Fundamental Research On The Granulation Technology Of Phosphate Concentrate By Sintering Process

Phosphorite is a very important chemical mineral raw material, which is applied very extensively. It can be used for making pure phosphorus(yellow phosphorus, red phosphorus) and chemical raw materials, and can also be used for preparing for animal feed. Electric furnace is the disposal process dealling with phosphorite to produce yellow phosphorus. Uniform particle size, less water and carbonate content and certain strength are necessary for the charging phosphorite to meet the requirements of production. More attention has been drawn to the phosphorite concentrate beneficiated from low-grade phosphorite due to few reserves of high grade phosphorite in China and the decrease of high-grade phosphorite. So, the agglomeration process is necessary for the phosphorite concentrate after beneficiation process, because of small particle size of phosphorite concentrate.At present, the mature way of agglomeration of phosphorite are sintering, pelletizing, briquetting and tumor. reducing of Energy consumption and improving the economic benefit can be obtained, because that the sinter has uniform particle size, less water and carbonate content, certain strength and good thermal stability. Therefore, sintering process is more suitable process for the low content of P, high carbonate content of phosphate rock,.Therefore, the research of sintering process of phosphorite is very important. Although, the feasibility of sintering of phosphorite in China was explored, but, the systemic research of basic properties of raw material and the sintering process is still lacking.The basic properties of granulation process and sintering process were studied by theoretical and experimental in this study. Several conclusions were shown as follow:① The content of Ca O was 47.08%, which belonged to sedimentary calcium phosphate rock ore.Compared with lump ore, the carbonate of concentrate after beneficiated was partly removed. The main phase of lump ore and concentrate were fluorine apatite(Ca5(PO4)3F), hydroxyapatite(Ca5(PO4)3(OH)). In addition, small amount of dolomite(Ca Mg(CO3)2) and quartz(Si O2) were also contented in phosphorite.② The particle size of More than 99% of phosphorite concentrate is less than 0.7mm. The contact of phosphorite concentrate and silica were 71.5° and 75.24°, the hydrophilic of them was poorer. The hydrophilic of mixture deteriorating with increasing the amount of silica and lump ore into mixture.③ The dolomite will decompose, and react with Si O2, forms new phase Ca Mg Si O4 apparently at 1250℃. The mass loss reaction caused by the decomposition of the dolomite is endothermic and the endothermic peak covers from 600℃ to 850℃. The activation energy of the decomposition of the dolomite is about 71.6 ~123.6k J/mol, the activation energy increase with increasing the reaction degree.The mechanism equation for the decomposition of the dolomite belong to the deceleration curves, which agree with the Valensi equation and G-B equation.④ The indicators of granulation improved with increasing water addition from 1% to 3%, and then almost invaried when water addition increased from 3%to 4%, so, the optimum water addition is 3%. The indicators of granulation improved when nuclear addition increased from 5% to 10%, and deteriorated with increasing nuclear addition to 15%. The indicators of granulation gradually deteriorated with increasing acidity from 0.35 to 0.80. The optimum water addition was 3% and 4% respectively when acidity were 0.60 and 0.80.⑤ When sintering with high-carbon coal, physical strength, yield, P2O5 content and Motlen droplet performance of sinter were influenced obviously by carbon dosage. The indicators of sinter improved obviously with increasing carbon dosage from 5% to 6%, and hardly varied when carbon dosage increased to 7%, and then deteriorated with increasing carbon dosage up to 8%. The optimum carbon dosage was 6% because of cost of sintering. Acidity mainly affected the permeability of sintering to influence physical strength, yield, P2O5 content, mineral phase and Motlen droplet performance of sinter. The mineral phase of sinter varied due to the chemical reaction duting sintering process. Physical strength, yield, P2O5 content and Motlen droplet performance of sinter deteriorated when acidity increased from 0.35 to 0.80.⑥ When sintering with low-carbon coal, physical strength, yield were influenced obviously by carbon dosage, but, P2O5 content and Motlen droplet performance of sinter hardly varied with increasing carbon dosage. The indicators of sinter improved obviously with increasing carbon dosage from 5% to 7%, and then deteriorated with increasing carbon dosage up to 8%. Physical strength, yield, P2O5 content and Motlen droplet performance of sinter deteriorated when acidity increased from 0.35 to 0.80.⑦ Mass loss of sinter during reducing atmosphere with 900℃, and reduction degradation index of sinter was above 96%, so, the reduction desintegration resistance of phosphorite was very good.⑧ Fluorapatite((Ca5(PO4)3)F), fuggerite(Ca2Mg Si2O7)and Si O2 were the main phase in the sinter while fuggerite(Ca2Mg Si2O7) is the main binder phase. Dolomite(Ca Mg(CO3)2) and hydroxyapatite(Ca5(PO4)3(OH)) compelet decomposition. The cooling of half molten fluoratite((Ca5(PO4)3)F) and fuggerite(Ca2Mg Si2O7) was the main reason for phosphorite beacoming block.⑨ Physical strength of sinter was infuluenced by the fixed carbon of coal, good physical strength could be obtained with less carbon dosage when the fixed carbon of coal is higher. P2O5 content and Motlen droplet performance of sinter were influenced obviously by ash content of coal, P2O5 content of sinter was lower and Motlen droplet performance of sinter was worse when the ash content of coal was higher.