Study On The Process And Mechanism Of The Carbothermic Reduction Reaction Of Phosphate Rock By Flux

In nature,phosphorus exists mainly in the form of phosphate rock in mineral resources.At the same time,yellow phosphorus is the basic raw material in many industries.It is produced with electric furnace method by using silica as a flux to lower the reaction temperature,reducing carbon as a reducing agent and a conductive agent to generate elemental phosphorus and being washed and refined to gain yellow phosphorus.In general,the operating temperature of the electric furnace is controlled between 1350 and 1450℃ and the electricity consumption per ton of yellow phosphorus is b etween 13000-15000 k W·h,so it is has become a high-energy-consuming industry.With the continuous development of the econom y in various countries in the world,the consumption of yellow phosphorus is constantly increasing.Therefore,how to develop energy s aving and cleaner production technology will become one of the research focus of the yellow phosphorus production industry.In this paper,three new flux（potassium shale,potassium feldspar,nepheline）were selected to compare with the traditional flux s ilica and determined the difference in the phosphorus reduction rate,kinetics,residue viscosity and liquidity;In order to verify the influence of alkali carbonate on the system,different alkali metal carbonates were added on the basis of silica system,and the phosphorus reduction rate,residue viscosity,fluidity and mechanism of action process were investigated.In this paper,thermodynamic calculation of Gibbs free energy of the reactions thatmayexistinthephosphaterock-anthracite-silica,phosphate rock-anthracite-potassium shale,phosphate rock-anthracite-potash feldspar and phosphate rock-anthracite-nepheline systems were completed by the HSC Chemistry5.1 software.The results showed that Phosphate rock-anthracite-silica and phosphate rock-anthracite-potassium shale system began to re act at a temperature of 1120℃,whilethephosphaterock-anthracite-potashfeldsparandphosphate rock-anthracite-nepheline began to react at a temperature of 905℃,we can see potassium feldspar,nepheline flux ca n reduce the reaction temperature of the production of phosphor and nephelone as the flux can reduce the reaction temperature of the production of phosphorus furnace.In the resistance furnace,the effects of the reduction temperature,the reduction time,the acid value and the excess coefficient of anthracite on the phosphorus reduction rate were investigated experimentally in the phosphate-anthracite-silica,phosphate rock-anthracite-potassium shale,phosphate rock-anthracite-potash feldspar and phosphate rock-anthracite-nepheline systems.The experimental results indicated that the higher temperature and time,the higher reduction ratio,and finally turns to be stable.But with the increase of acidity,it shows the first increase and then decrease.The optimum technological conditions for the carbothermal reduction of phosphate rock were confirmed as follows:t he reaction temperature is 1400℃,the reaction time is 40 min,the acidity is 1.02 and the excess coefficient of anthracite is 1.5.The dynamics of the four systems were studied.The results show ed that the reaction series of the four systems are not a certain constant,and the reaction rate increases with the increase of temperature.The activation energy of the four system flux followed by silica>p otassium shale>potash felds par>nepheline.The results to study of flow temperature and viscosities from residue show that potassium shale,potash feldspar,and nepheline enhanced the residue activity during fluxing.The effects of alkali metal carbonate additives on the phosphorus reduction rate,residual fluidity viscosity and other aspects in the carbothermal reduction of phosphate rock were studied.When the content of alkali metal is 10%and the reaction temperature is 1400℃,the phosphorus reduction rates of additive Na₂CO₃and K₂CO₃ are increased to 97.08%and 98.05%,respectively.Compared with the same condition without additives,the reduction rates are increased by 8.59%,9.56%.After measuring the residue flow temperature,it was found that th e addition of the alkali metal carbonate significantly decreased the flow temperature of the residue.The same reaction condit ions,the amount of 10%,1400℃ of the reaction residue,the flow temperature of Na ₂CO₃ and K₂CO₃ were 1263.33℃,1260.33℃.Compared with the silica system without alkali carbonate,the fl ow temperature decreased by5℃ under the same conditions with addition of Na ₂CO₃,and the flow temperature decreased by 8℃ after adding K₂CO₃.By measuring the high temperature of the residue,it was found that after the addition of Na ₂CO₃ and K₂CO₃,the spreading area after calcination at high temperature for 2 h was 2.4745 cm² and 2.5447 cm².