Apr., 1919
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
t h e titration is t o be completed with permanganate, t h e sulfuric acid solution is diluted t o 2 5 0 cc. with hot water and titrated a t 80' C. t o t h e first pink color. At t h e same time like quantities of sulfuric and hydrochloric acids are evaporated, diluted, and titrated in similar fashion t o obtain a blank correction for t h e vanadium. When t h e titration is t o be made electrometrically, t h e sulfuric acid solution is diluted t o 2 5 0 CC:. with hot water, oxidized with silver nitrate and ammonium persulfate as described elsewhere' b y one of US, and titrated with ferrous sulfate. The weight of variadlum so found is multiplied b y 1.784 t o convert it into t h e corresponding weight of t h e oxide Vs05. This weight is subtracted from t h e weight of the resiVzO5. The corrected weight of t h e oxide due UaOs USOSis converted into t h e corresponding weight of uranium by multiplying b y 0.8483 from which the percentage of uranium can be calculated. A solution of uranium was prepared b y dissolving about 4.5 g. of uranium nitrate in one liter of water. This salt was made by t h e J. T. Baker Chemical Company and was described as containing less t h a n 0.001 per cent of sulfur trioxide, and as being free from alkali metals, alkaline earth metals, uranous salts, and other foreign metals. We evaporated 50 cc. of this solution in a platinum dish and ignited t h e residue as described above. By this analysis we found 0.1340 g. of t h e oxide U308. I n another experiment we acidified 50 cc. of t h e solution with sulfuric acid, a n d added 0.05 g. aluminum, I g. ammonium phosphate, and 0 . 0 2 5 g. vanadium as ammonium vanadate. On carrying out t h e procedure described above, we found 0.1350 and 0.1343 g. of t h e oxide U308. Electrometric analysis of t h e uranium salt indicated less t h a n 0.1 mg. of vanadium in this amount of solution. Below we have given a few determinations of uranium in z samples of steel. One of these was a nickel-chromium steel in which t h e approximate respective percentages of manganese, nickel, a n d chromium were 0.35, 3.00, and 1.45. The other was a high-speed steel in which t h e approximate respective percentages of manganese, chromium, tungsten, vanadium, and cobalt were 0.25, 4.00, 14.00,2.00, and 5.00. T o both of these samples definite amounts of t h e uranium solution were added. The determinations appear below:
+
Per cent U Present
........... 5 . 6 9 High-speed S t e e l . . ................. 5 . 6 9 Nickel-Chromium Steel..
Per cent U Found 5.71 5.64 5.65 5.65
T h e determhation of uranium in ferro-uranium is similar t o t h e analysis of steel for this element. A I g. sample was dissolved in a small amount of concentrated nitric acid, and when solution was completed, hydrochloric acid was added cautiously t o t h e amount of 30 cc. The solution was then evaporated t o dryness with t h e object of separating silica. After t h e removal of silica, t h e procedure was identical with t h a t in t h e case of steel. RESEARCH DEPARTMENT MSDVALE STEELAND ORDNANCE COMPANY NICETOWN, PHILADELPHIA 1
J. A m Chem SOC., 88 (1916), 350.
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STUDIES ON MANGANATES AND PERMANGANATES-I THE COURSE O F THE REACTION BETWEEN MANGANESE DIOXIDE, POTASSIUM H Y D R O X I D E , AND OXYQEN, A N D THE MANUFACTURE OF P O T A S S I U M MANGANATE
B y H. I. SCHLESINGER, R. D. MULLINIX AND S. Poposal Received September 23, 1918
Among t h e important chemicals which in t h e past have been imported a t so low a price t h a t American manufacturers had not, up t o the time of the European war, undertaken its production t o any large extent is potassium permanganate. The obvious need for t h e product and its extreme scarcity have, however, made its manufacture in this country a necessity, and a number of plants are now engaged in producing it. Some of them encountered certain difficulties when t h e y began continuous operation a n d one of us was asked b y t h e Bureau of hiIines t o investigate t h e matter. Out of this investigation a number of results of both scientific and practical interest have developed and of these t h e most important are reported in this paper. There are several methods for manufacturing t h e permanganate; t h e most widely used is apparently'the one in which potassium manganate is first prepared as an intermediary product b y heating a mixture of potassium hydroxide and manganese dioxide in a current of air. The resulting mix is then extracted with water or a dilute solution of caustic potash and t h e solution of manganate thus obtained is converted into a solution of t h e permanganate. The methods employed for this latter step need not be discussed here as t h e research now t o be reported deals only with t h e first step. It is necessary, however, t o point out t h a t in this second step a large proportion of the caustic combined in t h e first is again liberated either in a form in which it can be directly utilized or in which i t can be used after suitable treatment, depending upon t h e process used for t h e second step. Furthermore, owing in part t o t h e spontaneous decomposition of manganate and permanganate solutions, in part t o manganese dioxide precipitated out in t h e second step and in part t o t h e fact t h a t t h e first step never results in complete interaction of t h e components, there is always a relatively large amount of manganese dioxide left over from each treatment. It is therefore self-evident t h a t economical working of the process not only requires as high a yield as possible of t h e manganate in t h e first step, but t h a t it is also necessary t h a t the neutralization of t h e residual and recovered manganese dioxide and potassium hydroxide must be highly successful. Difficulties have apparently been encountered in both of these phases of t h e process and we have therefore made a study of t h e factors which influence their successful carrying out. The conversion of manganese dioxide into potassium manganate b y heating it in a current of air with potassium hydroxide has been extensively investigated. The most recent and apparently t h e most thorough of these investigations are those of Askenasy and 1 This paper is taken from material presented to the faculty of the Univeisity of Chicago b y R. D. Mullinix and b y S. Popoff in part fulfillment of the requirements for the degree of Doctor of Philosophy.
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Klonowskil and of Sackur2 and his associates. T h e rotating drum, fitted with iron ribs parallel with t h e researches of t h e two groups of investigators do not axle and with openings for removing material for lead them t o t h e same conclusion. While t h e first analysis. T h e drum was rotated in an iron housing named seem t o hold t o t h e opinion t h a t t h e reaction and was heated by gas. T h e axle was hollow and follows t h e course usually found in t h e text books, broken i n t h e middle of t h e drum. Through one end represented by t h e equation of t h e hollow axle preheated air was introduced and into t h e other end a thermocouple was loosely fitted. 4KOH zMnO2 02 + zKzMn04 zHzO. Sackur concludes t h a t potassium manganate is never The charge, prepared as above, was placed in t h e drum formed i n this way, b u t t h a t t h e product obtained in and with it a fairly large number of 3//4 in. steel ball;. t h e reaction is a “mangani-manganate” which can be AS t h e d r u m rotated slowly ( 2 0 r. p. m.) t h e balls were represented by t h e formula, zK~WIn03,3K2Mn0~,lifted by t h e ribs in t h e sides of t h e drum and dropped 3 K z 0 . I n this conclusion he is corroborated by t h e back on t h e material, t h u s pulverizing t h e latter work of Auger3 who obtained a compound of similar thoroughly throughout t h e process. T h a t this concomposition b y heating potassium permanganate with tinuous pulverization, which is recommencizd by the excess of potassium hydroxide. If Sackur’s con- authors named above, considerably improves the yield clusion is correct it is clear t h a t t h e highest yield t h a t was corroborated by our own results, which need not I n only two particulars did we could be obtained in t h e reaction in terms of t h e be recounted here. depart from t h e method of Askenasy and Klonowski. amount of manganese dioxide oxidized t o t h e manganate stage could be only 60 per cent, since t h e I n t h e first place in making t h e mix we used ore and remaining 40 per cent must always remain as man- alkali i n varying proportions as described below while ganite. I n support of this consequence of his theory they used mixtures containing approximately equal of t h e course of t h e reaction Sackur cites his own parts by weight only. I n t h e second place we used a experiments which show a maximum yield of between somewhat lower temperature, keeping our mixes i n 5 5 and 66 per cent, t h e results of Askenasy and t h e rotators a t about 450’ C. I n one minor matter Klonowski who obtained similar yields, and t h e state- we also departed from t h e older investigation rements, made personally t o Sackur b y German manu- ferred to. T h e preliminary drying was carried out facturers, t h a t a yield of 60 per cent was t h e maximum in a n electrically-heated oven instead of over a free attained in p r a ~ t i c e . ~When we first undertook this flame, b u t this was merely a matter of convenience in investigation t h e manufacturers with whom we were regulating t h e temperature a t this stage and in avoidcooperating were not obtaining yields as high as those ing too great a contamination with carbon dioxide, demanded b y Sackur’s theory and we, therefore, which is likely to occur when t h e heating is carried attempted t o determine t h e best conditions for duplica- out over t h e free flame. T h e heat was so regulated ting his results. The outcome of this work has been i n this part of t h e process t h a t when t h e mix was t o show t h a t Sackur’s theory of t h e reaction is in- completely d r y its temperature remained in t h e correct, for we were able t o obtain yields corresponding neighborhood of 300’ C. T h e preliminary heating, while i t results i n t h e abt o a conversion of over 98 per cent of t h e manganese dioxide into t h e manganate by use of t h e methods of sorption of some oxygen and i n some experiments t o work and of t h e proportions of t h e reacting substances quite a large amount, is in general carried out merely t o prepare t h e material for t h e treatment in t h e r o t a r y which are discussed below. kilns in which t h e chief absorption usually takes I-THE COURSE O B T H E REACTION B E T W E E N MAKGANESE place. T h e mass was usually analyzed after t h e DIOXIDE, POTASSIUM HYDROXIDE A N D OXYGEN preliminary heating was completed and, after i t was I n our experiments we decided t o follow t h e pro- placed i n t h e kilns, analysis was repeated every few cedure of Askenasy and Klonowski.6 This procedure hours until oxygen absorption seemed t o cease. T h i s consists, briefly stated, in mixing t h e finely ground could be done without cooling off t h e whole mass beore with a concentrated solution of caustic potash, cause material could be withdrawn from t h e cylinders drying t h e mix in a current of air t o such a consistency through t h e openings mentioned. The method of t h a t when cool it can be well powdered and will no analysis was t h a t employed by Askenasy and longer become soft on raising it t o t h e higher tempera- Klonowski. tures t o which it is next exposed, and finally heating Before proceeding t o t h e discussion of t h e final this powdered material in a current of air in a n ap- results of this part of t h e investigation one important ’ paratus in which t h e mix can be continually ground detail must be taken up. I n one of our earlier experiwhile being heated. This apparatus consisted of a ments a mix was heated in t h e rotary kiln, as de1 Z . Eleklrochem., 16 (1910), 104, 170. scribed, first i n a n atmosphere of dry air and t h e n i n 2 Ber., 43 (1910), 381, 448; 44 (1911), 777; Z . Eleklrochem., 16 (1910), oxygen. T h e potassium manganate content in air 649; 18 (19101, 718; Z. unoyg. Chem., 73 (1912), 101. rose t o 54.6 per cent, which is about 60 per cent of t h e Compl. rend., i61, 69. 4 I t will be noted that the highest yields obtained by Sackur are a yield possible according t o t h e equation given above. little higher than permitted by his theory. Sackur gives an explanation Further heating in air caused a slight lowering of t h e of this which the work herein reported shows to be incorrect, Askenasy in one expeiiment obtained very much higher results than Sackur. The yield. I n oxygen t h e content of manganate rose t o experiment, however, has not been cited in refutation of Sackur’s criticism 63 per cent, a t which point absorption of oxygen came of Askenasy and it is, therefore, likely that the result was never confirmed. t o a n end. T h e mass was then treated with enough 5 LOG. cii., p . 1 7 5 .
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water so t h a t t h e mixture could be well stirred. It limits.‘ The experimental d a t a of this series are given was then dried as described above and reheated in in Table I and are reproduced graphically in Fig. I . oxygen in the kilns a t 4joO. The manganate content TABLEI-SHOWING T H E I N F L U E N C E O F VARYINQ T H E RELATIVEAMOUNTS OB POTASSIUM HYDROXIDE A N D MANGANESE DIOXIDE ON THE now rose t o 77.9 per cent and a repetition of this proY I E L D OF MANGANATE Ratio 1.20 1.55 2.11 2.28 2.43 2.49 2.62 2.79 3.12 3.62 4.21 cedure finally raised it t o 81 per cent, representing a Per cent yield of 92 per cent of t h e theoretical on t h e assumption KzMnOa 35.1 51.2 73.8 77.2 79.8 81.1 76.5 68.9 57.4 41.7 36.4 Per cent t h a t manganate and not mangani-manganate is the yield 29.5(a) 47.6(a) 79.4 R6.4 95.0 98.4 94.3 87.8 75.5 61.0 57.9 (a)In the experiments in which 1.2 and 1.55 moles of potassium hyproduct obtained. Frequent repetitions of analogous droxide, respectively, were used for each mole of manganese dioxide, there experiments showed t h a t it was t h e moistening with is not enough of the former t o convert all of the manganese dioxide into manganate. If the yield is calculated on the basis of the amount of potaswater which raised t h e final yields, as merely b y this sium hydroxide converted into manganate the results are 49.2 and 60.4 per cent, respectively. treatment and without t h e use of oxygen we have been able t o reproduce these and higher yields. Two I n t h e table the first row gives t h e value of t h e ratio questions were raised b y this result. I n t h e first moles of potassium hydroxide t o one mole of manplace it would seem as if manganate is not as sensitive ganese dioxide; t h e second row, t h e final content of t o moisture as usually stated. To bear this out t h e potassium manganate contained in t h e masses; and t h e following may be cited. Steam was passed over a third row, t h e per cent yield. The last set of d a t a product containing 78.6 per cent of potassium man- was obtained by determining for t h e final sample t h e ganate for 2 0 min. while t h e mass was kept at 4joO. content of potassium manganate and t h e total manA t t h e end of this time t h e manganate content had ganese,2 and calculating what per cent t h e manganate fallen only t o 76.8 per cent. I n t h e second place there found was of t h a t possible if all of t h e manganese had is a possibility t h a t moisture is necessary t o obtain t h e been converted into manganate. I n Fig. I t h e ratios highest possible yields. It is t o be noted t h a t in the mentioned above are plotted against t h e percentage experiment cited above t h e absorption of oxygen from yield. ( d r y air stopped a t about 6 0 per cent of t h e amount of manganate possible on t h e assumption t h a t it is t h e product formed. This accords with Sackur’s theory of t h e reaction. I n a similar experiment t h e absorption of oxygen from d r y air stopped a t t h e same point. I n two other experiments in which manganese dioxide from a different source was used the same thing was observed. But in a fifth experiment t h e content of manganate rose in dry air until a maximum yield of S7 per cent was reached without remoistening. On t h e other hand we find t h a t if instead of using dry air we employ air t h a t has been moistened b y passing it throtigh water there is much less likelihood t h a t t h e reaction will stop before t h e maximum possible oxidation has been attained. The bearing which these results may perhaps have on t h e theory of t h e reaction will be taken up below; t h e experimental results have been introduced a t this point t o explain how t h e maximum yields reported in t h e next paragraph were FIG. I obtained. Based on t h e results described above our procedure was invariably t o allow absorption of Inspection of t h e table and the curves shows t h a t t h e oxygen t o proceed as far as i t would in air, then t o yield of manganate varies with t h e relative amount of remoisten and reheat the material in air, and finally caustic potash used. From t h e curve it can be seen t o reheat in oxygen. The latter treatment seems t h a t t h e percentage of manganese converted into merely t o hasten t h e absorption of t h e last part of t h e manganate is directly proportional t o t h e relative oxygen and not t o raise t h e yield above t h a t which .amount of t h e alkali since t h e curve representing t h e could be reached in air if enough time and repeated relationship is a straight line. It is furthermore seen remoistening were employed.‘ t h a t this line intersects t h e abscissa representing comThe fact t h a t a yield of nearly I O O per cent of t h e plete conversion when there are z1/2 moles of potastheoretical can be attained-a fact t h a t is important sium hydroxide for each mole of manganese dioxide. because of its practical aspect and because it proves The equation for t h e reaction given above, which is Sackur’s theory of t h e course of the reaction incorrectt h e one t h a t was accepted before Sackur’s work and was discovered as t h e result of a series of experiments is t h e simplest one for t h e reaction, requires only z in which t h e relative amounts of manganese dioxide moles of t h e alkali. A number of hypotheses might and of potassium hydroxide were varied within wide 1 T h e manganese dioxide was in the form of commercial pyrolusite 1 Askenasy and Klonowski (LOG. cit , p. 11 1 ) describe one experiment in which they moistened the material from time t o time with a few drops of water. They seem t o lay no stress on this point and our experience is t h a t a few drops of water would be quite ineffective. Attention may also be called here t o the German Patent 266,347 (1912) issued to Bergius and Sackur in which moist mixes and oxygen under pressure are used
containing from 80 t o 87 per cent of manganese dioxide in various samples. Each sample was of course analyzed and amounts suitable t o produce the desired proportions were taken. The potassium hydroxide was taken from various sources and was also analyzed before use. 2 This was determined by Sackur’s modification of Volhard’s method, Ber., 43, 382.
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be advanced in explanation of this phenomenon. I n all of t h e manganese Into manganate by t h e use of an t h e first place t h e manganese dioxide used for these excess of very nearly one-half a mole of potassium experiments was pyrolusite containing about 87 per hydroxide over t h a t required by t h e simplest equation cent of t h e dioxide. Some of t h e impurities like for t h e reaction, i t also shows very clearly t h a t a silica are capable of reacting with t h e caustic, thus larger excess of t h e hydroxide again lowers t h e yield. decreasing t h e amount of free alkali in t h e mix. T h e It will be noticed t h a t of t h e points representing t h e same effect would be produced by carbonate originally larger excess of caustic, three lie on a straight line. contained in the caustic and by carbon dioxide ab- The fourth point no longer is on this line but corresorbed during t h e unavoidable manipulation of t h e sponds t o a yield of very nearly 60 per cent. T h e materials. I n this connection i t is interesting t o fifth point is also fairly close t o a 6 0 per cent yield. note t h a t the amount of alkali, uncombined as potas- Now it is practically impossible t o attain equilibrium sium manganate, is very nearly half a mole per mole at t h e temperature of these experiments (450’) with of manganese dioxide in mixes of every composition. mixes containing a very large excess of potassium hyAgainst this hypothesis t h e following facts must be droxide because t h e material becomes soft and sticky raised: I n the first place, t h e amount of alkali which and is soon so firmly attached t o the walls of t h e would have t o be used up by impurities is larger t h a n cylinder in which it is heated t h a t its removal for t h e impurities contained would be expected t o combine analysis and pulverization in t h e cylinders are alike with. I n t h e second place, t h e amount of alkali un- impossible. This was particularly noticeable in t h e combined as potassium manganate is not quite con- experiment in which t h e ratio was 4 . 2 moles of t h e s t a n t b u t increases steadily, if slightly, with decrease hydroxide t o one of t h e dioxide and t h e heating had in total alkali. Finally, t h e results of Sackur’s experi- t o be interrupted before absorption of oxygen had ments contradict this view as can be shown b y t h e stopped.1 Consequently we have indicated b y t h e following: I n experiments in which 2.0 moles of dotted line t h e course which t h e curve would probably alkali were used, every one of pure manganese dioxide, take had equilibrium been established in every case. he obtained yields as high as 66 per cent without reThe interpretation of t h e curve is simple. Calculapulverizing or remoistening t h e material. We should, tion, based on t h e d a t a presented, shows t h a t between therefore, expect t h a t his yields would be low. The 2 and 3 moles of potassium hydroxide are required mole needed for t h e comcurve reproducing our results indicates t h a t for this beyond t h e excess of composition of mix a yield of 7 2 per cent is t o be ex- plete conversion of manganese dioxide into manpected-a value not far from t h a t obtained b y Sackur ganate for t h e decomposition of one mole of potasin view of ‘ ‘ zxoerimental method. If, on t h e other sium manganate. This corresponds fairly well, though hand, w ? assume t h a t half a mole of t h e alkali in our not exactly, with t h e equation experi v e n t s is withdrawn from reaction b y impurity we should compare Sackur’s result with our d a t a for t h e ratio moles of alkali t o one of t h e dioxide. It seems t h a t t h e mangani-manganate described b y For this t h e yield would be only 4j.j per cent. It is Sackur is t h e final product of t h e reaction when a seen, therefore, t h a t Sackur’s work on pure dioxide large excess of alkali is used. It is not, however, t h e agrees quite well with ours on pyrolusite, thus indica- sole product of t h e reaction as Sackur thought and i s ting t h a t t h e impurities in t h e latter are without great nQt formed unless there is a n excess of alkali greater influence. It is, however not prmible t o give any t h a n ‘/z mole. It therefore plays no r8le in the manuadequate explanation for t h e phenomenon until t h e facture of manganate by t h e method discussed in this work has been repeated a t other temperatures in order t o ascertain whether t h e necessity of using an is not borne out by the one experiment in which in dry air a yield of over 60 per cent was obtained, but it is difficult t o exclude the possibility of the of half a mole of ,.he alkali llas theoretical presence of water retained in mixes prepaied as these are. On the other significance. At all events, it is Certain t h a t Sackur’s hand, the dark violet color of the mixes containing a n excess of alkali not conclusion t h a t mangani-manganate is the sole product greater than 1/z mole indicates t h a t manganates are formed even when the yield is only 60 per cent and t h a t the cessation of oxygen absorption is of t h e treatment of mixes of potassium hydroxide and due to incomplete mixing of the components before remoistening. Why the manganese dioxide in air and t h a t , therefore, t h e cessation of oxygen occurs so often a t 60 per cent yield can probably be maximum attainable yield is 60 per cent, is i n c o r r e ~ t . ~ explained ’ ~ ~ ~ as follows. In the first place, the absorption of oxygen after 60 per cent of the possible amount has been taken up is slow. In the While t h e curve shows t h a t it is possible t o convert second place, as will be seen from the curve, excess of alkali decomposes L
1 That the products are not mangani-manganates is borne out by their appearance Mangani-manganates are green’ qolid manganates are of a very dark violet, almost black hue, not unlike permwganates. All of the products corresponding t o the portion of the curve AIOW under discussion had this color. They were free from permanganate. 2 It is manifest that since excess of alkali is required, the yield can never reach 100 per cent if the amount of alkali used is taken as a basis. The maximum yield on this basis would be 80 per cent since mole of excess is required over the 2 moles demanded by the simplest equation. Even this arbitrary way of calculating departs very greatly from the maximum of 60 per cent demanded by Sackur. 8 It is interesting to consider the possibility presented by the experiments on the effect of moisture cited above. In view of the fact that quite a number of the experiments showed cessation of oxygen absorption when the yield was 60 per cent, one might be led t o believe t h a t the manganimanganates are formed in the absence of moisture and t h a t the catalytic action of water is required to effect their oxidation t o manganates. This
the manganate into mangani-manganate, As the alkali is the soluble component, i t is likely that certain portions of the dioxide are coated in the drying process with an excess of the alkali and these portions, therefore, are likely t o become converted into mangani-manganate Other portions of the dioxide, therefore, are deficient in alkali and do not get oxidized t o a maximum. T h a t the oxidation sbould appear t o stop a t 60 per cent is not. after all, very surprising, and we incline at present to the view that this phenomenon is a coincidence and not evidence t h a t water is required t o oxidize the mangani-manganatcs. 1 It is interesting t o note t h a t in the other experiments the data pre sented represent true equilibrium conditions, inasmuch as the final values have been obtained both by decomposing mixes high in manganate by addmg excess of alkali or of manganese dioxide and by starting with, potassium hydroxide and manganese dioxide. 2 Of the 5 mols. of manganate only 2 are decomposed t o manganite. Hence 3 moles of KOH are needed according t o this equation for one of t h e . manganate.
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paper.' This conclusion is borne o u t by t h e appearance of t h e mixes after the reaction is complete. T h e mixes which are deficient in alkali have the dark violet, almost black hue, characteristic of t h e manganates even though t h e reaction has gone only half way to completion as, for example, in t h e experiments in which 1.2 and 1.5 moles of caustic were used per mole of manganese dioxide. On t h e other hand, those mixes which contain an excess of alkali and which show a similarly low yield have the deep green color of ma.ngani-manganates.2 It is self-evident t h a t t h e results thus obtained are of great practical interest in addition t o t h e purely theoretical interest they possess, for they mean t h a t in order t o obtain good yields of manganate in this process t h e manufacturer must regulate very closely his proportions of manganese ore and caustic, as either a deficiency or a n excess of I O per cent of alkali will lower t h e yield by I O t o 15 per cent. I n the second place t h e curve shows exactly what yield should be obtained for whatever ratio may be employed for any given mix a n d will give t o the manufacturer a criterion for judging whether recourse t o remoistening will be profitable or whether recausticizing of the alkali is necessary. 11-THE
I N F L U E N C E O F I M P U R I T I E S , E S P E C I A L L Y SODIUM, O N T H E COURSE OF T H E REACTION
While t h e part of t h e investigation reported in t h e first section of this paper makes clear why previous investigators have not succeeded in converting all of t h e manganese dioxide into manganate, i t sheds no light on t h e question raised by t h e fact, reported t o us by a manufacturer, t h a t new caustic a n d new manganese dioxide m a y give very much higher yields t h a n are obtained when t h e residual and recovered materials are mixed with t h e new. It is manifest t h a t there can be only two possible causes for t h e deteriorationeither impurities are introduced into t h e materials in t h e course of t h e process or the manganese dioxide must become changed into a less active modification. 1 It must be explicitly stated t h a t the conclusions we have reached refer only t o the conditions obtaining a t 450'. Maay of Sackur's experiments were carried o u t a t nearly 900'. It is possible t h a t at temperatures as high as this manganates decompose into mangani-manganate5 even without a n excess of alkali, since the decomposition temperature of pure potassium manganate in an atmosphere of air is approximately 600'. Sackur would nevertheless not have been justified in applying his deductions t o conditions a t lower temperatures. The reason why a t lower temperatuies ha was unable t o obtain yields corresponding t o the formation of manganate i s that, as inspection of his data reveals, he used either too little or too much alkali. 2 There is a n apparent contradiction in the statements t h a t potassium hydroxide can decompose the manganate and t h a t a t the same time manganate is not formed unless a n excess of the hydroxide is present. Thus in the early stages of the treatment there is only a little of the manganate formed and there is, therefore, a large excess of alkali. Or, take for example, the result in the experiment in which the ratio of alkali t o dioxide is 1.55 moles of the former t o 1.0 of the latter. Here the yield is only 47.5 per cent. The final mix, therefore, contains 0.476 mole of the manganate and 0.6 mole of alkali, or an excess of about 1.2 moles of alkali for each mole of manganate, and it might be thought t h a t this excess ought t o decompose t h e manganate. This contradiction disappears, however, if the very logical assumption be made t h a t the potassium hydroxide and manganese dioxide combine initially t o form potassium manganite and t h a t this is subsequently oxidized to the manganate. I n this connection i t is interesting t o note t h a t when the components are first mixed and dried the mass has a green color. When the excess of alkali does not exceed 1/z mole, this color rapidly changes to t h a t of the true manganates. Apparently then manganiite and manganite do not combine t o form the double compound postulated except in the presence of excess of alkali.
321
I n order t o clear up this point we proceeded, after we had determined what vields might be expected as has been described, to work with the recovered alkali a n d t h e residual dioxide. While a few experiments were carried on in which both were used, the yields obtained were so very low t h a t we abandoned this line and a t tacked the question by working with new manganese d:oxide ore and recovered alkali in one set of experiments and with residual manganese dioxide and new caustic in another set. The first of these two sets of experjments was the one in which new ore and recovered caustic were used t o make up the mixes. T h e caustic was furnished us in t h e form of a fairly concentrated solution. I t was colored green by a small amount of unconverted manganate. After analysis' of t h e solution i t was mixed with enough of the ore t o produce a mix of t h e desired proportions. This was then treated exactly as has been described i n the earlier portions of t h e paper. The mixes were made up t o contain from 2.17 t o 2.33 moles of potassium hydroxide t o one mole of manganese dioxide-a proportion chosen because it conformed t o t h a t used by the manufacturer with whom we were cooperating and from whom we obtained all of the recovered or regenerated materials. Reference t o the curve will show t h a t with new caustic and new ore we should have obtained with these proportions yields of about 8 5 per cent When we substituted t h e recovered alkali for t h e new a very striking lowering of the yield resulted, for we were not able t o obtain one better t h a n about 2 7 t o 30 per cent and repeated remoistening and treatment with oxygen even under a pressure of 40 lbs.2 produced no improvement. There is, therefore, no doubt t h a t these solutions contain some impurity which interferes with the success of t h e reaction. T h e foreign substances present in greatest amount were carbonate, chloride, manganate, silicate, .and sodium. I t was found t h a t t h e first four named had no appreciable effect on t h e yield when they were separately added t o new materials. Likewise, no other impurities removable by calcium hydroxide could have been responsible for t h e difficulty, since careful causticization of the liquor did not improve it.3 The case was found t o be quite different when t h e effect of sodium was investigated. Analysis of t h e liquors furnished us showed in different samples t h a t from 2 5 t o 40 per cent of t h e alkali was in t h e form of sodium hydroxide. When mixes were made up from 1 Before analysis of the solutions, they were freed from manganate b y reducing i t t o manganese dioxide by the addition of a drop or two of Iormaldehyde solution. After the manganese dioxide had been filtered off, the clear solution could be titrated for free alkali or carbonate by any of the customary methods. The use of formaldehyde, while not entirely free from objection, introduced no error large enough t o be of importance for this work. 2 A series of experiments was conducted to determine the effect of oxygen under pressuie (20 t o 40 lbs.). So f a r as we have been able t o determine up t o the present such treatment merely hastens the oxidation but does not affect the final yield. 3 The recovered alkali must of course be causticized from time t o time since the carbonate is apparently quite inert a t the temperatures best employed for the manufacture of manganate. How often this should be done can easily be determined by use of the curve, which shows how great a reduction in yield a given decrease in free alkali will cause.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
322
new material in which we used pure sodium hydroxide and pure potassium hydroxide in these same proportions t h e yields resulting were, respectively, 3 8 and 2 7 per cent. I t was clear at once t h a t here lies t h e source of t h e difficulty. I n view of t h e fact t h a t , even if t h e original caustic contains only a small amount of sodium (the latter is bound t o accumulate as t h e caustic is used over and over again),' it seemed advisable t o subject t h e influence of sodium t o a systematic study, the results of which are discussed in t h e following paragraphs. For this purpose we made up a series of mixes from the pyrolusite and sodium' and potassium hydroxides in which t h e mole ratio of t h e alkali t o manganese dioxide was kept a t 2.28 t o 1.0, b u t in which t h e proportion of sodium hydroxide was varied in successive experiments from o t o I O O per cent of t h e total alkali. The results of this series are reproduced in Table 11. I n t h e table t h e first column contains t h e amount of sodium hydroxide in t h e total caustic expressed in weight per cent; t h e second column, t h e relative amount of sodium hydroxide in mole per cent; t h e third column, t h e per cent b y weight of manganate obtained b y t h e first, heating in moist air; t h e fourth column, t h e per cent of manganate obtained after remoistening and reheating in moist air as previously described; t h e fifth column, t h e per cent of manganate obtained when oxygen was passed over t h e mixes which no longer took up oxygen from air; and t h e sixth column, t h e percentage yield determined as already describedS2 THE EFFECT O F SODIUM HYDROXIDE ON THE YIELD MANGANATE Mole Mn04 MnO4 MnO4 Per cent in air Remoistened in 0 2 Yield NaOH Per cent Per cent Per cent Per cent 45.0 45.9 85.0 0 45.0 25 33.5 35.6 39.0 71.1 19.2 26.0 44.0 50 15.8 16.7 26.5 75 16.7' 15.5 100 15.2 15.0 15.5 23.4
T A B L E 11-SHOWING
Weight Per cent NaOH 0.0 19.5 41.5 68.2 100.0
OF
The depressing effect which substitution of sodium for potassium hydroxide exerts on t h e yield of manganate is strikingly shown b y t h e table. There are two possible hypotheses which may be used t o explain t h e phenomenon. The first is based on t h e work of Sackur? who found t h a t t h e mangani-manganate which he obtained a t high temperatures h a d t h e formula NazMnO3.NazMnO4.zNaSO and therefore represents a lower stage of oxidation t h a n does the potassium mangani-manganate of t h e 3 KzM n 04.3 K2 0. We have shown , formula z KzM n 03. however, t h a t a t t h e temperatures used in this investigation, as well as in practice, t h e manganate and not t h e mangani-manganate is formed when potassium hydroxide alone is used. If t h e explanation 1 This is due to the fact that sodium permanganate is extremely soluble and t h a t therefore only the potassium is removed when the permanganate is crystallized out. 2 The reader must note t h a t the percentages given in the third, fourth, and fifth columns refer t o per cent by weight of MnO4 and not to the amount of the sodium or the potassium salt. We have made this change because in those cases in which both sodium and potassium hydroxide are used, both the sodium and the potassium salt are probably formed The relative amount of the t w o is not known and therefore the method of expressing t h e results here used is the only one free from objection. * B e y . , 44 (1911), 777.
Vol.
11,
No. 4
based on Sackur's interpretation of t h e reaction is t o be used, we must assume t h a t sodium manganate is much less stable t h a n is t h e corresponding potassium salt. This assumption is not borne out b y some preliminary experiments made b y us on a fairly pure sample of sodium manganate prepared from sodium permanganate according t o t h e directions of Auger Our experiments indicate t h a t sodium manganate is fairly stable unless an excess of sodium hydroxide is present, under which conditions t h e sodium salt, like the potassium salt, decomposes into t h e manganimanganate. It seems much more likely, then, t h a t t h e behavior of mixtures of sodium hydroxide and manganese dioxide will prove t o be similar t o t h a t of mixtures of potassium hydroxide with t h e dioxide. It is, therefore, quite possible t h a t t h e peak in t h e curve for sodium hydroxide might correspond t o a different composition t h a n for potassium hydroxide, or t h a t t h e angle at t h e peak is a much smaller one.p The final interpretation must await t h e completion of experiments on sodium manganate which will be reported in a later paper. 111-DETERIORATION
OP
THE
RESIDUAL
MANGANESE
VARIATIONS I N T H E B E H A V I O R I N M A N G A N E S E D I O X I D E B R O M V A R I O U S SOURCES
DIOXIDE AND
Although we have shown in t h e preceding section of this paper one of t h e causes of t h e decrease in t h e efficiency of t h e process when recovered material is used, there is still t h e possibility t h a t t h e recovered manganese dioxide also may not be as satisfactory as t h e new ore. Manufacturers agree t h a t ores from various sources may differ greatly in t h e ease and completeness with which they can be converted into manganate although they may contain equal amounts of manganese dioxide. I n this connection one of our experiences is of interest. A second series like t h a t described in t h e second section of this paper was performed with a different ore containing approximately t h e same amount of manganese dioxide. The results of t h e two series are compared in Table I11 in which t h e first row gives the mole per cent of t h e total alkali present as sodium hydroxide, t h e second row t h e final yield obtained with t h e first ore, and t h e third row t h e final yield obtained with t h e second ore. TABLET I I - s € i O W I N C THE BFHAVIOROF DIFFERENT ORE5 25 SO 75 Mole per cent NaOH . . . . . , . . , , . . . , . . 0 Yield with first ore, pcr c e n t . . , , , . . . . . 8 5 . 0 71.; 44.00 26.5 Yield with second ore, per cent. ,. . , . . . 56.3 53. i 39 . O 25.6
100 23.4 21.5
It is seen t h a t the second ore gave very much lower yields when t h e alkali was all in t h e form of potassium hydroxide and t h a t t h e difference becomes smaller as more sodium is introduced. After many ineffectual efforts t o improve t h e yield with t h e second ore we finally found t h a t if it was remoistened more t h a n once as described in the first section of t h e paper t h e yield Compl. rend., 1 5 1 (1910), 69. The only indications we have a t the present as t o whether the ratio, 2.28 moles of sodium hydroxide t o 1.0 of manganese dioxide, lies on the upward or downward portion of the curve if such a curve exists, are contradictory. On the one hand a single experiment in which we used a larger amount of sodium hydroxide gave a considerably higher yield, b u t on the other hand the final mixes of the composition given above are green in color, whereas sodium manganate like potassium manganate is of a very dark violet hue. 1 2
A P . 7 1919
T H E J O U R N A L OF I N D U S T R I A L A N D E X G I J E E R I N G C H E M I S T R Y
for t h e mixture with no sodium was raised t o t h e same value as was obtained with t h e first ore. By this time, however, t h e mixes had been rotated for many hours in t h e kilns and h a d , therefore, become thoroughly pulverized. When we, therefore, ground t h e ore very fine before using i t t h e results were likewise improved. T h e s t a t e of division is n o t , however, t h e sole factor in t h e difference between t h e two ores for we have worked with ore coarser t h a n t h e second and obtained excellent results. A more important factor appears t o be t h e ease with which t h e ore becomes pulverized in t h e kilns (hardness). I n view of t h e facts stated, we therefore made another set of experiments in which we used recovered and residual manganese dioxide with new potassium hydroxide. T h e former was obtained from t h e same manufacturer who had furnished US with t h e recovered alkali described in t h e second section. The ratio of alkali t o manganese dioxide was again 2 . 2 8 moles of t h e former t o one of t h e latter. When t h e old manganese dioxide, as we may call t h e material for brevity, was used just as it was received, it gave uniformly low yields-from 2 j per cent t o 3 5 per cent of t h e theoretical-while we should have obtained about 8; per cent. Since it is well known t h a t manganese dioxide absorbs (or perhaps combines with) relatively large amounts of caustic alkalies, we suspected t h a t t h e old dioxide might be contaminated with considerable sodium hydroxide. We therefore washed i t very thoroughly with water and in some cases boiled i t with dilute nitric acid. When t h e recovered and residual dioxide was fresh i t responded very well t o this t r e a t m e n t ; material which had been kept for some time, and especially material which had dried out, was not much improved. These results point t o t h e conclusion t h a t i t was t h e absorbed sodium hydroxide which was responsible for t h e deteriorating of t h e dioxide and which becomes more difficult t o remove as t h e material dries out. Since the first section of the paper shows how large amounts of residual dioxide can be avoided and as it is not necessary to convert t h e manganate into permanganate by processes in which large amounts of dioxide are reprecipitated, it did not Seem necessary f o r us to follow up this point further. SUMMARY
I-It is found t h a t when manganese dioxide is heated with potassium hydroxide in a current of air t o produce potassium manganate, t h e reaction frequently stops before t h e maximum oxidation stage has been reached. This can be avoided by remoistening and reheating t h e mix; t h e use of moistened air also is helpful. 2-The yield of potassium manganate varies greatly with t h e proportion of potassi11m hydroxide in t h e mixes. At t h e temperatures a t which these exPeriments were carried out and with t h e pyrolusite used, practically all of t h e manganese dioxide is converted into manganate when 2 . 5 moles 'of potassium hydroxide are used for each mole of manganese dioxide. gPThe conclusions Of that in this mangani-manganates and not manganates are obtained
3 23
and t h a t t h e maximum yield attainable is, therefore, only 6 0 per cent is t h u s proved t o be incorrect. 4-Larger amounts of alkali, however, cause t h e manganate t o decompose into a mangani-manganate, similar to, if not identical with, t h a t postulated by Sackur. j-The substitution of sodium hydroxide for potassium hydroxide greatly lowers t h e yield if t h e proportions between alkali and manganese dioxide iiamed are employed. What t h e effect of other proportions would be is as yet undetermined. Care must be taken, therefore, not t o allow sodium t o accumulate in t h e recovered caustic when t h e operation is carried out continuously. 6-It is very important t o pulverize t h e ores very finely and t o keep them finely divided in t h e kilns in order t o obtain t h e highest possible yields. Some ores are more difficult t o handle in this respect t h a n are others. 7-The residual manganese dioxide sometimes deteriorates on repeated use. This may be caused b y absorption of impurities from t h e solution. If t h e dioxide before i t has had time t o d r y out is thoroughly washed with water or boiled with dilute nitric acid, its effectiveness for t h e process may be restored. This work is t o be continued along t h e lines suggested. A number of similar problems connected with t h e preparation of barium manganate remain t o be solved and work on these has also been begun. KENT CHeMrCAL
UNIVERSITY OF CHICAGO CHICAGO, ILLINOIS
THE DETERMINATION OF ZINC AND COPPER IN GELATIN1 B y GEORGES. JAMIESON
Received October 2, 1918
One method used f o r t h e determination of zinc and copper in gelatin is based upon the destruction of t h e organic matter b y digestion with nitric and sulfuric acids.2 After t h e digestion is completed, water is added, and the is made 'lightly alkaline with ammonium hydroxide. Then a measured quantity of hydrochloric acid is added. T h e copper is precipitated as sulfide and filtered. T h e filter containing t h e copper sulfide is digested with nitric and sulfuric acids until a colorless solution is obtained. T h e copper is finally titrated by t h e well known iodide-thiosulfate method. When t h e hydrogen sulfide has been removed from t h e filtrate containing t h e zinc, ammonium chloride is added along with ammonium hydroxide t o make t h e solution alkaline. Enough hydrochloric acid is added t o render t h e solution acid t o methyl orange. After adding a large excess of sodium or ammonium acetate, t h e zinc is precipitated with hydrogen sulfide and filtered. T h e zinc sulfide is dissolved in hydroch~oric acid and t h e resulting filtrate is boiled to t h e hydrogen sulfide. A small amount of ferric chloride is added and a basic acetate precipitation is made in t h e usual manner in by permission of the Secretary of Agriculture. Methods of analysis, A . 0.A . C.,1916, 175.
1 Published 2
