Studies on Properties and Reduction of Manganese Ores*

By Tetsllo Yagihashi**, KaZlio Asada***, Kjjji Atarashiya***, Shlln-ichi Ichinohe* * * and Hiromichi H anada* * *

Synopsis ready, preliminary reduction methods such as the To stuqy th e reducibility oj some manganese ores which are used Jor Elkem processl) and the Strategic-Udy process2) a re in Jerromanganese jJroducl'ion, the allthors investigated the jlrojJerties oj th ese use. Of course, the results of this investigation are ores by X-ray diffraction, differential thermal anarysis and thermal balance useful for these preliminary reduction processes. The anarysis, and the determination oj their mineral cOIll/Josition was disCIIssed. fundamental da ta on the prelimina ry reduction with Then, they studied manganese ore reduction with either CO gas or waste gas from the closed furnace were obtained. CO-C02 gas mixtures by the thermal balance anarysis method, and dis­ cllssed its reducibility in terms oj its mineral com/Josition. II. Tested Ores A great number of manganese minerals are known, I. Introduction and there are great differences in the properties of In the production of high carbon f, rromanganese, manganese ore deposits.3)-5) The properties of ore the properties of manganese ore have a n effect upon the deposits exert an inAuence on the mineral crystalliza ­ operative results. But, very little study has been made tion a nd the admixture of ores. R eally, manganese in connection with reduction reaction, because m an­ ores used for industry are generally complicated mix­ ganese ores have very complicated mineralogical com­ tures of various minerals. Importa nt minerals in pOSitIOns. Previous investigations of manganese ores ferromanganese production are m a nganese oxid e, have dealt almost exclusively with mineralogy. In h ydrated manganese oxide, manganese carbonate and order to determine how properties of manganese ores manganese silicate. Generaily, m anganese carbona te affect their reducibility, this investigation was carried ore is burnt and the burnt ore is supplied. out. Chemical compositions of tested m a nganese ores are Accompanying enlargement and closed opera tion shown in Table 1. Among these ores, Yakumo (A), of high carbon ferromanganese furnaces, the pre­ specia l Oe, common Oe, Jokoku (B) and J okoku (C) liminary treatment of ores has become serious. AI- are burnt ores and others are unburnt. All ores were

Table 1. Chemical analyses of manganese ores (Unit : wt%)

Mn MnO, SiO, F e AI,O, eao p

India n (H .G.) 47.87 59.68 8.36 1. 63 0.10 0.236 - ~---I- -- -- Indian (L.G.) 39.12 51.20 7.95 11.02 4.26 1. 02 0.1 31

South African (H .G.) 45.36 65.97 4.67 8.85 0.43 0.72 0.017 -1--- South African (L.G .) 41.47 59.94 6.28 10.41 3.98 0. 10 0. 135 ---- -I Brazilian 52.95 78.55 1.02 4.24 2.67 0.10 0. 105 ---- Ghanaian 49 .48 71. 56 8.88 3.00 3.05 0.10 0. 119

lndonesian 48.11 70.60 7.24 3.84 1. 88 1.34 0.093 ----- Australian 53.54 2 .75 I. 78 0.49 0.1 0 0.028 ------Yakumo (A) 14.84 3.61 1. 00 3.06 0.012

Oe (s pecial) 48.45 8.53 11 .98 0.61 1.85 0.029 --- -- O e (common) 21.98 10 12 0.66 0.94 0.015 1_ . _ 1 J okoku (0 ) 7.65 10 .98 I 0.43 - - - Jokoku (C) 14.81 1.59 -I I__ l~ 19 .80 5.93 2.79 I 63.00 7.48 I 5.48 4.87 Oshima 28.53 25.95 9.90 I 10.12 1. 24 7.58 Shibetsu 45.05 27.61 12.67 1.72 2. 19 2.85 I 0.065 ------_I * Lecture delivered before the 64th Grand Lecture Meeting of The Iron & Steel Institute of Japan in October 1962 in Hiro­ shima. J apanese text was printed in T etsu-to-Hagane (Journal, Iron & Steel Institute, J apan), 49 (1963), 7, 971 - 975; 8, 1059- 1065. ** Dr. Sci., ational R esearch Institute for M etals. *** N ippon Denko Co., Ltd.

Research Articles ( 12) Tetsu-to-Hagane O verseas Vol. 4 No.1 Mar. 1964

crushed finely under 200 mesh, and mixing of impuri­ H, SO. P, O, F low- meter Flow- meter ties was rigorously prevented. Guaranteed reagents, Mn02 and IVlnC0 were used for standard samples. nSample 3 holder

III. Exp erimental Apparatus and Procedure 1. Determination of Mineral Compositions furnace For the purpose of determining the mineral com­ positions, X-ray diffraction, differential thermal analy­ sis and thermal balance analysis were carried out. o ~tl ~ t L- X -ray diffraction apparatus is the oreleo X-ray

diffractometer. The FeKap lines excited at 35 kV and Or sat 6 rnA were used without filters. The appa ratus for gas anal yser

differential thermal analysis is the Shimadzu type CO, -bombe Thermal balance DT-I A. The tested ore was inserted in aPt-capsule. Fig. 1. Apparatus used for manganese ore reduction The a-A1 20 3 powder was used as a standard sample. The thermal balance is the Oyorika type ORK. with CO gas or CO-C02 gas mixtures Differential thermal analysis and thermal balance ed to a solenoid circuit to produce a variation of con­ analysis are very useful methods for the amorphous trary direction equal to the weight change.

phase where X-ray diffraction is not used. CO2 gas in the bombe was obtained commercially. Transformations of manganese ore observed in the It was generated through granular graphite heated at

air are as follows. Under 400°C departure of adsorbed 1,000°C. CO2 gas was dehydrated and dried through gas, adsorbed water and water of crystallization is H 2S04 and P 20 5, and one part was introduced into observed and the decomposition of manganite (MnO· the gas holder in that condition. The other part was OH) occurs. Next from 500°C to 700°C deoxidation is introduced into the gas holder through the CO gen­ observed. erator and gas washers in which residual CO2 gas 4Mn02 =21n20 a+ 0 2-39.4kcal ...... (1) was removed by soda lime, and CO gas was dried by L1Go= 38,880-50.40 T silica gel and P20 5 • As only CO gas was required, At about 1,000°C, gas flowed through the bypass of the CO-generator side. Mixing ratio of CO and CO gas was deter­ 6Mn203= 4Mn304+ 02- 49.9 kcal ...... (2) 2 mined by the flow volume of each side. While com­ L1Go= 49,440 - 31.60 T position of the gas was analysed by an Orsat gas such a reaction is observed. By the characteristic analyser, gas was introduced into the thermal balance changes of these reactions, mineral compositions are reaction tube. Experimental procedure was as fol­ determined. In air, deoxidation is stopped till haus­ lows. In the quartz sample holder, 500 mg of tested mannite (Mn30 4), and reaction (3) is no longer ore was weighed and inserted into the thermal balance observed under 1,000°C. reaction tube. 'While CO gas or CO-C02 gas mix­ 8 2Mn30 4 = 6MnO + 0 2- 11O.5 kcal...... (3) tures flowed at the rate of 50 cm per min., the air was L1Go= 109,920- 62.56 T expelled and the furnace temperature was raised at a Thermodynamical data of these deoxidations were rate of 5°C per min. The mechanism of reaction was quoted from J. P. Coughlin's table6}. The heat of discussed from the weight change of the samples. The reaction at 25°C is shown because its temperature samples obtained from intermediate states of reaction dependence is slight. It is shown that all reactions are were subjected to X-ray diffraction. X-ray di ffrac­ endothermic. In these reactions, the thermal change tion a pparatus is the Rigakudenki Geigerflex X-ray was detected by differential thermal analysis, and the diffractometer and FeKap and CuKa lines were weight change was detected by thermal balance used. analysis. Concerning manganese oxide reduction with CO gas, the discussion of the thermodynamics is as follows, 6 2. Manganese Ore Reduction with CO Gas or CO- C02 the data quoted from J. P. Coughlin's table ) being Gas Mixtures used. I. It The reduction apparatus is shown in Fig. is 2Mn02+ CO = Mn20 a+C02+ 47.9 kcal ... (4) a combination of thermal balance with a gas generator. L1Go= -48,060- 4.49T The principle of thermal balance is the zero method in 3Mn20a+ CO = 2Mna04+ C02+ 42.8 kcal which weight change is transformed into electric dis­ ...... (5) placement and is amplified selectively and then return- L1Go= -42,780+4.91 T

Research Articles Te tsu-to-Hagane O verseas Vol. 4 No. 1 Mar. 1964 ( 13 J

Mn30 4 +CO= 3MnO+C02 + 12 .4 kcal ... (6) It seems that the reduction to manganosite is very easy,

LlGo= - 12,540-10.57T because the composition of the gas is very rich in CO2

MnO+ CO = Mn+C0 2 - 24.4kcal ...... (7) at equilibrium. Therefore reactions (4) and (5) are LlGo= 24,480+ 3.23 T more feasible than reaction (6), because CO2 gas at Namely, reactions (4), (5) and (6) occur under 1,000°C, equilibrium increases more and more. Many other but reaction (7) does not occur. Regarding reaction reactions will be described later. (6) which produces final reduced manganosite (M nO ), the chemical equilibrium was discussed. Concerning IV. Exp erimental Results and Discussions this, studies by H. Ulich et alius were established7 ). The results of X-ray diffraction are described in the It is as follows at 1,000°C, the data described above first place. In the manganese oxide ores, the chief ore being used. is manganese dioxide ore with various phases such as

LlGo= -RT InK = - RT In(Pco,/pco) = 26,000 cryptomelane (cr-Mn02), pyrolusite (j3-Mn02) , r­

log K = log (Pco,/Pco) = 4.460 Mn02' birnessite (a-Mn02) and ramsdellite. With­ Pco,/Pco= 2.88 X 104 out cr- and j3- phases, manganese dioxide ores are generally incomplete crystals. So, it is difficult to (I I. 0 Indi an G.) :r..:r.. :r: recognize these phases . In the X -ray diffraction, 00" 00 0 strong peaks of cr-, (3- and a-phases overlap. There­ ;2U1~ ~~~ ~ . "",.,- "CO III ~- - - CO"'" lS fore determination by weak peaks is also significant . "! ! I - ,~~I ~ ! I I Indi an (L. G. ) The results of X-ray diffraction are given in Figs. 2 :5 CQ9 §~ and 3. The manganese dioxide group and the ] <;1 <;1 " ~ ~ ~:§ manganese silicate group are shown in Fig. 2, and the ::2",,, ~.G CO t.o ! ~ I~1 CO I 11 "'"I I IIF f I ! I I Sou th Ar,"ican (H. G. ) ."~ CO Yakumo (A) ~ ~~ ~ o::! c::! '"c· ~c ~ .- "0:) I Ii II I ill II 0 0 South African c (L.G.) :E ~ c$. c$. 0 I If) ,,If) cccnc JJ ee Oe (special ) "I "I ! I I I ! ! 11 " "I " 0 0 Brazil ian ,; c ~ :::: "'" I "," " "'- "'-"'-" IJ II I ~I I "! I II Oe (common ) 0 c 0 c Ghana ian :::: :;:: 0 ,; c$. iii If)>-- >-- >-- >-- !I I~ "'- Jokoku (8 ) 0 0 0 Indones ian :r: 0 c c 00 c :;:: .-<. :5 0 c c ~ .-<.-<. ,; c$. <;1",- "'- <;1 If) :;:: "'- :;:: ~~I "'- IJ D ! ! II ! I I '" I Jokok u (C) 0 0" 0 Australian ~ :E :E :<: ,; '0 " C!l " T,C I " " " " " " D Jokoku (unburnt) 0 u Kokko ~ :E ." ::2 ~ ! ! I ! " I U " " " " " Oshima CO 0 "U S hihetsu <5 os:: 00 0 0 ~ OUO U ~ U CO CO ." 0 ~~ ",- ",- CO U);E cnU [co U o:)~ CO CO CO :£'" iii CO :E:Eo::I '0 coco I I I I I ! ! ! ! ! ! I III I I I II I I '" I D D D

0 10 20 30 40 50 60 70 80 90 100 o 10 20 30 40 50 60 70 80 90 100 20' (Fe Ka ,p ) 28 ' ( Fe Ka.(3) Fig. 2. X-ray analyses of some manganese ores Fig. 3. X-ray analyses of some manganese ores

Research Articles [ 14 J Tetsu-to-Hagane Overseas Vol. 4 No.1 Mar. 1964

manganese carbonate group a nd its burnt ore are sam e bixbyite (a-Mn 20 a) after deoxida tion reaction shown in Fig. 3. As standard X-ray diffraction data ( I ). R eaction (2) with O shima ore occurred a t a of manganese minerals, ASTM X -ray powder data lower temperature. This is a unique phenomenon

were used. But for r-Mn02 , the data quoted by for rhodochrosite (MnCOa). Calcite (CaCOa) also W. F. Cole et a lii 8) were used , and about birnessite, existed , so decomposition of calcite occurred simul­ the clata quoted by Y. H a riya3 ) were employed. In ta neously. Because semicrystalline or amorphous bix­ fi gures, a, (3, rand (j are each manganese dioxide byite or manganese dioxide is produced when rhodo­

phases, B signifies braunite (3Mn20 3 • r,1nSi03) . chrosite is decomposed, afterwards deoxida tion occurs Sharp peaks were shown by the symbol S, and diffused easily. Yakumo (A) a nd J okoku (B) consisted chiefly peaks were shown by the symbol D or V. D. R elying of lower ox ide, so reaction ( I) was not observed . on these data the crystallization of ores was discussed. I The results of differential thermal a na lysis a re Oe (special) given in Fig. 4. With high grade Indian, low gra de Indian and Indonesian ores, decomposition of m a nga­ o~~==----~=------~------~----~ nite clearly appeared. It is shown that for each manganese dioxide, reaction ( I ) occurred at a gradual­ ly hi gher temperature in the order of 0-, r-, (3 - and 5 a-phases. The existing volumes of each of the phases were inferred from calorimetry. R eaction (2) occur­ red a t about I,OOO °C, and there was no appreciable 10 1------I----~ __ -=~,;;::~,y.~lndian (H. C.) difference in the reaction temperature in the ores. ~....,...... " Indian (L. C. ) Shibets'u This phenomenon seems to show that each character­ Brazi li an istic manganese dioxide phase was transformed to the 15 Kokko

o ~~----.------.------.---.

'$.

..c 5 .S' South " African " (H.G. ) '0 '" 10 6 '"0 .J Indonesian Afriran Ghanai,an c: (1..(;. ) South African .g 15 I(H.C.) <) "~ Indollt'sian Y-MnO, <) § ..:" 20 <5 (;hanaian -0 c: W l~ra 1. 11Ian 25

30~------4t------r------+---~

35

MnCO, 40~----~----~----~----~----~----~--~ o 200 400 600 800 1000 1200 o 200 400 600 800 1000 1200 Temperature ('C ) Tem:>e r.ture ('t; ) Fig. 4. Differentiah.thermakanalysis curves ·of some F ig. 5. Thermal balance curves of som e m anganese manganese ores in air ores in air

Research Articles Tetsu·to-Hagane O verseas Vol. 4 N o.1 Mar. 1 964 C 15 )

Shibetsu ore was braunite, so the endothermic volume by the symbols ttt , H , +, tr. and ? reaction was not observed. Foreign ores were mixtures of some mineral phases, The results of thermal balance analysis are shown but there was single-mineral ore like Ghanaian ore. in Fig. 5. Weight loss of Ghanaian ore was quite Domestic ores a re mostly m a nganese carbonate ores simila r to tha t of the standard reagent (r-Mn02), so or silicate ores, and the minera l compositions of burnt evidently Ghanaian ore was r -MnO ~ . For Indonesian ores represented variations in the burning temperature ore, the result of thermal balance a nalysis was similar and atmosphere. Namely, the ore which has a to tha t of differential thermal analysis. Reaction residual carbona te was burnt at the lowes t temperature, (l) occurred at a higher temperature than with r­ and with the increase in burning temperature, mineral Mn02, but cl ear deoxida tion was observed. So this compositions consisted chiefly of lower oxide. When ore was pyrolusite. As high grade South Ali'ican ore m anganese carbonate was burnt a t a temperature above was cryptomelane, reacti on (I) was not observed 1,OOO °C in the oxidized atmosphere, the mineral clearly a nd reaction (2 ) occurred. Brazilian ore was composition transformed to hausmannite. The burn­ pyrolusi te, so it was simila r to Indonesian ore. And ing atmosphere of special O e ore must be reduced or Kokko was cryptomelane, so it was similar to high inert atmosphere because manganosite exists in this grade South Africa n ore. The reaction of Indonesia n ore. ore was not observed evidently, and mixtures of some Furthermore, the characteristic properties of all mineral phases in this ore were observed. As special ores were described. The crys tallization of high O e increased in weight by heating, m a nganosite ex­ grade Indian ore was unsatisfactory. For low grade isted . The reaction of Shibetsu ore was characteris­ Indian are, crystallization was worse and several phases tically untidy, so this ore was braunite. were observed. High grad e South African ore con­ From the results d escribed above, mineral com­ sisted chiefl y of cryptomelane but low grad e South positions of some m a nga nese ores are shown in Table African ore had no characteristi c properties. In­ 2. Quantitative studies on such mineral composi­ donesian ore and Brazilia n ore were single p yrolusite tions were not described at this time, but the existing but considerable amorphous phases were observed. volume of minerals was described in the order of Crystallization of Australian ore was also unsatisfactory.

Table 2. Mineral compositions of manganese ores

- -I -- IH ydrated - - - a -MnO, fi-MnO, r-MnO, ()· MnO, MnO·OH Mn- M3MnS'OO" a -Mn,O, MnO MnCO, SiO, CaCO, I oxide ni l

Indian (H .C.) -++ -++ tr. -++ +

Indian (L.C.) + -++ + + -++ tr. -++ 1- ---1------·1-- South African (H.C.) -++ + + --1-1- South African (L .C.) + +

Brazilian + + + * + Ghanaian + ------1----1------1------Indonesian + + -++ +

Australian + + +

Yakumo (A) - --I tr. -++ + -++

O e (s pecial) 1- -++ + Oe (common) -1----:;- + -++ J okoku (B ) --1---1---++ + J okoku (C) -++ -++ ------1----1-- --1-- --1------1---1---1--- 11--- 1------Jokoku (un burnt) -++ ------1---- 1---1---1------I----i------1----1------Kokko + + tr. ------1- - - - 1----1---- 1------1---+- --1-- --1------Oshima -++ + tr. -++ + + ------1------1·---·1------Shibetsu tr. ------1-- *--1-- --11----1------1-- MnOz reagent

Research Articles ( 16 ) Tetsu-to-Hagane Overseas Vol. 4 No. 1 Mar. 1964

Characteristic ore in the domestic ore was O shima of CO-C02 mixed gas reduction are shown in Fig. 7.

ore. It had manganese carbonate and calcite. The composition of CO-C02 gas mixture was 65 %

Then, sili ca (Si02) in some manganese ores was CO gas and 35 % CO2 gas. This composition re­ discussed. Silica which took the form of a-quartz or sembles the waste gas from closed furnaces in the pro­ gangue and the form of manganese silicate is shown duction of ferromanganese.

in Table 2. There was no rhodonite (MnSi03) in O ~~~~~~~------,------,--~ manganese silicate ores. As the silica content of special O e ore and K okko ore was comparatively high by chemical analysis, the si li ca form was un­ - -+--- Oe (special) known. The ore in which the silica content was I especially low was Brazilian ore. - t----- Yakumo (A) Although the iron content of many ores was con­ siderably high, the iron form was not determined by 10 I----\___~ X-ray diffraction, differential thermal analysis and Jokoku (B) thermal balance analysis . This difficulty of form I analysis is due to the existence of substitutional ore 15 -,.<=-__ Jokoku (C) Indian (H. G. ) between manganese and iron, and mixed crystal like I MnC0 -FeC0 in carbonate ores. South African 3 3 I (L. G. ) Then, manganese ore reduction with CO gas or 20 ---'1------=-+====:South African (H. G. ) CO-C02 gas mixtures was described. The results of CO gas reduction are shown in Fig. 6, and the results

~ O ~~~~~------~------r---I -& '0; I ~ Indian (I-I. G. ) '0 VI VI 5 0 I ...I I Oe (special) Indian (L . G. ) L 10
o 1------\ ------=---- Brazillian

Oe (com mon ) 15 IS Jokoku (8) Indian (!-- . G. ) L-______-L ______L- ______-L __ ~ Ghanaian Australian I 20 Indones ian I ..J.---- South Af"iean Y- MnO, (L. G. ) 25 Os hima I I :::o ...I South Af"iean ---l------:-lndonesia1n (H. G. ) Os hima -,---- 30 Ghan r n

Australian 35 Jokoku (C )

40 1------+--r------+------+--__~

------1----- MnCOJ ~--- Y-MnO,

25 45 200 400 600 800 1000 1200 0~-~20~0~-4~0~0--~60~0~--~80~0--I~OLOO~-1~2LOO--~ Tem perature CC) Temper:.:ture ("C ) F ig. 6. Thermal balance curves of some manganese Fig. 7. Thermal balance curves of some manganese ores

ores in CO gas in CO-C02 gas mixtures (CO ca. 65 %)

Research Articles Tetsu-to-Hagane Overseas Vol. 4 No. 1 Mar. 1964 ( 17)

No change with variations of gas composltlOn was shown in Fig. 6, there is an overlap in the reduction observed except for carbon deposition. The increase curve and the carbon deposition curve. of weight shown in Fig. 6 was by carbon deposition After the final products were cooled in a CO gas and this phenomenon will be discussed later. flow, X-ray diffraction of the products was carried out. Manganese ores were classified into three groups Of all the ores only manganosite was observed by X-ray by reducibility. The first group was manganese di­ diffraction. Concerning admixtures, silica was ob­ oxide ores, in which a considerable weight loss was served in certain ores, but existing forms of other observed at 150 ° C~200 ° C, and a greater part of the components were not clear by X-ray diffraction. ore transformed to hausmannite at 270 ° C~300 ° C, There is scarcely any difference in reducibility with and manganosite was produced at 400 ° C~500 ° C. CO gas among all manganese dioxide phases, i.e., cr-, Bixbyite was not observed clearly. The second group (3 -, r- and v-phase. Only Ghanaian ore was most was burnt ore of manganese carbonate ores, in which reactive. It is due to the fact that r- and v-phase a sudden weight loss was observed at about 400°C, are incompletely crystalline and are transformed into and a reaction slowly occurred at about 600°C and bixbyite or hausmannite at a comparatively low tem­ manganosite was produced at about BOO°C. The perature through mere thermal decomposition. Re­ third group was braunite, in which the weight loss duction curves of r-Mn02 with CO-C02 gas mixtures gradually occurred from the start at about 120°C to in which the CO content was lower than 65 % , are the reaction's end at about BOO°C. The reduced form shown in Fig. B. When CO content was 10 % , re­ of the manganese compound was also manganosite. duction occurred with a slight difference. It was Reduction curves of the Oshima ore were peculiar, supported by the thermodynamical data described but the explanation of this phenomenon is as follows. above. Concerning manganese dioxide, reduction After manganese carbonate decomposed, reduction of to manganosite was complete at about 450°C. But, manganese oxide started and furthermore calcite de­ under low temperature reduction, the manganosite composed at about BOO °C. Concerning the curves was unstable in air aftcr cooling in a CO gas o flow, and caught fire immediately on a drug paper. Then, r-Mn02 reduction with CO gas at varying temperatures was carried out, and an investigation was made on the obtained manganosite. Manganese dioxide was reduced at 500°C, 600°C --i:r-- co 100 °;, 5 .-..- and 700°C respectively. Subsequently reoxidation CO 65 "" in air was carried out after quenching in the CO gas --0---- CO 30 "" flow. The appearance of these reactions is shown - x - CO 10 "" in Fig. 9. Considerable reoxidation of the obtained manganosite at 500°C and 600°C reduction was ob­ served, but with reduction at 700°C the obtained ~ 10 0' manganosite was rather stable in air. The X-ray diffraction charts of reoxidized manganosites are ~ .~ shown in Fig. 10. Only diffraction patterns ofmanga­ '"~ nosite were observed, but a diffused peak was obtained '0 for reoxidized manganosite after 500°C and 600°C V) 15 V) 0 reduction. This phenomenon is explained as fol­ ....I lows. Obtained manganosite under 600°C was in­ completely crystalline and was reoxidized easily. Possibly obtained manganosite was transformed into incomplete crystals of m a nganosite by reoxidation. 201------~~T_------~ Above 700°C the obtained manganosite was com­ pletely crystalline and stable. That is, for preliminary reduction of manganese ores, manganosite which is unstable in air is produced at a low temperature x,x_x_ reduction. So, in order to obtain stable manganosite 25~--____~ ______-L ______-L ______~ in air, a high temperature reduction is necessary. o 200 400 600 800 When r-Mn02 was exposed to CO gas for about Temperature ( OC ) one hour at room temperature, 7 ~B % weight loss Fig. 8. Thermal balance curves ot r-Mn02 in was observed. This phenomenon was a reduction

CO-C02 gas mixtures reaction, because the furnace temperature was slightly

Research A r ticles C 18 ) Tetsu-to-Hagane Overseas Vol. 4 No. 1 Mar. 1964

increased. Namely, these reductions were entirely Mnpa+ CO = 2MnO+C02 ········· ········· (10) exothermic reactions. Concerning the substance J Go= - 22,620- 5.41 T which was obtained by the reaction of r-Mn02 and tMn02 + CO = ~Mn + C02 ...... ( 11 ) CO at room temperature, only the strongest peak of JGo= - 5,430- 0.86 T hausmannite was observed in the X-ray diffraction 1/3Mn20 a+ CO = 2/3 Mn+C0 2 ...... (12) chart. Concerning samples which were obtained in LlGo= 8,780 + 0.35 T the midst of reduction of ores, only hausmannite was iMnp4+ CO =3/4Mn+C0 ••.• ... • .••.••• (13) observed. For reactions of all ores, the stage of bix­ 2 LlGo= 15 ,225-0.22T byitc was not clearly observed. It seems as follows. There is a little difference in the free energy change 3/2MnOz + CO = ~Mnp4 + C02 ... (8) between reaction (4) a nd reaction (8). So, there is LlGo= - 46,740- 2.14 T every possibility of producing bixbyite and hausman­ MnOz+CO = MnO + CO ...... (9) z nite at the sam e time. If bixbyite is produced, the re­ LlGo= -35,340 - 4.95 T duction to hausmannite occurs inwards from the 0 - - 0 surface of particle. 200 Why burnt ores have lower reducibility than dioxide ~ I " I 400 "" \" "J;' ores is explained as follows. Reactions (9) and 10 600 (10) occur more easily than reaction (6), by

15 800 comparison of free energy change. When oxygen of ~ : a higher oxide is removed by reduction, a porous inter­ 20 ) 1000 media te substance is produced easily. Therefore 25 t Air reducibility of bixbyite or hausmannite is lower than 0 ------0 " , 200 tha t of m anganese dioxide. Because burnt ore is a " , ,, decomposition product of manganese carbonate, ,0 , 400 - ~T' ...... -.. , .... 10 I P amorphous oxide is observed as in the case of a high 600 .c temperature transformation in air. Then, it seems .'; 15 ~ '" 800 0 ~ certain that the reducibility for burnt ore is increased . • c ~ ~ '0 20 Q. 1000 From a consideration of a new complete crystal growth :2 \.. ./ E ~ 25 t Air f-'" of bixbyite or hausmannite, it seems most reasonable 0 -- - to conclude that the reducibility of burnt ore is de­ , 200 ,, creased...... , ...... , - 400 As m entioned above, during manganese ore re­ 10 -\""" , , -- , , , 600 duction with CO gas, carbon deposition was observed --- Temp. 15 " in certain ores at a temperature above 400c C. It was - WI. 800 ~ remarkable in high iron-content ores. 20 ~ r--- 1000 Carbon deposition reaction is as follows : Air. 25 o 2CO = C + C02 ...... • (14) Time ( hi This reaction is accelerated by reduced iron which Fig. 9. Thermal balance curves of Mn02 reduction was produced at a low temperature. The equilibrium with CO gas reoxidation with the air of reaction (14) a nd the condition under which iron has a catalytic function were clear from investigations Heduction at soot made by W. Baukloh91 . From 'vV . Baukloh's results,

even when gas composition is 65 % CO and 35% CO2 , carbon deposition occurs. But the equilibrium ofrcac­ Redu c tion at 600 t tion (14) shifts to the left as opposed to the case of onl y CO reduction. Supposing that carbon deposition did not occur in this case, deposit carbon in the case of only CO reduction was obtained. The results are shown in Table 3. Except high grade Indian ore, the Iledu ction at 700 t A . amount of deposit carbon increased and decreased ..-v-.-~ ~~ with the iron content. The ores in which carbon

50 55 60 65 70 75 80 8~ deposition did not occur v"ere Australian, Oe, Yakumo, 2 0°, CuKa J okoku a nd Shibetsu ore. For burnt ores, carbon de­ Fig. 10. X-ray diffraction of reoxidized MnO after position was not observed although the iron content quenching from r eduction temperatures was considerably high.

Research Articles Tetsu-to-Hagane O ver seas Vol. 4 No. 1 Mar. 1964 [ 19 )

Table 3. Relationship between the amount of deposit carbon and temperature

Deposit carbon (mg/ore 500 mg) - Fe (wt ra) T emperature (0e) Ore -400 -450 -500 -550 -600 -650 -700 I Oshima 6 13 17 21 13 12 10 .08 ----- I Indian (H.G .) 10 6 5.07 - 1_ 18 South African (L.G .) 10 15 17 9 6 10.19 I Indian (L.G.) 10 19 I 10 10.49 ------South African (H .G.) 10 11 10 10 10 8 8.87 --- Indonesian 9 8 3.81 ------Ghanaian 3.17

Transforma tion of iron compounds during reduc­ ing that thermally easy decomposable and incomplete ti on was not clear. But theoretically metalli c iron crystalline r- or D-Mn02 is most reactive. should be produced according to the reaction9 ) . (5) Under low temperature reduction, the ob­ One might conclude that the weight loss of all tained ma nganosite was unstable in air aft er cooling tested ores during thermal balance analyses was a in a CO gas fl ow. Meanwhile it was shown that reduction of composing minerals. through reduction a t a temperature above 700°C, the obtained manganosite was rather stable in air after V. Conclusions cooling. X-ray diffraction showed that this phe­ nomenon was due to the crystalline structure. (1) Foreign manganese ores were mostly manga­ (6) During manganese ore reduction with CO gas, nese dioxide ores, and their a ttendant minera ls were carbon deposition was observed in certain ores ; manganite, braunite, hydrated manganese oxide a nd especially in high iron-content ores this tendency was silica. Manganese dioxide ores have a-, (3-, r- a nd /or remarkable. a-phase and most of them are these mixtures . (2) Domesti c ores were mostly manganese carbon­ a te ores or silicate ores, and the mineral compositions I) K . Lorck: Elkem Furnaces in Ferroall oy and Carbide of burnt ores represented variations in the burning Production, 1959, IV. Internati onal Congress on Electro­ temperature and atmosphere. H eat. (3) Reducibility decreased in the followi ng order, 2) M. C. Udy, M. J. Udy : Prod uction of Iron and Steel by the i. e., manganese dioxide ore, burnt ore of manga nese Strategic Udy process, Proceedings, Electric Furnace Con­ carbonate ore and manganese silicate ore. I twas ference, AIl\IE, 1958, P. 220. plain enough that every ore was reduced to manga­ 3) Y. H ari ya: J. of the Faculty oj Science, I-Iokkaido Univ., nosite with CO gas. Ser. I V, 10 ( 196 1), 641. (4) There was scarecely a ny difference in reducibi­ 4) H . ~li ya moto: Nippon Kosanshi, BI-C ( 1954), 56. lity with CO gas among all manganese dioxide phases, 5) T . Yoshimura: Manganese Deposits in J apan, ( 1952 ), Tokyo. i.e. , cryptomelane, pyrolusite, r-Mn02 and birnessite. 6) J. P. Coughlin : Bureau or l\IIines, Bull., 542 (1954). However, m a nganese dioxide transformed to the 7) H. U li ch et alius : Arch. EisenhIIUeIlw. , 14 (1940), 27. reduced state (till hausmannite) through mere thermal 8) W. F. Cole, et al ii: T rans. Electrochem. Soc., 92 ( 1947), decomposition simulta neously with reduction by CO 133. gas. Therefore the a uthors support the general reason- 9) W. Baukloh: Metallwirtsch. , 19 ( 1940), 463.

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