Study On The Process Of Phosphorus Enrichment During The Melting Adjustment Of Converter Slag

The yield of converter slag is so huge but the utilization is relatively low, although the recycling of slag in metallurgy field can enforce the internal reuse of slag in steelmaking plant, but the inevitable phosphorous cumulation may aggravate the smelting process. Phosphorous is an important strategic resource, the exploitation and utilization is being emphasized, but the dephosphorization technology of slag on the purpose of improving the internal utilization didn’t take the recycling and efficient reuse of phosphorous resource into consideration. The adjustment of converter slag through the addition of modifier with low basicity on the purpose of increasing the phosphorous content in phosphorous-rich phase based on the research of phosphorous enrichment in slag as well as the status and development tendency of ferrous metallurgy is introduced in this study. The amount of2CaO·Si02in slag was decreased by the adjustment, and large high-grade phosphorous-rich crystalline phase was obtained through the control of cooling rate. The heat treatment system of slag and the influence of basicity on phosphorous enrichment are also investigated, the results are as follows:(1) Through the adjustment, phosphorous was efficiently enriched by decreasing the basicity of slag, the phosphorous was completely enriched during the melting and cooling of slag, and there was no phosphorous left in slag after the enrichment.(2) The gain size of2CaO·Si02particle can be increased through the control of cooling rate which cause the formation of crystal nucleus mergered by the growth of crystal. Through giving much time for the growth of crystal, the grain size of2CaO·Si02particle was obviously increased from7.75μm to12.15μm by slowdown the cooling rate from furnace cooling to1℃/min. As the phosphorous-rich phase in slag was grown sufficiently under the cooling rate used in this study, and the interface between minerals which had steady composition was clear, the separation and extraction of phosphorous-rich phase was improved. (3) The amount and the grain size of2CaO·Si02particle in slag decreased with the decrease in basiticy under the same cooling rate. The tendency of phosphorus content in phosphorous-rich phase of slag with different basicity under different cooling rate remained the same, the phosphorus content was increased when the basicity decreased from2.7to1.3, but the content was obviously decreased during the basicity decreasing to1.0.Whether there is solid2CaO·SiO2particles during the holding of slag is of great significance to the phosphorous enrichment. There were solid2CaO·SiO2particles in slag with basicity of2.7,1.5and1.3during the holding due to their high melting points, so the phosphorous enrichment could be occurred during the holding and the enrichment was less influenced by the cooling rate, the phosphorous content increased with the decrease in basicity, when the phosphorous content in slag was5%, the phosphorous content in phosphorous-rich phase after enrichment was increased to about30%, the phosphorous was sufficiently enriched and there was no phosphorous left in slag. However, as the melting points of slag with basicity of1.1and1.0were lower than the holding temperature, there were no solid2CaO·Si02particles in slag during the holding, so the phosphorous couldn’t be enriched during the holding, and the enrichment was obviously influenced by the cooling rate, the enrichment wasn’t sufficient under the heat treatment system used in this study, phosphorous content in phosphorous-rich phase after enrichment was only about20%, and there was still some phosphorous left in slag.(4) The basicity of slag after adjustment should be controlled in the range from1.3to1.5based on the consideration of phosphorous enrichment effect and adjustment costs as well as the later treatment of slag.(5) The heat treatment system used in this study which holding the slag under its melting point made the phosphorous enrich during the holding of slag, it not only lead to a decrease in the influence of cooling rate on enrichment but also with high enrichment efficiency. The system was superior to the existent ones due to the decrease in melting adjustment time and high reusing ratio of the energy of slag as well as the decrease in heating costs during the melting adjustment.