The main varieties of feed phosphate is dicalcium phosphate, defluorinated phosphate followed. After more than ten years of development and technological improvement of feed calcium hydrogen phosphate, industrial production has been basically mature. Defluorinated calcium phosphate as a feed phosphate has not been formed into large-scale industrial production due to various factors such as raw materials, process technology and application development lag. The former Soviet Union's defluorinated calcium phosphate production scale is the largest, with a single set of equipment up to 50,000 tons / year production capacity, the main equipment rotary kiln up to 100m, production technology is quite mature. Yunnan Province is rich in phosphate resources, but the development of feed grade defluorinated calcium phosphate has not achieved real industrial production. In order to solve this problem, we conducted a mineral processing investigation on the Yunnan phosphate mine , basically determined the suitable minerals for the production of feed grade defluorinated tricalcium phosphate, and carried out experimental research on the process formula and control conditions, and the obtained products reached the current international market products. Quality requirements.
1 low-weight metal phosphate raw material of choice
According to the high-temperature sintering method of phosphate rock, the process of producing feed grade defluorinated tricalcium phosphate is carried out. The main raw material for the production is phosphate rock. The harmful element arsenic can be removed during the high-temperature sintering defluorination process, but heavy metals such as lead and cadmium are non-volatile substances. It is difficult to remove and all enter the product, which seriously affects the quality of the product. To this end, we conducted on-the-spot investigations on the main producing areas of Kunyang, Haikou, Jinning, Anning, Jiangchuan, Chengjiang and other phosphate mines distributed in Dianchi and Fuxian Lake areas of Yunnan Province. A total of more than 60 samples were collected and mined. The main content and impurity content of the sample were analyzed. It was found that the phosphate ore in some mining areas has high reactivity and low heavy metal content, which can meet the requirements of feed tricalcium phosphate production. In this experiment, two low-weight metal phosphates were selected for the process formulation conditions test, and the collected phosphate mines in Guizhou, Sichuan and Hubei were compared with the phosphate mines in our province.
2 Product reference quality standard <br> The determination of the quality standard and product analysis method of tricalcium phosphate product is the basis of the process test work. At present, there is no national or industry standard in China. Before the process evaluation test, we conducted extensive data survey on the quality index and analysis methods of feed grade defluorinated calcium phosphate products at home and abroad and the collection of tricalcium phosphate products at home and abroad, focusing on feed grade defluorinated calcium phosphate in Russia and Japan. Product quality standards and analytical methods were studied. The standards of Russia and Japan give the product quality control indicators more completely, but the analysis methods of some projects in Russia and Japan are not scientific and advanced, the actual operation is cumbersome, and the analysis error is large. To this end, we have carried out a large number of analytical methods and verification work in a targeted manner, fully taking into account the international market requirements for product quality, especially the strict requirements for impurities, and finally formulated Q/YHY 01-2003 "Feed Grade Phosphate III Calcium" corporate standards. This test uses this standard as the analytical standard for test samples (see Table 1).
3 Test content of process evaluation 3.1 Raw materials used in the test
The phosphate rock powder used in the evaluation test is a low-weight metal phosphate mine in Yunnan Province, numbered as two mineral samples, KA and KB. Its chemical composition is shown in Table 2:
3.2 Determination of softening point of phosphate rock Temperature is one of the important conditions of sintering reaction, and the softening point and melting point of ore are the basis for determining the defluorination reaction temperature of phosphate rock, which is an important parameter for selecting the production process conditions. Different minerals, different additives and additions have different effects on the softening point and melting point of the material. The evaluation test used a HR-3C ash melting point tester to determine the softening point and melting point of a mixture of multiple phosphate rock and different formulations. The adjustment of the reaction temperature was guided in the test based on the measured results.
It can be seen from the test results in Table 3 that the softening point and melting point of the phosphate ore are generally greater than 1500 °C. The addition of phosphoric acid or defluorination agent to the phosphate rock will cause changes in the softening point and melting point of the phosphate rock. The flow temperature (melting point) and softening temperature of the phosphate rock are continuously decreased as the amount of phosphoric acid added increases. Different phosphate rock producing areas, chemical composition, impurity content and formula, phosphate rock softening temperature is also different, the highest drop of more than 100 °C. Therefore, in the process of production, the influence of the formulation change on the softening point and melting point of the ore sample should be fully considered, and the process control parameters should be adjusted in time.
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