Industrial grade monoammonium phosphate sludge treatment method and liquid fertilizer

Abstract

According to the industrial-grade monoammonium phosphate sludge treatment method and the liquid fertilizer provided by the invention, the phosphoric acid solution is neutralized by ammonia water, and the pH value of the system is limited, so that impurities in liquid-phase monoammonium phosphate are reduced as much as possible, and an iron element is left in sludge; a citric acid solution is added into the sludge to carry out chelation reaction on metal ions in the sludge to control the pH value to be 4.0-7.0, then a raw material phosphoric acid solution for preparing monoammonium phosphate is added, the pH value of a system is adjusted to be not higher than 4.0, the water solubility and stability of iron elements in the sludge are remarkably improved, non-water-soluble ferric phosphate salt in the sludge is converted into a water-soluble chelate, and the water-soluble chelate is converted into the sludge. The obtained liquid fertilizer is more easily absorbed by crops, high-value utilization of sludge is achieved, the obtained liquid fertilizer can form a soil environment where beneficial microorganisms move, a good soil aggregate structure is formed, and the soil improvement effect is obvious.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and in particular relates to a method for treating industrial-grade monoammonium phosphate sludge and liquid fertilizer. Background Art

[0002] The iron content of northern phosphorus concentrate is relatively high, with an average value of between 2.0 and 2.5%. When using this mine to produce industrial-grade monoammonium phosphate, a large amount of sludge rich in trace element iron will be produced by the slurry precipitation and filtration process. Usually, the resource recovery method of this type of sludge is to directly add it to agricultural-grade monoammonium phosphate for fertilizer production, but this will reduce the water solubility of the product, and the iron element in the sludge is difficult to be absorbed and utilized by crops, which is easy to cause soil compaction and waste of resources.

[0003] In the prior art, it is difficult to obtain high-value utilization of sludge in the production of industrial-grade monoammonium phosphate. Summary of the invention

[0004] The invention provides a method for treating industrial-grade monoammonium phosphate sludge and a liquid fertilizer, which are used to solve the problem that the sludge produced in the production of industrial-grade monoammonium phosphate in the prior art is difficult to be utilized in a high-value manner.

[0005] In a first aspect, the present invention provides a method for treating industrial-grade monoammonium phosphate sludge, comprising the following steps:

[0006] (1) adding aqueous ammonia to a phosphoric acid solution for neutralization treatment until the pH value is 4.0 to 4.2, and obtaining a crude monoammonium phosphate in a liquid phase after solid-liquid separation;

[0007] (2) performing filter press separation treatment on the crude monoammonium phosphate to obtain liquid monoammonium phosphate and solid sludge;

[0008] (3) First, add citric acid solution to the sludge for chelating reaction, control the pH value of the system to 4.0-7.0, then add phosphoric acid solution until the pH value of the system is not higher than 4.0, perform dry filtration, and obtain liquid fertilizer.

[0009] Compared with the prior art, the invention is beneficial in that: the phosphoric acid solution is neutralized by ammonia water and the pH value of the system is limited, so that impurities in the liquid phase monoammonium phosphate are reduced as much as possible, and the iron element is retained in the sludge; the metal ions in the sludge are subjected to a chelation reaction by adding a citric acid solution to the sludge to control the pH value to be 4.0-7.0; and then the raw material phosphoric acid solution for preparing monoammonium phosphate is added to adjust the pH value of the system to not higher than 4.0, thereby significantly improving the water solubility and stability of the iron element in the sludge, converting the water-insoluble iron phosphate in the sludge into a water-soluble chelate, and the obtained liquid fertilizer is easier to be absorbed by crops, thus realizing the high-value utilization of the sludge, and the obtained liquid fertilizer can form a soil environment for the activity of beneficial microorganisms and form a good soil aggregate structure, and the soil improvement effect is obvious.

[0010] Furthermore, in step (3), the pH value of the citric acid solution is 4 to 4.5; and / or,

[0011] Add phosphoric acid solution until the pH value of the system reaches 3-4.0; and / or,

[0012] The pH value of the citric acid solution was adjusted using 20-25% ammonia water.

[0013] Furthermore, the mass percentage of the metal oxide in the sludge is 18-30%, and the average relative molecular mass of the metal oxide is 50-65; and / or,

[0014] The concentration of the phosphoric acid solution is 3 to 4 mol / L; and / or,

[0015] The concentration of the citric acid solution is 1 mol / L.

[0016] Furthermore, in step (3), the mass volume ratio of the sludge, the phosphoric acid solution and the citric acid solution is 1:(0.1-0.3):(2.5-4.0), wherein the sludge is measured in kilograms, and the phosphoric acid solution and the citric acid solution are measured in liters;

[0017] The temperature of the chelating reaction is 55-70°C.

[0018] Furthermore, the phosphoric acid solution includes the following components, which are calculated by mass percentage: 21.0-24.0% of phosphorus pentoxide, 0.2-0.3% of calcium oxide, 0.3-0.6% of magnesium oxide, 1.5-2.5% of ferric oxide, and 0.3-0.6% of aluminum oxide.

[0019] Furthermore, the sludge includes the following components, which are 13-22% of magnesium phosphate, 26-45% of iron phosphate, 11-18% of aluminum phosphate and 39-43% of phosphorus pentoxide in terms of mass percentage.

[0020] Furthermore, the method for preparing the phosphoric acid solution comprises the following steps:

[0021] Adding water to the phosphorus concentrate to perform slurry preparation to obtain phosphorus concentrate slurry with a water content of 25-28%;

[0022] Concentrated sulfuric acid is added to the phosphorus concentrate slurry for extraction treatment, and a liquid phosphoric acid solution is obtained after solid-liquid separation;

[0023] Among them, the phosphorus concentrate includes the following components, which are calculated by mass percentage: 29.5-33.5% of phosphorus pentoxide, 46.0-50.0% of calcium oxide, 0.5-0.9% of magnesium oxide, 2.0-3.5% of iron oxide, 0.5-1.0% of aluminum oxide, 3.0-5.0% of silicon dioxide, and 1.5-3.0% of fluorine.

[0024] Furthermore, in step (1), the neutralization treatment includes a first ammonia addition treatment and a second ammonia addition treatment;

[0025] In the first ammonia treatment, the neutralization degree of the control system is 0.93-0.96, and the pH value is 2.7-3.0;

[0026] In the second ammonia treatment, the system neutralization degree is controlled to be 1.03-1.05 and the pH value is 4.0-4.2.

[0027] Furthermore, the mass percentage of the iron element in the liquid fertilizer is 1.5-2.5%, and the chelation rate of the iron element in the liquid fertilizer is 95-100%.

[0028] In a second aspect, the present invention provides a liquid fertilizer prepared by the method for treating industrial-grade monoammonium phosphate sludge described in the first aspect. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In a first aspect, the present invention provides a method for treating industrial-grade monoammonium phosphate sludge, comprising the following steps:

[0031] (1) adding aqueous ammonia to a phosphoric acid solution for neutralization treatment until the pH value is 4.0 to 4.2, and obtaining a crude monoammonium phosphate in a liquid phase after solid-liquid separation;

[0032] (2) performing filter press separation on the crude monoammonium phosphate to obtain liquid monoammonium phosphate and sludge;

[0033] (3) First, add citric acid solution to the sludge for chelating reaction, control the pH value of the system to 4.0-7.0, then add phosphoric acid solution until the pH value of the system is not higher than 4.0, perform dry filtration, and obtain liquid fertilizer.

[0034] Among them, citric acid chelated iron has medium chelating strength. After the liquid fertilizer is absorbed by crops, it can slowly release metal ions, iron ions and citric acid. It has a small molecular weight, is easier to transport and absorb in crops, and has a high utilization rate. At the same time, citric acid can adjust the pH value of the soil environment to a slightly acidic state, which helps to form a soil environment for beneficial microbial activities and a good soil aggregate structure, with obvious soil improvement effects. The raw materials used have low heavy metal content, will not cause harm to the environment, are non-toxic and harmless, and are more green and environmentally friendly.

[0035] The method for treating industrial-grade monoammonium phosphate sludge provided by the present invention comprises the following steps: neutralizing a phosphoric acid solution with ammonia water and limiting the pH value of the system, thereby reducing impurities in the liquid phase monoammonium phosphate as much as possible and leaving the iron element in the sludge; controlling the pH value to be 4.0-7.0 by adding a citric acid solution to the sludge for a chelating reaction of metal ions in the sludge; then adding a raw material phosphoric acid solution for preparing the monoammonium phosphate to adjust the pH value of the system to be no higher than 4.0, thereby significantly improving the water solubility and stability of the iron element in the sludge; converting the water-insoluble iron phosphate in the sludge into a water-soluble chelate; and obtaining a liquid fertilizer that is more easily absorbed by crops, thereby realizing high-value utilization of the sludge; and the obtained liquid fertilizer can form a soil environment for the activities of beneficial microorganisms and a good soil aggregate structure, and has an obvious soil improvement effect.

[0036] Among them, the filtration separation treatment can be carried out using a filter press.

[0037] Furthermore, the pH value of the citric acid solution is 4 to 4.5, and the pH value of the citric acid solution is adjusted using ammonia water with a concentration of 20 to 25%.

[0038] By controlling the pH value of the citric acid solution between 4 and 4.5, the chelation efficiency of citric acid on the iron element can be improved, ensuring that the chelation reaction is fully carried out.

[0039] Furthermore, in step (3), adding phosphoric acid solution to the system pH value to 3-4.0 can further reduce the secondary precipitation of iron elements in the liquid fertilizer during use.

[0040] Specifically, the mass percentage of the metal oxide in the sludge is 18-30%, the average relative molecular mass of the metal oxide is 50-65; the concentration of the phosphoric acid solution is 3-4 mol / L; and the concentration of the citric acid solution is 1 mol / L.

[0041] By limiting the content and average relative molecular weight of metal oxides in the sludge, the characteristics of the raw materials are further clarified. By controlling the concentrations of phosphoric acid solution and citric acid solution, the efficiency and stability of the reaction system can be further improved, and the chelation rate and resource utilization rate can be improved.

[0042] Furthermore, in step (3), the mass volume ratio of the sludge, phosphoric acid solution and citric acid solution is 1:(0.1-0.3):(2.5-4.0), wherein the sludge is measured in kilograms, and the phosphoric acid solution and the citric acid solution are measured in liters.

[0043] By optimizing the mass volume ratio of the sludge, the phosphoric acid solution and the citric acid solution, the balance of the reaction system can be further improved and the efficiency of the chelating reaction can be improved.

[0044] In one embodiment, the temperature of the chelating reaction is 55-70°C.

[0045] By controlling the temperature of the chelation reaction, we can avoid the decomposition of citric acid due to high temperature or inadequate reaction due to low temperature, thus ensuring the smooth progress of the chelation reaction.

[0046] Specifically, the phosphoric acid solution includes the following components, which are calculated by mass percentage: 21.0-24.0% of phosphorus pentoxide, 0.2-0.3% of calcium oxide, 0.3-0.6% of magnesium oxide, 1.5-2.5% of ferric oxide, and 0.3-0.6% of aluminum oxide.

[0047] Each substance in the phosphoric acid solution usually exists in the form of ions, and the content of each substance is usually expressed in the form of its oxide. By further defining the specific composition and content of the phosphoric acid solution, the stability and controllability of the production process can be further improved.

[0048] Specifically, the sludge includes the following components, which are 13-22% of magnesium phosphate, 26-45% of iron phosphate, 11-18% of aluminum phosphate and 39-43% of phosphorus pentoxide in terms of mass percentage.

[0049] It can be understood that the sludge also includes other metal ions besides iron ions. By further preparing phosphorus concentrate to improve the types and existence forms of metal ions in the sludge, the soil improvement ability of the liquid fertilizer can be further improved, and the recovery and utilization rate of elements such as iron and magnesium can be improved.

[0050] In a specific embodiment, a method for preparing a phosphoric acid solution comprises the following steps: adding water to phosphorus concentrate to perform slurry treatment to obtain phosphorus concentrate slurry having a water content of 25-28%;

[0051] Concentrated sulfuric acid is added to the phosphorus concentrate slurry for extraction treatment, and a liquid phosphoric acid solution is obtained after solid-liquid separation;

[0052] Among them, the phosphorus concentrate includes the following components, which are calculated by mass percentage: 29.5-33.5% of phosphorus pentoxide, 46.0-50.0% of calcium oxide, 0.5-0.9% of magnesium oxide, 2.0-3.5% of iron oxide, 0.5-1.0% of aluminum oxide, 3.0-5.0% of silicon dioxide, and 1.5-3.0% of fluorine.

[0053] Among them, the main component of phosphorus concentrate is fluoroapatite, that is, calcium fluorophosphate, and the rest are mineral impurities containing iron, aluminum, magnesium, etc.

[0054] When the phosphorus concentrate slurry is extracted with concentrated sulfuric acid, the chemical reactions that occur are shown in Formula 1 and Formula 2:

[0055] Ca 5 F(PO 4 ) 3 +7H 3 PO 4 =5Ca(H 2 PO 4 ) 2 +HF↑ Formula 1

[0056] Ca(H 2 PO 4 ) 2 +H 2 SO 4 +2H 2 O=CaSO 4 ·2H 2 O↓+2H 3 PO 4 Formula 2

[0057] At the beginning of the extraction process, the phosphorus concentrate slurry reacts with sulfuric acid to obtain sulfur-phosphorus mixed acid. As the reaction continues and the process indicators are adjusted, a phosphoric acid solution is finally obtained.

[0058] Optionally, in step (1), the neutralization treatment includes a first ammonia addition treatment and a second ammonia addition treatment;

[0059] In the first ammonia treatment, the neutralization degree of the control system is 0.93-0.96, and the pH value is 2.7-3.0;

[0060] In the second ammonia treatment, the system neutralization degree is controlled to be 1.03-1.05 and the pH value is 4.0-4.2.

[0061] By adding ammonia step by step, the neutralization reaction can be further fully carried out, thereby improving the purity and yield of the crude monoammonium phosphate.

[0062] Furthermore, the mass percentage of the iron element in the liquid fertilizer is 1.5-2.5%, and the chelation rate of the iron element in the liquid fertilizer is 95-100%.

[0063] In a second aspect, the present invention provides a liquid fertilizer prepared by the method for treating industrial-grade monoammonium phosphate sludge described in the first aspect.

[0064] By converting sludge into water-soluble fertilizer, the iron in the liquid fertilizer exists in the form of water-soluble chelates, which are easily absorbed by crops, thus achieving high-value utilization of resources and solving the problem of low utilization rate of nutrients and trace elements in sludge.

[0065] Hereinafter, a method for treating industrial-grade monoammonium phosphate sludge provided by the present invention is described in detail through specific examples.

[0066] Example 1

[0067] (1) adding concentrated sulfuric acid to the phosphorus concentrate slurry for extraction treatment, and obtaining a liquid phosphoric acid solution after solid-liquid separation;

[0068] Among them, phosphorus concentrate includes 33.48% phosphorus pentoxide, 49.42% calcium oxide, 0.68% magnesium oxide, 3.46% ferric oxide, 0.78% aluminum oxide, 3.71% silicon dioxide, and 2.7% fluorine;

[0069] (2) adding aqueous ammonia to the phosphoric acid solution for neutralization, and obtaining a crude monoammonium phosphate in the liquid phase after solid-liquid separation;

[0070] The neutralization treatment includes a first ammonia treatment and a second ammonia treatment; in the first ammonia treatment, the system neutralization degree is controlled to be 0.95 and the pH value is 2.8; in the second ammonia treatment, the system neutralization degree is controlled to be 1.03 and the pH value is 4.2;

[0071] (3) subjecting the crude monoammonium phosphate to a filter press separation treatment to obtain liquid monoammonium phosphate and sludge; wherein the sludge comprises 13% magnesium phosphate, 26% iron phosphate, 11% aluminum phosphate and 40% phosphorus pentoxide;

[0072] (4) First, a citric acid solution is added to the sludge to carry out a chelating reaction at 60° C. for 40 minutes, and then a phosphoric acid solution is added to the sludge until the pH value is 3.5, and dry filtration is performed to obtain a liquid fertilizer; wherein the ratio of the sludge (kg), phosphoric acid solution (L) and citric acid solution (L) is 1:0.2:2.5.

[0073] Example 2

[0074] The difference between this comparative example and Example 1 is that in step (4), phosphoric acid solution is added until the pH value is 4.0.

[0075] Example 3

[0076] Compared with Example 1, the present embodiment is different in that the ratio of sludge (kg), phosphoric acid solution (L) and citric acid solution (L) is 1:0.2:2.3.

[0077] Comparative Example 1

[0078] The present embodiment is different from the embodiment 1 in that in step (2), the pH value of the system is controlled to be 4.8 in the second ammonia treatment, that is, the pH value of the liquid phase monoammonium phosphate is 4.8.

[0079] Comparative Example 2

[0080] The present embodiment is different from the embodiment 1 in that: in step (4), a citric acid solution is first added to the sludge to carry out a chelating reaction, and the pH value is controlled to be 2.

[0081] Test Example 1

[0082] Testing the liquid fertilizer in each of the above embodiments comprises the following steps:

[0083] (1) Determine the ratio of the amount of water-soluble phosphorus in the liquid fertilizer to the total amount of phosphorus in the sludge and the phosphoric acid solution to obtain the utilization rate of the effective phosphorus and judge the degree of chelation reaction; wherein the phosphorus content is measured according to GB / T 10209.2-2010;

[0084] (2) Add 2 drops of hematite indicator to 10 mL of liquid fertilizer for qualitative testing. If a blue color appears, the iron is in the free state; if no blue color appears, the iron is in the chelated state.

[0085] (3) Take another 30.0 mL of liquid fertilizer, add 10 mL of 10% potassium iodide solution, add 1-2 mL of 0.5% starch solution, and perform quantitative testing. If blue appears, chelation is incomplete. If no blue appears, all of the iron is chelated. Since chelated iron does not participate in redox reactions, the free iron content in the liquid fertilizer is determined using sodium thiosulfate standard solution.

[0086] (4) The iron content in the liquid fertilizer was determined by an atomic absorption spectrophotometer, and the chelation rate was calculated as (1-free iron / total iron) × 100%.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089] Group Water solubility of available phosphorus (%) Total iron content (%) Chelation rate (%) Example 1 100 2.50 100 Example 2 96 2.46 96 Example 3 97 2.42 97 Comparative Example 1 92 2.14 92 Comparative Example 2 92 2.34 90

[0090] As shown in Table 1, the treatment method of industrial-grade monoammonium phosphate sludge provided by the present invention significantly improves the water solubility and stability of iron elements in sludge, converts water-insoluble iron phosphate in sludge into water-soluble chelate, and greatly improves chelation efficiency. Among them, in Example 2, phosphoric acid and iron binding ability are strong, citric acid chelating ability is relatively weak, chelated iron stability is reduced, and iron element may be hydrolyzed; phosphoric acid, citric acid and iron binding ability establish a new balance in Example 3, only showing insufficient chelation amount; in Comparative Example 1, secondary ammonia is added to pH4.8 to control high, resulting in low iron content, and after the chelation reaction is complete, due to the large amount of balanced phosphoric acid added, the water solubility and chelation rate are reduced; Comparative Example 2 has too high acidity, low citric acid chelating ability, poor stability, and cannot meet product requirements.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein by equivalents. If these modifications and variations fall within the scope of the claims of the present invention and their equivalent technologies, they should be considered to be within the protection scope of the present invention.

Claims

1. A method for treating industrial-grade monoammonium phosphate sludge, characterized in that: The following steps are involved: (1) adding aqueous ammonia to the phosphoric acid solution for neutralization to a pH value of 4.0 to 4.2, and obtaining a crude monoammonium phosphate in the liquid phase after solid-liquid separation; (2) subjecting the crude monoammonium phosphate to a filter press separation treatment to obtain a liquid phase monoammonium phosphate and a solid phase sludge; (3) First, add citric acid solution to the sludge for chelation reaction, control the pH value of the system to 4.0-7.0, then add phosphoric acid solution until the pH value of the system is not higher than 4.0, and perform dry filtration to obtain liquid fertilizer.

2. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: In step (3), the pH value of the citric acid solution is 4 to 4.5; and / or, Add phosphoric acid solution until the pH value of the system reaches 3-4.0; and / or, Use 20-25% ammonia water to adjust the pH value of the citric acid solution.

3. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: The mass percentage of the metal oxide in the sludge is 18-30%, and the average relative molecular mass of the metal oxide is 50-65; and / or, The concentration of the phosphoric acid solution is 3-4 mol / L; and / or, The concentration of the citric acid solution is 1 mol / L.

4. The method for treating industrial-grade monoammonium phosphate sludge according to claim 3, characterized in that: In step (3), the mass volume ratio of the sludge, phosphoric acid solution and citric acid solution is 1:(0.1-0.3):(2.5-4.0), wherein the sludge is measured in kilograms, and the phosphoric acid solution and the citric acid solution are measured in liters; The temperature of the chelating reaction is 55~70℃.

5. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: The phosphoric acid solution includes the following components, which are calculated by mass percentage: 21.0-24.0% phosphorus pentoxide, 0.2-0.3% calcium oxide, 0.3-0.6% magnesium oxide, 1.5-2.5% iron oxide, and 0.3-0.6% aluminum oxide.

6. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: The sludge includes the following components, which are magnesium phosphate 13-22%, iron phosphate 26-45%, aluminum phosphate 11-18% and phosphorus pentoxide 39-43% in percentage by mass.

7. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: The method for preparing a phosphoric acid solution comprises the following steps: Adding water to the phosphorus concentrate to perform slurry preparation to obtain phosphorus concentrate slurry with a moisture content of 25-28%; Concentrated sulfuric acid is added to the phosphorus concentrate slurry for extraction treatment, and a liquid phosphoric acid solution is obtained after solid-liquid separation; Among them, phosphorus concentrate includes the following ingredients, which are calculated by mass percentage: 29.5~33.5% phosphorus pentoxide, 46.0~50.0% calcium oxide, 0.5~0.9% magnesium oxide, 2.0~3.5% iron oxide, 0.5~1.0% aluminum oxide, 3.0~5.0% silicon dioxide, and 1.5~3.0% fluorine.

8. The method for treating industrial-grade monoammonium phosphate sludge according to claim 1, characterized in that: In step (1), the neutralization treatment includes a first ammonia addition treatment and a second ammonia addition treatment; Among them, in the first ammonia treatment, the neutralization degree of the control system is 0.93~0.96, and the pH value is 2.7~3.0; In the second ammonia treatment, the system neutralization degree is controlled to be 1.03~1.05 and the pH value is 4.0~4.

2.

9. The method for treating industrial-grade monoammonium phosphate sludge according to any one of claims 1 to 8, characterized in that: The mass percentage of iron in liquid fertilizer is 1.5~2.5%, and the chelation rate of iron in liquid fertilizer is 95~100%.

10. A liquid fertilizer, characterized in that: The product is prepared by the method for treating industrial-grade monoammonium phosphate sludge according to any one of claims 1 to 9.