Background and Overview[1]
Phosphate fertilizer is one of the important raw material fertilizers in agricultural production. Phosphate rock is the main raw material for phosphate fertilizer production. Its resource distribution in my country has the following characteristics: (1) The distribution is relatively concentrated, with “more in the south and less in the north”; ( 2) Resources are “abundant but not abundant”, with the average grade of ore being only 17%; (3) Mining is difficult and resource utilization is low. The above characteristics of phosphate rock resources have restricted the development of my country’s phosphate fertilizer industry to a certain extent. Calcium magnesium phosphate fertilizer is also called molten calcium magnesium phosphate fertilizer. A thermal phosphate fertilizer. It is composed of a mixture of phosphorus pentoxide, magnesium oxide, calcium oxide and silicon dioxide, and is vitreous.
Industrial products are gray-white, brown or gray-green fine particles or powders with a particle size that can pass an 80-mesh sieve and a moisture content of less than 1%. The industrial production method is to melt phosphate rock and magnesium-calcium-containing ores such as olivine, serpentine, dolomite, etc. at 1300 to 1450°C, drench the melt with cold water, and then grind it finely. It is a weakly alkaline fertilizer containing 16-20% of effective phosphorus pentoxide. It can dissolve 95% in 2% citric acid solution, so it is easily dissolved and absorbed by crop root exudates. It does not absorb water, does not agglomerate, is non-toxic, non-corrosive, and is very convenient for packaging, transportation and application.
The silicon, calcium, magnesium and other elements contained in it are all necessary for the growth of crops, and it also contains small amounts of zinc, molybdenum and other trace elements needed by plants, which is beneficial to the growth of crops. Calcium-magnesium phosphate fertilizer is most suitable for application on acidic soil, neutral soil and magnesium-deficient sandy soil. Continuous fertilization will not cause soil compaction and can improve acidic soil. It is used as base fertilizer and should not be used as top dressing. According to the USDA’s greenhouse trials, calcium, magnesium and phosphate fertilizers are more effective than superphosphate when applied to acidic soils. Experiments by Japanese experts in Datong and Shijiazhuang cities in China have shown that the application of calcium, magnesium and phosphate fertilizers is particularly beneficial to the development and growth of crops, because the magnesium contained in it is the main substance that makes up plant chlorophyll.
Apply[2-3]
Calcium-magnesium phosphate fertilizer is one of the traditional phosphate fertilizer varieties in my country. Domestic calcium-magnesium phosphate fertilizer manufacturers are concentrated in Yunnan, Guizhou and Hubei provinces. Calcium-magnesium phosphate fertilizer not only contains medium elements such as P2O5, MgO, CaO, SiO2, but also trace elements such as iron, manganese, and zinc. It has the advantages of being difficult to lose, slow-release, and long-lasting. Diethanolamine occupies a place in the fertilizer market. In recent years, my country’s average annual demand for calcium, magnesium and phosphate fertilizers has been around 2 million tons. The market demand for calcium magnesium phosphate fertilizers has developed to use in multiple channels and across fields, and its demand targets are diversified: (1) as an auxiliary raw material for organic or inorganic compound fertilizers; (2) as a special base fertilizer for economic crops; ( 3) Sold as semi-finished products.
Calcium magnesium phosphate fertilizer is one of the few fertilizers allowed to be used in my country’s “green food” and is recognized as a pollution-free and environmentally friendly fertilizer in Southeast Asian countries. Calcium, magnesium and phosphate fertilizers are often used as base fertilizers in agricultural production or to improve acidic soil. Relevant experiments have shown that after the application of calcium, magnesium and phosphate fertilizers, plants have strong stress resistance, their root systems are elongated and are not prone to lodging, and calcium, magnesium and phosphorus elements can be deposited in the epidermal cell membranes of stems and roots, playing a role in resisting the invasion of pathogens.
Some studies have found that Ca2+, as a competitive ion for Cd2+ in the soil, usually competes with Cd2+ in the soil for adsorption sites and transport channels on the root surface, thereby reducing the absorption of Cd by plants and promoting plant growth and development. Therefore, using calcium magnesium phosphate fertilizer as a soil conditioner and combining heavy metal groups into the soil environment can significantly reduce the bioavailability of Cd in the soil. Mg2+ indirectly affects the absorption of Cd by plants by affecting the physiological metabolic processes of plant roots and above-ground parts, or affecting the migration and transport of Cd in plants, reducing the amount of Cd in plants. At the same time, calcium, magnesium, and phosphorus are essential nutrients for plant growth. Through processes such as competition and antagonism between elements, it is feasible to reduce the bioavailability of heavy metals in contaminated soil.
Preparation[1]
A method for preparing calcium-magnesium phosphate fertilizer using the blast furnace method of phosphate rock flotation tailings, including the following steps:
⑴ Using flotation phosphate tailings slurry as raw material, the mass percentage of P2O5 on a dry basis in the slurry is 8 to 12%. The tailings filter cake is obtained through dehydration treatment with a thickener and filter, and the water content of the tailings filter cake is controlled. At 20‑40%;
⑵ Use a granulator to granulate the tailings filter cake obtained in step ⑴ or the tailings stored in the tailings pond, with a particle size of 10-40mm, and dry it with a dryer until the water content is <5%;
⑶Crush other raw phosphate rocks, silica, and coke containing P2O5 for combustion into lumps with a particle size of 30 to 60 mm; in step (3), the mass percentage of raw phosphate rocks containing P2O5 is ≥ 23%.
⑷Control the mass ratio of flotation phosphate tailings and other phosphate rock raw materials to 100:8~90, so that the weight percentage of P2O5 on a dry basis when mixed into the furnace is 13~19%;
p>Original dispersant imported from Germany
⑸Add metered and mixed smelting raw materials into the blast furnace. The metering ratio of various minerals in the smelting raw materials is:
Step ⑷ mixes 100 parts of phosphate rock raw materials, 18 to 35 parts of coke, 0 to 15 parts of serpentine, and 2 to 20 parts of silica.
⑹ Use the raw materials obtained in step (5) to prepare calcium magnesium phosphate fertilizer by the blast furnace method.
The preparation of calcium magnesium phosphate fertilizer using the blast furnace method in step ⑹ is carried out according to the following production operation steps:
①Add the melting raw materials prepared in step ⑸ into the blast furnace, control the furnace temperature at 1350~1450℃ for high-temperature melting, the melting time is 35~50 minutes, and the melt is obtained from the slag discharge port;
② Apply the melt toQuenching, using water with a water temperature of 25 to 45°C, the solid material after quenching is fished out, drained, dried, crushed and sieved to obtain the finished calcium magnesium phosphate fertilizer.
Main reference materials
[1] Social Dictionary of Science and Technology·Chemistry
[2] CN201410533131.6 A method for activating calcium magnesium phosphate fertilizer with low molecular organic acid
[3] Effects of calcium, magnesium and phosphate fertilizers on soil Cd bioavailability and brown rice Cd content
[4] CN200910218353.8 A method for preparing calcium magnesium phosphate fertilizer by using phosphate rock floatation tailings blast furnace method
