KAMATA, R., KIZU, Y., and TSUJIMURA, H. The production of special SiMn using the Gas and Powder Injection Process. INFACON 6.

Proceedings a/the 6th International Ferl'oal/oys Congress, Cape TawIL Volume 1. Johannesburg, SAIMM. 1992. pp. [39-143.

The Production of Special SiMn Using the Gas andPowder Injection Process

R. KAMATA, Y. KIZU, and H. TSUJIMURA

Nippon Denko Co. Ltd, Tokyo, Japan

The slag produced during the refining of high-carbon ferromanganese usuallycontains 20 to 30 per cent manganese. Several methods have been tried in the pastto recover this manganese. However, there were various problems associated witbthese methods: use could not be made of the thermal energy in the molten slag, andthe manganese recovery rate was low, etc. The Gas and Powder Injection Processwas developed by Nippon Denko to solve these problems. In this process, ferro­silicon and/or silicon metal are added to the molten slag held in the ladle and arestirred by the injection of a large quantity of nitrogen, or some other inert gas, at ahigh flowrate from a lance immersed in the slag. Silicomanganese is thus producedby a silicothermic reaction.

The Tokushima Works of Nippon Denko are producing low-phosphorus, low­carbon silicomanganese directly from molten slag by this process.

IntroductionThe slag produced during the refining of high-carbonferromanganese contains 20 to 30 per cent manganese. Ingeneral, the following two methods are used for therecovery of this manganese.(1) The solidified slag is crushed and screened, and is

melted in an electric furnace. Manganese is reduced bycarbon, and is recovered in the form of asilicomanganese metal.

(2) Ferrosilicon andlor silicon metal are added to themolten slag, the slag is stirred, and manganese isrecovered in the form of silicomanganese by asilicoLhermic process.

The first method is simple technologically and is themethod most commonly used, but it does not allow theutilization of the lhennal energy contained in the molten slag.

The second method is superior to the first from the pointof view of efficient energy usage. Various processes suchas the shaking-ladle process, reladle process, and othermethods, which differ primarily in the method of stirringthe molten slag, have been proposed. However, thetechnologles used in these methods all embody one or moreof the following problems.

(1) Owing to insufficient mixing of the molten slag withthe silicon metal, the manganese recovery rate is low.and a high proportion of manganese remains in the slagand must be discarded.

(2) The amount of thermal energy becomes insufficientbecause the process requires a long reaction time. It

therefore becomes necessary to provide a secondarysupply of heat (e.g. by heating of the silicon metal andcausing it to melt before being added).

(3) Wave motion in the molten slag iu the ladle duringmixing makes it impossible to increase the amount ofmaterial processed at one time.

In order to solve these problems, Nippon Denkodeveloped the 'Gas and Powder Injection Process'. Bymeans of this process, it has become possible to producesilicomanganese efficiently from high-carbon ferro­manganese slag with a high manganese recovery rate, andwith almost no provision of external heat. Thesilicomanganese produced in this way is extremely low inphosphorus and carbon.

An outline of the process as established and operatedsatisfactorily by Nippon Denko at its Tokushima Works ispresented below.

Production MethodHigh-carbon ferromanganese slag (referred to as 'H slag')tapped from an electric furnace is conducted into a ladle forrefining purposes. Ferrosilicon and/or silicon metal areadded as the reducing agent, together with a flux when it isnecessary to adjust the basicity of the slag. The slag is thenstirred by the injection of nitrogen or some other inert gas,and silicomanganese is produced as the result of asilicothennic reaction. The reducing agents are added to themolten slag by means of a chute, and the flux is injectedinto the molten slag using the gas as carrier. Burnt lime inpowder fonn is generally used as the flux.

THE PRODUCTION OF SPECIAL SiMn USING THE GAS AND POWDER INJECTION PROCESS 139

Refining ladleThe ladle, which is lined on the inside with refractorymaterial, is capable of holding approximately 20 t of slag.The contents of the ladle are discharged through a slidingnozzle.

ElectricfurnaceThe electric furnace is a closed-type submerged-arc furnacewith a 40,5 MYA transformer. It has two tapholes, one formetal and one for slag. The H slag discharged from thetaphole into the slag pool is supplied to the ladle after thecoke that is discharged at the same time has been removed.

LancesThe lances for both gas injection (GI) and powder injection(PI) are covered with refractory material. The total lengthof the GI lance is approximately 5 m, and the lance has twoholes facing sideways on its forward edge. The PI lance hasa total length of approximately 4 m, and has onedownward-facing hole on its forward edge.

Refractory

AI,03-MgO castableAl,03-MgO-SiC castableHigh-A 1,03 castable

I23

Step

Changes in lance and ladle refractoryAs the cost of the refractory accounts for a large proportionof the refining costs, various materials were tested in orderto reduce this expense. A summary of changes in lancerefractory is shown in Table I. and a summary of changesin ladle refractory in Table II.

TABLE ICHANGES IN LANCE REFRACTORY$UOIIIG NOZZLE I'OR M[TAl TAPPING

PI LMC[

GI LMC[ <t-.H-I

EquipmentThe equipment used is shown in Figure 1.

FIGURE 1. Equipmem for the Gas and Powder Injection Process

Ferrosilicon and silicon metalThree 4 m3 bins contain the ferro silicon and silicon metal.The amount to be introduced into the slag is adjustedaccording to the mass measured by the load cells attachedto the bins. The bins are discharged by means of a rollfeeder, and the discharged metal is conducted along a chuteinto the ladle.

Step

I23

TABLE IICHANGES IN LADLE REFRACTORY

Refractory

MgO-CaO brickHigb-Al,03 castableMgO-C brick

FluxOne 6 m3 tank contains the flux. The amount to beintroduced is adjusted according to the mass of a load cellattached to the tank. The discharged flux is conductedalong a flexible chute, together with the carrier gas, and isinjected into the molten slag within the ladle through thepowder-injection lance.

Refining Method

Raw materialsRepresentative compositions of the ferrosilicon, silicon,metal, and lime used in the process are shown in Table III.

TABLE illANALYSIS OF RAW MATERIALS

MaterialSi%

C%

P%

Fe%

CaO%

Sizemm

FerrosiliconSilicon metalLime

7497

0,20,050,15

0,020,0080,008

220,5

97

0-100-100-1

140 INFACON6

TABLE IVREFINING SCHEDULE

Time, min o 2 4 6 8 10 12 14 16min

Slag inputSi chargeGas injectionPowder injectionSeparation

1-------------11 5 min

1

5 min

3,5 min6min4 min

Conditions of injectionRepresentative injection conditions for the process areshown in Table V.

RefiningThe si Iicomanganese produced by this process has farlower phosphorus and carbon contents than thesiljcomanganese produced in an electric furnace. Someproduction examples are shown in Table VI.

Refining scheduleA representative refining schedule for the process is shownin TablelV.

After GI has been completed, the mixture is allowed tosettle for approximately 5 minutes, and is then tapped afterthe slag has been separated from the metal during settling.

Results

[2)B = (CaO) + 1,39(MgO)

(Si02)

In example I, ferrosilicol1 is added to the H slag, and GIis carried out while lime is injected by PI. Silicomanganesewith a silicon content of 12 per cent is produced.

In example 2, hoth silicon metal and ferrosilicon areadded to the H slag, and GI is carried out concurrently withLime addition by PI. Silicomanganese with a silicon contentof 18 per cent is produced.

In example 3, silicon metal is added to the H slag andonly GI is carried out; silicomanganese with a siliconcontent of 22 per cent is produced. in this example. becausethe basicity of the H slag is comparatively high and thesilicon grade of the metal produced is also high. it isunnecessary to control the basicity by the PI of flux.

The phosphorus content in all of the above examples isaround the 0,0 I per cent level, which is far lower than thatof any material produced in an electric-furnace process.

Manganese and Silicon YieldThe main reducing reaction that takes place in the ladle isgiven by

2 MnO + Si -> 2 Mn + Si02. [IJ

The manganese content of tbe slag produced whenrefining has heen completed (when reaction [I) has reachedequilibrium) is determined from the silicon content of themetal produced and the hasicity of the slag generated.Formula [2) is used in the calculation of the basicity:

PI

6-72-4

50- 300

5-67 - 12

1200-2200

TABLE V

CONDITIONS OF INJEcrION

OJParameter

Gas pressure, kg/cm2

Gas volume, Nm3/minGas speed, Nm/sRatio of powder/gas (mass)

TABLE VIPRODUCTION EXAMPLES

Analysis (%) QuantityEx. Component

Mn Si02 CaO MgO Si C P kg/batch

I Input Hslag 24,5 25,3 23,1 5,4 0,008 0,003 19270FeSi 74,2 0,217 0,018 1730Lime 97,8 0,148 0,007 1070

Output Metal 76,1 12,3 0,187 0,Ql8 3870Slag 9,6 35,9 30,2 5,7 18200

2 Input Hslag 26,3 25,5 20,5 3,2 0,005 0,003 17 640Si mefal 97,1 0,048 0,006 I 180FeSi 73,7 0,189 0,021 1040Lime 97,4 0,162 0,010 1350

Output Metal 76,6 17,8 0,122 0,014 4850Slag 5,5 40,0 30,1 3,4 16380

3 Input Hslag 21,6 26,2 26,4 3,5 0,010 0,003 19030Si metal 97,5 0,063 0,008 2180

Output Metal 76,1 22,4 0,055 0,012 4800Slag 2,8 42,5 30,6 4,1 16420

THE PRODUCTION OF SPECIAL SiMn USING THE GAS AND POWDER INJECTION PROCESS 141

The relationship between the manganese content of theslag, the silicon content of the metal, and the basicity of theslag obtained in approximately 500 refining runs is shownin Figure 2. The regression formula is

where B represents the basicity of the slag,

(CaO), the CaO content of the slag,

(MgO), the MgO content of the slag, and

(SiO,), the SiO, content of the slag.

So, the amount of Si that is transferred to themetal, and

Si, the amount of Si inserted.

The silicon efficiency ratio of the method approachesapproximately 95 per cent. This means that, of the totalamount of silicon added, 95 per cent contributes to thereduction of MoO or is transferred to the metal produced.

Change in Temperature and Heat Balance

Examples or" the change in temperature during refining areshown in Figure 3.

(Mn) = - 6,9[Si]0.5 - 8, I B + 42,1, [3]

FIGURE 2. Relationship between (Mn) in slag and lSi] in metal

A- 0,256xMo+So x 100(expressedas%) [4]Si

3 4 5 6 7

G. I.

2

P. I.

TIlle (1IIn)

SI ehule

o

1440

14Z0

1400 .

"1380

IJ60

1340

13Z0

1300

lZ80

1200

1240

1220

1200

Lifetime of ladle inner-lining bricksThe area of the ladle inner-lining bricks that exhibits theheaviest corrosion is the slag line at the time of refining. Ifa certain thickness of brick remains in other areas, thecorroded area is repaired with castable and re-used. Whenthe average remaining thickness of the inner-lining brickshas been reduced to approximately one half its value at thetime the ladle was put into operation, the ladle is regarded

Refractories

The temperature of the molten slag during refining dropsinitially because of the the addition of silicon metal at roomtemperature and the PI of the flux. It increases with theprogress of the silicothermic reaction, and then decreasesagain owing to the radiation of heat after the reaction hasreached equilibrium.

The heat balance for this example is shown in Figure 4.The heat of reaction and the heat of formation of the slagand metal serve to preserve the latent heat of the rawmaterials. the sensible heat of the gas. and the radiation.

As the refinjng tjme is short, the amount of heat radiatedis small, which makes it possible to introduce the siljconmetal and flux at room temperature.

FIGURE 3. Change in temperature during refining

252010 15rs I J %

5

(Mn) represents the manganese content of theslag produced,

lSi] is the silicon content of the metal produced,and

B is the basicity of the slag produced.

20

~

0; 15

~

1 a

5

a0

where A represents the silicon efficiency,

Mo, the amOllnt of Mn that is transferred to themetal reduced from H slag,

where

A comparison of the results of refining by this methodwith those obtained by other methods is shown in TableVII.

The manganese content of the slag produced by the Gasand Powder Injection Process is lower than that of slagproduced by the former methods, owing to the strongstirring during the process. The manganese yield achievedis high.

The silicon efficiency ratio is defined as

TABLE VIICOMPARISON OF REFINING IU'_'.;uLTS

Process Mil in final slag, % Si in metal, % Basicity Mn yield, %

GI, PI processShaking-ladle processRe-ladle process

4,39,5

16,1

18,818,818,8

0,940,950,94

846639

142 INFACON6

Lifetime ofGllance castableThe part of tbe GI lance cas lab Ie lbal undergoes theseverest corrosion 'is the area that is immersed in the slag atthe time of refining. When the thickness of the remaining

as having reached the limits of usability, and is relined. Theaverage time a ladle can be used before relining is that forapproximately 400 heats, with repairs being carried outonce or twice during this period. Corrosion is limited to theside areas of the ladle, and hardly any erosion of the bottomlining occurs. The average loss of refractories per heat isapproximately 22 kg.

FIGURE 4. Heat balance

(Mn) = - 6,9[Si]0.5 - 8,1 8 + 42,1,

where (Mn) represents the Mn content of the slagproduced,

[Si], the Si content of the metal produced, and

B, the basicity of the slag.

(4) Approximately 95 per cent of the silicon added in theprocess contributes to the reduction of MoO or istransferred to the produced metal.

Conclusions

(l) It is possible to produce silicomanganese withoutexternal heating by the addition of ferro silicon and/orsilicon metal to molten ferromanganese slag, andvigorous stirring by means of gas injection.

(2) The silicomanganese produced in this way can have aphosphorus content of 0,02 per cent or less and acarbon content of 0,1 per cent or less, provided thatsuitable grades of ferrosilicon and/or silicon metal andsuitable production conditions are used.

(3) There is a correlation between the manganese contentof tbe generated slag, the silicon content of the metalproduced, and the basicity of the slag generated. Theregression formula for this correlation is

castable has been reduced to half its initial value when thelance was first put into operation, it is considered to havereached the limits of usability, and repair work is carriedout. A lance can be used for approximately 12 heats, andthe average amount of material lost per heat isapproximately 25 kg.

5.9%RolOIATION

20.3%7.1 ~

ArACTIOHSLAC ronH,l,TIOII

~-7

&5.696

S(h'SlBU: HEAT or SLAG

•.0 96MtTAL RlRHATION68.6 51>

SEHSI91r II[AT or SLAG

IN

0.5% I \4.9 ~SOI5I81.[ lOT Of GAS SfJjSlBIL lI£,lT Of H[TAL

13,2 ~LATENT I/£,lT 01" RAW MAlLlllALS

THE PRODUCTION OF SPEClAL SiMn USING THE GAS AND POWDER INJECTION PROCESS 143