Method for improving cadmium removal efficiency in phosphoric acid

Abstract

The invention relates to a method for improving cadmium removal efficiency in phosphoric acid, which comprises the following steps: (1) adding a pretreating agent into phosphoric acid containing P2O5 with the mass concentration of 20-85%, with the molar ratio of the added pretreating agent to Fe < 3 + > and Cu < 2 + > being (1.2-2): 1, and stirring and reacting for 5-10 minutes at the rotating speed of 150-400 rpm at the temperature of 40-80 DEG C; and (2) adding a cadmium removal auxiliary agent, the addition amount of which is 0.1-0.5% of the total mass of the phosphoric acid, stirring at 40-80 DEG C at 150-3000rpm to react for 1-20 minutes, and filtering to obtain purified phosphoric acid, wherein the addition amount of the cadmium removal auxiliary agent is 0.1-0.5% of the total mass of the phosphoric acid. According to the method, refined phosphoric acid is deeply decolorized, metal ions are more efficiently removed, and the cadmium removal efficiency is improved; the consumption of the cadmium removal auxiliary agent can be reduced.

Description

TECHNICAL FIELD

[0001] The application relates to a method for improving the cadmium removal efficiency in phosphoric acid and belongs to the technical field of wet-process phosphoric acid purification. BACKGROUND

[0002] As a core raw material for phosphate fertilizer and fine phosphorus chemical industry, the purity of wet-process phosphoric acid directly affects the quality of downstream products. However, the widely associated heavy metal cadmium (Cd) in ores becomes a key pollution source. The wet-process phosphoric acid process occupies the mainstream production route due to cost advantages, but 70-80% of cadmium will enter the downstream product with phosphoric acid, leading to soil cadmium pollution through the application of phosphate fertilizer, and ultimately threatening human health through the food chain (such as causing bone pain disease, kidney damage and other diseases). Global regulation continues to tighten (for example, the European Union requires that the cadmium content of phosphate products be less than 60 mg / kg P2O5, and the efficient removal of cadmium (Cd 2+ ) in phosphoric acid has become a rigid demand of the industry. However, high concentrations of metal ions such as iron (Fe 3+ 500-3000 ppm), copper (Cu 2+ 30-200 ppm) in wet-process phosphoric acid seriously interfere with the removal of cadmium by cadmium removal aids. Fe 3+ , Cu 2+ is easy to react with cadmium removal aids (such as Na2S, NaHS, dialkyldithiophosphates or dialkyldithiophosphoric acid) in priority, consuming a large amount of cadmium removal aids. When the content of Fe 3+ , Cu 2+ in phosphoric acid is low, the cadmium removal aid reacts with cadmium ions, resulting in more than 60% of the cadmium removal aid being consumed invalidly, and the cadmium removal rate being reduced from the theoretical value of 95% to 60%.

[0003] The prior art needs to change the pH of the system, resulting in loss of phosphoric acid hydrolysis, or use a masking agent (such as citric acid, tartaric acid) with insufficient stability. The masking agent with insufficient stability cannot long-term inhibit the activity of iron / copper in the strong acid environment of pH 1-3 and high temperature of 50-80℃ in the wet-process phosphoric acid. To compensate for the consumption of interfering Fe 3+ and Cu 2+ ions, the cadmium removal aid (Na2S, NaHS, dialkyldithiophosphates or dialkyldithiophosphoric acid) needs to be added by 40-60%. SUMMARY

[0004] The purpose of the present application is to overcome the problems existing in the prior art, and to provide a method for improving the cadmium removal efficiency in phosphoric acid. The cadmium removal rate of the method is improved to >96%, and the consumption of cadmium removal aids is reduced by 40-60%.

[0005] The technical scheme adopted by the present application is as follows: A method for improving the cadmium removal efficiency in phosphoric acid, characterized by comprising the following steps: (1) adding a pretreatment agent to phosphoric acid containing P2O5 with a mass concentration of 20-85%, the molar ratio of the added pretreatment agent to Fe 3+ and Cu 2+ is 1.2-2:1, stirring at a rotation speed of 150-400 rpm at 40-80℃ for 5-10 minutes; (2) adding a cadmium removal aid, the addition amount of the cadmium removal aid being 0.1%-0.5% of the total mass of the phosphoric acid, stirring at 150-3000 rpm at 40-80℃ for 1-20 minutes, and then filtering to obtain purified phosphoric acid.

[0006] The pretreatment agent is a mixture of one or more than two of a reducing agent, a chelating agent, and an adsorbent.

[0007] The reducing agent is a mixture of one or more than two of thiourea, reduced iron powder, sodium hydrosulfite, ascorbic acid, and sodium thiosulfate.

[0008] The chelating agent is a mixture of one or more than two of sodium diethyldithiocarbamate, hydroxyethylidene diphosphonic acid, amino-tris(methylene phosphonic acid), diethylenetriamine pentaacetic acid (DTPA), and ethylenediamine disuccinic acid (EDDS).

[0009] The adsorbent is a mixture of one or more than two of activated carbon, graphene, sulfonated polystyrene resin, and chitosan.

[0010] The cadmium removal aid is a mixture of one or more than two of Na2S, NaHS, dialkyldithiophosphate, and dialkyldithiophosphoric acid.

[0011] The beneficial effects of the present application are as follows: The present application pretreats phosphoric acid containing high concentrations of Fe 3+ and Cu 2+ , can convert Fe 3+ and Cu 2+ into precipitates or chelates for removal from the phosphoric acid solution, and obtains purified phosphoric acid. The present application makes the refined phosphoric acid more efficient in deep decolorization and metal ion removal, improves the cadmium removal efficiency, and reduces the consumption of the cadmium removal aid. DETAILED DESCRIPTION

[0012] The technical solutions of the present application are described in further detail below by way of listing some optional embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0013] Embodiment 1 The composition of the phosphoric acid of a foreign phosphorus chemical enterprise: Cd2+ 20 ppm, Fe 3+ 1500 ppm, Cu 2+ 30 ppm, P2O5 mass concentration 25%; Take 500g phosphoric acid, add thiourea 0.0163mol (thiourea and Fe 3+ and Cu 2+ The molar ratio is 1.2:1), the temperature is 40℃, and the stirring speed is 200rpm for 10min, then add cadmium removal additive sodium black medicine, the addition amount is 0.1% of the total mass of phosphoric acid, the temperature is 60℃, and the stirring speed is 300rpm for 20min, filter the purified phosphoric acid after the reaction is completed, and measure the Cd 2+ 0.8 ppm, Fe 3+ 120 ppm, Cu 2+ 0.2 ppm.

[0014] Example 2 The composition of phosphoric acid of a foreign phosphate chemical enterprise: Cd 2+ 50 ppm, Fe 3+ 3500 ppm, Cu 2+ 65 ppm, P2O5 mass concentration 50%; Take 500g phosphoric acid, add DTPA 0.0413mol (DTPA and Fe 3+ and Cu 2+ The molar ratio is 1.3:1), the temperature is 80℃, and the stirring speed is 300rpm for 8min, then add cadmium removal additive NaHS, the addition amount is 0.2% of the total mass of phosphoric acid, the temperature is 65℃, and the stirring speed is 500rpm for 10min, filter the purified phosphoric acid after the reaction is completed, and measure the Cd 2+ 0.6 ppm, Fe 3+ 80 ppm, Cu 2+ 0.2 ppm.

[0015] Example 3 The composition of phosphoric acid of a foreign phosphate chemical enterprise: Cd 2+ 50 ppm, Fe 3+ 3500 ppm, Cu 2+ 65 ppm, P2O5 mass concentration 50%; Take 500g phosphoric acid, add sodium diethyldithiocarbamate 0.0476mol (sodium diethyldithiocarbamate and Fe 3+ and Cu 2+molar ratio of 1.5:1), at a temperature of 60°C, stirring at a speed of 400 rpm for 5 min, then adding the cadmium removal auxiliary dibutyl dithiophosphoric acid in an amount of 0.2% of the total mass of the phosphoric acid, stirring at a speed of 2000 rpm for 2 min at a temperature of 65°C, and then filtering the purified phosphoric acid, and measuring the Cd in the purified phosphoric acid 2+ 0.3 ppm, Fe3 + 60 ppm, Cu 2+ 0.1 ppm.

[0016] Example 4 The composition of the phosphoric acid of a foreign phosphorus chemical enterprise: Cd 2+ 70 ppm, Fe 3+ 5000 ppm, Cu 2+ 80 ppm, P2O5 mass concentration 75%; Take 500g of phosphoric acid, add thiourea 0.045mol and sodium diethyl dithiocarbamate 0.045mol (wherein the molar ratio of thiourea and sodium diethyl dithiocarbamate to Fe 3+ and Cu 2+ is 2:1), at a temperature of 70°C, stirring at a speed of 400 rpm for 5 min, then adding the cadmium removal auxiliary dibutyl dithiophosphoric acid in an amount of 0.2% of the total mass of the phosphoric acid, stirring at a speed of 3000 rpm for 1 min at a temperature of 70°C, and then filtering the purified phosphoric acid, and measuring the Cd in the purified phosphoric acid 2+ 0.2 ppm, Fe 3+ 60 ppm, Cu 2+ 0.1 ppm.

[0017] Example 5 The composition of the phosphoric acid of a foreign phosphorus chemical enterprise: Cd 2+ 20 ppm, Fe 3+ 1500 ppm, Cu 2+ 30 ppm, P2O5 mass concentration 25%; Take 500g of phosphoric acid, add graphene 0.0203mol (the molar ratio of graphene to Fe 3+ and Cu 2+ is 1.5:1), at a temperature of 65°C, stirring at a speed of 300 rpm for 9 min, then adding the cadmium removal auxiliary sodium butyl xanthate in an amount of 0.1% of the total mass of the phosphoric acid, stirring at a speed of 900 rpm for 8 min at a temperature of 65°C, and then filtering the purified phosphoric acid, and measuring the Cd in the purified phosphoric acid 2+ 0.6 ppm, Fe 3+ 100 ppm, Cu 2+ 0.2 ppm.

[0018] It is to be understood that the above description is intended to be illustrative and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading the above description. The scope of the application should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with their full scope of equivalents.

Claims

1. A method for improving the cadmium removal efficiency in phosphoric acid, characterized in that... Includes the following steps: (1) Add a pretreatment agent to phosphoric acid containing 20-85% P2O5 by mass. The added pretreatment agent reacts with Fe 3+ and Cu 2+ The molar ratio is 1.2-2:1, and the mixture is stirred at 150-400 rpm for 5-10 minutes at 40-80℃. (2) Add cadmium removal agent, the amount of cadmium removal agent added is 0.1%-0.5% of the total mass of phosphoric acid, stir and react at 150-3000 rpm for 1-20 min at 40-80℃, and then filter to obtain purified phosphoric acid.

2. The method for improving cadmium removal efficiency in phosphoric acid according to claim 1, characterized in that: The pretreatment agent is one or a mixture of two or more of the following: reducing agent, chelating agent, and adsorbent.

3. The method for improving cadmium removal efficiency in phosphoric acid according to claim 1, characterized in that: The reducing agent is one or a mixture of two or more of the following: thiourea, reduced iron powder, sodium hydrosulfite, ascorbic acid, and sodium thiosulfate.

4. The method for improving cadmium removal efficiency in phosphoric acid according to claim 1, characterized in that: The chelating agent is one or a mixture of two or more of sodium diethyldithiocarbamate, hydroxyethylidene diphosphonic acid, aminotrimethylphosphonic acid, DTPA, and EDDS.

5. The method for improving cadmium removal efficiency in phosphoric acid according to claim 1, characterized in that: The adsorbent is one or a mixture of two or more of the following: activated carbon, graphene, sulfonated polystyrene resin, or chitosan.

6. The method for improving cadmium removal efficiency in phosphoric acid according to claim 1, characterized in that: The cadmium removal aid is one or a mixture of two or more of the following: Na2S, NaHS, dialkyl dithiophosphate, dialkyl dithiophosphite, and dialkyl dithiophosphate.