Study On Removal And Migration Behavior Of Alkali Metals And Zinc In Blast Furnace Smelting Process

In recent years,with the rapid development of iron and steel production,the price of high-quality iron ore keeps rising.In order to reduce production costs,many iron and steel enterprises choose a large number of low-grade ores and add a large number of iron-bearing metallurgical solid wastes to the raw materials.These low-grade ores and metallurgical wastes contain a large number of harmful elements,including alkali metals（potassium,sodium）and zinc,etc.The load of alkali and zinc in a blast furnace is greatly increased.Alkali and zinc are enriched in the form of alkali and zinc vapor in the blast furnace.In the process of circulation,they will inevitably contact with metallurgical raw materials and blast furnace lining,which accelerates the melting loss of coke,leads to abnormal expansion of pellets,reduction pulverization of sinter,erosion of blast furnace lining,etc.,which brings adverse effects on production and seriously affects the running and life of blast furnace.Taking the blast furnace of a steel plant as the research object,the balance of alkali metal and zinc is investigated and analyzed.Secondly,taking sinter as raw material,the influence of different reduction temperatures,reduction atmospheres,and reduction time on the removal ability of alkali metals and zinc was studied,and the conversion law of alkali metals and zinc in the massive blast furnace was analyzed.At the same time,in the soft melting zone of the blast furnace,the reduction experiment was carried out by using high-temperature droplet furnace equipment,and the phase morphology of analytes was detected by scanning an electron microscope and X-ray diffractometer.The influence of different reduction temperatures on the removal ability of alkali metals and zinc was studied,and the phase change,migration,and transformation law of alkali metals and zinc in the soft melting process was clarified.Finally,the concentration status of potassium vapor on the sinter and its influence on the properties of the sinter was studied by the method of gas-phase enrichment of potassium vapor on the sinter,so as to clarify the occurrence from the transformation rule of potassium vapor on the sinter.The main conclusions are as follows.（1）The loading of alkali and zinc in the blast furnace of a domestic steel mill is7.77kg/t and 0.65kg/t respectively,which is much higher than the average level in the industry.The equilibrium analysis shows that the alkali metals and zinc are mainly brought into the blast furnace by the sinter,and the alkali discharge rate is 92.28%and the zinc discharge rate is 124.54%.The alkali metals are mainly discharged by slag,and the zinc is mainly discharged by bagged ash and gravity ash,and the blast furnace is in the alkali-rich stage and zinc discharge stage.（2）In the massive zone of the blast furnace,the removal of potassium,sodium,and zinc is almost unaffected by changing the gas-solid reaction conditions.In sinter,potassium,and sodium mainly exist in the form of silicate,aluminosilicate,and a small amount of ferrite,while zinc mainly exists in the form of ferrite,a small amount of silicate,and oxide.In the temperature range of 800℃～1000℃,the phase of alkali metals did not change and still exists in the form of silicate,aluminosilicate,and ferrate.Zn Fe₂O₄ will decompose into Zn O,but the temperature required for Zn O reduction is higher,and zinc still exists in the form of silicate,ferrite,and oxide.（3）In the soft melting zone of the blast furnace,the removal rate of potassium and sodium in the sinter is low,and the removal rate of zinc is significantly increased.When the reduction temperature is 1400℃,the maximum removal rate of potassium,sodium,and zinc is 3.10%,1.26%,and 71.96%.In the temperature range of 1150℃～1400℃,potassium and sodium in sinter still exist in the form of silicate,aluminosilicate,and ferrate,and some potassium silicate may be reduced to potassium vapor.Almost all zinc compounds are reduced to zinc vapor.（4）With the increase of potassium vapor content,the concentration rate of potassium increased,the adsorption rate first increased and then decreased,and the changing trend of low-temperature reduction index RDI_+3.15mm was opposite to the adsorption rate.With the increase of reduction temperature,the concentration rate of potassium increased,the adsorption rate decreased,and the RDI_+3.15mm decreased.Potassium vapor will exist in the sinter in the form of physical adsorption and chemical adsorption.In the process of potassium vapor rising with gas,the occurrence form of potassium vapor on the sinter is as follows:When the temperature is 1000℃～1200℃,potassium vapor mainly exists in the form of KAl Si O₃;When the temperature is 800℃,potassium vapor mainly exists in the form of KCl.When the temperature is 400℃～600℃,potassium vapor mainly exists in the form of K₂CO₃.KFe O₂ and K₂Si O₃ exist in all temperature ranges.