, based on Example 1, no ammonium dibutyl dithiophosphoric acid was added, and only sodium diisobutyl dithiophosphoric acid (50.10%) was used as the removing agent for cadmium in wet-process phosphoric acid. In step (3) l, 0.70 g of the removing agent was measured and added into the crude phosphoric acid solution to be treated, and reacted at 20-25 °C for 1 h; after the reaction was completed, the crude phosphoric acid after removal of cadmium and the metal chelate filter cake were obtained by filtration. The cadmium content in the crude phosphoric acid was reduced from 8.75 mg / L to 0.589 mg / L, and the removal rate was 93.27%.

[0077] Comparative Example 2

[0078] In this comparative example, based on Example 1, no sodium diisobutyl dithiophosphoric acid was added, and only ammonium dibutyl dithiophosphoric acid (91.33%) was used as the removing agent for cadmium in wet-process phosphoric acid. In step (3) l, 0.55 g of the removing agent was measured and added into the crude phosphoric acid solution to be treated, and reacted at 20-25 °C for 1 h; after the reaction was completed, the crude phosphoric acid after removal of cadmium and the metal chelate filter cake were obtained by filtration. The cadmium content in the crude phosphoric acid was reduced from 8.75 mg / L to 0.566 mg / L, and the removal rate was 93.53%.

[0079] As can be seen from Example 1 and Comparative Examples 1-2, when a single DTP is used for removal of cadmium from the crude phosphoric acid, even if the molar amount of the added collector is excessive relative to the metal ions, the removal efficiency of cadmium from the crude phosphoric acid by a single DTP is lower than that by the use of different DTP combinations. This is likely because the different DTPs complement each other through spatial structure and electronic effect (e.g. NH4 + and Na + ), which helps to form more stable Cd chelates, thereby improving the removal efficiency of Cd.

[0080] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art will understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions, or combinations of the technical features in the above examples, do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A remover of heavy metal cadmium in phosphoric acid, characterized in that: The invention comprises a solvent and a thiophosphate collector A and a thiophosphate collector B dispersed in the solvent; the thiophosphate collector A and the thiophosphate collector B are different types of thiophosphate collectors, and the thiophosphate collector A and the thiophosphate collector B are independently selected from one of alkyl dithiophosphates or salts thereof, phenolic dithiophosphates or salts thereof, and amino dithiophosphates or salts thereof, and at least one alkyl dithiophosphate or salt thereof is selected; the salt is a sodium salt or an ammonium salt; the solvent is water or an alkaline aqueous solution; and the removing agent further contains 0.5-2% of a thiourea derivative.

2. A method for removing heavy metal cadmium from phosphoric acid, characterized in that: The steps include: S1, fully dissolving the thiophosphate trapping agent A and the thiophosphate trapping agent B in a solvent to obtain a cadmium remover; The thiophosphate collector A and the thiophosphate collector B are different types of thiophosphate collectors, and the thiophosphate collector A and the thiophosphate collector B are independently selected from one of a hydrocarbon dithiophosphate or a salt thereof, a phenolic dithiophosphate or a salt thereof, and an amino dithiophosphate or a salt thereof, and at least one hydrocarbon dithiophosphate or a salt thereof is selected; the salt is a sodium salt or an ammonium salt; the solvent is water or an alkaline aqueous solution, and the removing agent further contains 0.5-2% of a thiourea derivative; S2. Detect the contents of three metal ions, Cd, Cu, and Zn, in the crude phosphoric acid to be de-cadmiumized, and calculate the theoretical value of the thiophosphate trapping agent in the removal agent. The theoretical value is more than twice the total molar amount of the three metal ions, Cd, Cu, and Zn, and the removal agent is measured according to the theoretical value. S3. Add a removal agent to the crude phosphoric acid to carry out a precipitation reaction. After the reaction is completed, filter to remove the precipitate. The filtrate is cadmium-removed phosphoric acid, and the filter residue is the metal chelate.

3. The removal method according to claim 2, wherein In S1, the hydrocarbon dithiophosphoric acid or its salt is selected from the group consisting of dibutyl dithiophosphoric acid, ammonium dibutyl dithiophosphoric acid, sodium dibutyl dithiophosphoric acid, diisobutyl dithiophosphoric acid, ammonium diisobutyl dithiophosphoric acid, and sodium diisobutyl dithiophosphoric acid; the phenolic dithiophosphoric acid is selected from the group consisting of dicresol dithiophosphoric acid, ammonium dicresol dithiophosphoric acid, and sodium dicresol dithiophosphoric acid; and the amino dithiophosphoric acid or its salt is selected from the group consisting of diphenylamino dithiophosphoric acid, ammonium diphenylamino dithiophosphoric acid, and sodium diphenylamino dithiophosphoric acid.

4. The removal method according to claim 2, wherein In S1, the alkaline aqueous solution is an aqueous solution containing at least one solute selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia; and the pH range of the alkaline aqueous solution is 10-13.

5. The removal method according to claim 2, characterized in that In S1, the solvent temperature is 0-45°C.

6. The removal method according to claim 2, characterized in that In S3, the precipitation reaction temperature is 0-60° C.; the reaction time is 1-100 min; and the precipitation reaction is accompanied by stirring at a stirring speed of 200-400 rpm.

7. The removal method according to claim 3, characterized in that In S1, the thiophosphate collector A and the thiophosphate collector B in the remover are two dihydrocarbyl dithiophosphates with different hydrocarbon chain lengths.

8. The removal method according to claim 2, characterized in that In step S3, the removal agent is added to the crude phosphoric acid and 0.1‰ of a flocculation aid is added at the same time.

9. The removal method according to claim 2, characterized in that: The metal chelate obtained in S3 can be dechelated with nitric acid or dilute sulfuric acid, and hydrogen peroxide is added to generate CdO, which is collected by filtration; the filtrate is then adjusted to pH 5-6 with NaOH, and the organic phase is extracted and then back-extracted with dilute acid to recover the dialkyl dithiophosphate capture agent DTP.

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