Molybdenum-containing Waste Slag Calcium Molybdate For Ferromolybdenum Smelting And Its Optimization Research

In view of the high content of molybdenum in the secondary molybdenum waste resource of calcium molybdate,which is difficult to be utilized and many problems in the production of ferromolybdenum by the furnace method,this study used calcium molybdate and molybdenum oxide as raw materials and coke as reducing agent to carry out direct reduction-melting separation experiment by pellet process.Based on the analysis of the thermodynamic theory of molybdenum-containing raw materials and coke reduction,the optimum parameters of pellet preparation were obtained by orthogonal experiment and single factor experiment.The effects of calcium molybdate addition,melting temperature,holding time and alkalinity on the recovery rate of Mo metal were determined,and analyzed by chemical analysis,XRD and SEM-EDS.The effects of various factors on the phase change of ferromolybdenum and the enrichment and removal of impurity elements during the preparation of ferromolybdenum by carbon reduction method were determined.Finally,the optimum process parameters were determined.The main conclusions are as follows:（1）Through the thermodynamic analysis of molybdenum-containing raw materials and coke reduction and the simulation analysis of alloy melting point and slag system alkalinity,it can be concluded that the temperature of solid-solid reaction between MoO3 and MoO2 and coke is 671℃ and 401℃,respectively.The temperature of direct and indirect reduction of CaMoO4 with coke and CO is 1470℃ and 1322.6℃,respectively,and about 28%CaO will be decomposed during the process.Due to the presence of coke as a reducing agent,the alloying process will be affected by atomic affinity and atomic radius.Mo element mostly exists in the form of carbides.According to the phase diagram basis and Factsage simulation calculation,the melting temperature is set at 1450-1550℃,and the basicity is set at about 1.32,which can inhibit the occurrence of carburizing reaction and is conducive to the separation of slag and iron and the removal of impurity elements.（2）Through orthogonal experiments and single factor experiments,the preparation experiment of ferromolybdenum pellets was conducted.When the calcium molybdate dosage was fixed at 10%,the effects of bentonite addition,pellet moisture,and pelletizing time on pellet performance were investigated.The results showed that moisture had the greatest impact on pellet performance,followed by bentonite addition and pelletizing time.The degree of influence was 49.5%,46.1%,and 4.4%,respectively.Based on this,the optimal parameters for the molybdenum iron pellet process were determined:water content of 8%,bentonite addition of 2%,and pelletizing time of 22minutes.（3）Through the analysis of the results of direct reduction-melting separation experiment of ferromolybdenum pellets,it can be concluded that the amount of calcium molybdate affects the viscosity and alkalinity of the slag system.The higher the content,the more unfavorable the separation of slag and iron.When the amount of calcium molybdate is less than 10%,the recovery rate of Mo in the alloy can be greater than99%.The best melting parameters are melting temperature of 1525℃,holding time of25 min,and basicity of 1.3.Under this condition,the recovery rate of Mo metal and the content of impurity elements are relatively small.The phase composition mainly includes Mo2C,Fe3Mo3C and Mo3Fe.The main reason is the difference in carbon content.If the melting temperature is too high or the holding time is too long,the amount of carburizing will increase,which will cause phase change.In contrast,the basicity has the smallest change in the alloy phase.（4）Through the analysis of impurity elements in alloys and slag systems through direct reduction-melting experiments,it can be found that the influence trends of various factors in the melting process on P,S,C,and Si are inconsistent.Under the optimal melting conditions,the content of P,S,and C in the three phases Mo2C,Fe3Mo3C,and Mo3Fe decreases sequentially,while the distribution of Si has no obvious regularity.The slag system is a CaO-SiO2 binary slag system,with a molybdenum content of less than 0.1%in the slag.It has a similar composition system to ordinary glass,and the content of P element in the slag is as follows:＿In the form of₄^3-,element S will exist in the slag system in the form of sulfide Ca S,and element C will enter the slag system along with iron in the form of carburization.