Investigation On Technology And Mechanism Of High Carbon Ferromanganese Alloys By Pelletization-Reducing Smelting Process Using Manganese Ore Fines Containing High Combined Water

There is in short supply of manganese ore in the world in recent years.Due to exploit for many years,the high grade manganese ores have been declined sharply,and no longer meet the demands,more tonnages of manganese ore fines have been imported,properties of which become more and more complicated.High grade ores and lumps are decreased rapidly,while fines and concentrates,especially,those with high combined water are markedly increased.In order to decrease the producing cost and promote the market competitiveness of ferromanganese alloys,it is an effective way to use the cheap ore fines and improve the agglomeration of ore fines and concentrates to enhance the smelting.How to utilize the imported manganese ore fines containing high combined water to make good quality,and then to smelt high carbon ferromanganese alloys was studied.The study used pelletization-electric furnace smelting process,which can gain high carbon ferromanganese alloys from manganese ore fines containing high combined water.The contents of this investigation include:the pretreating of ore fines and large-scale pelleting in grate-kiln, and parameters of reducing smelting processing,etc.The mechanism of the pretreating and the consolidation of fired manganese ore pellets were also investigated.Using the manganese ore fines which less than 8mm,with high combined water to make pellets,roll crushing-high press roll grinding(HPRG) process are recommended.Firstly the fines should be passed the roll crushing machine to make sure the size of fines bellow 1mm.then the sample was pretreated twice by HPRG,which pressure can be fixed at 2.5×10³N/cm²,rotate speed at 68r/min,its specific surface area can reach 2653cm²/g,and it can satisfy the demand of production.Experimental investigation shown that the pretreated manganese fines mixed with 2.0%bentonite,balled for 7min in disc pelletizer,the drop number,compressive strength and thermal shock temperature of green balls reach 23.1 times/0.5m,10.20 N per pellet,and 540℃, respectively.After drying in oven,green balls were preheated at 1050℃for 10 minutes and fired at 1335℃for 15 minutes,the compressive strength of pretreated and fired pellets can reach 594N per pellet and 2567 N per pellet,respectively.The large-scale experiment which adopted two-staged pretreating is finished in the grate-kiln.The first preheating temperature is between 500℃and 700℃for 4min,while the second preheating temperature is fixed at 1050℃for 10min to 15min. The entire preheating flow rate is 2.4m/s.At the bed height of 220mm, fired at 1330℃for 15min,the compressive strength can reach 2947N per pellet,the tumble index and the abrasion index reaches 93.35%and 1.79%,respectively.Therefore,these pellets are high quality burden for blast furnace or electric furnace due to high mechanical strength and high grade of Mn at 49.11%and low detrimental elements.The consolidation mechanism of fired manganese ore pellets indicates that:the main mineral composition is pyrolusite,which is over 60 percent,while hematite is above 10 percent.The pyrolusite is made up of extremely tiny partical,while,under the high temperature,these particals can be interconnected.The manganate liquid phase can be greatly formed with multicomponents,mainly Mn and Si.It has a good fluidness and can be blocks and the granular particals integrated, maintaining the pellets high strength.Using fired pellets made by large-scale experiment to make reduction smelting,the effect of reduction smelting temperature,time, slag basicity,MgO,Al₂O₃ etc.elements at the quality of ferromanganese alloys is studied.It's shown that the temperature of smelting impart significant influence over the separation of metals from slag.High temperature can make the heat transferring strengthened,and.it's profitable in melting and decreasing the slag viscosity.When reducing smelting pellets 5^# at 1600℃for 30min,high quality ferromanganese was produced.The basicity(CaO/SiO₂) of slag highly affects,the proper basicity is 1.3.The proper MgO content can make the slag viscosity lower and get good slag fluidity.In the experiment,5%MgO content reaches good result.And the content of Al₂O₃ must keep at a certain value, 15%Al₂O₃ content can reach best result.The final chemistry analytical of the ferroalloy indicates that the grade of Mn is 74.31%,Fe is 16.42%,C is 7.4%,Si is 1.60%,P is 0.20%,and S is 0.020%,respectively,it can reach the quality standards of brands FeMn74C7.5.