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UBC Theses and Dissertations

Preparation of manganates and permanganates of metals of alkali and alkaline earth groups Wright, Charles A.H. 1920

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PREPARATION OF MANGANATES AND PERMANGANATES OF METALS OF ALKALI AND ALKALINE EARTH GROUPS. T h e s i s s u b m i t t e d f o r t h e M.Sc. d e g r e e by * T H E S I S . - * .Preparation of Manganates and Permanganates of Metals of Alkali and Alkaline Earth Groups* 1* Previous Work on Manganates and Permanganates» The poverty and conf l ic t in the avai lable l i t e r a t u r e on the chemical reac t ions taking place during the manufacture of permanganates, together with t h e great need for t h i s commodity, as indicated by the rapid r i s e in pr ices on curtailment of the European supply has led to t h i s invest igat ion* Although the permanganate in (1) most general use to-day i s tha t of potassium, our work has been pr imari ly concerned with the sodium s a l t on account of the expected s imi la r i ty in the reac t ions for the preparat ion of the manganates of the two metals, , together with the r e l a t i v e cost of caust ic and potash* Results ind ica te t h a t , contrary to expecta t ions , the react ions a re d iss imi lar so the inves t iga t ion of the sodium compound has been follov/ed by a study of the reac t ions involved when unaer similar working conditions potassium hydroxide, barium hydroxide and barium dioxide, strontium hydroxide, calcium hydroxide, aluminium hydroxide and the oxides of magnesium, copper and zinc in turn are subs t i tu ted for the sodium hydroxide used i n the preparat ion of sodium manganate. Potassium permanganate i s manufactured on a large scale by a two-stage process consis t ing of the preparation of manganate by roas t ing a potassium hydroxide,-manganese-dioxide mix, followed by conversion of manganate to permanganate by ex t rac t ing the mix with water. This inves t igat ion l i m i t s i t s e l f almost en t i r e ly to the -9 # 2. -2-first stage, namely the manufacture of manganates since the change to permanganates takes place easily on acidifying or oxidizing electrolytically. The most recent study on manganages and permanganates has been made by Schlesinger, Mullinix and Popoff who summarize previous investigations and the results of their own work as follows. "The conversion of manganese dioxide into potassium manganate by heating it in a current of air v/ith potassium hydroxide has been extensively investigated. The most recent and apparently • the most thorough of these investigations are those of Askenasy and iQonowski and of Sackur and his associates. The researches of the two groups of investigators do not lead them to the same conclusion. While the first named seems to hold to the opinion that the reaction follows the course found in the text books represented by the equation. {!) A JiOH +• 2 Mn02 + 0 2 * 2K2 Mn04 +• 2H20 Sackur concludes that potassium manganate is never formed in this way but that the product obtained in the reaction is a mangani manganate which can be represented by the formula 2 KgMnOj,3K2Mn04,3K20 In this conclusion he is corroborated by the work of Auger^ who obtained a compound of similar composition by heating potassium permanganate with excess of potassium hydroxide. If Sackur*s conclusion be correct it is clear that the highest yield that -3-could be obtained in the reaction in terms of the amount of manganese dioxide oxidized to the manganate stage could he only 60 per cent since the remaining 40 per cent must always remain as manganite. In support of this consequence of his theory of the course of the reaction, Sackur cites his own experiments which show a maximum yield of 55 to 66 per cent, the results of Askenasy and Klonowski who obtained similar yields, and the statements made personally to Sackur by German manufacturers that a yield of 60 per cent was the maximum attained in practice. When we first undertook this investigation the manufacturers with whom we were cooperating were not obtaining yields as high as those demanded by Sackur*s theory and we therefore attempted to determine the best conditions for duplicating his results. The outcome of this work has been to show that Sackurfs theory is incorrect, for we were able to obtain yields corresponding to a conversion of over 98 per cent of the manganese dioxide into the manganate." Results of this investigation have confirmed those obtained by Schlesinger Mullinix and Popoff in case of the potassium salt, but with sodium hydroxide or dioxide the maximum yield was found to be 60 per cent, which fact lends support to Sackur*s theory of the foundation of a inangani manganate as represented by the equations (2) 32 NaOH -+-10 Mn02 4- ^ 62 « 2(2Na2 Mn03,3Na2l£n04,3Na20) *• 16H20 # (3) 16 Na202+10 Mn02 a 2( » " " " " )+ 502 - 4 -2 . P r e l imina ry expe r imen t s t Appara tus , methuats aua ^ ^ c e ^ . In p re l imina ry experiments i t was found t h a t con t inua l s t i r r i n g of the mix had s l i g h t e f f e c t on the r a t e of r e a c t i o n , and the y i e l d , hut t h a t t h e s i z e of p a r t i c l e of manganese d ioxide had a marked e f f e c t , as shown i n t h e fo l lowing s e r i e s -Table 1 . Showing in f luence of f i n e n e s s of o r e on the y i e l d of manganate< Mesh* j , flaoMnCU 1 . Through J>0 over .50 2.3 • 2 . » 80 » 100 8.2 3 . « 100 " 150 11.9 4 . " 150 • 200 24 .1 5 . « 200 26.7 Manganese d iox ide o r e , v a r y i n g i n Mn02 from 60 to 8j> p e r c e n t , and sodium hydrox ide , potass ium hydrox ide , e t c . , were p u l v e r i z e d , t he former t o p a s s through a 200 mesh s c r een , the l a t t e r t o an impalpahle powder, by use of a mechanical p u l v e r i z e r , and then s t o r ed in a i r t i g h t b o t t l e s . The mix f o r r o a s t i n g was prepared by weighing t h e requi red amounts in to r e f r a c t o r y c o n t a i n e r s and s t i r r i n g thoroughly to i n t i m a t e m i x t u r e . The a p p a r a t u s in which t h e mix was r o a s t e d cons i s t ed of a small e l e c t r i c fu rnace , the tempera ture of which could "be mainta ined cons tan t w i t h i n a few degrees a t any p o i n t between 100°C t o 1000°C. The furnace was made by s p i r a l winding a muffle c l o s e d , e x c e p t for gas e n t r a n c e , a t one end,wi th nichrome w i r e , so t h a t d i s t a n c e between consecu t ive windings was about i i n c h . A cover ing of a g e l a t i n o u s mixture of sodium s i l i e a t e (water g l a s s ) and powdered Alumina-asbestos w S « mixture was spread over the muffle and wires to a depth of about £ inch and t h i s was placed asbestos s t r i p s of about 1^ inch thickness and bound into pos i t ion by use of i ron wi re . The covered muffle was allowed to stand fo r a few days; the gelatinous mater ia l hardened thus f ix ing asbestos s t r i p s and making a most sa t i s fac to ry furnace. The furnace,during the passage of an a i r current , was standardized by varying the voltage across the terminals and taking the corresponding temperature readings by use of a thermo-couple. The curve of va r i a t ion of temperature with voltage regulated by res i s t ance was very useful in the determination of the required voltage across the te rminals , for any desired temperature in the muffle. The heat ing of the mixes was eas i ly control led by a var iable r e s i s t ance and a current of water, carbon dioxide free a i r eas i ly obtainable by use of compressed a i r . The diagram below wi l l i l l u s t r a t e the main features of the apparatus used. - 6 -In the work of Schlesinger, Mullinix and Popoff, and t h a t of Askenasy and KLonowski, the procedure consisted of mixing the f ine ly ground ore with a concentrated solut ion of caus t i c , drying the mix in a current of a i r to such a consistency tha t when cool i t could he well powdered and f ina l ly heat ing powdered mater ial in a current of a i r in an apparatus in which the mix could he continual ly ground while being heated* This apparatus consisted of a drum ro t a t i ng in an iron housing and f i t t e d with openings for removing mater ial for analysis ,and was . heated by gas. The axle v/as hollow and broken in the middle of the drum. Through one end of t he hollow axle preheated a i r was introduced and into the other a thermo-couple v/as loosely f i t t e d . The charge prepared as above was placed in the drum and with i t a f a i r l y la rge number of •§• inch s t e e l b a l l s . As the drum rota ted slowly (20 r .p .m.) the b a l l s were l i f t e d by the r i b s in the s i de s of the drum and dropped back on the mater ia l , thus pulver iz ing the l a t t e r thoroughly throughout the p rocess . In our apparatus the mixing of the mate r i a l s was probably not so intimate as in the case of the ro ta t ing drum, but the e l e c t r i c muffle had the advantage of g rea te r s implic i ty of cons t ruc t ion , ease of control of temperature and a i r current , and permitted 4 or 5 experiments to be run simultaneously. In the determination of the optimiun temperature weights of sodium hydroxide and manganese dioxide in the molecular r a t i o of 3.2 : 1 were used. Table 11 experimental data shows the influence of temperature on the y ie ld of ifaanganate - j>00°C for 1 hour produces -7-the highest yield and consequently this was the temperature maintained in the furnace during the subsequent roasting. Table 11 • Showing influaace of temperature on yield of manganate* Temp. °G» . Time - hrs. Yield % Na2Mu04 400° — — — i . — - — 3 20..5 4^0° 3 — — — . 24.4 500° —• 1 — — — — — 25.0 ^ o ° — • — i 25.0 6oo° — — - 1 25.0 7000 . 1 — — 19.8 900° -. 1 18.5 Since most pyrolusite contains only 60 per cent to 85 per cent MnO? it is essential to know if the impurities present exercise any influence on the formation of manganate. From experimental data included in Table 111 it is seen that the impurities other than possibly uniting with a portion 0 f the alkali present do not appreciably, if at all, affect the amount of manganate formed. Table 111* Showing influence of impurities in ore* % MnOp in Ore 63 76.6 88.7 97 12 NaOH Molecular RatioMnO£ 4 „_.-_._B-63 76.8 88. ; , , _ . |„ : Wa2Mn04 33.3 38*0 42.1 39.0.:25.6 32.8 37.1 % Yield 60.1 . 62.9 63.8 59.l|40.0 46.2 52.; wxmv # J & -8-The analysis of the manganate mix was determined by the following method - ^ -'gram of the calcine-finely r)Owdered-(1) dissolved in about 100 cubic centimetres of water, is allowed to stand for a few hours until hydrolysis is complete. (4) 3 Ha2 Mn04 •*- 2 HgO • 2 Ha Mn04 +• I&1O2 -»- 4NaOH The residue and precipitated manganese dioxide is separated from the permanganate solution by filtration through glass wool and asbestos, packed in an ordinary funnel. The filtrate is acidified with 15 cubic centimetres of sulphuric acid (1:1) and permanganate determined by titrating with a standard solution - in our work N/3 - of ferrous ammonium sulphate* In connection with the above method of manganate mix analysis, •it is worthy of note that the solution should not contain acid and should not be boiled before filtration; if acid be present or the solution be boiled while manganese dioxide is present, a reduction of the permanganate due probably to the reducing action of the hydrogen peroxide formed by action of Manganese dioxide and acid in the one case and a catalytic action in case of boiling,results. The follo?/ing experimental data illustrates the effect of acid carbon dioxide and boiling before filtration. Table IV. Effects of acid, C0? and Boiling. Boiling HQ.0 CO2 H?S6A Hydrolysis (cold) l.c.c.FeS04S§i»n. 16.7 17.0 15.8 17.6 2. " 17.5 18.0 16.8 18.8 3. " 17.9 17.8 18.0 19.2 4. " 18.0 18.2 17.6 19.0 J V* * The percentage y i e ld has been ca lcula ted on the bas i s of manganese dioxide to manganate. The pyrolus i te used was f i r s t analyzed for manganese dioxide by a determination of t h e oxidizing power and from t h i s analysis weight of manganese dioxide in 1 gram of mix before roas t ing could be determined* Prom the percentage of manganate in the ca l c ine , i t i s an easy matter t o determine the equivalent weight of manganese dioxide in 1 gram and hence to ca lcu la te the y i e l d . This method would be accurate i f there were no difference in weight of the mix before and a f t e r r o a s t i n g . Prom equations ( l ) , ( 2 ) , or (3) i t is quite evident that the re must be a difference in weight , the mix before heat ing being t h e heavier of the two, hence the calculated yield ic in s l i gh t excess of t he t rue y i e l d . 3». Results of experiments with NaOH. MnO? mixtures . Prom a long se r i e s of experiments i t was shown quite conclusively t h a t the maximum yie ld of manganate obtainable in the case of sodium was 60 per cent of that possible according to the general theory as represented in the text-books. The experimental da ta obtained by roast ing manganese dioxide and sodium hydroxide through a range of molecular r a t i o s from .5 to 6.0, i s given in the following t a b l e . r-10 Table V. Showing the influence of variable molecular ratios of sodium hydroxide and manganese dioxide on the yield of manganate. » Brown : Green (dark to light) — — •»•—-^Mn02 in ore 76.8 63 63 63 / 63 63 63 63 63 63 63 63 %. 8 Molecular ratio NaOH .3 1*19 1.34 1.99 2.47 2.92 3.14 3.38 3*77 3.97 ^.37 4.42 3.0 6 Mn02 foNa2Mn04 — Trace 3 .3 8.0 16.0 22.0 23.2 32.0 34 .0 34.0 33 .0 33»0 31*3 27 / . Y i e l d — Trace 4 .3 10.3 22.9 33.9 40 .9 34.8 39*3 61.3 62.6 60.8 39»2& In above t a b l e row 1 i s s e l f exp l ana to ry , r e p r e s e n t i n g t h e percen tage of manganese d ioxide i n t h e o r e . Row 2 r e p r e s e n t s the r a t i o of moles of sodium hydroxide to t h e moles of manganese d i o x i d e . I f equa t ion (1) r e p r e s e n t e d t h e form of t h e r e a c t i o n t h e r a t i o 1.99 should correspond t o a y i e l d approximat ing 100 per c e n t ; t h e small y i e l d of 10.3 per cen t i n d i c a t e s t h a t equa t ion (1) does not r e p r e s e n t the form of the r e a c t i o n . Row 3 r e p r e s e n t s the pe rcen t age of manganate i n t h e mix a f t e r r o a s t i n g ( see a n a l y s i s page 8 ) . The l a s t row r e p r e s e n t s the c a l c u l a t e d y i e l d which, a s exp la ined above, i s probably i n s l i g h t e x c e s s . By a n a l y s i s of the mix f o r manganate and t o t a l manganese, an a c c u r a t e c a l c u l a t i o n of y i e l d could be made, or by a n a l y s i s of t h e t o t a l mix f o r manganate an a c c u r a t e r e s u l t could be o b t a i n e d . The l a t t e r sugges t ion i s no t p r a c t i c a b l e under most c o n d i t i o n s , and t h e former makes t h e work much more e x t e n s i v e . The approximat ion made gave r e s u l t s c l o s e enough to the a c c u r a t e fo r our purpose . $f *2 ^ - 1 1 -The above r e s u l t s have been obtained as a resul t of heat ing the eaus t i c -pyro lus i t e mix in a current of a i r freed of carbon dioxide and moisture by bubbling i t through sodium hydroxide and concentrated sulphuric ac id , before passing over the surface of t he mix. I f water or carbon dioxide be present in the a i r the mix becomes coated with a brov/n layer of permanganate which gradually works i t s way throughout the mix u n t i l the l a t t e r i s a l l of a brown color , giving MnOJj. ions in so lu t ion . The brown colored substance r e s u l t i n g from the roas t ing of a mix in which manganese dioxide i s in great excess i s due, probably, to the formation of a compound other than manganate or permanganate, II f since ne i ther the manganate ion I&1O4 nor the permanganate ion MnO^  i s produced on ex t rac t ion of the calcine with water . From the molecular r a t i o of 2.47 to molecular r a t i o 6.0 the color of the compound formed, believed to be a mangani-manganate (See Eq.2) i s green, varying from a dark to a l i g h t e r shade as the r a t i o i s increased. Beyond the r a t i o 4 to 5, dependent on percentage composition of ore, the mix becomes pasty when roas ted and therefore around these r a t i o s i t is d i f f i c u l t to work with accuracy. The formation of mangani-manganates in t h i s case and not manganates i s borne out by the appearance of the products . Mangani-manganates are green, while manganates a re of a v i o l e t , almost black, hue. All the products from r a t i o 2.47 to 6.0 were green and none of them v/ere of the manganate color . The maximum yie ld a t t a ined - namely 60 per cent - also points to the formation of a compound other than manganate. This maximum y ie ld , according to our experimental r e s u l t s , -12-itj reached by use of sodium hydroxide and manganese dioxide in the molecular r a t i o of 3«8« This i s in excess of the t h e o r e t i c a l r a t i o ^ • 2 , according to equation (2) and although the reason for the excess has not been proven by other experimenters, i t i s probably due to the impuri t ies - mainly S i l i c a - in the p y r o l u s i t e . Whether or not the excess had t heo re t i ca l s ignif icance might be ascer ta ined * by a determination of the y i e ld a f t e r roas t ing pure Bodium hydroxide with pure manganese dioxide in the molecular r a t i o of 3«2» Table 111 A, because of the excess molecular r a t i o 4«0, does not present any evidence as regards the pa r t played by the impuri t ies in the reac t ion for the formation of manganate* By use of a smaller r a t i o such as ^ , 0 , in which mixture tne maximum y ie ld i s not reached, the ef fec t of the impuri t ies has been noted and the experimental da ta included in Table 111 B. The lower y ie lds that have resu l ted from the use of ores r e l a t i v e l y low in manganese dioxide suggests tha t a por t ion of t he sodium hydroxide i s un i t ing with the impur i t i es , and hence i t is to be expected t h a t for the maximum y ie ld of 60 per cent an excess of sodium hydroxide over the theore t ioa l would be necessary* Jb» Results of experiments with Ha909tl£nOp Mixtures, The data immediately following - table ' Yl - contains the experimental r e s u l t s obtained when the dioxide of sodium was roas ted, instead of the hydroxide, with pyro lus i te in varying molecular r a t i o s , under the seme conditions as those t h a t governed the roas t ing of the hydroxide mix* -13-Table 71• Showing the influence of variable molecular ratios o"? sodium dioxide ana manganese dioxide on the yield of manganate* i i . . . . . . . . . . --Green—-—--——.-.—-i02 in ore 77.8 77.8 77.8 77.8 77.8 77.8 77.8 77.8 1 1.25 1.^0 1.75 2.00 2.50 2.75 5.00 .ecular ratio fag02 lB.^SaOA 19.7 27.0 36.8 37.2 38.2 32.0 2?.6 27.2 field 23.3 35.O 53.O 57.5 63.7 61.3 6O.5 58.7 9 : 5 ' By a comparison of tables Y and Yl and curves 1 and 11 ee below) , and remembering that one mole of sodium dioxide is equivalent two moles of sodium hydroxide, i t is seen that the two series of results bained by use of the two oxides are very similar. If equation (3) presents the course of the reaction between the two dioxides and oxygen, have had to use an excess over the theoretical ratio of 1.6 to obtain r maximum - 60 per cent - yiela of maganate and, as previously mentioned, e excess probably is due to the impurities of an acidic nature in the ore, e yield as calculated is liable to be in slight excess of 60 per cent, previously explained (see equation (3J). T^e gradual decrease of the eld of manganate after passing the maximum yield is probably due to the rmation of small amounts of hydrogen peroxide, with i ts consequent iducing action, from the excess sodium dioxide in the calcine. The color f the product was green, as in oase of sodium hydroxide roasting, bearing it Sackur»s view of the formation of a mangani manganate. The graphical representation of the data contained in ibles V ana Yl is shown on the following page by curves 1 ana 11. Curve 1 fe±/o fdct w t > -14-represents the course of the reaction between sodium hydroxide, manganese dioxide and oxygen, and Curve 11 the reaction with the dioxide substituted for the hydroxide. Since both curves are straight lines, the yield must be directly proportional to the relative amounts of the hydroxide or dioxide used* The maximum yield of 60 per cent is reached when the molecular ratio reaches the value 3*6 - 3*8, the excess over the theoretical J.2 being due, as previously explained, probably to the impurities in the ore* Above the ratio 4, the mixture becomes pasty and it ie difficult to obtain an accurate sample, hence the irregularity in the curves. The hydroxide presented greater difficulties when used in mixtures of high ratios than the dioxide, and hence Curve 1 shows greater irregularity than Curve 11 • The descending portion of Curve 11, after the ratio 4.0 is passed, is probably due to the reduction of permanganate caused by the hydrogen peroxide formed from the excess dioxide. The green product when exposed to the action of the atmosphere changes to a. brown compound, which on examination was found to be permanganate. This change is the effect of the action of the moisture and. carbon dioxide present in the air, and may be represented by the following equations -(4) 3 Ha2Mn04 \. 2E20 = 2 Na Mn04 A- Mn02 + 4 NaOH (5) 3 Na2Mn04 + 2C02 = 2 Na Mn04 + Mn02 +- Na2C0j M -15-Prom the experimental data included in the preceeding pages we conclude that in the case of sodium a complex compound of the form 2Na2Mn0^  3Na2 Mn04 3Na2 0 is formed when the hydroxide or dioxide is roasted with manganese-dioxide in the presence of oxygen or air , and that the maximum yield obtainable is therefore 60 per cent. * 4» Results of experiments with KOH MnOg Mixtures. The results obtained by use of potassium hyaroxide as the alkali in the reaction for the formation of manganate have been determined under similar working conditions as those used in the case of sooium. Contrary to expectations the two alkalies, caustic and potash, were found to be- dissimilar in the reaction for the formation of manganate. A yield of 6u per cent of the sodium salt was found to be the maximum attainable, while by the roasting of potassium hydroxide and manganese dioxide in the proper molecular ratio, a yield of 100 per cent of manganate was obtained. Schlesinger, Mullinix and Popoff worked with the potassium salt and obtained a yield approximating the theoretical of 100 per cent, showing that the reaction progressed according to the following equation -(6) ft EOH -h 2Mn02 + 02 • 2Z2Mn04 4- 2H20 Table Vll. Showing the influence of variable molecular ratios of potassium hydroxide and manganese dioxide on the yield of manganate. in ore 76.8 7b78 76.8 • 76.8 77.8 77.8 76.8 76.8 lar ratio .67 1.39 1.83 2.16 2.30 2.43 2.77 3.6 r2 <4 Trace 34.3 38.4 64.3 71.O 73.7 3?.2 41.2 a 34.3 67.2 80.6 92.4 100.8 83.4 38.8 ) ) -16-This series of results agrees very well with those obtained by Schlesinger, Mullinix and Popoff. It will be notioed in above series, Table Vll, that as in the case of sodium an excess over the theoretical of potassium hydroxide is necessary to obtain the maximum yield. This excess , as was the case with sodium, is probably due to the impurities in the pyrolusitea The potassium hydroxide used was considered 90 per cent KOH, due to a variation in the material of from 85 - 90% pure potassium hydroxide* Schlesinger, Mullinix and Popoff in their recent paper, pay great stress on the influence of moistening the mixture on the yield of manganate. They write - "The potassium manganate in air ro8e to 54.6 per cent, which is about 60 per cent of the yield possible according to the equation 6, given above. Further heating in air caused, a slight lowering of the yield. In oxygen the content manganate rose to 63 per cent, at which point absorption of oxygen came to an end. The mass was then treated with enough water so that the mixture could be well stirred. It was then dried, as described above, anu reheated in oxygen in the kilne at 450°. The manganate content now rose to 77«9 per cent, and a repetition of thie procedure finally raised it to 81 per cent, representing a yield of 92 per cent of the theoretical on the assumntion that manganate, and not nangani-manganate is the product obtained, frequent repetitions of analogous experiments showed that it was the moistening with water which raised the final yields, as merely by this treatment and without the use of oxygen we have been able to produce these and higher yields"* Farther -« J J 1 ' -17-"Askenasy and Klonowski (Loc.cit.,p.lll) describe one experiment in which they moistened the material from time to time with a few drops of water. They seem to lay no stress on this point, and our experience is that a few drops of water would he quite ineffective. Attention may also he called here to the German patent 266,347 (1912) issued to Bergius and Sackur, in which moist mixes and oxygen under pressure are used". In our experiments with sodium and potassium re-moistening of the mixes was carried out in several cases, hut in none did we find that the yield of manganate was increased thereby. In some cases the yield, of manganate seemed to he decreased by moistening the mix and reheating. The yields obtained in our experiments were the result of roasting in a dry atmosphere without remoistening. Curve 111 £see below) represents graphically the course of the reaction. It will be noticed that the yield of manganate is proportional to the relative amounts of potassium hydroxide in the mix and that after passing the ratio 2.4jS - the ratio of maximum yield - the yield decrease* regularly as represented by BC. If the reaction follows that represented by equation it should theoretically reach 60 per cent, at a ratio of ^.2, but as expected, it is slightly in excess of this ratio, due to the effect of impurities present in the ore. A brown compound similar to that formed with sodium hydroxide mix, with manganese dioxide in great excess, was not noticed with potassium and a compound similar to the bright green - 1 8 -4fft f O T crVttr i r i ! ( • 1 i \ -< * ;, Ctfntbs jfegfirifa *c * . . ; | 0 * 1 \ \ \ :-.:r/.:i/...;...: \ j : 1- h S 1 R M M f l l allirft .A. , , i ; ,/, i ' i * \ • i i • 1 • « ,!' •" -I1 N£ , ; i <ST 1 1 II t- \ I i I 7- • : ; F-i 1 | • . •• i 1. ... z ; 3 . \ J i i | 1 ~i f *" fe I . . . . . 1 • — I ; : | i , • « V r • . ^ i p i ' \ 1 iV ' - i -r—i i r T- r - r-n-r-i i • 5 C P?o/<s<t/for f&tio _ 1 I ' -18-colored mangani-manganate obtained with caustic was evident in this series only when a great excess, as in ratio 4, of potassium hydroxide was present; with intermediate molecular ratios the color of the compound formed was very dark, almost black, and this compound on addition of excess potash, changed to the green mangani-manganate* As in the case of sodium, the compound formed with potash, if exposed to atmospheric action for a few hours, changes to the permanganate of potash. Authorities state that manganates are of a very dark violet hue, while mangani manganates are green. This statement supports the view that in the case of sodium a mangani manganate is formed,while in case of potassium the pure manganate is first formed and then by presence of excess potash the green mangani-manganat-e results. (See the following equation). (7). 5 Z2lfa04 "•" &E0H = 2K2Mn03 5K2Mn04 JE20 •+-3H20 +• 02. 5• Results of experiments with BaOgMnO? Mixtures. A series of tests similar to those in case of sodium and potassium was run with Barium dioxide as the basic material. Experimental data is contained in the following table: Bote: The dioxide was used instead of the hydroxide because of the similarity in the fualitative results and greater accuracy in the determination of the yjeld. -19-Table Vll. Showing the influence of variable molecular ratios of b*arium dioxide and manganese dioxide on the yield of nanganafe^ bre 76.8 76.8 76.8 76.8 76.8 76.8 76.3 76.8 76.8 76.8 76.8 76.8 76.8 ecular .5 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.8 3.0 4.0 5.0 io BaOg B5D"£ r" >04 5 . 1 28.2 25.6 2 J . 8 21.5 24 .1 25 .1 27.7 28.7 28.7 — « l e ld 4.4 51.1 31.6 32.5 32.2 41.5 4S.2 52.5 58.0 65.7 — The green compound formed by the interaction of Barium dioxide, manganese dioxide and oxygen, as indicated by yield, is not a simple manganate as obtained in case of potassium, but a more complex body, probably similar to the sodium compound. It will be noticed in above table that yield is apparently constant - about 30 per cent - from a ratio of 1 to a ratio of 1.6 and beyond this ratio the yield increases regularly to about 60 per cent. Beyond the ratio 2.8 the hydrogen peroxide produced by action of the acid on the excess Barium dioxide vitiated the results of analysis. It is of interest in this connection to note the difficulties met with in the analysis of the calcine containing manganate, barium dioxide and manganese dioxide. The difficulty arose when it was noticed that hydrogen peroxide,formed by the action of acid on barium dioxide, was reducing the permanganate. It was met by attempting to get rid of barium dioxide by use of sulphuric acid, carbon dioxide and sulphur dioxide in turn, anr» then changing manganate to permanganate, by addition of nitric acid* Results showed that in the attempted -20 removal of "barium dioxide the manganate had "been affected. It had "been noticed, however, that with ratios less than J> there was little or no effervescence^on addition of nitric acid so method finally adopted consisted of addition of nitric acid, filtering through ashestos and glass wool and titrating v/ith standard ferrous sulphate solution. This method was not applicable to ratios greater than 3. The analysis of the latter might possibly be accomplished by taking a weight of the calcine and decomposing barium dioxide by heating at 1000°G, the decomposition temperature of barium dioxide. The green compound, after several days* exposure to the atmosphere was apparently unaffected* The course of the reaction up to the ratio 3.0 is represented by Curve IV. The curve indicates that the reaction goes in two stages, dependent on the molecular ratio of barium dioxide and manganese dioxide. Apparently a yield of 30 per cent is obtained by ratios of 1.0 to 1.6, due probably to the formation of one type of manganite manganate with a constitution of 30 per cent manganate. When a ratio in excess of 1.6 is used the yield is increased, proportionally to the excess, to a yield of 60 per cent, due probahly to the formation of another type of mangani-manganate with a constitution of 60 per cent manganate. Large quantities of hydrogen peroxide are produced during the analysis of a mix of ratio greater than 3. which would -seem to indicate that in excess of this ratio a portion of the barium dioxide was left uncombined, i.e., up to ratio 3 practically all of harium dioxide has combined to form a mangani manganate with manganese dioxide; this ratio is further i* -21 evidence against an equation similar to (1) as representing the course of the reaction* 6. Experiments with Sr (0H)2 MnO? mixtures* A series of tests similar to those in case of other metals was run with strontium using the hydroxide as the basic material. Experimental data is contained in. the following %able. Table Till* Showing the influence of variable molecular ratios _J strontium hydroxide and manganese dioxide on the yield of manfeanate. % Mn02 in ore 76.8 76.8 76.8 76.8 76.8 76.8 Molecular Ratio Sr (OH)2 .6 .8 1.0 1.2 1.8 2.6 Mn02 % Sr. MnOg 12.0 9.1 11.2 4.5 .6 trace % Yield 13.? 17.0 20.6 9.4 1.7 In the case of strontium from a r a t i o .6 to 1.0 the color of the compound changed from a l i gh t to a dark green, and above the r a t i o of 1.0 to a brown. Above r a t i o 1.0 the y i e l d , which in any case i s small, drops 6ff suddenly u n t i l a t r a t i o 1.8 there is only a t r ace of manganate present in the brown substance, which is probably a compound. This r e s u l t i s jus t the opposite of t h a t obtained in case of sodium, which with r a t i o s l ess than 1.0 formed a brovm substance, apparently some compound, while with strontium a brown substance i s formed y * «r when a r a t i o g r e a t e r than 1 i s used* The smal l y i e l d ob ta ined must r e p r e s e n t , a s i n c a s e of t h e o ther meta ls except po tass ium, the format ion of a complex mangani luanganate. The. g reen mangani manganate of s t r o n t i u m i s unaf fec ted when exposed to atmospheric a c t i o n . 7» Experiments w i th Ca(OH)gMnOp and Al(OH),MnOg m i x t u r e s . Tes t s were a l so run wi th calcium hydroxide and aluminium hydroxide in v a r y i n g molecular p ropo r t i ons wi th manganese d i o x i d e , hu t i n t h e s e cases an i n a p p r e c i a b l e amount of manganate -i f any a t a H - was formed. 8• Experiments wi th MgO, MnOg, OuO MnOp and ZnO MnOg m i x t u r e s . Magnesium ox ide , copper oxide and z inc oxide when r o a s t e d with p y r o l u s i t e do n o t r e a c t to form manganate a t temper-a t u r e s between 0°C - 1Q00°C. Summary. 1. It is found that when manganese dioxide is roasted with potassium hydroxide in a current of air, a yield of 100 per cent of potassium manganate is obtainable, but with sodium hydroxide, sodium peroxide, or barium dioxide, the maximum yield of manganate is found to be 60 per cent. With strontium hydroxide, manganese dioxide mix roasted in a current of water, carbon dioxide free air, the maximum yield is found to be 20 per cent. With calcium hydroxide and aluminium hydroxide, or magnesium oxide, copper oxide and zinc oxide roasted with manganese dioxide at temperatures ranging from _ _._ ct a -23-500° - 1000° C. it is found that no manganate is formed. 11. The yield of manganate varies greatly with the proportion of hydroxide in the mix. The molecular ratios corresponding to the maximum yields at the temperature j>00°C. are as follows -Yield of Manganate Molecular Ratio Potassium hydroxide Sodium " " dioxide Barium " Strontium hydroxide Calcium " Aluminium " Magnesium oxide Copper " Zinc " The above series is representative of the variation of yield with elements of increasing atomic weight and increasing basicity and it would probably be found that with the bases, stronger than potassium, namely rubidium end caesium, a yield of 100 per cent manganate would result and by the same process of reasoning, with radium and lithium hydroxides, we would expect a yield of 60 per cent manganate. 100% 60?o 60fo 6 Of. 20?o 2.4J 3.77 3.74 2.5 1.9 11 -24 -I I I . In our work moistening and reheat ing did not increase the y ie ld of manganate. This resu l t i s contrary to that of Schlesinger, Mullinix and Popoff• IV. The conclusions of Schlesinger, Mullinix and Popoff in the case of potassium have been proved correot.and those of Sackur, i n t h i s connection, i nco r r ec t , Saokuris conclusion t h a t a mangani manganate i s formed in case of sodium i s supported by our experiments, which also point to the formation of a complex manganate compound in the case of barium and strontium* V. In the case of potassium excess a lka l i causes the manganate to decompose into a mangani manganate, s im i l a r t o , i f not iden t i ca l with tha t postulated by Sackur. VI. In the case of barium excess a lka l i causes a decomposition of the permanganate formed when the mix i s extracted with water and n i t r i c acid -on account of the reducing act ion of the hydrogen peroxide formed. 711 . I t i s found tha t the manganatet; of potassium and sodium are changed to the corresponding permanganate by the ac t ion of the carbon dioxide and water in the atmosphere, while those of barium and strontium are loaaffected by theee agencies . The l a t t e r manganate8 cannot be changed, quan t i t a t ive ly , by use of sulphuric acid, carbon dioxide or sulphur dioxide. Hi t r i c acid af fec ts a quant i ta t ive change* iw ** Suggestions for the manufacture of Uanganates. I. From Schlesinger Mullinix and Popoff -(a) "It is very important to pulverize the ores very finely, and to keep them finely divided in the kilns in order to obtain the highest possible yields. Some ores are more difficult to handle in this respect than others." (b) "The residual manganese dioxide sometimes deteriorates on repeated use. This may be caused by absorption of impurities from the solution of the dioxide before it has haet time to dry out is thoroughly washed with water or boiled with dilute nitric acid, its effectiveness for the process may be restored." II. It is advisable to use ores of a relatively high degree of purity, since impurities, such as silica, unite with sodium hydroxide at the temperature (£00°C) of the process and thus lower the yield. Ill* For the test yields it is advisable to use a water, carbon dioxide free current of air. Although continual stirring is unnecessary it is no doubt advisable to keep materials intimately mixed. IV. The time required to complete the oxidation to manganate with mixes of -£ inch thickness, stirred at half hourly intervals, is from one to two hours. V. It is well to remember that in case of sodium and potassium the manganate can be changed to the permanganate by (T V > -26 -hydrolysis, while in case of "bari-am and strontium, nitric acid is well suited to affect the transformation. -) 1 . f - 2 7 -Uotes : (1) Potassium permanganate has been employed i n t h e l a b o r a t o r y fo r a long time a s an o x i d i z i n g agen t , and is l a r g e l y used in vo lumet r ic a n a l y s i s * Hoffman in 1859 showed t h a t t h i s s a l t toge th er w i th o t h e r manganates and permanganates a c t s as a v a l u a b l e d i s i n f e c t i n g agen t and i t s a p p l i c a t i o n fo r t h i s purpose has now become so g e n e r a l t h a t t h e s e compounds, which a t t h a t t ime were found only i n t h e l a b o r a t o r y , a r e now made in thousands of tons* (2) Manganate e x t r a c t e d with w a t e r r e a c t s by h y d r o l y s i s to form permanganate accord ing to t h e fo l lowing equat ion -3K2 Mn04 +• 3H20 s 2KMn04 -4- Mn02 + 6K0H The r a t e of t h i s r e a c t i o n i s i n c r e a s e d by a d d i t i o n of a c i d , or by b o i l i n g , o r by pass ing carbon d i o x i d e , su lphur d i o x i d e , or c h l o r i n e through the s o l u t i o n * Secondary r e a c t i o n s r e s u l t i n some c a s e s , due to the p re sence of manganese d i o x i d e , caus ing a r educ t ion of t h e permanganate* (3) Journa l of I n d u s t r i a l and Engineer ing Chemistry -Vol . 1 1 , Wo. 4 (191? ) , Page 317-323-(3a) Z. Blektrochem, 16(1910) 104, 170. (3b) Ber. 43(1910), 381, 448; 44 (1911), 777; Z.Elektrochem, 16(1910), 649; 18(1910), 718; Z. anorg.Chem., 73(1912),101. (3c) Compt. rend*, 151, 69.-


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