Study On Fluorine Emitting From Continuous Casting Mould Fluxes

Fluorine not only contaminates the environment, but also erodes the equipments. The recycle cooling water and the second-segment cooling water at the continuous casting department in two domestic steel plants were investigated to test the F- content,and the pH value cooling water was tested one by one.The lab experiment was also carried out to simulate the molten mould fluxes cooled by the water. The F- content in the water was tested, and the water quenching sample corrosion experiment was also researched. Composition of the mould fluxes was designed by simplicity grid method, and the ion-selective electrode method was used to test the content of F-. Effect of content of F-,Li₂O,B₂O₃ on F- in the quenched water was measured by density , viscosity and smelting temperature of F-.The result of investigation showed that: the F- content of the cooling water at the re-cooling segment in the continuous casting department exceed the standard F- content of waste water in China(≦10mg/L), and the recycling water in the continuous casting department have not been processed to reduce F-. When the fluxes with low fluorine contents used in plant, the increased F- concentration in secondary cooling water was 1.2mg/L, the water behaved in neutrality. While a flux containing high fluorine was used, the increased F- concentration in the secondary cooling water reached at 24.3～57.9mg/L, and the water behaved in acidity. The higher of fluorine content in the fluxes and the longer of the fluxes soaked in the water, the more of the fluorine will transfer into the water. Controlling the fluorine in the fluxes less than 3 wt%, is helpful to reduce the hazard effects of the mould fluxes to the secondary cooling water.The results in the lab experiment were as follows: Li₂O,B₂O₃,TiO₂,MnO,Na₂O have effect on the viscosity, melting temperature, and the F- concentration in the quenched water. The quenching time of the mould fluxes and F- concentration in quenched water was the linear relationship.