Investigation On Calcination-Digestion-Acidolysis Process And Iodine Migration And Distribution Of Low-grade Phosphate Ore

Phosphate ore is an important mineral resource.The reserves of phosphate ore resources in China rank second in the world.Most of the phosphate mines belong to the medium-low grade[w?P₂O₅?<30%]Calcium-magnesium carbonate type phosphate ore,and about 1/3 of the phosphate ore is associated with fluorine,iodine,rare earth and other elements.The medium-low grade colloidal phosphate mineral particles are small and closely embedded,and the gangue minerals such as dolomite,quartz and iron-aluminum are high in content,which meet the requirements of wet processing phosphorus ore by mineral processing.In general,phosphate ore reverse flotation technology can meet the requirements of wet processing of phosphate ore in most cases,but it is difficult to meet the requirements of production processes such as water-soluble fertilizer,polyphosphoric acid,ammonium polyphosphate,and high-tower granulation of nitrophosphate.At the same time,phosphate ore flotation also has problems such as relatively low phosphorus recovery rate,insufficient resource utilization,and large amount of tailings.Pretreatment of the phosphate ore by roasting-digesting chemical beneficiation method and recycling of tailings can obtain high-quality phosphate concentrate and reduce tailings slag discharge.Phosphate ore calcination-digestion process can effectively remove calcium and magnesium impurity minerals in phosphate ore and recover co-associated iodine,thermal decomposition of impurity dolomite,hot water digestion of decomposition products CaO and MgO,and migration of iodine associated with phosphate ore distribution behavior is closely related.In this paper,the iodine-precipitated phosphorus ore from Guizhou was used as raw material to study the effects of phosphate ore calcination-digestion process on thermal decomposition and digestion of dolomite,P₂O₅ grade and MgO removal rate of phosphate ore,and investigation of calcination-digestion-acidolysis.The migration and distribution behavior of iodine in the process of phosphate ore was evaluated,and the acid hydrolysis effect of calcination-digesting phosphate concentrate ore was evaluated.It provides basic theory and technical support for the enhancement of the production process of nitrophosphate and the comprehensive utilization of phosphine.?1?The P₂O₅ grade change of phosphate ore and the three-phase migration and distribution of associated iodine in the calcination-digestion process were studied.The results showed that the P₂O₅ grade of phosphate ore reached the highest 32.56%under the optimal experimental conditions of calcination temperature 990°C,calcination time52 min,phosphate ore particle size-160 mesh,digestion temperature 60°C,digestion time 30 min,liquid-solid ratio 2.Three-phase migration distribution rates of associated iodine in gas,liquid and solid were:88.30%,1.77%,and 9.93%.?2?The change of P₂O₅ decomposition rate of phosphate ore and the three-phase migration distribution of accompanying iodine were studied.The results showed that under the optimal experimental conditions of acidolysis temperature 60°C acidolysis time 50 min,nitric acid concentration 51.6%,acid solution ratio 1.25,the decomposition rate of phosphate ore P₂O₅ reached 98.90%,and the gas,liquid and solid three-phase migration distribution of iodine were 81.73%,9.69%,and 8.58%,respectively.?3?The P₂O₅ decomposition rate and the three-phase migration and distribution of iodine in the denitrification and digestion of phosphate concentrate ore and flotation phosphate concentrate ore were analyzed and compared.The results showed that under the same process conditions,the P₂O₅ decomposition rate of the calcination and digestion phosphate concentrate ore was higher,and the iodine migrated more into the gas phase.Compared with the flotation phosphate concentrate ore,the acidolysis time and acidolysis ratio of the calcination and digestion phosphate concentrate ore were relatively lower.?4?The thermal decomposition process of impurity dolomite in medium and low-grade phosphate ore was studied by thermal analysis.The results showed that the thermal decomposition of dolomite in phosphate ore was divided into two stages.The first stage was that the decomposition temperature of MgCO₃ with lower decomposition temperature in dolomite CaMg?CO₃?₂ begins to decompose first.As the temperature increases,a small part of CaCO₃ decomposed.The second stage was the continued decomposition of CaCO₃ after the complete decomposition of MgCO₃.The thermal decomposition mechanism of the first and second stages of dolomite thermal decomposition followed the two-dimensional phase interface reaction?cylindrical symmetry,n=1/2?and three-dimensional diffusion?spherical symmetry,Jander equation?mechanism,two stages of thermal decomposition.The activation energies E were 111.9 kJ/mol and 176.9 kJ/mol,respectively,and the kinetic equations were:...