关键词: 磷矿, 新工艺, 冷冻结晶, 硝酸磷肥

Abstract: Considering the features of the mid-grade phosphate rocks in China，a new technology for producing the high-grade nitrophosphate fertilizer was presented.Two key problems have been solved，i.e.the filtration of acidolysis solution and calcium ions removing.The filtration intensity was accelerated by selecting phosphogypsum as a filter aid. The technology of two times removal of calcium was applied.Most of calcium ions were removed by the freezing crystallization at first.A further removal of calcium ions was carried out by adding only a small amount of sulfuric acid to insure the product can reach the national standards.The technology was systematically studied by using the phosphate rock from Hubei Province as raw material.And the optimal conditions were: nitric acid amount of 105%，nitric acid mass fraction of 55%，crystallization time of 4 h，and final temperature of 0 ℃.Under these conditions，73.17% of first calcium removing rate was reached.The second calcium removing rate was 85.25% by adding sulfuric acid.The prepared product accorded with the top grade nitrophosphate fertilizer stipulated in Nitrophosphate Fertilizer and Nitric Phosphate Potassium Fertilizer，GB/T 10510—2007.

Key words: phosphate rocks, new technology, freezing crystallization, nitrophosphate fertilizer