WO2021203923A1 - Liquid silicon-calcium fertilizer, preparation method therefor, and use thereof - Google Patents

Abstract

The present invention relates to the field of silicon fertilizers, and disclosed are a liquid silicon-calcium fertilizer, a preparation method therefor, and the use thereof. The method comprises: (1) putting white mud, a calcium source and an alkali liquor into contact with one another, carrying out a first reaction at 90-110ºC, and subjecting the resulting first product to solid-liquid separation to obtain a first solid; (2) slurrying the first solid to obtain an aqueous slurry, adding a mixed acid solution to the aqueous slurry under stirring conditions for a second reaction, and then subjecting the resulting second product to solid-liquid separation to obtain a second liquid; and (3) adjusting the pH of the second liquid with a pH regulator to 5.5-10, so as to obtain the liquid silicon-calcium fertilizer. The liquid silicon-calcium fertilizer provided by the present invention has a low sodium content, and not only has a higher silicon content, but also has a higher stability.

Description

Liquid calcium silicate fertilizer and its preparation method and application

Cross-references to related applications

This application claims the rights and interests of the Chinese patent application 202010275496.9 filed on April 9, 2020, the content of which is incorporated herein by reference.

Technical field

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

Background technique

Silicon is a necessary medium nutrient element in the growth process of crops, and is listed as the fourth most important element after nitrogen, phosphorus, and potassium by the international soil community; calcium is a typical medium element fertilizer, which is normal for crops. An indispensable element for growth. Silicon-calcium fertilizer can not only provide active silicon-calcium nutrient elements to the soil, but also can adjust soil pH value, improve soil structure, solidify heavy metals and other soil improvement and restoration functions.

Silicon fertilizer is divided into water-soluble silicon fertilizer and citrate-soluble silicon fertilizer (solid silicon fertilizer). The water-soluble silicon fertilizer has good water solubility, fast absorption by crops and fast fertilizer efficiency. Silicate is very easy to polycondensate and gel in an acidic environment, precipitate in the form of silica gel, and cannot be absorbed and utilized by crops. Because the alkali metal elements Na and K are usually combined with them to form water-soluble sodium metasilicate and potassium (that is, water glass). Its alkalinity is too high to be applied directly, so it is usually used as a foliar spray after being diluted with water at a large rate. In addition, although potassium is an essential nutrient element for plant growth, its cost is relatively high; sodium is a general surplus element in the soil, and the introduction of sodium element in fertilizers is generally avoided to avoid the risk of soil salinization. At present, the most common type of water-soluble silicon fertilizer on the market is organosilicon, which uses organic matter to chelate silicon elements to form liquid organosilicon that can remain stable in a low pH environment. However, the process is complicated and the preparation cost is higher, which is not conducive to market acceptance. There are technical contradictions among the key indicators of effective silicon content, alkalinity (sodium content), stability, and production cost. The existing technologies and products cannot meet the requirements at the same time, which leads to the restriction of the use and promotion of inorganic water-soluble silicon fertilizers. Therefore, there is an urgent need for a low-cost, high-available silicon content, good stability, low-sodium and low-alkali liquid silicon fertilizer.

On the other hand, fly ash is rich in silicon with high reactivity. Theoretically, the use of fly ash (or the residue of acid extraction of aluminum from fly ash) as a raw material to prepare silicon fertilizer has more advantages than traditional mineral resources such as potash feldspar. Good energy saving and consumption reduction advantages. China has a huge stock of fly ash, and the demand for its consumption and resource utilization is also becoming increasingly urgent. Therefore, there is an urgent need for a simple and convenient method for preparing liquid silicon fertilizer from fly ash (and/or white mud). The prepared silicon fertilizer is convenient to apply and has high silicon utilization rate.

Summary of the invention

The purpose of the present invention is to overcome the problems of high cost of water-soluble silicon fertilizer, complicated preparation process, low effective silicon content, excessive sodium (alkalinity) and other problems existing in the prior art, and to provide liquid silicon-calcium fertilizer and a preparation method thereof And application.

In order to achieve the above objective, the first aspect of the present invention provides a method for preparing liquid calcium silicate fertilizer, including:

(1) The white mud, calcium source and lye are contacted, and the first reaction is carried out at 90-110°C, and the obtained first product is separated into the first solid after solid-liquid separation;

(2) The first solid is slurried to obtain an aqueous slurry, and the mixed acid solution is added to the aqueous slurry under agitation to perform a second reaction, and the second product obtained is subjected to solid-liquid separation to obtain a second liquid;

(3) Use a pH regulator to adjust the pH of the second liquid to 5.5-10 to obtain a liquid calcium silicate fertilizer.

The second aspect of the present invention provides a liquid calcium silicate fertilizer prepared by the method described in the first aspect of the present invention.

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

The third aspect of the present invention provides the application of the liquid silicon-calcium fertilizer prepared by the method of the first aspect of the present invention to increase the yield and/or efficiency of crops.

Preferably, the crops include grass crops.

More preferably, the crop is rice or wheat.

The raw materials used in the method of the present invention are all cheap and easily available inorganic materials, and the reaction conditions are mild and the operation is simple; the raw materials such as Ca source, phosphoric acid, and nitric acid used are finally converted into nutrients such as Ca, N, P, etc., which are beneficial to crops. Does not produce side effects. The liquid silicon fertilizer provided by the present invention has low sodium content, not only has a high silicon content but also has high stability. In addition, since the sodium content in the liquid silicon fertilizer of the present invention is extremely low, it will not affect the content of other elements. Absorb, and can avoid soil salinization caused by excessive application.

Detailed ways

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the end values of each range, between the end values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges. These values The scope should be considered as specifically disclosed herein.

The first aspect of the present invention provides a method for preparing liquid calcium silicate fertilizer, including:

(1) The white mud, calcium source and lye are contacted, and the first reaction is carried out at 90-110°C, and the obtained first product is separated into the first solid after solid-liquid separation;

(2) The first solid is slurried to obtain an aqueous slurry, and the mixed acid solution is added to the aqueous slurry under agitation to perform a second reaction, and the second product obtained is subjected to solid-liquid separation to obtain a second liquid;

(3) Use a pH regulator to adjust the pH of the second liquid to 5.5-10 to obtain a liquid calcium silicate fertilizer.

In this article, white mud is the residue after extracting aluminum from fly ash, also called dealuminated fly ash. The white mud may be residues produced by other acid extraction processes for aluminum.

In order to avoid the occurrence of "aluminum damage" and "iron damage" caused by the introduction of excessive aluminum and iron elements in silicon-calcium fertilizer or soil conditioner products, preferably, the content of alumina in the white mud is 0-20%, The content of iron trioxide is 0-6%.

Preferably, the white mud mainly contains 50-80 wt% SiO ₂ , 10-40 wt% Al ₂ O ₃ , and 5-10 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 the alkali in the lye is 5-20wt%, preferably 15-20wt%, more preferably 16-18wt%;

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

In order to facilitate the extraction of active silica in the white mud, 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. _{In this context, "active silica" refers to SiO 2} that can be dissolved out by a 15wt% NaOH solution with a solid-to-liquid ratio of 1:4 (kg/L) at 95°C for 1 h after stirring.

Preferably, the reaction conditions of the first reaction include: a temperature of 95-105°C, preferably 95-100°C.

The first product is obtained through the first reaction, and the first solid and the first liquid are obtained by solid-liquid separation of the first product. The first solid is washed with water, and the washing water and the first liquid (concentrated lye) are collected for the next batch of production. Preferably, in the first solid (citric soluble calcium silicate fertilizer), _{the effective silicon content calculated as SiO 2} is 30-50 wt%, preferably 40-50 wt%, and the calcium oxide content calculated as CaO is 20-40 wt% , Preferably 20-30wt%. The method for determining the effective silicon content is: take 0.2g solid sample and add 150mL dilute hydrochloric acid (0.5mol/L), shake (180rpm) at 30±2℃ and react for 80min. The mass of _{SiO 2 dissolved in the liquid phase accounts for} The percentage of the initial mass (0.2g) of the solid sample.

According to the present invention, the first solid is slurried to obtain an aqueous slurry. Preferably, the solid content in the aqueous slurry is 5-20 wt%, for example, 10 wt%.

According to the present invention, a mixed acid solution is added to the water slurry. Preferably, the mixed acid is a mixture of nitric acid and phosphoric acid.

In particular, in this application, a mixture of nitric acid and phosphoric acid is used instead of dilute hydrochloric acid (HCl) or dilute sulfuric acid (H ₂ SO ₄ ), because Cl ion is an excess element in the soil, and excessive introduction of Cl is harmful to crop growth; Sulfate will form ^{insoluble precipitated calcium sulfate with Ca 2+} , which will affect the water solubility or dispersion stability of the product. Use a mixture of nitric acid and phosphoric acid to obtain calcium nitrate and calcium hydrogen phosphate (and/or calcium dihydrogen phosphate) through the second reaction to act as a stabilizer to inhibit the condensation, agglomeration or sedimentation of silica particles. The content and lower pH level maintain the stability of liquid silicon fertilizer.

^{Preferably, the H +} ion concentration in the mixed acid solution is 0.03-0.12 mol/L, preferably 0.05-0.1 mol/L, more preferably 0.05-0.08 mol/L. ^{If the H +} ion concentration in the mixed acid solution is lower than 0.03 mol/L, the Si element in the first solid is not sufficiently dissolved, and the silicon content in the obtained liquid silicon-calcium fertilizer is too low; as in the mixed acid solution, H ⁺ If the ion concentration is higher than 0.12mol/L, silicic acid will excessively polycondensate to form large-size gel or even precipitate, which will reduce the stability of liquid silicon-calcium fertilizer and affect the utilization efficiency of Si element by crops.

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

In particular, in step (2), the mixed acid solution is added to the water slurry under stirring conditions for the second reaction. The mixed acid solution is added to the water slurry under stirring conditions. The reason is that the slurry is alkaline, the mixed acid is acidic, and when the acid is slowly dripped into the slurry, the pH around the silicate ion at the reaction interface Slow reduction to avoid local excessive acidification, which is conducive to controlling the degree of polycondensation of silicic acid and obtaining stable oligosilicic acid (small particle size hydrated silica particles) similar to silica sol. On the contrary, if the water slurry is added to the mixed acid solution, it will cause excessive polycondensation of silicate ions in the slurry and even produce gel, and a highly uniformly dispersed silica sol system cannot be obtained.

Preferably, the mixed acid solution is added dropwise to the water slurry under stirring conditions, for example, the dropping speed of the mixed acid solution is 0.8-1.0 L/h; for example, the stirring speed during the dropping process is 600-1000 rpm.

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

Preferably, in step (3), the pH of the second liquid is adjusted to 5.5-10, preferably to 6-8, using a pH adjusting agent, to obtain a sol-like transparent liquid silica-calcium fertilizer initial solution, the sol-like transparent The initial liquid of the liquid calcium silicate fertilizer is concentrated by evaporation to obtain the sol-like liquid calcium silicate fertilizer. The evaporation and concentration can be achieved by using common technical means in the field, as long as it does not affect the performance of the liquid calcium silicate fertilizer.

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 slurried to obtain a water slurry, the solid content of the water slurry is controlled to be 5-20 wt%, for example, 10 wt%, and the mixed acid solution is slowly added to the water slurry ; The mass ratio of the mixed acid solution to the water slurry is 10-12:1; the dropping speed is controlled at 0.8-1.0L/h, and the stirring speed is 600-1000rpm during the dropping process. After the mixed acid solution is added dropwise, transfer the whole system to the reactor, shake and react for 20 minutes at 15-20℃; the resulting solid-liquid mixture is naturally settling to remove solid insolubles, and the resulting translucent liquid is then added with 30% concentrated ammonia Adjust the pH to 6-8 to obtain the sol-like transparent liquid silicon-calcium fertilizer initial solution. The sol-like transparent liquid silica-calcium fertilizer initial liquid is evaporated and concentrated at a low temperature to prepare a liquid silica-calcium fertilizer (the effective silicon content in terms of silicon dioxide is 8-20 wt%, preferably 10-20 wt%).

The raw materials used in the method of the present invention are all inexpensive and easily available inorganic materials. In particular, the white mud used is industrial waste, and the reaction conditions are mild and the operation is simple; the raw materials such as Ca source, phosphoric acid, and nitric acid used are finally converted into Nutrient elements such as Ca, N, and P, which are beneficial to crops, do not produce side effects; in addition, the method of the present invention can effectively control the content of harmful components such as sodium, aluminum, iron, and heavy metals.

The second aspect of the present invention provides the liquid calcium silicate fertilizer prepared by the method of the first aspect of the present invention.

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

Preferably, the calcium oxide content as calcium oxide in the liquid calcium silicate fertilizer is 6-15 wt%, preferably 8-14 wt%.

In the liquid calcium silicate fertilizer of the present invention, Si element exists in a form similar to silica sol, can maintain long-term stability, and can be directly absorbed and utilized by crops.

The liquid silicon fertilizer provided by the present invention can be directly applied, not only has high effective silicon content and high stability, but also contains N, P, and Ca nutrient elements; in addition, excessive Na ⁺ and Cl ^- ions in the soil will antagonize The absorption of nutrients such as Ca ²⁺ , Mg ²⁺ , NO ₃ ^-by crops; the content of Na and Cl in the liquid silicon fertilizer of the present invention is extremely low, and the use process will not affect the efficient absorption and utilization of other nutrient elements, and at the same time It can reduce the risk of soil salinization (waterlogging). Compared with conventional fly ash-based silicon fertilizer products, the liquid silicon-calcium fertilizer raw material (white mud) has undergone a strong acid method to remove impurities (Al, Fe, heavy metal elements, etc.), so the product contains harmful components such as aluminum, iron, and heavy metals. The content is extremely low, the product safety is better, and the scope of application is wider.

The third aspect of the present invention provides the application of the liquid silicon-calcium fertilizer prepared by the method of the first aspect of the present invention to increase the yield and/or efficiency of crops.

Preferably, the crops include grass crops.

More preferably, the crop is rice or wheat.

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

Hereinafter, the present invention will be described in detail through examples.

The white mud samples used in the examples and comparative examples have a moisture content of 30wt%, a dry basis SiO ₂ content of 77wt%, an Al ₂ O ₃ content of 16wt%, a carbon content of 7wt%, and an active silica content of about 50wt% %.

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

(1) Test of effective silicon content in liquid silicon-calcium fertilizer:

The liquid sample of the liquid silicon-calcium fertilizer is allowed to stand for 6 hours, and the upper layer is taken and diluted with water to an appropriate multiple; the Si content (μg/mL) in the solution is determined by the ICP-AES method, and then converted to the SiO ₂ mass fraction (%) in the sample. For detailed measurement method, please refer to NYT2272-2012.

(2) Stability test of liquid silicon-calcium fertilizer

Under stirring conditions (180rpm), add concentrated hydrochloric acid to the liquid silica-calcium fertilizer sample, adjust the pH of the system to 5, then take 100mL of liquid and transfer it into a 100mL transparent glass measuring cylinder. After standing for 24h, measure the height of the supernatant (mm). Settlement height; the smaller the settlement height, the better the stability.

Example 1

(1) Put 10g of white mud, 4.6g of CaO and 30mL of 20% NaOH solution in a reaction kettle, and carry out the first reaction at 95°C and normal pressure. After 3 hours of reaction, solid-liquid separation, the resulting filtrate (concentrated lye) is collected and reused, the resulting filter cake is washed with water, and the washing water (dilute lye) and the filtrate (concentrated lye) are mixed together for the next round of production. The filter cake obtained by washing (ie, the first solid) has _{an effective silicon content of 40% by weight in terms of SiO 2} and a calcium oxide content of 20% by weight in terms of CaO after testing.

(2) The obtained first solid is slurried with water to obtain 190 mL of water slurry with a solid content of 10 wt%. ^{Then slowly add 1900 mL of a mixed acid solution with a H +} ion concentration of 0.1 mol/L (the molar ratio of nitric acid: phosphoric acid is 4:1) to the water slurry, and the dropping rate of the mixed acid solution is 0.8 L/h. The adding process is accompanied by rapid stirring, and the stirring speed is 600 rpm. After the dropwise addition of the mixed acid liquid is completed, the whole is transferred to the reactor, and the second reaction is carried out at 20°C, and the reaction time is 30 minutes; ).

(3) Adding 30% ammonia water to the second liquid to adjust the pH to 6 to obtain a sol-like transparent liquid silicon-calcium fertilizer initial liquid. The initial liquid of the liquid calcium silicate fertilizer was evaporated and concentrated at 60°C for 3 hours to prepare the liquid calcium silicate fertilizer A1, wherein the effective silicon content was 15wt%, the calcium oxide content calculated as calcium oxide was 7.5wt%, and the sedimentation height was 1.5mm.

Example 2

(1) Put 10g of white mud, 5.1g of CaO and 30mL of KOH solution with a mass fraction of 10% in a reaction kettle, and conduct the first reaction at 110°C and normal pressure. After 4 hours of reaction, solid-liquid separation, the resulting filtrate (concentrated lye) is collected and reused, the resulting filter cake is washed with water, and the washing water (dilute lye) and the filtrate (concentrated lye) are mixed and used in the next round of production. The filter cake obtained by washing (ie, the first solid) has _{an effective silicon content of 40 wt% in terms of SiO 2} and a calcium oxide content of 35 wt% in terms of CaO after testing.

(2) The obtained first solid is slurried with water to obtain 100 mL of a water slurry with a solid content of 20 wt%. ^{Then slowly add 1900 mL of a mixed acid solution with a concentration of H +} ion of 0.05 mol/L (the molar ratio of nitric acid: phosphoric acid is 6:1) into the water slurry, and the dropping rate of the mixed acid solution is 1.0 L/h. The adding process is accompanied by rapid stirring, and the stirring speed is 800 rpm. After the dropwise addition of the mixed acid liquid is completed, the whole is transferred to the reactor, and the second reaction is carried out at 18°C, and the reaction time is 20 minutes; ).

(3) Add 30% ammonia water to the second liquid to adjust the pH to 7, to obtain a sol-like transparent liquid silicon-calcium fertilizer initial liquid. The initial liquid calcium silicate fertilizer was evaporated and concentrated at 60°C for 3 hours to prepare a liquid calcium silicate fertilizer A2, wherein the effective silicon content was 16wt%, the calcium oxide content calculated as calcium oxide was 14wt%, and the sedimentation height was 1mm.

Example 3

(1) Put 10 g of white mud, 4.8 g of Ca(OH) ₂ and 32 mL of a NaOH solution with a mass fraction of 18% in a reaction kettle, and conduct the first reaction at 100° C. under normal pressure. After 4.5 hours of reaction, solid-liquid separation, the filtrate (concentrated lye) obtained is collected and reused, the filter cake obtained is washed with water, and the washing water (dilute lye) and the filtrate (concentrated lye) are mixed and used in the next round of production. . The filter cake obtained by washing (ie, the first solid) has _{an effective silicon content of 50% by weight in terms of SiO 2} and a calcium oxide content of 20% by weight in terms of CaO after testing.

(2) The obtained first solid is slurried with water to obtain 200 mL of a water slurry with a solid content of 10 wt%. Then, slowly add 2000 mL of ^{a mixed acid solution with a H +} ion concentration of 0.08 mol/L (the molar ratio of nitric acid: phosphoric acid is 5:1) into the water slurry, and the dropping rate of the mixed acid solution is 0.9L/h. The adding process is accompanied by rapid stirring, and the stirring speed is 1000 rpm. After the dropwise addition of the mixed acid liquid is completed, the whole is transferred to the reactor, and the second reaction is carried out at 15°C, and the reaction time is 30 minutes; ).

(3) Add 30% ammonia water to the second liquid to adjust the pH to 8 to obtain a gel-like transparent liquid silica-calcium fertilizer initial liquid. The initial liquid calcium silicate fertilizer was evaporated and concentrated at 60°C for 3 hours to prepare a liquid calcium silicate fertilizer A3, wherein the effective silicon content was 20wt%, the calcium oxide content calculated as calcium oxide was 8wt%, and the sedimentation height was 0.5mm.

Example 4

The liquid calcium silicate fertilizer was prepared according to the method in Example 3, except that the H ⁺ ion concentration in the mixed acid solution used was 0.12 mol/L, and the rest was the same as in Example 1. Finally, a liquid calcium silicate fertilizer A4 is obtained, in which the effective silicon content is 12wt%, the calcium oxide content calculated as calcium oxide is 8wt%, and the sedimentation height is 2mm.

Example 5

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that the H ⁺ ion concentration in the mixed acid solution used was 0.02 mol/L, and the rest was the same as Example 1. Finally, a liquid calcium silicate fertilizer A5 is obtained, in which the effective silicon content is 12.4 wt%, the calcium oxide content calculated as calcium oxide is 7.8 wt%, and the sedimentation height is 0.5 mm.

Example 6

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that, under the condition that the ^{concentration of H +} ions remains unchanged, the molar ratio of nitric acid to phosphoric acid in the mixed acid solution is 3:1, and the rest is the same as Example 1. Finally, a liquid calcium silicate fertilizer A6 is obtained, wherein the effective silicon content is 13.3 wt%, the calcium oxide content calculated as calcium oxide is 6 wt%, and the sedimentation height is 2 mm.

Example 7

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that, under the condition that the ^{concentration of H +} ions remained unchanged, the mass ratio of nitric acid to phosphoric acid in the mixed acid solution was 7:1, and the rest was the same as in Example 1. Finally, a liquid calcium silicate fertilizer A7 is obtained, in which the effective silicon content is 12.8% by weight, the calcium oxide content in terms of calcium oxide is 8.2% by weight, and the sedimentation height is 3mm.

Comparative example 1

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that ^{under the condition that the concentration of H +} ions remained unchanged, nitric acid solution was used instead of the mixed acid solution, and the rest was the same as that of Example 1. In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is 8.6% by weight.

Comparative example 2

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that, under the condition that the ^{concentration of H +} ions remained unchanged, phosphoric acid solution was used instead of the mixed acid solution, and the rest was the same as that of Example 1. In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is 6.2wt%.

Comparative example 3

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that the step (1) is as follows:

Put 10g of white mud, 4.6g of CaO and 30mL of 30% NaOH solution in a reaction kettle, and conduct the first reaction at 120°C under autogenous pressure. After 5 hours of reaction, solid-liquid separation, the obtained filtrate (concentrated lye) is collected and reused, the resulting filter cake is washed with water, and the washing water (dilute lye) and the filtrate (concentrated lye) are mixed together for the next round of production. The filter cake obtained by washing (ie, the first solid, _{the effective silicon content in terms of SiO 2} is 22 wt%, and the calcium oxide content in terms of CaO is 32 wt%); the rest is the same as in Example 1. In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is 7.6% by weight.

Comparative example 4

The liquid calcium silicate fertilizer was prepared according to the method of Example 3. The difference is that in step (2), under the condition of stirring, the water slurry is added dropwise to the mixed acid solution for the second reaction. The acceleration is 0.9L/h, the dripping process is accompanied by rapid stirring, and the stirring speed is 240 rpm. The rest is the same as in Example 1. In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is 5.5 wt%.

Comparative example 5

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that the citric acid solution was used instead of the mixed acid solution under the condition of ^{ensuring the same H + ion concentration, and the rest was the same as that of Example 1.} In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is only 8.1 wt%, and the stability of the obtained liquid calcium silicate fertilizer is poor due to the turbidity and precipitation of calcium citrate.

Comparative example 6

The liquid calcium silicate fertilizer was prepared according to the method of Example 3, except that in step (3), 30% ammonia water was added to the second liquid to adjust the pH to 5, and the rest was the same as Example 1. In the finally obtained liquid calcium silicate fertilizer, the effective silicon content is only 10.2wt%, and the sedimentation height is 4.5mm.

It can be seen from the foregoing examples and comparative examples that, compared with comparative examples 1-5, the silicon content in the liquid calcium silicate fertilizer obtained by the methods described in examples 1-7 of this application is higher, reaching more than 10wt%, and the liquid calcium silicate The stability of fertilizer is good.

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as disclosed in the present invention.

Claims (11)

1. A method for preparing liquid calcium silicate fertilizer includes:

   (1) The white mud, calcium source and lye are contacted, and the first reaction is carried out at 90-110°C, and the obtained first product is separated into the first solid after solid-liquid separation;

   (2) The first solid is slurried to obtain an aqueous slurry, and the mixed acid solution is added to the aqueous slurry under agitation to perform a second reaction, and the second product obtained is subjected to solid-liquid separation to obtain a second liquid;

   (3) Use a pH regulator to adjust the pH of the second liquid to 5.5-10 to obtain a liquid calcium silicate 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 the white mud mainly contains 50-80 wt% SiO ₂ , 10-40 wt% Al ₂ O ₃ , and 5-10 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 lye is 5-20wt%, more preferably 16-18wt%;

   Preferably, the volume-to-mass ratio of the lye 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 _{effective silicon content in terms of SiO 2} in the first solid is 30-50 wt%, preferably 40-50 wt%, and the content is calculated as CaO The calcium oxide content is 20-40 wt%, preferably 20-30 wt%.
6. The method according to claim 1, wherein in step (2), the solid content of the water slurry is 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, the H +} ion concentration in the mixed acid solution is 0.02-0.12 mol/L, preferably 0.05-0.1 mol/L, more preferably 0.05-0.08 mol/L.
8. The method according to claim 1, wherein the reaction conditions of the second reaction include: a temperature of 10-30°C, preferably 15-20°C;

   Preferably, in step (3), the pH adjusting agent is selected from at least one of ammonia, liquid ammonia and ammonium bicarbonate.
9. The liquid calcium silicate fertilizer produced by the method of any one of claims 1-8;

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

   More preferably, the calcium oxide content as calcium oxide in the liquid calcium silicate fertilizer is 6-15 wt%, preferably 8-14 wt%.
10. The application of the liquid silicon-calcium fertilizer prepared by the method of any one of claims 1-8 to increase the yield and/or efficiency of crops;

    Preferably, the crops include grass crops,

    More preferably, the crop is rice or wheat.
11. The application according to claim 10, wherein at least one of organic fertilizer, nitrogen fertilizer, and phosphate fertilizer is applied together with the liquid silicon-calcium fertilizer, and the nitrogen fertilizer does not include ammonium bicarbonate.