Desulfurization And Recarburizing Of Phosphorus Pig Iron For Electrolysis Of Aluminium And Their Influence On Fe-C Voltage Drop

Phosphoretic pig iron is one of the essential anode materials for electrolytic aluminum, however, during the recycling process, its compositions may change at high temperature, causing the variation of its properties such as conductivity, coll brittleness and fluidity etc., which is unfavorable for the proper functioning of electrolytic anode and will increase the energy consumption for per ton of electrolytic aluminum. After adjusting the constituents, i.e. reducing the sulfur content and increasing the carbon content of phosphoretic pig iron by using magnesium-based desulfurizer and graphite carburant, the pig iron low temperature fluidity and cooling performance as well as the conductivity are enhanced and its casting performance is reduced during anode assembling. The composition adjustment of phosphoretic pig iron effectively reduces the Fe-C voltage drop in the anode. Therefore, research on the composition adjustment of phosphoretic pig iron has an attractive application prospect.In this paper, passivated granular magnesium, calcium carbide, quick lime and calcium carbonate were used as desulfurizers and graphite as carburant. The high frequency induction furnace was employed for the desulfurization and recarburizing. The influences of various desulfurizers and recarburizer on desulfurization and recarburizing were studied. These influence factors include desulfurization efficiency, desulfurization conditions, desulfurizer ratio, recarburizer granularity and carburizing method. In addition, the experimental methods were also practiced in real anode rodding siaop for electrolytic aluminium. The main achievements are as follows:1. When using the lime-based desulfurizers for sulfur removal, CaC2can replace the element S from FeS in the iron liquid and CaO is able to increase the basicity of the slag, reducing the sulfur content in phosphoretic iron liquid. Furthermore, CaCC>3is capable of generating CO2within the iron liquid and on the slag surface, agitating the iron liquid and enhancing the fluidity of slag thereby preventing sulfur from coming back to the molten iron.2. The desulfurization effect of magnesium-based desulfurizer is well above that of lime-based desulfurizer. However, the price for magnesium-based desulfurizer is quite expensive, and extra close-ended blowing equipment is also needed because of the severe splash phenomenon during the desulfurization process. On the contrary, lime-based desulfurizer has relatively higher sulfur removal effect with popular price and only simple equipments are needed, which makes it an optimal choice for desulfurization. Nevertheless, in the real industrial practice of desulfurization, the type of desulfurizer is chosen on the basis of different requirements.3. During the later stage of the desulfurization process, calcium oxide can adjust the pH value of the iron slag. The more CaO contained in the desulfurizer, the easier the original acid slag changing into basic slag. In fact, CaO and CaCO3in the lime-based desulfurizer are both able to create a basic atmosphere in the furnace, which is more propitious to alter the slag properties.4. The rates of solubility diffusion and scaling loss differ in accordance with the particle size of carburant. Generally, the larger particle size and less scaling loss, the lower the rate of diffusion is. Conversely, the solubility diffusion speeds. Therefore, the choice of the particle size for carburant in the real production process should take both the furnace chamber size and capacity into consideration.5. After recarburizing of phosphoretic pig iron by adding graphite carburant, a large amount of evenly distributed non homogeneous nuclei for graphite are generated, which decreases the under cooling degree of phosphoretic pig iron, eventually generating A-type graphite dominated cast iron microstructure which can effectively decrease the voltage drop of Fe-C.6. In order to achieve the goal of sulfur removal, the basic atmosphere must be created in the iron liquid during the desulfurization process by lime-based desulfurizer, resulting in the erosion of acid lining by basic environment. Consequently, it is suggested that the lining of high frequency induction furnace should be replaced by basic ones, which will not only reduce or avoid being corroded, but also contribute to the improvement of desulfurization effects.7. The proper way of using graphite carburant to carburet the phosphoretic pig iron in the high frequency induction furnace is:selecting graphite carburant with particle sizes around10mm and with high concentrate of fixed-carbon; employing the bottom carbureting method which means pressing the carburant into the bottom of the furnace via unmelted phosphoretic pig iron thereby preventing the carburant from getting in touch with air; Moreover, the amount of carburant addition can be reasonably adjusted in line with the variation of carbon content in phosphoretic pig iron, and agitate equipment can be added if necessary, speeding up the dissolution of carburant.