1. The method for preparing the calcium-magnesium suspended fertilizer by using the nanofiltration seawater to trap the carbon dioxide product is characterized by comprising the following steps of: adding nanoscale calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide in nanofiltration seawater into a citrate aqueous solution, keeping the temperature at 20 ℃, sequentially adding a thickening agent, a dispersing agent and a wetting agent in the stirring process, adding a certain amount of light sodium oxide to adjust the pH value of the solution to 7-9 after the solution is uniform and stable, and continuously stirring for 30min to obtain the calcium-magnesium suspended fertilizer.

2. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the fineness of calcium carbonate and magnesium carbonate generated by trapping carbon dioxide by the nanofiltration seawater is 10nm-1000nm, the purity of the calcium carbonate and the magnesium carbonate is 60-99%, and the addition amount of the calcium carbonate and the magnesium carbonate is 10-30% of the specific gravity of the suspended fertilizer.

3. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the citrate aqueous solution is one or a mixture of more than two of sodium citrate aqueous solution, potassium citrate aqueous solution and sodium dihydrogen citrate aqueous solution, and the mass concentration is 5-20%.

4. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the thickening agent is one or a mixture of more than two of acacia, gelatin, methylcellulose and carboxymethyl cellulose, and the dosage of the thickening agent is 0.1-3% of the specific weight of the suspended fertilizer.

5. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the dispersant is one or a mixture of more than two of sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate, and the dosage of the dispersant is 0.1-1% of the specific weight of the suspended fertilizer.

6. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the wetting agent is one or a mixture of more than two of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene and polyoxypropylene, and the dosage of the wetting agent is 0.1-1% of the specific weight of the suspended fertilizer.

7. The method for preparing calcium-magnesium suspended fertilizer by using nanofiltration seawater to capture carbon dioxide product according to claim 1, wherein the method comprises the following steps: the surfactant is one or a mixture of more than two of alkyl glucoside (APG), fatty glyceride, sorbitan fatty acid, polysorbate, stearic acid and sodium dodecyl benzene sulfonate, and the dosage of the surfactant is 0.1-1% of the specific weight of the suspended fertilizer.

Background

Climate change is a global problem facing human beings, and with carbon dioxide emission of various countries, greenhouse gases are increased rapidly, thus forming a threat to life systems. For this reason, countries around the world reduce greenhouse gas in a global contractual manner, and thus our country proposes carbon peak-reaching and carbon neutralization targets.

The mineral used in the natural world for carbonating mineral has abundant reserves, such as serpentine [ Mg ]₃Si₂O₅(OH)₄]Talc [ Mg ]₃Si₄O₁₀(OH)₂]Or olivine (Mg)₂SiO₄) And the like, which allows for long term carbon dioxide capture, but which is energy intensive making it cost-effective unacceptable. And the carbonation reaction between gas and solid needs to be carried out under the harsh conditions of high temperature, high pressure and the like, and has the defects of high cost, high energy consumption, incapability of recycling products with high added values and the like. The prior art has CO₂Low mineralization reaction rate, harsh reaction conditions, low added value of products and the like, which lead to CO₂The mineralization technology is difficult to implement industrially.

Enriched in Mg compared to solid materials²⁺/Ca²⁺Can save Mg by using the aqueous solution²⁺And Ca²⁺The operating costs of the leaching process. Thus by being Mg-rich²⁺/Ca²⁺May be another promising approach to the carbon dioxide problem. Especially the use of carbon dioxide by seawater/concentrated seawater is very attractive, since it solves two problems simultaneously, on the one hand CO₂On the other hand, the problem of seawater pretreatment or brine waste from a seawater desalination plant can be solved. Theoretical analysis shows that more than 90% of Ca is contained in seawater²⁺And Mg²⁺Can be converted into MgCO in a precipitated form₃And dolomite [ MgCa (CO) ]₃)₂]，1m³Can fix the natural seawater to about 1.34m³Or 2.65kg CO₂(gas volume, standard conditions). It not only can realize CO₂The permanent fixation of the composite material can also generate a large amount of carbonate byproducts, namely nano-scale calcium carbonate and magnesium carbonate.

Calcium is an element that makes up the cell wall, the intercellular layer of which is composed of calcium pectate. In the absence of calcium, cell wall formation is hindered, cell division is affected, or new cell walls cannot be formed, and multinucleated cells appear. Magnesium is mainly present in young organs and tissues, and plants concentrate on seeds when they mature. Magnesium ions can activate various phosphogutases and phosphokinases in the process of photosynthesis and respiration. Similarly, magnesium, which is one of the synthetic components of chlorophyll, activates the synthesis of DNA and RNA.

CN110734335A discloses a high-calcium-content medium-element water-soluble fertilizer and a preparation method thereof, wherein the full-water-soluble suspended calcium fertilizer is prepared from the following raw materials in parts by weight: EDTA, boric acid, anhydrous copper sulfate, manganese chloride, zinc chloride, sodium molybdate, potassium hydroxide, urea, magnesium chloride, calcium formate, calcium ammonium nitrate, ferrous chloride, a stabilizer, a surfactant, a thickening agent and water. The invention can make the high-content calcium and the trace elements stably exist in the liquid phase at the same time through the process control of the charging sequence, the reaction condition and the like and the selection of the additives such as the thickening agent, the stabilizing agent and the like, and can realize the simultaneous supplement of the high-content calcium and the trace elements. CN111362745A discloses an oily suspended magnesium and calcium fertilizer, and a preparation method and a device thereof, wherein the oily suspended magnesium and calcium fertilizer comprises magnesium hydroxide mineral powder, light calcium carbonate mineral powder, a wetting agent, a dispersing agent, a thickening agent, vegetable oil, an antifreezing agent and water, and the pH value is adjusted to 8.0-9.0 by potassium hydroxide. Shearing magnesium hydroxide ore powder and light calcium carbonate ore powder to nano level by shearing, and passing through Mg²⁺And Ca²⁺Has affinity for dispersant and vegetable oil, and can keep stable suspension state. CN 112441854A discloses a preparation process of a high-concentration liquid suspended magnesium fertilizer, which comprises crushing brucite, pulverizing with a Raymond mill, performing ultrafine pulverization with an airflow pulverizer, grinding with oxidation pickaxe beads to make the brucite powder generate polarity, and dispersing, emulsifying, homogenizing, and treating with an intermediate kettle to obtain the high-concentration liquid suspended magnesium fertilizer with high dispersion degree, good fluidity, high stability, no layering, and good quality. The process for preparing the suspended calcium-magnesium fertilizer in the patent is complicated, and the used amount of the material is too much, so that the production cost of the product is not reduced.

Disclosure of Invention

The invention aims to provide a method for preparing calcium-magnesium suspended fertilizer by using a product of carbon dioxide trapped by nanofiltration seawater.

The technical scheme adopted by the invention is as follows:

the method for preparing the calcium-magnesium suspended fertilizer by using the nanofiltration seawater to trap the carbon dioxide product is characterized by comprising the following steps of: adding nanoscale calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide in nanofiltration seawater into a citrate aqueous solution, keeping the temperature at 20 ℃, sequentially adding a thickening agent, a dispersing agent and a wetting agent in the stirring process, adding a certain amount of light sodium oxide to adjust the pH value of the solution to 7-9 after the solution is uniform and stable, and continuously stirring for 30min to obtain the calcium-magnesium suspended fertilizer.

The fineness of calcium carbonate and magnesium carbonate generated by trapping carbon dioxide by the nanofiltration seawater is 10nm-1000nm, the purity of the calcium carbonate and the magnesium carbonate is 60-99%, and the addition amount of the calcium carbonate and the magnesium carbonate is 10-30% of the specific gravity of the suspended fertilizer.

The citrate aqueous solution is one or a mixture of more than two of sodium citrate aqueous solution, potassium citrate aqueous solution and sodium dihydrogen citrate aqueous solution, and the mass concentration is 5-20%.

The thickening agent is one or a mixture of more than two of acacia, gelatin, methylcellulose and carboxymethyl cellulose, and the dosage of the thickening agent is 0.1-3% of the specific weight of the suspended fertilizer.

The dispersant is one or a mixture of more than two of sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate, and the dosage of the dispersant is 0.1-1% of the specific weight of the suspended fertilizer.

The wetting agent is one or a mixture of more than two of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene and polyoxypropylene, and the dosage of the wetting agent is 0.1-1% of the specific weight of the suspended fertilizer.

The surfactant is one or a mixture of more than two of alkyl glucoside (APG), fatty glyceride, sorbitan fatty acid, polysorbate, stearic acid and sodium dodecyl benzene sulfonate, and the dosage of the surfactant is 0.1-1% of the specific weight of the suspended fertilizer.

The invention uses the by-product obtained by trapping carbon dioxide with the nanofiltration seawater for secondary utilization, and prepares the magnesium carbonate and the calcium carbonate into the suspended fertilizer for agricultural production and absorption and utilization of crops.

The invention has the following outstanding advantages:

the calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide by the nanofiltration seawater has small particles and high purity, is very suitable for preparing suspended calcium magnesium fertilizer, and the consumption of the required dispersing agent, wetting agent and thickening agent is obviously less than that of other suspended fertilizers. In addition, the nano-sized calcium and magnesium are beneficial to being absorbed by crops, and the suspended calcium and magnesium fertilizer can be well absorbed and utilized by the crops, so that the quality of the crops is improved.

Detailed Description

The present invention will be further described with reference to examples. The examples are given in mass percent.

Example one

Nano calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide in nanofiltration seawater with the mass accounting for 10% of the suspended fertilizer are added into sodium citrate aqueous solution with the mass concentration of 10% (the sodium citrate aqueous solution accounts for 87.6%) with the fineness of 10nm and the purity of 60%, the temperature is kept at about 20 ℃, carboxymethyl cellulose accounting for 1% of the suspended fertilizer is added in the continuous stirring process, sodium silicate accounting for 0.1% of the suspended fertilizer, polyoxyethylene accounting for 0.1% of the suspended fertilizer and sodium dodecyl benzene sulfonate accounting for 0.2% of the suspended fertilizer are sequentially added after the solution is stirred for 20min, light sodium oxide accounting for 1% of the suspended fertilizer is added after the solution is uniform and stable to adjust the pH value of the solution to 8, the stirring is continued for 30min, and the calcium magnesium suspended fertilizer can be obtained, wherein the stable period of the suspended fertilizer is 90 days.

Example two

Nano calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide in nanofiltration seawater with the mass accounting for 15% of the suspended fertilizer are added into sodium citrate aqueous solution with the mass concentration of 5% (the sodium citrate aqueous solution accounts for 82% of the suspended fertilizer), the temperature is kept at about 20 ℃, methyl cellulose accounting for 1% of the suspended fertilizer is added in the continuous stirring process, after the stirring is carried out for 20min, sodium tripolyphosphate accounting for 0.5% of the suspended fertilizer, polyoxyethylene fatty alcohol ether accounting for 0.5% of the suspended fertilizer and stearic acid accounting for 0.5% of the suspended fertilizer are sequentially added, after the solution is uniform and stable, light sodium oxide accounting for 0.5% of the suspended fertilizer is added to adjust the pH value of the solution to 7, the stirring is continued for 30min, and the calcium magnesium suspended fertilizer can be obtained, wherein the stable period of the suspended fertilizer is 90 days.

EXAMPLE III

Nano calcium carbonate and magnesium carbonate which are obtained by trapping carbon dioxide with nanofiltration seawater with the mass accounting for 10% of the suspended fertilizer are added into sodium citrate aqueous solution with the mass concentration of 20% (the sodium citrate aqueous solution accounts for 86.1% of the suspended fertilizer), the temperature is kept at about 20 ℃, Arabic gum accounting for 1% of the suspended fertilizer is added in the continuous stirring process, after the stirring is carried out for 20min, sodium pyrophosphate accounting for 0.2% of the suspended fertilizer, polyoxyethylene alkylphenol ether accounting for 0.2% of the suspended fertilizer and fatty glyceride accounting for 0.5% of the suspended fertilizer are sequentially added, after the solution is uniform and stable, light sodium oxide accounting for 2% of the suspended fertilizer is added to adjust the pH value of the solution to 9, the stirring is continued for 30min, and the calcium-magnesium suspended fertilizer can be obtained, wherein the stable period of the suspended fertilizer is 90 days.

Example four

Nano calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide in nanofiltration seawater with the mass accounting for 30% of the suspended fertilizer are added into sodium citrate aqueous solution with the mass concentration of 10% (the sodium citrate aqueous solution accounts for 64.5% of the suspended fertilizer), the temperature is kept at about 20 ℃, gelatin accounting for 3% of the suspended fertilizer is added in the continuous stirring process, after the stirring is carried out for 20min, sodium hexametaphosphate accounting for 0.8% of the suspended fertilizer, polyoxyethylene alkylphenol accounting for 0.2% of the suspended fertilizer and polysorbate accounting for 0.7% of the suspended fertilizer are sequentially added, after the solution is uniform and stable, light sodium oxide accounting for 0.8% of the suspended fertilizer is added to adjust the pH value of the solution to 8, the stirring is continued for 30min, and the calcium-magnesium suspended fertilizer can be obtained, wherein the stable period of the suspended fertilizer is 90 days.