A method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid

Abstract

The present invention discloses a method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid. The method of the present invention is to first dilute the waste phosphoric acid, drip alkali solution to adjust the pH, then filter press, add heavy metal chelating agent and the like to the filtrate, stir and filter press, add phosphoric acid to the filtrate to adjust the pH to 4.2-4.6, and obtain a dihydrogen phosphate pretreatment liquid; then distill and concentrate, cool and crystallize, and finally centrifuge, and the obtained precipitate is the dihydrogen phosphate product. The method of the present invention reduces the aluminum content in the finished sodium dihydrogen phosphate, and the heavy metal chelating agent is reused in the reaction, which can achieve a better aluminum removal effect while saving production costs.

Description

Technical Field

[0001] The invention belongs to the technical field of generating disodium hydrogen phosphate from aluminum-containing phosphoric acid, and in particular relates to a method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid. Background Art

[0002] Phosphoric acid is widely used in aluminum oxidation processes. Direct discharge of waste phosphoric acid produced in the aluminum oxidation process not only pollutes the environment, but also causes waste of resources. Since phosphoric acid can react with alkali to prepare disodium hydrogen phosphate, waste phosphoric acid is usually reused to prepare disodium hydrogen phosphate and other products. However, since waste phosphoric acid generally contains a certain amount of aluminum, the neutralization method is usually used to directly prepare sodium dihydrogen phosphate, but the aluminum in phosphoric acid will cause the product crystal form to change, thereby affecting the product quality. The existing process uses SBA-15 molecular sieve chelating adsorbent to remove aluminum ions from the pretreatment liquid, and then concentrates and crystallizes. However, this method can only remove aluminum to 10ppm, and the residual aluminum will cause the sodium dihydrogen phosphate crystals to appear in a planar shape, and the surface sodium dihydrogen phosphate will have a high moisture content. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid. The present invention first removes aluminum from the aluminum-containing phosphoric acid and then adds disodium ethylenediaminetetraacetate to further chelate with aluminum ions to reduce the aluminum content in the finished sodium dihydrogen phosphate. At the same time, disodium ethylenediaminetetraacetate is repeatedly used in the reaction, and its concentration is limited, which can achieve a better aluminum removal effect while saving costs.

[0004] An object of the present invention is to provide a method for improving the quality of dihydrogen phosphate generated from aluminum-containing phosphoric acid, comprising the steps of:

[0005] S1. The waste phosphoric acid is brought to a stirring tank A#, and while stirring, water is added to dilute the waste phosphoric acid to obtain a dilution;

[0006] S2. The alkali solution is added dropwise into the stirring tank A# for neutralization until the pH of the solution in the tank is adjusted to 6-7, and the addition is stopped; the solution in the stirring tank is filtered, and the filtrate I is filtered into the stirring tank B#, and the filter residue I is collected;

[0007] S3. Add a heavy metal chelating agent or a heavy metal chelating agent and a non-ionic polymer flocculant to the stirring tank B#, stir for 30 minutes, and then filter press. Filter the filtrate II to the stirring tank A#, and collect the filter residue II; (Before filtering, activated carbon can be added to the stirred solution and continue stirring for 30 minutes, and then filter press. Activated carbon can assist filtering. In this step, at least one of activated carbon and non-ionic polymer flocculant needs to be added to filter cleanly.)

[0008] S4. The phosphoric acid is added to the stirring tank A#, and the pH in the tank is adjusted to 4.2 to 4.6 to obtain a dihydrogen phosphate pretreatment solution;

[0009] S5. The dihydrogen phosphate pretreatment solution is transferred to a distillation kettle and concentrated by distillation to obtain a dihydrogen phosphate concentrate;

[0010] S6. Cool the dihydrogen phosphate concentrate to 40°C for crystallization, and then centrifuge it to obtain the dihydrogen phosphate product.

[0011] Furthermore, in step S1, the concentration of the waste phosphoric acid dilution solution is 10-12 mol / L.

[0012] Furthermore, in step S2, the alkali solution is a potassium hydroxide solution or a sodium hydroxide solution; the mass concentration of the alkali solution is 15-20%; the dropping speed of the alkali solution is 400-500 L / h; during the dropping process, the temperature of the stirring tank is controlled to be less than 60°C.

[0013] Furthermore, in step S2, the pressure of the filter press is 5 to 8 kg / cm 2 , the time is 60 to 100 minutes.

[0014] Furthermore, the filtrate I is a mixed solution of dihydrogen phosphate and disalt of hydrogen phosphate, and the main body of the filter residue I is aluminum hydroxide precipitate.

[0015] Furthermore, in step S3, the heavy metal chelating agent is disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid or trisodium phosphate; the heavy metal chelating agent is preferably disodium ethylenediaminetetraacetate.

[0016] Furthermore, when sodium hydroxide is used as the alkali solution and disodium ethylenediaminetetraacetate is used as the heavy metal chelating agent, the quality of the dihydrogen phosphate obtained is better than that of other heavy metal chelating agents;

[0017] Furthermore, when potassium hydroxide is used as the alkali solution and dipotassium ethylenediaminetetraacetate is used as the heavy metal chelating agent, the quality of the dihydrogen phosphate obtained is better than that of other heavy metal chelating agents;

[0018] Furthermore, in step S3, the amount of the heavy metal chelating agent added is 0.2 to 1 kg of heavy metal chelating agent per ton of filtrate I.

[0019] Furthermore, in step S3, the nonionic polymer flocculant is polyacrylamide with a mass concentration of 1-3%; the amount of the nonionic polymer flocculant added is 0.5-1 g / T filtrate I, and the amount of activated carbon added is 1-2 kg of activated carbon per ton of filtrate I; the stirring speed is 50-70 r / min; the pressure of the filter press is 5-8 kg / cm 2The compacting pressure is 1.5-1.7Mpa and the time is 60-100 minutes.

[0020] Furthermore, the filtrate II is a dihydrogen phosphate solution, and the filter residue II is a metal precipitate chelated by activated carbon and a chelating agent.

[0021] Furthermore, in step S4, the purity of the phosphoric acid is 75-90%; and the dropping speed of the phosphoric acid is 400-500 L / h.

[0022] Furthermore, in step S5, the pressure of the distillation concentration is -0.04 to -0.08 MPa, the temperature is 100 to 140°C, and the concentration ratio is 3.5 to 4.5:1; the density of the dihydrogen phosphate concentrate is 1.15 g / cm 3 .

[0023] Furthermore, in step S6, before cooling and crystallization, it also includes a process of adding potassium ferrocyanide to the dihydrogen phosphate concentrate.

[0024] Furthermore, in step S6, the amount of potassium ferrocyanide added is 1.1 to 1.5 g of potassium ferrocyanide per ton of dihydrogen phosphate concentrate.

[0025] Another object of the present invention is to protect a dihydrogen phosphate obtained by the above method.

[0026] Another object of the present invention is to protect a method for improving the quality of sodium dihydrogen phosphate produced by aluminum-containing phosphoric acid, comprising the steps of:

[0027] S1. The waste phosphoric acid is brought to a stirring tank A#, and while stirring, water is added to dilute the waste phosphoric acid to obtain a dilution;

[0028] S2. Sodium hydroxide is added dropwise into the stirring tank A# for neutralization until the pH of the solution in the tank is adjusted to 6-7, and the addition is stopped; the solution in the stirring tank is filtered, and the filtrate I is filtered into the stirring tank B#, and the filter residue I is collected;

[0029] S3. Add a heavy metal chelating agent to the stirring tank B# or add a heavy metal chelating agent and a non-ionic polymer flocculant in sequence, stir for 30 minutes, directly filter press, or add activated carbon and continue stirring for 30 minutes, then filter press, filter the filtrate II to the stirring tank A#, collect the filter residue II, in this step, at least one of the activated carbon and the non-ionic polymer flocculant needs to be added to filter cleanly;

[0030] S4. The phosphoric acid is added to the stirring tank A#, and the pH in the tank is adjusted to 4.2 to 4.6 to obtain a sodium dihydrogen phosphate pretreatment solution;

[0031] S5. The sodium dihydrogen phosphate pretreatment solution was transferred to a distillation kettle and concentrated by distillation to obtain a sodium dihydrogen phosphate concentrate;

[0032] S6. The sodium dihydrogen phosphate concentrate is directly cooled and crystallized or potassium ferrocyanide is added to the sodium dihydrogen phosphate concentrate, and then cooled and crystallized. The solution is cooled to 40° C. and then centrifuged. The resulting precipitate is the sodium dihydrogen phosphate product.

[0033] Among them, the process parameters in step S1-6 are the same as the above-mentioned conditions for improving the production of dihydrogen phosphate from aluminum-containing phosphoric acid.

[0034] Another object of the present invention is to protect a method for improving the quality of potassium dihydrogen phosphate generated from aluminum-containing phosphoric acid, comprising the steps of:

[0035] S1. The waste phosphoric acid is brought to a stirring tank A#, and while stirring, water is added to dilute the waste phosphoric acid to obtain a dilution;

[0036] S2. The potassium hydroxide is added dropwise into the stirring tank A# for neutralization until the pH of the solution in the tank is adjusted to 6-7, and the addition is stopped; the solution in the stirring tank is filtered, and the filtrate I is filtered into the stirring tank B#, and the filter residue I is collected;

[0037] S3. Add a heavy metal chelating agent to the stirring tank B# or add a heavy metal chelating agent and a non-ionic polymer flocculant in sequence, stir for 30 minutes, directly filter press, or add activated carbon and continue stirring for 30 minutes, then filter press, filter the filtrate II to the stirring tank A#, collect the filter residue II, in this step, at least one of the activated carbon and the non-ionic polymer flocculant needs to be added to filter cleanly;

[0038] S4. The phosphoric acid is added to the stirring tank A#, and the pH in the tank is adjusted to 4.2 to 4.6 to obtain a potassium dihydrogen phosphate pretreatment solution;

[0039] S5. The potassium dihydrogen phosphate pretreatment solution was transferred to a distillation kettle and concentrated by distillation to obtain a potassium dihydrogen phosphate concentrate;

[0040] S6. Directly cool the sodium dihydrogen phosphate concentrate to crystallize or add potassium ferrocyanide to the potassium dihydrogen phosphate concentrate, cool to 40°C, and then centrifuge to obtain the precipitate, which is the potassium dihydrogen phosphate product.

[0041] Among them, the process parameters in step S1-6 are the same as the above-mentioned conditions for improving the production of dihydrogen phosphate from aluminum-containing phosphoric acid.

[0042] The beneficial technical effects of the present invention are:

[0043] The invention uses heavy metal chelating agents such as disodium ethylenediaminetetraacetic acid to chelate trace aluminum ions contained in a dihydrogen phosphate solution, reduces the aluminum ion content, reduces the influence of the aluminum ions on the crystallization of the dihydrogen phosphate, and improves the quality of the dihydrogen phosphate.

[0044] The present invention removes part of aluminum by adding alkali solution first, adjusting pH, and then further removing trace aluminum by adding heavy metal chelating agent. Compared with chelation first, the amount of chelating agent is reduced, and the production cost is saved. The addition of activated carbon can improve the filtration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0047] The invention first removes aluminum in aluminum-containing phosphate by adjusting the pH value, and then uses heavy metal chelating agents such as disodium ethylenediaminetetraacetic acid (disodium EDTA) to chelate the remaining trace aluminum ions, so that the factors affecting the quality of sodium dihydrogen phosphate or potassium dihydrogen phosphate products are close to zero.

[0048] The present invention shows that the phosphoric acid content and the concentration of the alkali solution, the pH of each process node, and the addition amount of the heavy metal chelating agent and / or potassium ferrocyanide have an important influence on the aluminum content in the final sodium dihydrogen phosphate or potassium dihydrogen phosphate product.

[0049] If the concentration of the phosphoric acid solution obtained by diluting the waste phosphoric acid with water is too high, the reaction will be too violent, and a large amount of crystals will be produced when sodium hydroxide or potassium hydroxide is added for neutralization. Therefore, in one embodiment of the present invention, the waste phosphoric acid is diluted with water to 12 mol / L.

[0050] Too high a concentration of sodium hydroxide or potassium hydroxide solution will lead to a violent reaction and will also produce a large amount of crystals during neutralization. Therefore, in one embodiment of the present invention, the concentration of sodium hydroxide is 20%.

[0051] The generation of sodium dihydrogen phosphate or potassium dihydrogen phosphate from aluminum-containing phosphoric acid belongs to the reuse of process waste liquid, therefore, the cost control requirement is relatively high. The present invention studies the use of heavy metal chelating agents to remove aluminum first, and then add alkali solution for neutralization. The results show that the consumption of the heavy metal chelating agents used is significantly increased, and the production cost is significantly improved compared with the process of the present invention. At the same time, the dihydrogen phosphate produced without adding heavy metal chelating agents has a higher water content and a low content, which affects the reuse rate.

[0052] The present invention adjusts the pH to 6-7 to remove most of the aluminum in the phosphoric acid. If the pH is lower than 6, a large amount of sodium dihydrogen phosphate will be produced, resulting in a large amount of crystal precipitation.

[0053] In one embodiment of the present invention, the dropping speed of sodium hydroxide or potassium hydroxide is controlled to be 500 L / h and the temperature is below 60° C. By controlling the speed and temperature, the reaction can be prevented from being too violent.

[0054] As an embodiment of the present invention, adding disodium ethylenediaminetetraacetate at a rate of 1 kg per ton of reagent will not affect the content of potassium dihydrogen phosphate due to excessively high content, nor will it lead to low heavy metal removal efficiency due to excessively low content.

[0055] As an embodiment of the present invention, activated carbon is added after PAM is added. The precipitate produced by centrifugation of disodium ethylenediaminetetraacetic acid chelated metal is too fine to be filtered clean in one go. Adding PAM for coagulation and adding activated carbon for filtration can improve the efficiency of filtration.

[0056] In one embodiment of the present invention, after adding disodium ethylenediaminetetraacetate and filtering the reaction, the aluminum content in the filtrate II is less than 1 ppm.

[0057] After adding phosphoric acid, the pH is adjusted to 4.2-4.6, and the obtained potassium dihydrogen phosphate content is the highest. When the pH is higher than 4.6, the content of potassium monohydrogen phosphate will increase with the increase of pH value.

[0058] In one embodiment of the present invention, potassium ferrocyanide is added after the concentration process. Potassium ferrocyanide is added as an anti-caking agent, which can slightly affect the crystallization.

[0059] The scheme of the present invention is specifically described by comparing with examples and comparative examples below.

[0060] Example 1

[0061] A method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid, the method comprising the following steps:

[0062] S1. Put 1 ton of waste phosphoric acid containing 700 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 12 mol / L by adding water while stirring;

[0063] S2. 20% sodium hydroxide was added to the stirring tank A# at a drop rate of 500 L / h for neutralization, and the pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C), no crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared; the filter was filtered using a filter press, and the pressure of the filter press was 8 kg / cm 2 , the time is 100 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 25 ppm), and the filter residue I is collected;

[0064] S3. Disodium ethylenediaminetetraacetate and 3% PAM (the amount of disodium ethylenediaminetetraacetate added is 1 kg / ton of filtrate I, and the amount of PAM added is 0.5 kg / ton of filtrate I) are added to the stirring tank B# containing filtrate I in sequence, stirred at 70 r / min for 30 minutes, and activated carbon is added and stirred for 30 minutes. The amount of activated carbon added is 1 to 2 kg of activated carbon per ton of filtrate I, and then a filter press is used for filtration, and the pressure of the filtration is 8 kg / cm 2 , the time is 100 minutes, the filtrate II is filtered to the stirring tank A# (the aluminum content is determined to be 0.25ppm), and the filter residue II is collected;

[0065] S4. Phosphoric acid (acidity 75%) was added to the stirring tank A# containing the filtrate II at a rate of 500 L / h, the pH in the tank was adjusted to 4.5, cooled to room temperature, and no crystals were precipitated to obtain a sodium dihydrogen phosphate pretreatment solution;

[0066] S5. The sodium dihydrogen phosphate pretreatment liquid was transferred to a distillation kettle and distilled and concentrated at 100°C and -0.06Mpa pressure, during which negative pressure feeding was performed, and the concentration ratio was 4.5:1 to obtain a sodium dihydrogen phosphate concentrate (at this time, the material specific gravity was 1.15g / cm 3 )

[0067] S5. The sodium dihydrogen phosphate concentrate is transferred to a crystallization kettle for stirring and cooling crystallization. The solution is cooled to 40°C, a large amount of crystals appear, and the solution is centrifuged. The aluminum content in the centrifuged water is 10 ppm, and the resulting precipitate is the sodium dihydrogen phosphate product. At this time, most of the sodium dihydrogen phosphate crystals are needle-shaped, and a small amount is granular, with a content of 98.93%, a moisture content of 1.05%, and an aluminum content of 0.007%.

[0068] Products that pass inspection are put into storage, and the centrifuged water returns to the distillation kettle for repeated distillation and subsequent operations.

[0069] Example 2

[0070] A method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid, the method comprising the following steps:

[0071] S1. Put 1 ton of waste phosphoric acid containing 700 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 12 mol / L by adding water while stirring;

[0072] S2. 20% sodium hydroxide was added to the stirring tank A# at a drop rate of 500 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. Sodium hydroxide was continued to be added to adjust the pH to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter was filtered using a filter press, and the pressure of the filter press was 8 kg / cm 2, the time is 100 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 25 ppm), and the filter residue I is collected;

[0073] S3. Disodium EDTA and 3% PAM (the amount of disodium EDTA added was 1 kg / ton of filtrate I, and the amount of PAM added was 0.5 kg / ton of filtrate I) were added to the stirred tank B# containing the filtrate I in sequence, stirred at 70 r / min for 30 minutes, and then filtered using a filter press, the pressure of the filter press was 8 kg / cm 2 , the time is 100 minutes, the filtrate II is filtered to the stirring tank A# (the aluminum content is determined to be 0.30ppm), and the filter residue II is collected;

[0074] S4. Phosphoric acid (acidity 75%) was added to the stirring tank A# containing the filtrate II at a rate of 500 L / h, the pH in the tank was adjusted to 4.5, cooled to room temperature, and no crystals were precipitated to obtain a sodium dihydrogen phosphate pretreatment solution;

[0075] S5. The sodium dihydrogen phosphate pretreatment liquid was transferred to a distillation kettle and distilled and concentrated at 100°C and -0.06Mpa pressure, during which negative pressure feeding was performed, and the concentration ratio was 4.5:1 to obtain a sodium dihydrogen phosphate concentrate (at this time, the material specific gravity was 1.15g / cm 3 )

[0076] S5. The sodium dihydrogen phosphate concentrate is transferred to a crystallization kettle for stirring and cooling crystallization. The solution is cooled to 40°C, a large amount of crystals appear, and the solution is centrifuged. The aluminum content in the centrifuged water is 12 ppm, and the resulting precipitate is the sodium dihydrogen phosphate product. At this time, most of the sodium dihydrogen phosphate crystals are needle-shaped, and a small amount of crystals are granular, with a content of 99.04%, a water content of 0.92%, and an aluminum content of 0.004%.

[0077] Products that pass inspection are put into storage, and the centrifuged water returns to the distillation kettle for repeated distillation and subsequent operations.

[0078] Example 3

[0079] A method for improving the quality of sodium dihydrogen phosphate generated from aluminum-containing phosphoric acid, the method comprising the following steps:

[0080] S1. Put 1 ton of waste phosphoric acid containing 500 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 12 mol / L by adding water while stirring;

[0081] S2. 20% sodium hydroxide was added into stirring tank A# at a drop rate of 500 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. The pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter press was used for filtration. The pressure of the filtration was 8 kg / cm 2 , the time is 100 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 27 ppm), and the filter residue I is collected;

[0082] S3. Disodium ethylenediaminetetraacetate and 3% PAM (the amount of disodium ethylenediaminetetraacetate added is 1 kg / ton of filtrate I, and the amount of PAM added is 0.5 kg / ton of filtrate I) are added to the stirring tank B# containing filtrate I in sequence, stirred at 70 r / min for 30 minutes, and activated carbon is added and stirred for 30 minutes. The amount of activated carbon added is 1 to 2 kg of activated carbon per ton of filtrate I, and then a filter press is used for filtration, and the pressure of the filtration is 8 kg / cm 2 , the time is 100 minutes, the filtrate II is filtered to the stirring tank A# (the aluminum content is determined to be 0.28ppm), and the filter residue II is collected;

[0083] S4. Phosphoric acid (acidity 75%) was added to the stirring tank A# containing the filtrate II at a rate of 400-500 L / h, the pH in the tank was adjusted to 4.5, cooled to room temperature, and no crystals were precipitated to obtain a sodium dihydrogen phosphate pretreatment solution;

[0084] S5. The sodium dihydrogen phosphate pretreatment liquid was transferred to a distillation kettle and distilled and concentrated at 100°C and -0.06Mpa pressure, during which negative pressure feeding was performed, and the concentration ratio was 4.5:1 to obtain a sodium dihydrogen phosphate concentrate (at this time, the material specific gravity was 1.15g / cm 3 )

[0085] S5. After adding potassium ferrocyanide (1.5 g per ton) to the sodium dihydrogen phosphate concentrate, transfer to a crystallization kettle for stirring and cooling crystallization, cool to 40°C, a large number of crystals appear, centrifuge, and measure the aluminum content in the centrifuged water to be 8 ppm. The resulting precipitate is the sodium dihydrogen phosphate product. At this time, most of the sodium dihydrogen phosphate crystals are granular, and a small amount of crystals are needle-shaped, with a content of 99.15%, a moisture content of 0.80%, and an aluminum content of 0.004% (potassium ferrocyanide is added as an anti-caking agent, which will change the properties of the crystals).

[0086] Products that pass inspection are put into storage, and the centrifuged water returns to the distillation kettle for repeated distillation and subsequent operations.

[0087] Example 4

[0088] A method for improving the quality of potassium dihydrogen phosphate generated from aluminum-containing phosphoric acid, the method comprising the following steps:

[0089] S1. Put 1 ton of waste phosphoric acid containing 1000 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 11 mol / L by adding water while stirring;

[0090] S2. 18% potassium hydroxide was added to the stirring tank A# at a drop rate of 450 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. The pH was adjusted to 6.5 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter was filtered using a filter press, and the pressure of the filter press was 7 kg / cm 2 , the time is 80 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 30 ppm), and the filter residue I is collected;

[0091] S3. Disodium EDTA and 2% PAM (the amount of disodium EDTA added was 0.8 kg / ton of filtrate I, and the amount of PAM added was 0.8 kg / ton of filtrate I) were added to the stirring tank B# containing the filtrate I in sequence, stirred at 60 r / min for 30 minutes, and then filtered using a filter press, the pressure of the filter press was 7 kg / cm 2 , the time is 80 minutes, the filtrate II is filtered to the stirring tank A# (the aluminum content is determined to be 0.51ppm), and the filter residue II is collected;

[0092] S4. Phosphoric acid (acidity 75%) was added to the stirring tank A# containing the filtrate II at a rate of 450 L / h, the pH in the tank was adjusted to 4.2, cooled to room temperature, and no crystals were precipitated to obtain a potassium dihydrogen phosphate pretreatment solution;

[0093] S5. The potassium dihydrogen phosphate pretreatment liquid was transferred to a distillation kettle and distilled and concentrated at 140°C and -0.08Mpa pressure, during which negative pressure feeding was performed, and the concentration ratio was 4.5:1 to obtain a potassium dihydrogen phosphate concentrate (at this time, the material specific gravity was 1.15g / cm 3 )

[0094] S6. The potassium dihydrogen phosphate concentrate is transferred to a crystallization kettle for stirring and cooling crystallization, cooled to 40°C, a large amount of crystals appear, and centrifuged. The aluminum content in the centrifuged water is determined to be 15ppm, and the resulting precipitate is the potassium dihydrogen phosphate product. At this time, most of the potassium dihydrogen phosphate crystals are needle-shaped, and a small amount of crystals are granular, with a content of 98.98%, a moisture content of 0.99%, and an aluminum content of 0.018%.

[0095] Products that pass inspection are put into storage, and the centrifuged water returns to the distillation kettle for repeated distillation and subsequent operations.

[0096] Example 5

[0097] A method for improving the quality of potassium dihydrogen phosphate generated from aluminum-containing phosphoric acid, the method comprising the following steps:

[0098] S1. Put 1 ton of waste phosphoric acid containing 700 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 10 mol / L by adding water while stirring;

[0099] S2. 15% potassium hydroxide was added to the stirring tank A# at a drop rate of 500 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. The pH was adjusted to 6 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter was filtered using a filter press, and the pressure of the filter press was 5 kg / cm 2 , the time is 60 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 28ppm), and the filter residue I is collected;

[0100] S3. Disodium EDTA and 1% PAM (the amount of disodium EDTA added was 0.2 kg / ton of filtrate I, and the amount of PAM added was 1.0 kg / ton of filtrate I) were added to the stirring tank B# containing the filtrate I in sequence, stirred at 50 r / min for 30 minutes, and then filtered using a filter press, the pressure of the filter press was 5 kg / cm 2 , the time is 60 minutes, the filtrate II is filtered to the stirring tank A# (the aluminum content is measured to be 0.46ppm), and the filter residue II is collected;

[0101] S4. Phosphoric acid (acidity 75%) was added to the stirring tank A# containing the filtrate II at a rate of 400 L / h, the pH in the tank was adjusted to 4.2, cooled to room temperature, and no crystals were precipitated to obtain a potassium dihydrogen phosphate pretreatment solution;

[0102] S5. The potassium dihydrogen phosphate pretreatment liquid was transferred to a distillation kettle and distilled and concentrated at 120°C and -0.04Mpa pressure, during which negative pressure feeding was performed, and the concentration ratio was 4.5:1 to obtain a potassium dihydrogen phosphate concentrate (at this time, the material specific gravity was 1.15g / cm 3 )

[0103] S6. The potassium dihydrogen phosphate concentrate is transferred to a crystallization kettle for stirring and cooling crystallization, cooled to 40°C, a large amount of crystals appear, and centrifuged. The aluminum content in the centrifuged water is determined to be 10 ppm, and the resulting precipitate is the potassium dihydrogen phosphate product. At this time, most of the potassium dihydrogen phosphate crystals are needle-shaped, and a small amount is granular, with a content of 98.93%, a moisture content of 1.05%, and an aluminum content of 0.007%.

[0104] Products that pass inspection are put into storage, and the centrifuged water returns to the distillation kettle for repeated distillation and subsequent operations.

[0105] Comparative Example 1

[0106] A method for generating sodium dihydrogen phosphate from aluminum-containing phosphoric acid, the method comprising the following steps:

[0107] S1. Add 1 ton of waste phosphoric acid (acidity 80-90%) containing 700 ppm aluminum to a stirring tank A#;

[0108] S2. 30% sodium hydroxide was added to the stirring tank A# at a drop rate of 500L / h for neutralization. The reaction was quite intense. When the pH was adjusted to 4-5, crystals were precipitated. The pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). The crystals decreased and a large amount of white precipitate (aluminum hydroxide) appeared. The filtrate I was filtered by a filter press and filtered to the stirring tank B# (the aluminum content in the filtrate I was determined to be 58ppm). The filter residue I was collected. The filter residue contained a large amount of crystals, making it difficult to prepare sodium dihydrogen phosphate. The experiment ended. Because the reaction process was quite intense, it was difficult to operate in actual production. The filter residue contained a large amount of crystals, which affected the recovery and reuse of phosphoric acid.

[0109] Comparative Example 2

[0110] A method for generating sodium dihydrogen phosphate from aluminum-containing phosphoric acid, the method comprising the following steps:

[0111] S1. Put 1 ton of waste phosphoric acid (acidity 80-90%) with an aluminum content of 700 ppm into a stirring tank A#, and dilute the phosphoric acid to 12 mol / L (acidity of about 75%) by adding water while stirring;

[0112] S2. 30% sodium hydroxide was added to the stirring tank A# at a dropping speed of 500L / h for neutralization. The reaction was relatively violent. When the pH was adjusted to 4-5, crystals were precipitated. The pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). The crystals decreased and a large amount of white precipitate (aluminum hydroxide) appeared. The filter press was used for filtration. The filtrate I was filtered to the stirring tank B# (the aluminum content in the filtrate I was determined to be 45ppm). The filter residue I was collected. The filter residue contained a small amount of crystals. The experiment was terminated and sodium dihydrogen phosphate could not be successfully prepared. In this comparative example, the reaction was relatively violent, and it was difficult to operate in actual production. The filter residue still contained a small amount of crystals, which affected the recovery and reuse of phosphoric acid.

[0113] Comparative Example 3

[0114] A method for producing sodium dihydrogen phosphate from aluminum-phosphoric acid, the method comprising the following steps:

[0115] S1. 1 ton of waste phosphoric acid (acidity 80-90%) with an aluminum content of 700 ppm is added to a mixing tank A#;

[0116] S2. 20% sodium hydroxide was added to the stirring tank A# at a dropping speed of 500 L / h for neutralization. The reaction was quite violent. When the pH was adjusted to 4-5, crystals precipitated. The pH was adjusted to 7 by adding more sodium hydroxide (when adjusting the pH, the temperature in the tank was controlled below 60°C). The crystals decreased and a large amount of white precipitate (aluminum hydroxide) appeared. The filtrate I was filtered by a filter press and the filtrate I was filtered into the stirring tank B# (the aluminum content in the filtrate I was determined to be 47 ppm). The filter residue I was collected. The filter residue contained a small amount of crystals and the experiment was terminated (the reaction was quite violent and the actual production was difficult to operate. The filter mud still contained a small amount of crystals, which affected the recovery and reuse of phosphoric acid.

[0117] Comparative Example 4

[0118] A method for producing sodium dihydrogen phosphate from aluminum-phosphoric acid, the method comprising the following steps:

[0119] S1. Put 1 ton of waste phosphoric acid (acidity 80-90%) with an aluminum content of 7000ppm into a stirring tank A#, and dilute the phosphoric acid to 12mol / L by adding water while stirring;

[0120] S2. 20% sodium hydroxide was added into stirring tank A# at a drop rate of 500 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. The pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter press was used for filtration. The pressure of the filtration was 8 kg / cm 2 , the time is 100 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 28ppm), and the filter residue I is collected;

[0121] S3. Phosphoric acid (acidity 75%) was injected into the stirring tank B# containing the filtrate I at a rate of 500L / h, the pH in the tank was adjusted to 4.5, cooled to room temperature, no crystals were precipitated, distilled and concentrated at 100°C and -0.06Mpa pressure, negative pressure feeding during the period, concentration ratio 4.5:1, then transferred to the crystallization kettle for stirring cooling crystallization, cooled to 40°C, a large number of crystals appeared, centrifuged, and the aluminum content in the centrifuged water was determined to be 102ppm, and the resulting precipitate was the sodium dihydrogen phosphate product. The sodium dihydrogen phosphate crystals were in the form of a surface, with a content of 95.16%, a water content of 4.71%, and an aluminum content of 0.02%.

[0122] Comparative Example 5

[0123] A method for generating sodium dihydrogen phosphate from aluminum-containing phosphoric acid, the method comprising the following steps:

[0124] S1. Put 1 ton of waste phosphoric acid containing 700 ppm aluminum into a stirring tank A#, and dilute the phosphoric acid to 12 mol / L by adding water while stirring;

[0125] S2. 20% sodium hydroxide was added into stirring tank A# at a drop rate of 500 L / h for neutralization. The reaction was relatively slow. When the pH was adjusted to 4-5, almost no crystals were precipitated. The pH was adjusted to 7 (when adjusting the pH, the temperature in the tank was controlled below 60°C). No crystals were precipitated, and a large amount of white precipitate (aluminum hydroxide) appeared. The filter press was used for filtration. The pressure of the filtration was 8 kg / cm 2 , the time is 100 minutes, the filtrate I is filtered into the stirring tank B# (the aluminum content in the filtrate I is determined to be 32ppm), and the filter residue I is collected;

[0126] S3. To the stirred tank B# containing the filtrate Ⅰ, 0.95 kg of sodium sulfide and 3% PAM (the amount of sodium sulfide added was 1 kg / ton of filtrate Ⅰ, and the amount of PAM added was 0.5 kg / ton of filtrate Ⅰ) were added, stirred at 70 r / min for 30 minutes, and then filtered using a filter press, the pressure of which was 8 kg / cm 2 , the time is 100 minutes, the filtrate II is filtered into the stirring tank A# (the aluminum content is determined to be 10ppm), and the filter residue II is collected;

[0127] S4. Phosphoric acid (acidity 75%) was pumped into the stirring tank A# containing filtrate II at a speed of 500L / h, the pH in the tank was adjusted to 4.5, cooled to room temperature, no crystals were precipitated, distilled and concentrated at 100℃, -0.06Mpa pressure, negative pressure feeding during the period, concentration ratio 4.5:1, then stirred and cooled to 40℃, a large number of crystals appeared, centrifuged, and the aluminum content in the centrifuged water was determined to be 56ppm. The resulting precipitate was the sodium dihydrogen phosphate product. Most of the sodium dihydrogen phosphate crystals were in the form of planes, and a small amount of crystals were in the form of needles, with a content of 96.25%, 3.70% water, and 0.015% aluminum.

[0128] Test example:

[0129] The aluminum content in the filtrate of Examples 1-3 and Comparative Examples 1-5, the dihydrogen phosphate content, moisture content, aluminum content, aluminum content in centrifuged water, and the crystal shape of the dihydrogen phosphate finally obtained were determined. The aluminum content was determined by ICP, the dihydrogen phosphate content was titrated according to the national standard, and the moisture content was determined by a solid moisture meter. The test results are shown in Table 1.

[0130] Table 1 Performance parameters related to embodiments and comparative examples

[0131]

[0132]

[0133] As shown in Table 1, when the acidity of phosphoric acid is high and the alkalinity of liquid alkali is high, the reaction is more violent, and the actual production is more difficult to operate. A large amount of crystals are contained in the filter mud, which affects the recycling of phosphoric acid. When the acidity of phosphoric acid is 75% and the alkalinity of liquid alkali is 20%, the sodium dihydrogen phosphate produced by neutralization is a nearly saturated solution, which is convenient for production. The aluminum content in filtrate II will affect the crystal form of sodium dihydrogen phosphate, resulting in a high moisture content of the final product, thereby affecting the content of sodium dihydrogen phosphate. Disodium ethylenediaminetetraacetic acid can effectively chelate the aluminum content in filtrate I. It is confirmed by experiments that the addition amount of disodium ethylenediaminetetraacetic acid is 0.1% of the mass of the solution, which is the best (aluminum content is less than 1ppm). A trace amount of potassium ferrocyanide can also change the crystal form and improve the content slightly (only after disodium ethylenediaminetetraacetic acid is removed by aluminum). Example 3 shows that the addition of potassium ferrocyanide changes the crystal form of dihydrogen phosphate. At the same time, when the dosage (heavy metal chelating agent) content is too high, the content of dihydrogen phosphate in the finished product will be low.

[0134] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for improving the quality of dihydrogen phosphate generated from aluminum-containing phosphoric acid, characterized in that: The method comprises the following steps: S1. The waste phosphoric acid is brought to a stirring tank A#, and while stirring, water is added to dilute the waste phosphoric acid to obtain a dilution; S2. The alkali solution is added dropwise into the stirring tank A# for neutralization until the pH of the solution in the tank is adjusted to 6~7, and the addition is stopped; The solution in the stirring tank is filtered, and the filtrate I is filtered into the stirring tank B#, and the filter residue I is collected; S3. Add a heavy metal chelating agent to the stirring tank B#, stir for 30 minutes, and then filter press, filter the filtrate II to the stirring tank A#, and collect the residue II; S4. The phosphoric acid is added to the stirring tank A#, and the pH in the tank is adjusted to 4.2-4.6 to obtain a dihydrogen phosphate pretreatment solution; S5. The dihydrogen phosphate pretreatment solution is transferred to a distillation kettle and concentrated by distillation to obtain a dihydrogen phosphate concentrate; S6. The dihydrogen phosphate concentrate is cooled and crystallized, cooled to 40°C, and centrifuged to obtain a dihydrogen phosphate product; In step S1, the concentration of the waste phosphoric acid dilution is 10-12 mol / L; The mass concentration of the alkali solution is 15-20%; Step S3 also includes adding a non-ionic polymer flocculant while adding the heavy metal chelating agent; the non-ionic polymer flocculant is polyacrylamide with a mass concentration of 1-3%; the amount of the non-ionic polymer flocculant added is 0.5-1 kg / ton of filtrate I; Step S3 also includes adding activated carbon after stirring for 30 minutes and continuing stirring for 30 minutes, wherein the amount of activated carbon added is 1-2 kg of activated carbon per ton of filtrate I; the stirring speed is 50-70 r / min; the pressure of the filter press is 5-8 kg / cm 2 , time is 60~100 minutes; The dropping speed of the alkali solution is 400-500 L / h; during the dropping process, the temperature of the stirring tank is controlled to be less than 60°C; In step S6, before cooling and crystallization, potassium ferrocyanide is added to the dihydrogen phosphate concentrated solution, and the amount of potassium ferrocyanide added is 1.1-1.5 g of potassium ferrocyanide per ton of dihydrogen phosphate concentrated solution.

2. The method according to claim 1, characterized in that In step S2, the alkali solution is potassium hydroxide solution or sodium hydroxide solution; the pressure of the filter press is 5-8 kg / cm 3 , the time is 60~100 minutes.

3. The method according to claim 1, characterized in that In step S3, the heavy metal chelating agent is disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, or ethylenediaminetetraacetic acid.

4. The method according to claim 1, characterized in that: In step S3, the amount of heavy metal chelating agent added is 0.2-1 kg of heavy metal chelating agent per ton of filtrate I.

5. The method according to claim 1, characterized in that In step S4, the purity of the phosphoric acid is 75-90%; and the dropping speed of the phosphoric acid is 400-500 L / h.

6. The method according to claim 1, characterized in that In step S5, the distillation concentration pressure is -0.04~-0.08 Mpa, the temperature is 100~140°C, and the concentration ratio is 3.5~4.5:1; the density of the dihydrogen phosphate concentrate is 1.15g / cm 3 .

7. The method according to claim 1, characterized in that In step S3, the heavy metal chelating agent is disodium ethylenediaminetetraacetate.

Images