Research On Carbothermal Reduction And Self-pulverization Of Converter Steel Slag

Pulverization is one of effective ways for mass utilization of converter steel slag.However, the main problem is that the poor grindability of steel slag restricts its pulverization.Correlational research has showed that 30%~60% of silicate minerals could be contained in converter slag in which main component is C2 S. The isothermal phase transformation could be happened to the C2 S at 725?, whose crystal structure changes from ?-C2 S to ?-C2 S. This process is accompanied by 11% volume expansion, so the slag could self-pulverize under strong internal stress, improving the grindability of converter steel slag. Nevertheless, due to the presence of phosphorus in practical steel slag, such phase transformation of C2 S has been restricted, which makes self-pulverization of steel slag difficult to be achieved. Moreover, at the present, the most common way of converter steel slag recycling is iron recovery from the slag. Normally converter steel slag contains 20%~30% of iron oxide. If this part of ferrous could be recycled effectively, it will enhance the application level of converter steel slag comprehensive utilization.Based on the preliminary self-pulverization experiments of synthetic steel slag,carbonthermal reduction method has been proposed in this paper to make practical converter slag pulverized and improve the iron recovery. With the purpose of further resources recycling, P has been extracted from converter steel slag with carbonthermal reduction method to make phase transformation of C2 S happen, which promotes the self-pulverization and grindability of the steel slag. At the same time, it makes iron recovery easier.Using the coal powder that contains 82.06% carbon as reducing agent, the influence of different conditions on self-pulverization of converter steel slag and iron recovery have been studied in this paper. According to carbonthermal reduction experiments on modified steel slag and original steel slag, the effects on adding amount of coal powder, reduction temperature, holding temperature time and basicity has been analyzed. Pulverization rate and iron recovery rate have been introduced to evaluate reducing effectiveness.Experimental results showed that the temperature and its holding time, the adding amount of coal powder have positive effects on carbonthermal reduction reaction. Higher temperature, longer holding time and more adding amount of coal powder presented better results for self-pulverization of steel-slag and iron recovery.For original steel slag:for 20% coal powder adding amount and 30 minutes holding time, increasing reduction temperature from 1400? to 1600?, the pulverization rate of steel slag increased from 20.75% to 22.77%. For 1600?reduction temperature and 20% coalpowder adding amount, the holding time increased from 30 min to 60 min, the self-pulverization rate of steel slag increased from 22.77% to 23.52%. For 1600? reduction temperature and 30 min holding time, the adding amount of coal powder increased from 30%to 50%, the pulverization of the slag increased from 24.61% to 29.09%. After direct carbonthermal reduction, the pulverization rate was low, and no visible iron was found in slag. But shiny white iron attached to black massive slag could be found by light microscope.For modified converter steel slag, adding Si O2 to the slag, the basicity R decreased from4.24 to 1. With R=1, for 40% coal powder adding amount and 40 min temperature holding time, it was found that the pulverization rate of slag and iron recovery rose with the increasing temperature. Moreover, the pulverization rate and iron recovery rate reached28.7% and 65.9% respectively at 1600 ?. And different size of Fe-C-P balls have been obtained from slag. What's more, there is a obvious effect difference when using highly pure graphite powder and coal powder. With 40 g carbon material, for R=1, using coal powder as reduction, the iron recovery rate and pulverization rate reached 65.9% and 28.7 respectively.However, using the highly pure graphite powder as reduction, the iron recovery rate and pulverization rate only reached 5.9% and 49.97% respectively. For R=0.8, when using the coal powder as reduction, the iron recovery rate and pulverization rate reached 42.93% and49.97% respectively. But when using the highly pure graphite powder as reduction, the iron recovery rate and pulverization rate reached 36.95% and 8.98% respectively.Adding Si O2 to steel-slag, the modified slag could pulverize better. The pulverization rate of steel-slag increased with decreasing basicity. After reduction, little modified slag presented consolidation state, which was beneficial to separate the iron from slag and improved iron recovery.