Technology Of Pyrolyzing Carbonate In Medium-low Grade Phosphate Ores With Yellow Phosphorus Off-gas

Phosphate ores are very important non-renewable mineral resource.But most of the existing phosphate ores are poor and difficult to use.After years of mining,high-grade phosphate ore resources are consumed too fast,and the guarantee period of resources is less than 43 years.Yellow phosphorus off-gas is discharged into the atmosphere,not only valuable CO resources are wasted,but the environment is seriously polluted,which affects human health.Therefore,the comprehensive utilization of yellow phosphorus off-gas and medium-low grade phosphate ores is of great significance to the sustainable development of resources.In this paper,yellow phosphorus off-gas was used as a fuel to calcinate medium-low grade phosphate ores to decompose carbonate impurities.The decomposition mechanism was analyzed.The thermodynamic and kinetic parameters of the decomposition reaction were calculated.The effects of yellow phosphorus off-gas,calcination temperature,time,and particle size of phosphate ores on decomposition were studied.The best technology and conditions of pyrolyzing carbonate from medium-low grade phosphate ores with yellow phosphorus off-gas are explored.The medium-low grade phosphate ores can be utilized,and a new way to efficiently use yellow phosphorus off-gas is obtained.The corresponding results are demonstrated as follow:1?The general reaction formula for carbonate decomposition in medium-low grade phosphate ores is CaMg(CO₃)₂?CaO+MgO+2CO₂?.First,dolomite in phosphate ores begin to decompose into calcium carbonate,magnesium oxide and carbon dioxide at the temperature of 400?.And then calcium carbonate begins to decompose into calcium oxide and carbon dioxide at the temperature of 700?.Both reactions exist simultaneously between 700 and 800?.The faster the heating rate is,the higher the decomposition temperature is.2?The carbonate decomposition in medium-low grade phosphate ores is controlled by a random nucleation and subsequent growth mechanism function(n=3/4).The activation energy E is187.15 k J·mol^-1,Pre-Factor A is 550373352.3s^-1.The kinetic expression is G(?)=(-ln(1-?))^3/4=10^{10.08-10280.421/T}.3?Theoretically,as a whole,the temperature of the decomposition reaction of carbonates in medium-low grade phosphate ores is higher than 541?.The higher the temperature,the less heat absorbed,the lower the Gibbs free energy and the higher the standard equilibrium constant.The increase of temperature is propitious to the decomposition of carbonate.4?The higher the pressure of yellow phosphorus off-gas after combustion,the higher the temperature of spontaneous decomposition of carbonate.The lower the grade of phosphate ores,the greater the amount of yellow phosphorus off-gas required.In theory,when the pressure of the gas after combustion is lower than the standard atmospheric pressure,as long as the temperature is above 536?,the decomposition reaction will spontaneously proceed.5?Calcination temperature and time are the key factors of carbonate decomposition in phosphate ores.The higher the calcination temperature and the longer the time,the more complete the decomposition of carbonate.Calcined in a muffle furnace to decompose carbonates in phosphate rock at 700?for 257 to 290minutes.The time is at 65 to 85 minutes at 800?.90%of CO₂is removed by calcining at 900?for 30 minutes,the mass fraction of CO₂is less than 6%,and the mass fraction of P₂O₅is more than 29%.6?The best process for calcining medium-low grade phosphate ores with yellow phosphorus off-gas is a two-step process,which means that after the yellow phosphorus off-gas is burned in the combustion furnace,the high-temperature gas is passed into the calcination furnace to pyrolyze the carbonate in the phosphate ores.The calcination temperature is between 700 and 900?,and the calcination time close to 900? is?1h,which can prevent the phosphate ore from agglomerating.The carbonate in the medium-low grade phosphate ores is basically decomposed after 8hours of calcination,with a CO₂mass fraction of<5% and a P₂O₅mass fraction corresponding increase.