Due to the single nutrient content and low content, the production process will cause pollution. In addition to the current progress in the production of phosphate fertilizers and the development of compound fertilizer and sustained release, the development of ordinary and general calcium enterprises has encountered bottlenecks. However, as the number of high-grade phosphate ore decreases and low-grade phosphate rock needs to be developed, Pu-Cal also faces new opportunities for development. After years of practice and reflection, we believe that in the new situation, the real way out for the upgrading of ordinary calcium should be compounding rather than taking the path of “heavy calciumâ€.
The basic reason why the calcium-adsorption outbreak is “revenient†rather than “heavy†is that although the acid used to dissolve the phosphorus is different between precalcium and heavy calcium (the former uses sulfuric acid and the latter uses phosphoric acid), the nutrient content is different, but the main components of the fertilizer are all It is calcium dihydrogen phosphate and its molecular formula is Ca(H2PO4)2·H2O. However, the ratio of phosphorus pentoxide (P2O5) and calcium oxide (CaO) used in the production of heavy calcium, and the activity of ore, etc. are all higher than that of the production of calcium sulphate in order to guarantee high conversion rate, and the production of heavy calcium needs to be used. Phosphoric acid, which produces a large amount of by-product phosphogypsum, is not conducive to environmental protection. Therefore, in order to adapt to the development of modern agricultural production, the development of calcium sulphate should ensure that phosphorus is mainly in the form of soluble H2PO4- (P in the calcium (Ca2O4)2.H2O in precured calcium is in the form of H2PO4-) Under the premise of compounding. However, such compounding does not involve the production of primary calcium and the compounding or compounding of nitrogen, potassium, and other fertilizers (in fact, due to the high water content of primary calcium, this compounding is very difficult), and the process should be reformed. In the process of producing Ca(H2PO4)2·H2O (or compounds containing H2PO4- existed) during the process of multi-element synchronous recombination, the nitrogen, phosphorus, and potassium ratios can be used directly (not like phosphorous The use of multiple compound fertilizers such as ammonia, which is mainly used as a basic fertilizer for the production of other compound fertilizers due to inappropriate proportions of nitrogen and phosphorus, has led to the development and upgrading of general calcium production processes. The best method at present is to use a solution or solid of sulfuric acid urea (also known as urea sulfate or urea sulfuric acid) instead of the traditional phosphoric acid to dissolve phosphorous. The difference is that the former is still a wet process, and the latter is a dry process.
In the 1950s, foreign countries developed a process for producing complex fertilizers containing Ca(H2PO4)2·H2O with the participation of water and the use of urea sulfate as a phosphate solubilizer. This process has also been researched and developed in China. There are several patent applications, and a nitrogen-phosphorus compound fertilizer containing Ca(H2PO4)2·H2O that meets the national standard has been produced (tripotential compound fertilizer is added in the production of potassium salt). All of these belong to the upgrading technology of Pu-calcium, which is more advanced and improved than the traditional process, but in fact it is still in the category of wet process and does not break through the tradition of producing H2PO4-containing Ca(H2PO4)2·H2O in the factory production process. In practice, a large amount of water must be added during the production process, and then dehydrated after drying, which is inconsistent with the requirements for energy saving and water saving. Although the addition of urea will reduce the emission of hydrogen fluoride (HF), it is still difficult to completely eliminate, and environmental pollution and health hazards still exist.
In the 1980s and 1990s, China's patented dry process was proposed and broke through the traditional concept of factory-fertilizer production. Firstly, urea sulphate is used as a solid phosphorus solubilizer, which is then dry mixed with dry rock phosphate in production and pelletized directly. Nitrogen and phosphorus binary compound fertilizer can be obtained without drying (adding potassium salt during granulation Three yuan compound fertilizer). Moreover, the fertilizer does not have a phosphate-solubilizing reaction during the production process, and thus no Ca(H2PO4)2.H2O is generated, no HF is released, and no pollution is caused to the environment. When the fertilizer comes into contact with water or when it is applied to the soil, the phosphorus release reaction occurs, and in-situ production of Ca(N2H4CO)4(H2PO4)2 that can be absorbed by the plant containing H2PO4-. The nitrogen in urea can also be absorbed by plants, and because it is in the complex state, it also has a sustained release effect, and the utilization rate can be increased by about 20%.
This process of producing Ca(N2H4CO)4(H2PO4)2 containing in situ the H2PO4-containing precursed calcium produced under anhydrous conditions preserves the advantages of the traditional pre-calcium product and overcomes its shortcomings. There is no HF and "three wastes" emissions, will not pollute the environment and harm health, the product does not need to be dried, compared with the new wet process water saving, energy saving, process is simpler, the process is shorter, the area is less, the investment is more provincial, The higher utilization of nitrogen is an innovative technology for the upgrading of ordinary calcium. The process produced a large number of fertilizers that met the national standard fertilizer standards during the pilot and industrial tests of the National Science and Technology Projects during the “Seventh Five-Year Plan†and “Eighth Five-Year Plan†(water-soluble phosphorus accounted for 50% to 70% of available phosphorus). The results of a large number of agricultural experiments conducted on different varieties of crops in different regions of the country show that this in situ phosphate-solubilization reaction is feasible and effective, and the fertilizer effect is good. In 2007, the thiourea-phosphate production plant with an annual output of 100,000 tons established in Chongqing using this process passed the national acceptance. The experts affirmed the reliability and promotion value of the process, and they all agreed that this is a transformation and upgrading of general calcium. A more advanced process. At present, the process is being promoted throughout the country with a view to transforming it into productivity as soon as possible.
To sum up, the way out of calcium sulphide is "recovery" rather than "heavy", especially when China's phosphate ore is rich, low, and plentiful. The use of urea sulphate as a phosphate solubilizer instead of sulphuric acid to synchronize the production of calcium complex, direct production of nutrients can be adjusted, more suitable for alternative soil fertilization of organic - inorganic phosphorus compound fertilizer, is the correct path for the development of calcium upgrading. It must be pointed out that both the wet and dry processes can be used directly with low-grade phosphate rock, and the dry process can even use phosphorus ore and tailings with P2O5 content of about 15%, and magnesium that cannot be used in new and old wet processes. High phosphorus content of aluminum ore, so the dry process has a broader space for development.
UCPACK , https://www.packpioneers.com