Oxidation Behavior of Silicon, Phosphorus and Vanadium in

Carbon-saturated Iron Melt with Sodium Carbonate*

By Ryo INOUE** and Hideaki SUITO**

Synopsis When Na2C03 was reacted with a solid Fe--54%V alloy at 1100°C,

the following equation was derived for the oxidation reaction of vanadium with soda ash.

Na2C03+4/5V = Na20+2/5V205+C The oxidation behavior of phosphorus, vanadium and silicon in carbon-saturated iron melt have been studied by use of soda flux (Na2C03, Nat. C03 Fe203) at 1 300 °C. The oxidation of phosphorus and vanadium were initially retarded if a small amount of the flux was added by in-stallments and the reversions of phosphorus and vanadium occurred after the final flux addition. In comparison with the results obtained in the addition of soda flux by a lump, the retardation of the initial oxidation is explained by the fact that the reversion rates of phosphorus and vanadium are considerably, fast. The effect of Fe203 addition to the flux was found to be significant in both the lump and installment additions. The extensive removal of vanadium was observed by the addition of Fe203 in the install-ments, while neither the dephosphorization reaction nor the vanadium reversion takes place. The same oxidation behavior, found in the Na2C03 Fe203 flux was obtained in the Ca0-CaF2 Fe203 flux.

I. Introduction

In the pretreatment of hot metal with soda ash, the removals of vanadium and nitrogen have been well known to occur in addition to the simultaneous removals of phosphorus and sulfur. Several investi-

gations dealing with the recovery of vanadium from hot metal have been previously published.1--5) In a new steelmaking process proposed in Japan, which is called the soda ash refining process, vanadium is recovered from a treated soda ash slag together with sodium and phosphorus. The behavior of vanadium in both the desiliconization and soda ash refining

processes should be clarified in order to raise the degree of vanadium recovery. The present authors recently have studied the vanadium distribution be-tween MgO-saturated CaO-MgO-FeOx SiO2 slags and liquid iron in the temperature range between 1 550 °C and 1 650 °C,6~ and have discussed the oxida-tion behavior of phosphorus and vanadium in the desiliconization process as compared with the results for the phosphorus distribution. It was found, as a result, that the vanadium distribution ratio (V)/

[V] were about an order of magnitude higher than those for the phosphorus distribution ratios (P)/[P], while the (V)/[V] ratios between the slag and a carbon-saturated iron melt at 1 300 °C were much smaller than those for phosphorus. This article deals with the oxidation behavior of silicon, phosphorus and vanadium in the soda ash refining process. Many studies on the vanadium recovery from vanadium-bearing iron ores or slags

by the oxidation sodic roasting process have been carried out so far. Further, the investigations in which vanadium is recovered by the addition of soda ash or sodium compound directly into molten pig iron together with oxygen blowing and/or iron ore have been made by Eichholz and Oelsen'~ and Vorobev et al.8~ It is explained in the later paper that the reaction product FeO. V2O3 surrounded by the additive containing sodium improves the vana-dium recovery due to the formation of a water-soluble compound, which eliminates the necessity for acid leaching. On the other hand, it is found in the former

paper that vanadium can be recovered through the formation of the water-soluble compound such as 3Na2O V2O5.

Recently, Marukawa et al.9~ and Baokui et a1.'°"1> have reported the results on the recovery of vana-dium in hot metal by the soda ash treatment. Their results, however, are inconsistent with each other with respect to the oxidation sequence ofsilicon, phosphorus and vanadium. That is, silicon, phosphorus and vanadium are simultaneously oxidized in the experi-ment of Baokui et al., whereas in that of Marukawa et al. silicon is first rapidly oxidized, phosphorus secondly and then vanadium starts to be oxidized after the silicon and phosphorus contents fall to the low values. In the present work, to make clear the causes of the retardation of reaction, the oxidation behavior of silicon, phosphorus and vanadium in carbon-saturated iron melts has been investigated at 1 300 °C by use of the Na2CO3, Fe2O3, Na2CO3 Fe2O3 and CaO-CaF2 Fe2O3 fluxes. Besides, the experi-ments on the valency of vanadium in the slags and the reaction of Na2CO3 with vanadium were carried out, since the oxidation state of vanadium in the slaps is of practical importance for the recovery of vanadium as a water-soluble compound from the slags.

II. Experimental

1. Reaction of Na2CO3 with Vanadium

The experimental procedure for the examination of the reaction mechanism between Na2CO3 and vanadium was the same as that described in detail elsewhere.12~ A Fe-2.74%C-2.11 %V alloy (24.7 g) was reacted with pieces of reagent grade Na2CO3

(3.0 g) premelted for 5 min at 1 400 °C in an alumina crucible. The crucible containing the melts was taken out of the furnace. Total V (T.V), V4+, total Fe (T.Fe) and precipitated carbon in the slag, and

*

**

Received July 8, 1982. © 1983 ISIJ Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Katahira, Sendai 980.

(578) Research Article

Transactions 'Sri, Vol. 23, 1983 (579)

V and C in the metal were analyzed. Similarly, Na2CO3 (5.4750g) and the Fe-54.31 %V (1.5261 g) were melted in an alumina crucible for 4.5 min at 1 100 °C. Total Na, C03-, T.V, V4+, T.Fe and precipitated carbon in the slag and V in the unreacted Fe-V alloy were analyzed.

2. Oxidation State of Vanadium

40 g of Na2CO3 was added every 30 sec in an 8 g

portion to the carbon-saturated iron melt (420 g) containing 0.16 % Si, 0.18 % P and 0.09 % V at 1 270 °C. During the experiment, stirring was per-formed by a graphite rod. The metal and the slag were sampled by graphite and silica samplers, re-spectively. Silicon, phosphorus and vanadium in the metal and the ratios of V5~, V4+ and V3+ to T.V were determined as functions of time. The Na2CO3

(40 g)-FeO (20 g) flux was added every 30 sec in a 12 g portion to the carbon-saturated iron melt (0.35 % Si, 0.20 % P and 0.09 % V) in order to study the effects of the iron oxide and initial silicon contents upon the valency of vanadium in the slag.

3. The Oxidation Order of Silicon, Phosphorus and Vana- dium

The experimental apparatus and procedure were the same as those described in the previous paper.l3) In the experiment for the flux of 20 or 40 g, the flux compressed in a cylindrical form was added at a 1 min interval by 4 or 8 g portion, but in the experi-ment for 6 or 12 g, the flux wrapped with a thin sheet of vinyl was added every 30 sec in a 0.6 or 1.2 g portion. Stirring was continued to be performed even after the final flux addition so as to observe the reversions of phosphorus and vanadium. The slag compositions even after the experiments were not determined because of the insufficient amounts of the slaps for the analysis. Details of the methods for the chemical analysis were already described elsewhere.12,13) In the experiment on the reaction between Na2CO3 and vanadium, vanadium in the metal more than 1 % was determined by the iron

(II) ammonium sulfate titration (JIS-G-1221) and that less than 1 % by the N-BPHA extraction ab-sorptiometry (JIS-G-1221). The valency of vana-dium was determined by the potassium permanganate titration14-ls) on the assumption that vanadium in

the slag is present as either V5+ and V4+ or V4+ and V3+. These valenci.es for vanadium were corrected by the iron contents determined by the atomic absorptiometry (JIS-M-8204) on the assumption that the total iron in the slag is present as FeO.

III. Results and Discussion

1. Reaction of Na2CO3 with Vanadium

The chemical compositions of metal and slag before and after the experiment on the reaction of Na2CO3 with the Fe-C-V alloy are given in Table 1. The carbon content (2.74 %) in the initial Fe-C-V alloy increases to 3.15 % after the experiment, while the initial vanadium content (2.11 %) decreases to 0.276 %. Vanadium in the slag was analyzed to be present as almost V205. The following reaction between Nat CO3 and vanadium can be derived from the experi-mental findings described above on the assumption that no CO gas is evolved except for the reaction of Na2CO3 with carbon during the experiment.

Na2CO3+4f5V = Na20+2J5V205+C ......(1)

The above reaction is of the same type previously found in the reaction of Na2C03 with phosphorus. The increment of carbon given in Table 1 was found to be in disagreement with that predicted from the above reaction. This may account for the reduc-tion of Na2CO3 and/or that of V205. In the subsequent experiment, Na2CO3 (5.4750 g)

was reacted with the Fe-54.31%V alloy (1.5261 g) at 1 100 °C for 4.5 min. The results are summarized in Table 2, indicating the slag and metal compositions before and after the experiment. The numbers of moles of the reactants and the products for the reac-tion given by Eq. (1) were calculated from the results

Table 1. Reaction of Na2C03 with Fe-2.74%C-2.11

%V melt in an A1203 crucible. (In argon at 1 400 °C after 5 min)

Table 2. Reaction of Na2C03 with Fe-54%V alloy in an A120, crucible. (In argon at 1 100°C after 4.5 min)

(580) Transactions ISIJ, Vol. 23, 1983

given in Table 2. The results are also included in Table 2, where powder in Table 2 denotes the residue after dissolving the slags. One may see that the stoichometric numbers for the reactants and the prod-ucts involved in the reaction are in an excellent agreement with those calculated from the experi-mental data. These experimental findings indicate that the reaction of Na2C03 with vanadium can be expressed by Eq. (1).

2. Oxidation State of Vanadium 40 g of Na2CO3 was added to the carbon-saturated iron melt (0.16 % Si, 0.18 % P and 0.09 % V) at 1 270 °C in an 8 g portion. The results are shown in Fig. 1 in which silicon, phosphorus and vanadium are continuously oxidized with time even after the final flux addition. As is shown in Fig. 1 the ratios of V4+/(V5++V4+) and V3+/(V4++V3+) increase with time. It means that V205 produced by Eq. (1) is

gradually reduced by carbon and/or silicon, even when C03- is present in the slags. The scales of V3+, V4+ and V5+ on the axis of ordinates in Figs. 1 and 2 denote the ratio V3+/(V4++V3+)=1~ V4+/(V5++V4+) =1 and 0, respectively. As previously described, V5+ is desirable in the slag for the purpose of the recov-ery as a water-soluble compound. The Na2C03 (40 g)-Fe0 (20 g) flux was added to the carbon-saturated iron melt (0.35 % Si, 0.20 % P and 0.09 % V) so as to keep V5+ in the slag as much as possible. The results are illustrated in Fig. 2, where the silicon, phosphorus and vanadium contents in the metal as well as the vanadium content and the variation of vanadium valency in slag are plotted as functions of time. The reason why Fe0 is added as an iron oxide instead of Fe203 is simply due to the difficulties in the chemical analysis of vanadium valency in the presence of Fe2+ and Fe3+ ions. Silicon was first oxidized and then phosphorus, while the oxidation of vanadium was suppressed until the con-tents of silicon and phosphorus decrease below 0.03 %. Such a retardation of the reaction has been noted in the oxidation of hot metal in a BOF converter. The retardation shown in Fig. 2 occurs because a high silicon content lowers the oxygen potential at the slag/metal interface to such an extent that vanadium is not oxidized. The retardation tends to occur when the flux is added by installments and the initial silicon content is high. The reason will be discussed later. It is clear that the addition of Fe0 makes the vana-dium almost V5+ in the slag until the final flux addi-tion. The retardation of reaction is greatly related to the amount of the flux, the methods of addition in a lump or installments as well as the initial concen-trations of the elements such as silicon etc. This will be discussed in detail in the following section.

3. The Oxidation Order of Silicon, Phosphorus and Vanadium 1 . Initial Contents of Phosphorus and Vanadium and the

Amount of Fluxes The flux (Na2C03 (20 g), Fe203 (20 g) or Na2C03

(20 g)-Fe203 (20 g)) was added every 1 min by five

installments at 1 300 °C to the carbon-saturated iron melt (420 g) containing phosphorus (0.1 or 0.2 %) or vanadium (0.1 or 0.2 %) or the both (0.1 % P and 0.1 % V) with 0.03 % Si. The results are shown in Figs. 3 to 5. As shown in Fig. 3 indicating the result for the Na2C03 flux, there is little or no difference in the dephosphorization rate between the experiments with 0.1 % P and 0.2 % P. There is also little or no difference in the oxidation rate of vanadium be-tween the experiments with 0.1 % V and 0.2 % V, whereas in the experiment with 0.1 % P and 0.1 % V, the initial rate of vanadium oxidation is retarded.

Fig. 1. Variations of Si, P and V in metal, and the content

and valency of V in slag with time for Na2CO3 flux.

Fig. 2. Variations of Si, P and V in metal, and the content

and valency of V in slag with time for Na2CO3

FeO flux-Effects of FeO addition and initial

content of Si.

Transactions Is", Vol. 23, 1983 (581)

The reversion rate of vanadium to the metal is much

greater than those of phosphorus. Moreover vana-dium appears not to return to the initial value and tends to reach a plateau. This may be explained as follows : the slag becomes solidified to some extent and the poorer physical contact to the metal by the reduction of the slags with carbon. In this work the amount of the slag was too small because of the low initial silicon and phosphorus contents. Thus, the phase diagrams on vanadium oxides were used for the consideration of the physical properties of the slags.

It is seen that the degree of the vanadium reversion in the case of 0.1 % P and 0.1 % V is greater than the other two. This seems to indicate that the Na2O content in the slag increases with increase in the P2O5 content and the slag remains in the molten state. The rate of the phosphorus reversion starts after the rate of the vanadium reversion becomes slower, but the former is slower than the latter. No marked retardation of the reactions was observed in the above experiment, because of the excess addition of the flux (20 g) although the behavior of phosphorus and vanadium were slightly different and depended on the initial concentration in the metal. Figure 4 indicates the results of the Na2CO3 (20 g)-Fe2O3 (20 g) flux. The oxidation rates of phospho-rus and vanadium increase by the Fe2O3 addition

(20 g) to the Na2CO3 flux. Furthermore, the retarda-tion of the vanadium oxidation was not initially observed and the reversions of phosphorus and vana-dium were suppressed to considerable extents by the Fe2O3 addition. The reason why the phosphorus reversion is suppressed is considered to be due to the

phosphorus evaporationl3~ as well as the increase in the oxygen potential at the slag/metal interface with

the addition of Fe2O3. The formation of a com-

pound with the high melting point, FeO • V2O3 (1 750 °C),1?) appears to suppress the reversion of vanadium. 20 to 30 % of phosphorus is oxidized by the addi-tion Fe2O3 (20 g) in the case of 0. 1 % P or 0.2 % P as shown in Fig. 5. The dephosphorization con-tinues even after the final flux addition and thereafter

Fig. 3. Variations of P and

installments addition

initial content.

V in

of

metal with time by

Na2C03 flux-Effect

the

ofFig. 4. Variations of P and V in

installments addition of

Effect of initial content.

metal with time

Na2C03 Fe203

by the

flux-

Fig. 5. Variations of P and V

installments addition

initial content.

in

of

metal with time by

Fe203 flux-Effect

the

of

(582) Transactions ISIJ, Vol. 23, 1983

phosphorus returns to the initial value. It is of interest to note that the removal of phosphorus occurs by Fe203 only without help of any basic oxides. The degree of vanadium oxidation by Fe203 addition is almost the same as that by the Na2CO3 or Na2C03 Fe203 flux, but the rate of the vanadium reversion is so sluggish because of the formation of a high melting

point compound (Fe0.V203). It was found from the above experimental evidence that the amount of the flux should be much less than the ones added in these experiments in order to investigate noticeable

phenomena of the suppression for the vanadium and phosphorus oxidations.

Thus, the following experiment was carried out to know how much the flux is required in the installments so that the retardation would appear in the carbon-saturated iron melt containing silicon, phosphorus and vanadium. The results are shown in Fig. 6, where the Na2CO3 flux has been added every 30 sec in a 0.2 g portion to the carbon-saturated iron melts containing i) 0.1 % Si (Fig 6 (a)), ii) 0.05 % Si and 0.1 % P (Fig. 6 (b)), and iii) 0.04 % Si and 0.1 % V (Fig. 6 (c)). It can be seen that the desiliconization reaction proceeds, but no removals of phosphorus and vanadium occur. When Fe203 (2 g) was added by ten installments, both silicon and vanadium were oxidized as shown in Fig. 6 (d). 2. Na2C03, Fe203 and Na2C03 Fe203 Fluxes

The flux (Na2CO3 (6 g), Fe203 (6 g) or Na2CO3

(6 g)-Fe203 (6 g)) was added every 30 sec in a 0.6 or 1.2 g portion to the carbon-saturated iron melt (420 g) containing 0.1 % Si, 0.1 % P and 0.1 % V. The results are shown in Fig. 7. The decreasing order of the oxidation of silicon, phosphorus and vanadium in the experiment of the Na2CO3 or Nat

C03 Fe203 flux is as follows: Si>>P>V. As would be expected, the suppression of the oxidation reactions for phosphorus and vanadium was observed in such an amount of the flux added. Besides, both phos-

phorus and vanadium return to their initial content, and no evaporation of phosphorus occurs in the in-stallment addition. The decreasing order of the oxidation may be explained by the magnitude of the free energy change for the reactions between Na2CO3 and silicon, phosphorus or vanadium. On the other hand, however, if the oxidation rates of phosphorus and vanadium are same, the order of the oxidation may be explained by the differences in the rates of the reversions of phosphorus and vanadium; that is, the rate of the reversion of vanadium is much greater than that of phosphorus as shown in Fig. 3. The reasons for the difference are not clarified experi-mentally at present, but the present authors presume that they are attributed to the differences in the free-energy changes of the reactions as well as the fluidity of the slags which affects the rates of the reversions markedly.

It can be seen in the case of a carbon-saturated iron melt without silicon in Fig. 3 that the reversions of

phosphorus and vanadium occurs by the carbon reduction. But, as indicated in Fig. 7 their reversion is mainly ascribed to the silicon reduction, since silicon is continuously oxidized even after the final flux addition and the calculated amount of silicon oxidation after the addition is nearly equal to the sum of the calculated amounts of the phosphorus and vanadium reversions on the assumption that

phosphorus and vanadium pentoxide are reduced by silicon:

P205+5/2Si = 2P+5/2SiO2 and

V205+5/2Si = 2V+5/2SiO2.

No dephosphorization reaction occurs in the ex-

Fig. 6. Variations of Si, P and V in metal with time by the installments addition of Na2C03 (a N c) or Fe203 (d) flux--Effect of flux weight.

Fig. 7. Variations of Si, P and

installments addition of

Fe203 flux.

V in metal with

Na2C03, Fe203

time by the

or Na2C03

Transactions ISIJ, Vol. 23, 1983 (583)

periment with Fe203 (6 g) which was added by ten installments, while it does in the case of the large flux addition (20 g) as shown in Fig. 5. In the ex-

periment with Fe203 the oxidation rate of vanadium is found to be considerably high and no reversion of vanadium takes places at all. From thermodynamic

point of view, Fe0•V203 the oxidation product for vanadium can be reduced by carbon and/or silicon. Actually, however, no reversion of vanadium occurred to any appreciable extent despite the process in which the melt was stirred by a graphite rod. This indicates that the extremely increasing viscosity of the slag due to the partial solidification is very much preferable to the prevention of vanadium reversion. No silicon is oxidized after the end of the flux addition because vanadium does not return at all. This observation is different from that found in Na2CO3 or Na2C03 Fe203 flux.

After the experiment for Fe203 (15.5 min), 6 g of Na2CO3 was added every 30 sec by a 0.6 g portion into the residual slag. As a result, phosphorus is oxidized and after the end of the flux addition returns to be the initial value, whereas the vanadium reversion occurs even during the flux addition. These findings can be explained by the kinetic considerations, that is, the oxidation product for vanadium FeO • V203 becomes molten by the addition of Na2CO3 flux, and the better physical contact between the slag and the metal is resulted in. 3. The Method of Flux Addition It was found that the oxidation behavior of silicon,

phosphorus and vanadium was influenced by the amounts of the fluxes as well as the kinds used such as Na2CO3 and Fe203. The reversions of phospho-rus and vanadium are expected to be suppressed if the flux is added by a lump instead of the installments. Therefore, the Na2CO3 (6 g) or Na2CO3 (6 g)-Fe203

(6 g) flux is added by a lump to a carbon-saturated iron melt. These results are shown in Fig. 8 where the degrees of the oxidation of silicon, phosphorus and vanadium are in the order Si P>V. First vanadium starts to return to the metal and levels off below the initial vanadium content. The phosphorus reversion then starts to occur after vanadium approaches to a plateau. The fact that phosphorus does not return to the initial value is considered due to the phosphorus evaporation.13~ This is different from the results observed by the addition in installments. It was also found in a lump addition that the desiliconization reaction occurs during the reversions of phosphorus and vanadium. Besides, the degrees of the initial oxidation of silicon, phosphorus and vanadium in a lump addition for the Na2C03 Fe203 flux were two times greater than those for the Na2CO3 flux. The results for the lump or installment addition of the Na2CO3 or Na2C03 Fe203 flux are compared in Figs. 9 and 10. The degrees of the initial oxidation of phosphorus and vanadium are much greater in the case of the lump addition, but silicon is oxidized to a higher level in the case of the installments addition. The phosphorus reversion tends to retard initially in the experiment o f the lump addition, whereas it does

not in the case of the installments addition. This

explanation is : In the case of the installments addi-tion, the vanadium reversion is rapidly completed

because of the small degree of vanadium oxidation, but in the case of the lump addition, vanadium reverses slowly because of the large degree of vana-

dium oxidation, and the phosphorus reversion occurs

after the end of vanadium reversion. In the lump addition the phosphorus content does not return to the original value because the phosphorus evaporation

easily occurs.l3~ Similarly, the vanadium one does

not return to the original value in the lump addition

because sodium as well as phosphorus easily evaporates in the addition. As the result of this evaporation, the

difpicultly-fused compound such as FeO • V203 is formed.

The following conclusions can be drawn from the

present results ontained by a lump and installment additions. If the small amount of flux is added in the installments, phosphorus and vanadium are not

apparently oxidized on accounts of the fast rates of

phosphorus and vanadium reversions. Thus, the addition in the lump is more effective than that in

the installments for the improvement in the oxidations of phosphorus and vanadium. In the former case, however, one disadvantage is the excess sodium

evaporation loss due to the reduction of Na2CO3 by

carbon. The high degrees of the oxidations of phos-

phorus and vanadium in the case of the lump addi-tion is explained by the fact that the large contact area between the slag and the metal results in the

high oxygen potential at the interface. This high

oxygen potential suppresses the reversions of phos-

phorus and vanadium. On the contrary, the degrees of the oxidations of phosphorus and vanadium is not

Fig. 8. Variations

the lump

flux.

of Si, P

addition

and V in metal with time by

of Na2C03 or Na2C03 Fe203

(584) Transactions ISIT, Vol. 23, 1983

expected to be high in the installment addition, since the oxygen potential at the slag/metal interface be-comes to the low value determined by C (ac =1)/ CO (Pco=1 atm) or [Si]/(Si02) immediately after the end of the installments addition. The reversions of phosphorus and vanadium can be suppressed by the following methods for the high oxygen potential at the slag/metal interface :

i) the oxygen blowing

ii) the continuous addition of iron oxide iii) the interruption of the stirring after the end

of flux addition. Accordingly, it can be expected that the degrees of the oxidations of phosphorus and vanadium, when the proper amount of flux is added by the installments, become higher than those in the lump addition in which the sodium evaporation loss cannot be neglected. It can be said from the present results that the

retardations of phosphorus and vanadium in Maru-kawa et al.'s9~ experiment may be attributed to the high silicon content and to the installments addition of flux, while no retardation in Baokui's10~ experiment may be due to the lump addition of flux and no silicon content in the metal. 4. Ca0-CaF2-Fe203 Flux Figure 11 shows the comparison between the oxidations of silicon, phosphorus and vanadium by the CaO-CaF2 Fe203 flux and those by the Na2C03 Fe203 flux. Vanadium is hardly oxidized with the lime flux. In the soda flux it is oxidized after the initial suppression, but the content returns finally to the initial value. In both the fluxes, the dephos-phorization reaction occurs to the same degree after the initial retardation. The degree of desiliconiza-tion is almost equal to each other during the period of the flux addition, but the reaction proceeds further along with the reversions of phosphorus and vana-dium after the final flux addition in the soda flux. The extent of the desiliconization in the lime flux is observed to be smaller than that in the soda flux, since the vanadium reversion does not occur in the former flux.

Iv. Summary

The results obtained are summarized in the

following.

Fig. 9. Variations of Si,

the installments

flux.

P

or

and V in

a lump

metal with time by

addition of Na2CO3

Fig. 10. Variations of Si,

the installments

Fe2O3 flux.

P

or

and V

a lump

in metal with time by

addition of Na2C03

Fig. 11. Variations of Si, P and V in metal with time

the installments addition of Ca0-CaF2-Fe203

Na2C03 Fe203 flux.

by

or

Research Article

Transactions Is", Vol. 23, 1983 (585)

(1) The reaction of Na2C03 with vanadium is found to express by

Na2C03+4/5V = Na20+2/5V205+C.

(2) Vanadium should be V5+ in the soda slags for the recovery as a water-soluble compound. But V205 was found to gradually reduce by carbon and or silicon and the valency changed in V5+ --~ V4+ -~ V3+. The reduction rate of the vanadium oxide was reduced by the addition of Fe0 to the flux.

(3) The retardation in the oxidations of phos-phorus and vanadium was observed when the amount of the soda flux was small. In the installments addi-tion the reversions of phosphorus and vanadium pro-ceeded along with the desiliconization reaction after the end of the flux addition. The degree of the initial oxidation by the lump addition was in the order of Si P>V and the phosphorus reversion pro-ceeds along with the desiliconization after the vana-dium reversion approaches to a plateau. The effect of Fe203 flux by the installments addition, the desili-conization reaction occurred to the same extent and the degree of vanadium oxidation was seven times as much as those in the soda flux. In this flux, neither oxidation of phosphorus nor vanadium reversion oc-curred.

(4) In the Ca0-CaF2 Fe203 flux, the oxidations of silicon and phosphorus occurred to the same degree as those in the Na2C03 Fe203 flux, but the oxidation degree of vanadium was found to be less.

Acknowledgements

The support of the Ministry of Education, Science and Culture (Grant-in-Aid for Encouragement of Young Scientist in 1982) for this project is gratefully acknowledged.

REFERENCES

1) H. Zieler : Stahl u. Eisen, 58 (1938), 749. 2) A. Harr: Stahl u. Eisen, 59 (1939), 1145. 3) A. Harr: Stahl u. Eisen, 59 (1939), 1174. 4) H. Zieler : Stahl u. Eisen, 62 (1942), 795. 5) W. Bading: Stahl u. Eisen, 66/67 (1947), 137. 6) R. Inoue and H. Suito: Trans. ISIJ, 22 (1982), 705. 7) W. Eichholz and W. Oelsen: Ger. Pat. 968504, Feb. 27,

1958. 8) Yu. P. Vorobev, N. A. Vatolin, V. G. Vinokurov, P. I.

Volkova, S. V. Mikhailikov and G. I. Chufarov : Dokl. Akad. JVauk SSSR, 183 (1968), April, 885. 9) K. Marukawa, M. Hashio and Y. Shirota: Tetsu-to-Hagane, 67 (1981), S190.

10) N. Baokui : Iron Steel, 16 (1981), Sept., 26. 11) Y. Nakamura, K. Harashima, Y. Fukuda and N. Baokui :

Tetsu-to-Hagane, 67 (1981), S 191. 12) R. Inoue and H. Suito : Trans. ISIJ, 21 (1981), 545. 13) H. Suito, A. Ishizaka, R. Inoue and Y. Takahashi: Trans.

ISIJ, 21 (1981), 156. 14) W. D. Johnston : J. Amer. Ceram. Soc., 48 (1965), 184. 15) G. J. Kakabadse and E. Vassiliou: Phys. Chem. Glasses, 6

(1965), 33. 16) S. Kumar : Phys. Chem. Glasses, 5 (1964), 107. 17) F. Korber and W. Oelsen: Stahl u. Eisen, 60 (1940), 948.