Release Of Halogen In Phosphate Rock During Calcination And Leaching

This paper takes Wengfu phosphate ore as the research object,studies the halogen release,grade change and environmental impact of phosphate ore in different temperature conditions and subsequent residue digestion;The effects of different acidity leachate on halogen leachate release and environment in phosphate ore were investigated.The form of halogen in phosphate ore and its roasting and leaching residue was determined by chemical extraction step by step;The grade of phosphate ore and its concentrate was determined by the percentage content of phosphorus pentoxide（P₂O₅%）;The contents of fluorine,chlorine and iodine in solution and solid samples were determined by ion chromatography（IC）and high temperature hydrolyzed ion chromatography（PIC）.The conclusions are as follows:（1）When calcined at 900～1100℃,the release rate of fluorine in phosphate ores was 19.31～45.92%,and that of chlorine was 95.36～98.34%.Iodine is released rapidly at 200～300℃and 700～1000℃.It was almost completely released at 1000℃,and the release rate was 96.6%.（2）Under the optimal digestion conditions（liquid-solid ratio 2.5:1,digestion temperature 60℃,digestion time 50 min）,the phosphate ore roasted residue at 900～1100℃can be digested with a higher grade（P₂O₅%>30%）of phosphorus concentrate;The phosphorus concentrate with the highest grade（P₂O₅%=33.24%）was obtained after the digestion of the roasted residue at 1000℃.It can be seen that the grade of phosphate ore can be effectively improved by roasting and subsequent digestion.In addition,the halogens released during the roasting of phosphate ores will cause equipment corrosion and air and water pollution to a certain extent.（3）When the leaching time is 157 h,150 h,152 h and 154 h,respectively,the release of fluorine reaches the maximum,and the leaching rate of fluorine is 1.53%,2.66%,2.71%and 2.25%,respectively.（4）The leaching time of chlorine from phosphate ore was 104 h,90 h,97 h and 86 h with different pH 1.8,3.8,6.5 and 8.5 solutions,respectively.Chlorine leaches out very hard,and the leaching chlorine could be completely released.The leaching rates were 8.07%,15.28%,7.84%and 8.63%,respectively.When pH is 3.8 and leaching time is 65 h,the maximum concentration of chlorine in the leached solution reaches 223.8μg/m L.（5）Iodine was leached from phosphate ore with different pH 1.8,3.8,6.5 and 8.5 solutions.When the leaching time was 65 h,93 h,90 h and 165 h,the release of iodine reached the maximum value,and the maximum leaching rates were 5.28%,1.24%,0.550%and 1.08%,respectively.The average iodine concentration in the leached solution was 2.3,0.378,0.164 and 0.189μg/m L,respectively.When the pH value is 1.8,the leached iodine is mainly in the ion exchange state and carbonate bound state.When the pH value is 3.8,6.5 and 8.5,the iodine leached is mainly in the water-soluble and ion-exchange forms.（6）The concentration of fluorine and iodine in the water will increase after the leaching of phosphate ore.Should not be drinking.