阅读说明：本技术 液体硅钙肥及其制备方法和应用 (Liquid calcium silicon fertilizer and preparation method and application thereof ) 是由 刘汇东 陈爱国 于 2020-04-09 设计创作，主要内容包括：本发明涉及硅肥领域,公开了液体硅钙肥及其制备方法和应用。该方法包括：(1)将白泥、钙源与碱液接触在90-110℃下进行第一反应,得到的第一产物经固液分离后得到第一固体；(2)将所述第一固体制浆得到水浆料,在搅拌条件下将混合酸溶液加入至所述水浆料中进行第二反应,得到的第二产物经固液分离后得到第二液体；(3)使用pH调节剂调节所述第二液体的pH至5.5-10,得到液体硅钙肥。本发明提供的液体硅肥含钠量低,不仅具有较高的硅含量并且具有较高的稳定性。(The invention relates to the field of silicon fertilizers and discloses a liquid silicon-calcium fertilizer as well as a preparation method and application thereof. The method comprises the following steps: (1) contacting white mud, a calcium source and alkali liquor, and carrying out a first reaction at 90-110 ℃, and carrying out solid-liquid separation on an obtained first product to obtain a first solid; (2) pulping the first solid to obtain water slurry, adding a mixed acid solution into the water slurry under the stirring condition to perform a second reaction, and performing solid-liquid separation on an obtained second product to obtain a second liquid; (3) and (3) adjusting the pH value of the second liquid to 5.5-10 by using a pH regulator to obtain the liquid calcium silicon fertilizer. The liquid silicon fertilizer provided by the invention has low sodium content, higher silicon content and higher stability.)

1. A method for preparing a liquid calcium silicon fertilizer, comprising the following steps:

(1) contacting white mud, a calcium source and alkali liquor, and carrying out a first reaction at 90-110 ℃, and carrying out solid-liquid separation on an obtained first product to obtain a first solid;

(2) pulping the first solid to obtain water slurry, adding a mixed acid solution into the water slurry under the stirring condition to perform a second reaction, and performing solid-liquid separation on an obtained second product to obtain a second liquid;

(3) and (3) adjusting the pH value of the second liquid to 5.5-10 by using a pH regulator to obtain the liquid calcium silicon fertilizer.

2. The method according to claim 1, wherein, in step (1), the calcium source is CaO and/or Ca (OH)₂；

Preferably, the molar ratio of the calcium source to the active silica in the white mud is (0.8-1.2): 1, preferably (0.9-1): 1.

3. the method according to claim 1, wherein said lime mud consists essentially of 50-80 wt% SiO₂10-40 wt% of Al₂O₃5-10 wt% carbon.

4. The method according to claim 1, wherein, in step (1), the alkali in the lye is selected from at least one of NaOH, RbOH, CsOH and KOH;

preferably, the concentration of alkali in the alkali liquor is 5-20 wt%, more preferably 16-18 wt%;

preferably, the volume mass ratio of the alkali liquor to the white mud is (2.8-3.5): 1(L/kg), preferably (3-3.2): 1 (L/kg).

5. The method according to claim 1, wherein, in step (1), the first solid is in SiO₂The effective silicon content is 30-50 wt.%, preferably 40-50 wt.%, and the calcium content, calculated as CaO, is 20-40 wt.%, preferably 20-30 wt.%.

6. The process of claim 1, wherein in step (2), the aqueous slurry has a solids content of 5-20 wt%.

7. The method according to claim 1, wherein, in step (2), the mixed acid is a mixture of nitric acid and phosphoric acid;

preferably, the molar ratio of nitric acid to phosphoric acid is (4-6): 1, preferably (4-5): 1;

preferably, H in the mixed acid solution⁺The ion concentration is 0.02 to 0.12mol/L, preferably 0.05 to 0.1mol/L, more preferably 0.05-0.08mol/L。

8. The method of claim 1, wherein the reaction conditions of the second reaction comprise: the temperature is 10-30 ℃, preferably 15-20 ℃;

preferably, in the step (3), the pH adjusting agent is selected from at least one of ammonia water, liquid ammonia, and ammonium bicarbonate.

9. A liquid calcium silicon fertilizer prepared by the method of any one of claims 1 to 8;

preferably, the effective silicon content of the liquid calcium silicon fertilizer calculated by silicon dioxide is 7-20 wt%, preferably 10-20 wt%;

more preferably, the liquid calcium silicon fertilizer has a calcium oxide content of 6-15 wt%, preferably 8-14 wt%, calculated as calcium oxide.

10. Use of a liquid calcium silicon fertilizer prepared by the method of any one of claims 1 to 8 for crop yield and/or efficiency enhancement;

preferably, the crop plants include gramineous crops,

more preferably, the crop is rice or wheat.

11. The use of claim 10, wherein at least one of an organic fertilizer, a nitrogen fertilizer and a phosphate fertilizer is applied with the liquid calcium silicate fertilizer, and the nitrogen fertilizer does not include ammonium bicarbonate.

Technical Field

The invention relates to the field of silicon fertilizers, in particular to a liquid silicon-calcium fertilizer and a preparation method and application thereof.

Background

Silicon is an essential medium nutrient element in the growth process of crops and is a fourth major element which is listed as the following elements of nitrogen, phosphorus and potassium by the international soil boundary; the calcium industry is a typical medium element fertilizer and is an indispensable element for the normal growth of crops. The silicon-calcium fertilizer can provide active silicon-calcium nutrient elements for soil, and can also play a role in regulating the pH value of the soil, improving the soil structure, solidifying heavy metals and other soil improvement and restoration functions.

The silicon fertilizer is divided into water-soluble silicon fertilizer and citrate-soluble silicon fertilizer (solid silicon fertilizer), and the water-soluble silicon fertilizer has good water solubility, fast crop absorption and fast fertilizer efficiency. Silicate is extremely easy to condense and gel under an acid environment, is precipitated in a silica gel form and cannot be absorbed and utilized by crops. Because alkali metal elements Na and K are combined with the alkali metal elements to form water-soluble sodium metasilicate and potassium metasilicate (namely water glass). The alkalinity of the fertilizer is too high to be directly applied, so the fertilizer is usually diluted by water at a large rate and used for foliage spraying. In addition, potassium is a necessary nutrient element for plant growth, but the cost is high; sodium is a common surplus element in soil, and the introduction of sodium element in fertilizers is generally avoided so as to avoid the risk of soil salinization. The most common type of water-soluble silicon fertilizer in the market at present is organic silicon, namely, organic matters are utilized to chelate silicon elements to form liquid organic silicon which can still keep stable in a low-pH environment. But the process is complex, the preparation cost is higher, and the market acceptance is not facilitated. The technical contradiction exists among several key indexes of effective silicon content, alkalinity (sodium content), stability and production cost, and the prior art and products can not be simultaneously met, so that the application and popularization of the inorganic water-soluble silicon fertilizer are limited. Therefore, a low-sodium low-alkali liquid silicon fertilizer with low cost, high effective silicon content and good stability is needed.

On the other hand, the fly ash is rich in silicon element with high reaction activity, and the fly ash (or fly ash acid aluminum extraction residue) is theoretically used as a raw material for preparing the silicon fertilizer, so that the silicon fertilizer has the advantages of better energy conservation and consumption reduction compared with the traditional mineral resources such as potash feldspar and the like. China has huge fly ash storage, and the requirements of the fly ash storage on the consumption and the resource utilization are increasingly urgent. Therefore, a method for simply preparing liquid silicon fertilizer from fly ash (and/or white mud) is needed, and the prepared silicon fertilizer is convenient to apply and high in silicon utilization rate.

Disclosure of Invention

The invention aims to solve the problems of high cost, complex preparation process, low effective silicon content, excessive sodium (over-high alkalinity) and the like of a water-soluble silicon fertilizer in the prior art, and provides a liquid silicon-calcium fertilizer and a preparation method and application thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for preparing a liquid calcium silicon fertilizer, comprising:

(1) contacting white mud, a calcium source and alkali liquor, and carrying out a first reaction at 90-110 ℃, and carrying out solid-liquid separation on an obtained first product to obtain a first solid;

(2) pulping the first solid to obtain water slurry, adding a mixed acid solution into the water slurry under the stirring condition to perform a second reaction, and performing solid-liquid separation on an obtained second product to obtain a second liquid;

(3) and (3) adjusting the pH value of the second liquid to 5.5-10 by using a pH regulator to obtain the liquid calcium silicon fertilizer.

In a second aspect, the invention provides a liquid calcium silicon fertilizer prepared by the method of the first aspect of the invention.

Preferably, the content of silicon dioxide in the liquid calcium silicon fertilizer is 7-20 wt%, preferably 10-20 wt%.

In a third aspect, the invention provides the application of the liquid calcium silicon fertilizer prepared by the method in the first aspect in the yield increase and/or efficiency increase of crops.

Preferably, the crop comprises a gramineous crop.

More preferably, the crop is rice or wheat.

The raw materials used in the method are cheap and easily-obtained inorganic materials, and the method has mild reaction conditions and simple and convenient operation; the used raw materials such as Ca source, phosphoric acid, nitric acid and the like are finally converted into Ca, N, P and other nutrient elements beneficial to crops, and no side effect is generated. The liquid silicon fertilizer provided by the invention has low sodium content, not only has higher silicon content but also has higher stability, and in addition, as the sodium content in the liquid silicon fertilizer is extremely low, the absorption of other elements is not influenced, and the salinization of soil caused by excessive application can be avoided.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides a method for preparing liquid calcium silicon fertilizer, which comprises the following steps:

(1) contacting white mud, a calcium source and alkali liquor, and carrying out a first reaction at 90-110 ℃, and carrying out solid-liquid separation on an obtained first product to obtain a first solid;

(2) pulping the first solid to obtain water slurry, adding a mixed acid solution into the water slurry under the stirring condition to perform a second reaction, and performing solid-liquid separation on an obtained second product to obtain a second liquid;

(3) and (3) adjusting the pH value of the second liquid to 5.5-10 by using a pH regulator to obtain the liquid calcium silicon fertilizer.

Herein, white mud is the residue after aluminum extraction from fly ash, also referred to as dealuminated fly ash. The white mud can be residue generated in other acid method aluminum extraction processes.

In order to avoid the occurrence of aluminum damage, iron damage and the like caused by introducing excessive aluminum and iron elements into the calcium silicon fertilizer or the soil conditioner product, the content of aluminum oxide in the white mud is preferably 0-20%, and the content of ferric oxide is preferably 0-6%.

Preferably, the lime mud comprises mainly 50-80 wt% SiO₂10-40 wt% of Al₂O₃5-10 wt% carbon.

Preferably, in step (1), the calcium source is CaO and/or Ca (OH)₂。

Preferably, in step (1), the alkali in the lye is selected from at least one of NaOH, RbOH, CsOH and KOH. Preferably, the concentration of alkali in the alkali liquor is 5-20 wt%, preferably 15-20 wt%, more preferably 16-18 wt%;

preferably, the volume mass ratio of the alkali liquor to the white mud is (2.8-3.5): 1(L/kg), preferably (3-3.2): 1 (L/kg).

In order to be more beneficial to extracting the active silicon dioxide in the white mud, the molar ratio of the calcium source to the active silicon dioxide in the white mud is (0.8-1.2): 1, preferably (0.9-1): 1. as used herein, "activated silica" refers to SiO dissolved out by a 15 wt% NaOH solution in a solid-to-liquid ratio of 1:4(kg/L) under stirring at 95 ℃ for 1 hour₂。

Preferably, the reaction conditions of the first reaction include: the temperature is 95 to 105 ℃ and preferably 95 to 100 ℃.

Obtaining a first product through a first reaction, and respectively obtaining a first solid and a first liquid through solid-liquid separation of the first product. The first solid is washed with water to obtain washing water and the first liquid (concentrated alkali liquor) is collected for the next batch of production. Preferably, SiO is added into the first solid (citrate soluble calcium silicon fertilizer)₂The effective silicon content is 30-50 wt.%, preferably 40-50 wt.%, and the calcium oxide content, calculated as CaO, is 20-40 wt.%, preferably 20-30 wt.%. The determination mode of the effective silicon content is as follows: taking 0.2g solid sample, adding 150mL diluted hydrochloric acid (0.5mol/L), oscillating (180rpm) at 30 + -2 deg.C, reacting for 80min, dissolving SiO in liquid phase₂The mass is a percentage of the initial mass (0.2g) of the solid sample.

According to the invention, the first solid is slurried to obtain an aqueous slurry, preferably having a solids content of 5-20 wt%, for example 10 wt%.

According to the invention, a mixed acid solution is added to the aqueous slurry, preferably the mixed acid is a mixture of nitric acid and phosphoric acid.

In particular, in the present application, a mixture of nitric acid and phosphoric acid is used, without using dilute hydrochloric acid (HCl) or dilute sulfuric acid (H)₂SO₄) The reason is that Cl ions are excessive elements in soil, and excessive introduction of Cl is harmful to crop growth; sulfate radicals will react with Ca²⁺Insoluble precipitated calcium sulfate is generated, and the water solubility or dispersion stability of the product is influenced. The mixture of nitric acid and phosphoric acid is used for secondary reaction to obtain calcium nitrate and hydrogen phosphateCalcium (and/or monocalcium phosphate) acts as a stabilizer, inhibits condensation, agglomeration or sedimentation of silica particles, and maintains the stability of the liquid silicon fertilizer at higher silica contents and lower pH levels.

Preferably, H in the mixed acid solution⁺The ion concentration is 0.03 to 0.12mol/L, preferably 0.05 to 0.1mol/L, and more preferably 0.05 to 0.08 mol/L. As in H in the mixed acid solution⁺If the ion concentration is lower than 0.03mol/L, the Si element in the first solid is not sufficiently dissolved out, and the silicon content in the obtained liquid calcium silicon fertilizer is too low; as in H in the mixed acid solution⁺The ion concentration is higher than 0.12mol/L, and silicic acid is excessively condensed to form large-particle-size gel and even precipitate, so that the stability of the liquid calcium silicon fertilizer is reduced, and the utilization efficiency of crops on Si elements is influenced.

More preferably, the molar ratio of nitric acid to phosphoric acid is (4-6): 1, preferably (4-5): 1.

specifically, in the step (2), the mixed acid solution is added to the aqueous slurry under stirring to perform the second reaction. The mixed acid solution was added to the aqueous slurry with stirring for the following reasons: the slurry is alkaline, the mixed acid is acidic, and when the acid solution is slowly dripped into the slurry, the pH around silicate ions at the reaction interface is slowly reduced, so that local excessive acidification is avoided, the control of the condensation polymerization degree of the silicic acid is facilitated, and the stable oligomeric silicic acid (small-particle-size hydrated silicon dioxide particles) similar to silica sol is obtained. On the contrary, if the aqueous slurry is added to the mixed acid solution, excessive condensation polymerization of silicate ions in the slurry and even gelation may occur, and a highly uniformly dispersed silica sol system may not be obtained.

Preferably, the mixed acid solution is added dropwise to the water slurry under stirring, for example, the dropping speed of the mixed acid solution is 0.8-1.0L/h; for example, the stirring speed during the dropping is 600-.

Preferably, the reaction conditions of the second reaction include: the temperature is 10-30 deg.C, preferably 15-20 deg.C.

Preferably, in the step (3), the pH of the second liquid is adjusted to 5.5-10, preferably 6-8 by using a pH regulator to obtain a sol-like transparent liquid calcium silicon fertilizer initial liquid, and the sol-like transparent liquid calcium silicon fertilizer initial liquid is evaporated and concentrated to obtain a sol-like liquid calcium silicon fertilizer. The evaporation concentration can be realized by using the technical means commonly used in the field as long as the performance of the liquid calcium silicon fertilizer is not influenced.

Preferably, the pH adjusting agent is selected from at least one of ammonia water, liquid ammonia, and ammonium bicarbonate.

In a specific embodiment, the first solid is pulped to obtain an aqueous slurry, the solid content of the aqueous slurry is controlled to be 5-20 wt%, for example 10 wt%, and then the mixed acid solution is slowly added into the aqueous slurry; the mass ratio of the mixed acid solution to the water slurry is 10-12: 1; the dropping speed is controlled to be 0.8-1.0L/h, and the stirring speed is 600-1000rpm during the dropping process. After the mixed acid solution is dripped, transferring the whole system into a reactor, and carrying out oscillation reaction for 20min at the temperature of 15-20 ℃; and naturally settling the obtained solid-liquid mixture to remove solid insoluble substances, adding 30% concentrated ammonia water into the obtained semitransparent liquid to adjust the pH to 6-8, and thus obtaining sol transparent liquid silicon-calcium fertilizer primary liquid. And evaporating and concentrating the sol transparent liquid silicon-calcium fertilizer primary liquid at low temperature to obtain the liquid silicon-calcium fertilizer (the effective silicon content calculated by silicon dioxide is 8-20 wt%, preferably 10-20 wt%).

The raw materials used in the method are cheap and easily-obtained inorganic materials, particularly, the used white mud is industrial waste, the reaction condition is mild, and the operation is simple and convenient; the used raw materials such as Ca source, phosphoric acid, nitric acid and the like are finally converted into Ca, N, P and other nutrient elements beneficial to crops, and no side effect is generated; in addition, the method can effectively control the content of harmful components such as sodium, aluminum, iron, heavy metals and the like.

In a second aspect, the invention provides a liquid calcium silicon fertilizer prepared by the method of the first aspect.

Preferably, the effective silicon content of the liquid calcium silicon fertilizer calculated by silicon dioxide is 8-20 wt%, preferably 10-20 wt%.

Preferably, the content of calcium oxide in the liquid calcium silicon fertilizer is 6-15 wt%, preferably 8-14 wt% calculated by calcium oxide.

In the liquid calcium silicon fertilizer, Si exists in a form similar to silica sol, can keep long-term stability, and can be directly absorbed and utilized by crops.

The liquid silicon fertilizer provided by the invention can be directly applied, has higher effective silicon content and higher stability, and also contains N, P, Ca nutrient elements; in addition, excessive Na in the soil⁺、Cl^-Ion antagonism of Ca in crop²⁺、Mg²⁺、NO₃ ^-Absorption of nutrient substances; the liquid silicon fertilizer has extremely low Na and Cl contents, does not influence the efficient absorption and utilization of other nutrient elements in the using process, and can reduce the risk of salinization (staining) of soil. Compared with the conventional fly ash based silicon fertilizer product, the liquid silicon calcium fertilizer raw material (white mud) is subjected to impurity removal (Al, Fe, heavy metal elements and the like) by a strong acid method, so that the content of harmful components such as aluminum, iron and heavy metals in the product is extremely low, the product is better in safety, and the application range is wider.

In a third aspect, the invention provides the application of the liquid calcium silicon fertilizer prepared by the method in the first aspect in the yield increase and/or efficiency increase of crops.

Preferably, the crop comprises a gramineous crop.

More preferably, the crop is rice or wheat.

In a preferred embodiment, at least one of an organic fertilizer, a nitrogen fertilizer and a phosphate fertilizer is applied together with the liquid calcium silicon fertilizer of the present invention, and the nitrogen fertilizer does not include ammonium bicarbonate.

The present invention will be described in detail below by way of examples.

The white mud samples used in the examples and comparative examples had a water content of 30 wt% and a dry SiO content₂77 wt% of Al₂O₃The content was 16 wt%, the carbon content was 7 wt%, and the active silica content was about 50 wt%.

The test methods used in the examples and comparative examples are as follows:

(1) testing the effective silicon content in the liquid calcium silicon fertilizer:

standing the liquid sample of the liquid silicon-calcium fertilizer for 6 hours,adding water into the supernatant to dilute by a proper time; measuring the content of Si (mu g/mL) in the solution by adopting an ICP-AES method, and converting the content of Si into SiO in a sample₂Mass fraction (%). The detailed measurement method is referred to NYT 2272-2012.

(2) Stability test of liquid calcium silicon fertilizer

Adding concentrated hydrochloric acid into a liquid calcium silicon fertilizer sample under the stirring condition (180rpm), adjusting the pH value of the system to be 5, then transferring 100mL of liquid into a 100mL transparent glass measuring cylinder, standing for 24h, and measuring the height (mm) of supernatant to obtain the sedimentation height; a smaller sedimentation height indicates better stability.

Example 1

(1) 10g of white mud, 4.6g of CaO and 30mL of a 20% NaOH solution were placed in a reaction kettle, and a first reaction was carried out at 95 ℃ under normal pressure. After reacting for 3h, carrying out solid-liquid separation, collecting and recycling the obtained filtrate (concentrated alkali liquor), adding water into the obtained filter cake for washing, and blending the washing water (dilute alkali liquor) and the filtrate (concentrated alkali liquor) for the next production. The filter cake (i.e., first solid) obtained by washing was detected as SiO₂The effective silicon content was 40 wt% in terms of CaO and the calcium oxide content was 20 wt% in terms of CaO.

(2) The resulting first solid was slurried with water to give 190mL of an aqueous slurry having a solids content of 10 wt%. Then 1900mL of H is slowly added into the water slurry⁺The mixed acid solution with the ion concentration of 0.1mol/L (the molar ratio of nitric acid to phosphoric acid is 4:1) is added at the dropping speed of 0.8L/h, and the dropping process is accompanied by rapid stirring at the stirring speed of 600 rpm. After the mixed acid solution is dripped, the whole mixed acid solution is transferred into a reactor, and a second reaction is carried out at the temperature of 20 ℃ for 30 min; the resulting second mixture was naturally settled to separate the insoluble solids, yielding a translucent liquid (second liquid).

(3) And adding 30% ammonia water into the second liquid to adjust the pH to 6, thus obtaining sol transparent liquid silicon-calcium fertilizer primary liquid. The liquid silicon-calcium fertilizer primary liquid is evaporated and concentrated for 3 hours at the temperature of 60 ℃ to prepare liquid silicon-calcium fertilizer A1, wherein the effective silicon content is 15 wt%, the calcium oxide content calculated by calcium oxide is 7.5 wt%, and the sedimentation height is 1.5 mm.

Example 2

(1) Will 10g of white mud, 5.1g of CaO and 30mL of KOH solution with the mass fraction of 10% are placed in a reaction kettle, and a first reaction is carried out at 110 ℃ and normal pressure. After 4 hours of reaction, solid-liquid separation is carried out, the obtained filtrate (concentrated alkali liquor) is collected for reuse, the obtained filter cake is washed by adding water, and the washing water (dilute alkali liquor) and the filtrate (concentrated alkali liquor) are mixed and used for the next production. The filter cake (i.e., first solid) obtained by washing was detected as SiO₂The effective silicon content was 40 wt% in terms of CaO and the calcium oxide content was 35 wt% in terms of CaO.

(2) The first solid obtained was slurried with water to give 100mL of an aqueous slurry having a solid content of 20 wt%. Then 1900mL of H is slowly added into the water slurry⁺The mixed acid solution (nitric acid: phosphoric acid molar ratio is 6:1) with the ion concentration of 0.05mol/L, the dropping speed of the mixed acid solution is 1.0L/h, the dropping process is accompanied with rapid stirring, and the stirring speed is 800 rpm. After the mixed acid solution is dripped, the whole mixed acid solution is transferred into a reactor, and a second reaction is carried out at the temperature of 18 ℃ for 20 min; the resulting second mixture was naturally settled to separate the insoluble solids, yielding a translucent liquid (second liquid).

(3) And adding 30% ammonia water into the second liquid to adjust the pH to 7, thus obtaining sol transparent liquid silicon-calcium fertilizer primary liquid. The liquid silicon-calcium fertilizer primary liquid is evaporated and concentrated for 3 hours at the temperature of 60 ℃ to prepare a liquid silicon-calcium fertilizer A2, wherein the effective silicon content is 16 wt%, the calcium oxide content calculated by calcium oxide is 14 wt%, and the sedimentation height is 1 mm.

Example 3

(1) Mixing 10g of white mud, 4.8g of Ca (OH)₂And the mixture and 32mL of NaOH solution with the mass fraction of 18% are placed in a reaction kettle, and the first reaction is carried out at 100 ℃ and normal pressure. After 4.5h of reaction, solid-liquid separation is carried out, the obtained filtrate (concentrated alkali liquor) is collected for reuse, the obtained filter cake is washed by adding water, and the washing water (dilute alkali liquor) and the filtrate (concentrated alkali liquor) are mixed and used for the next production. The filter cake (i.e., first solid) obtained by washing was detected as SiO₂The effective silicon content was 50 wt% and the calcium oxide content was 20 wt% as CaO.

(2) The first solid obtained was slurried with water to give 200mL of an aqueous slurry having a solid content of 10 wt%. Then 2000mL of H was added slowly to the aqueous slurry⁺The mixed acid solution (nitric acid: phosphoric acid molar ratio is 5:1) with the ion concentration of 0.08mol/L, the dropping speed of the mixed acid solution is 0.9L/h, the dropping process is accompanied with rapid stirring, and the stirring speed is 1000 rpm. After the mixed acid solution is dripped, the whole mixed acid solution is transferred into a reactor, and a second reaction is carried out at 15 ℃ for 30 min; the resulting second mixture was naturally settled to separate the insoluble solids, yielding a translucent liquid (second liquid).

(3) And adding 30% ammonia water into the second liquid to adjust the pH to 8, thus obtaining sol transparent liquid silicon-calcium fertilizer primary liquid. And evaporating and concentrating the primary liquid of the liquid calcium silicon fertilizer at 60 ℃ for 3 hours to obtain a liquid calcium silicon fertilizer A3, wherein the effective silicon content is 20 wt%, the calcium oxide content calculated by calcium oxide is 8 wt%, and the sedimentation height is 0.5 mm.

Example 4

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was added to the acid mixture⁺The ion concentration was 0.12mol/L, and the same as in example 1 was repeated. Finally obtaining the liquid silicon-calcium fertilizer A4, wherein the effective silicon content is 12 wt%, the calcium oxide content calculated by calcium oxide is 8 wt%, and the sedimentation height is 2 mm.

Example 5

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was added to the acid mixture⁺The ion concentration was 0.02mol/L, and the rest was the same as in example 1. Finally obtaining the liquid silicon-calcium fertilizer A5, wherein the effective silicon content is 12.4 wt%, the calcium oxide content calculated by calcium oxide is 7.8 wt%, and the sedimentation height is 0.5 mm.

Example 6

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was ensured⁺Under the condition that the ion concentration is not changed, the molar ratio of nitric acid to phosphoric acid in the mixed acid liquid is 3: 1, the rest is the same as example 1. Finally obtaining the liquid silicon-calcium fertilizer A6, wherein the effective silicon content is 13.3 wt%, the calcium oxide content calculated by calcium oxide is 6 wt%, and the sedimentation height is 2 mm.

Example 7

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was ensured⁺Under the condition that the ion concentration is not changed, the mass ratio of nitric acid to phosphoric acid in the mixed acid liquid is 7: 1, the rest is the same as example 1. Finally obtaining the liquid silicon-calcium fertilizer A7, wherein the effective silicon content is 12.8 wt%, the calcium oxide content calculated by calcium oxide is 8.2 wt%, and the sedimentation height is 3 mm.

Comparative example 1

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was ensured⁺The same procedure as in example 1 was repeated except that nitric acid solution was used instead of the mixed acid solution without changing the ion concentration. The effective silicon content in the finally obtained liquid silicon-calcium fertilizer is 8.6 wt%.

Comparative example 2

A liquid calcium silicon fertilizer was prepared as in example 3, except that H was ensured⁺The same procedure as in example 1 was repeated except that the mixed acid solution was replaced with a phosphoric acid solution without changing the ion concentration. The effective silicon content in the finally obtained liquid silicon-calcium fertilizer is 6.2 wt%.

Comparative example 3

A liquid calcium silicon fertilizer was prepared according to the method of example 3, except that the step (1) was as follows:

10g of white mud, 4.6g of CaO and 30mL of a 30% NaOH solution were placed in a reaction kettle, and a first reaction was carried out at 120 ℃ under autogenous pressure. After 5h of reaction, solid-liquid separation is carried out, the obtained filtrate (concentrated alkali liquor) is collected for reuse, the obtained filter cake is washed by adding water, and the washing water (dilute alkali liquor) and the filtrate (concentrated alkali liquor) are mixed and used for the next production. The filter cake obtained by washing (i.e. the first solid, in SiO)₂An effective silicon content of 22 wt% in terms of CaO and a calcium oxide content of 32 wt% in terms of CaO); the rest is the same as in example 1. The effective silicon content in the finally obtained liquid silicon-calcium fertilizer is 7.6 wt%.

Comparative example 4

A liquid calcium silicon fertilizer was prepared as in example 3, except that, in step (2), the aqueous slurry was added dropwise to the mixed acid solution under stirring at a rate of 0.9L/h for the second reaction, the addition was accompanied by rapid stirring at a stirring rate of 240 rpm. The rest is the same as in example 1. The effective silicon content in the finally obtained liquid silicon-calcium fertilizer is 5.5 wt%.

Comparative example 5

A liquid silico-calcium fertilizer was prepared according to the method of example 3, except that the same H was ensured⁺The same procedure as in example 1 was repeated except that citric acid solution was used in place of the mixed acid solution in the case of the ion concentration. The effective silicon content of the finally obtained liquid silicon-calcium fertilizer is only 8.1 wt%, and the obtained liquid silicon-calcium fertilizer has poor stability due to the turbidity and the precipitation of calcium citrate.

Comparative example 6

A liquid calcium-silicon fertilizer was prepared as in example 3, except that in the step (3), 30% ammonia water was added to the second liquid to adjust the pH to 5, and the same procedure as in example 1 was repeated. In the finally obtained liquid silicon-calcium fertilizer, the effective silicon content is only 10.2 wt%, and the sedimentation height is 4.5 mm.

From the above examples and comparative examples, it can be seen that, compared with comparative examples 1 to 5, the liquid calcium silicon fertilizer obtained by the methods of examples 1 to 7 of the present application has a high silicon content of 10 wt% or more, and the liquid calcium silicon fertilizer has good stability.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, numerous simple variants can be made to the technical solution of the invention, including combinations of the individual features in any other suitable way, which should likewise be regarded as disclosed in the present invention.