262
T H E J O U R i V A L OF I ! V D U S T R I A L AND Eh’GINEERIiYG C H E M I S T R Y .
analyzed for iron, sulfur, volatile matter and ash. The results follow: TABLEVIII. Bituminous coal.
-
Anthracite.
-_L__,
Exp. I. Per cent.
Constituent. ’ Iron . . . . . . . . . . . . . . 0.65 Sulfur. . . . . . . . . . . . 1 . 0 2 Vol. matter.. 32.49 Ash.. . . . . . . . . . . . . 6.83
......
,
-
Exp. 11. Exp. I. Exp. 11. Per cent. Per cent. Per cent. 0.55 1.07 31.80 6.74
0.48 1.15 5.77 8.37
0.58 1.18 6.13 8.34
We see from these experiments that the greater oxidation in the case of soft coal could scarcely be due to the greater amounts of iron and sulfur present, as these constituents are present to almost an equal amount in the two cases. Rather, the greater oxidation must be due to the fact that the moisture is not so rapidly expelled from the soft coal. The curves shown in Figs. A and B serve to indicate very clearly the general character of the results. The temperatures are plotted as abscissae and the per cent. of moisture as ordinates. The curves of Fig. A represent the results for the bituminous coal, those of Fig. B the results for the anthracite. The total decrease in weight of the coal during the first three hours, which is shown in curve I of Fig. A is practi-
1912
the coal when heated in nitrogen, but this is not much greater for I Z O O than for 75’. Curve IV showing the moisture weighed a t the different temperatures is more difficult t o draw than the others as the results are not as regular. Obviously the result for 100’ is worthless. However, for the sake of completeness the points are indicated. The above considerations show that the errors made in the determination of moisture by the official method are much more serious in the case of bituminous coal than for anthracite. The determination being of little value in the former case, as a t present carried out, we suggest that for this class of coals the method be modified, and that the coals be heated in a current of dry air a t a temperature of a t least I I O O . the moisture given off being weighed directly after absorbing it by anhydrous granular calcium chloride. The results for one coal would then be comparable with those of another while a t present this is not the case. S U M M A R Y. 1t7e may briefly summarize our results as follows: ( I ) K h e n the determination of moisture in coals is carried out according to the official method, the result is much lower than it should be, the error
?SO?
7 9
cally the same for all the different temperatures, the curve being practically a straight line. Curve I1 shows the gradual increase in moisture given off b y %he coal as the temperature rises. Here too we have practically a straight line. Curve 111 represents the variation in the weight of the bituminous coal when heated for three hours a t the different temperatures, in nitrogen. For temperatures above I O O O the weight is constant. This curve lies throughout its whole length far above Curve I, showing the effect of oxidation when the coal is heated in air. The relation of the amount of moisture given off to the temperature when the coal is heated in nitrogen is set forth by Curve IV. The upper portion of the curve lies a little below Curve 11. This could be accounted for by assuming the synthesis of a small amount of water from the oxygen of the air and hydrogen present in the coal. The curves for the anthracite (Fig. B) resemble in some respects those for the bituminous coal. Curve I , showing the relationship between the change in weight of the coal and the temperature a t which i t is heated (in a current of air), is a straight line, as in the case of the soft coal. The total moisture given off by the coal when heated in air shows a maximum a t about 105’ (Curve 11). From Curve I11 we see that there is a continual loss in weight of
April,
1 1 ’ ’
!
I
’
I
’
~
!q-LlIl 100
Fy,B
110 O
1 1 1 I /zo
amounting in the case of some bituminous coals t o 4 0 7 ~of the true moisture. ( 2 ) The oxidation of iron or sulfur or both, and the non-expulsion of a considerable part of the water which probably accounts for the largest errors here involved, are much greater in the case of bituminous coal than with anthracite: due on the one hand t o the moisture remaining in contact with the coal a t a high temperature for a much longer time, and further to the more porous nature of the softer coal. (3) It was suggested that for bituminous coals the method be modified and that the coal be heated in a current of dry air a t a temperature of a t least IIO’, the moisture given off being weighed directly, after absorbing i t in anhydrous calcium chloride. CHEMICAL LABORATORY, SYRACUSE UNIVERSITY.
A METHOD FOR THE UTILIZATION O F LEAD FURNACE FUME. B y L. S. HUGHES. Received Dec. 18, 1911.
A large item of expense in the operation of lead smelting plants is the treatment of furnace fume. Where the so-called “open-hearth” furnaces are employed this by-product frequently amounts t o more than twenty per cent. of the total ore charge and
April, 1912
T H E JOL’R.VAL OF I S D C S T R I A L
carries approximately that proportion of the original metallic values. Ordinarily, “open-hearth” furnaces are arranged in a single battery below a common flue which receives the fume from all the furnaces. This flue delivers into a series of collecting chgmbers in which the furnace dusts and ashes are deposited. The fan which supplies the necessary draft is placed beyond these chambers and the fume proper is forced b y its exhaust into a cloth filter system of the bag room type which retains the solid fume and filters i t from the furnace gases. From the filter bags the fume falls into a closed brick chamber and is allowed t o accumulate there until i t is several feet in depth. The pile is then set on fire and slowly smolders until the sulfide and carbonaceous ingredients are oxidized. This burning occupies several days and in order to avoid interruption of the furnace operation several independent filt.er systems are used so t h a t any one may be cut off whenever it is necessary to burn the fume therein. TVhen i t is finished the fume is converted into a whitish cinder of approximately the following composition. Per cent. Lead sulfate.. .............................. 55 Lead monoxide . . . . . . . . . . . . . . . 44 Zinc oxide., ............................ 1 Ferric oxide.. ............................... traces
If a sufficient settling system has been employed between the furnaces and the bag room there will be no more than traces of the non-volatile constituents of the furnace charge. Hitherto rio better means of disposing of the burned fume has been devised than that of using i t as a smelting material: most commonly by reduction in a blast furnace, but occasionally in an open-hearth furnace. Attempts have been made to use the unburned fume as a pigment and there is a .small market for i t in the paint trade, but its variable color and certain difficulties in its manipulation sharply limit the demand and the total tonnage thus consumed is too small to affect the problem. The remarkable freedom of the fume from nonvolatile impurities and the fact that i t represents a mixture of almost absolutely pure oxidized lead compounds after burning, presented i t as a promising raw material for conversion into lead compounds, but the problem proved by no means easy of solution. An examination of the literature disclosed several processes devised for the conversion of lead sulfate into other compounds in the wet way. Some of these were manifestly worthless from a commercial standpoint as the inventors had proceeded with a reckless disregard of the cost of reagents: others, which appeared t o be conceived in a spirit of practicality, were carefully checked experimentally. While i t was desired t o find a plan which would yield a product of lead oxide or hydrate, compounds not only merchantable per se, but readily convertible b y ordinary processes into an indefinite number of compounds, methods for the direct conversion of the sulfate or sulfate-containing mixture into com-
pounds of special desirability, such as the chromates, were included in the list of possibly available methods. Prior methods proved disappointing in every instance, and in some cases a most grievous discrepancy developed between the facts, as revealed by experiment, and the statements published. Even where the methods had been the basis for patents, instances were found which strongly indicated that the claimants had neglected empirical verification of their ideas. Attempts were made to convert the pulverized cinder directly into lead chromate by treatment with a soluble chromate, but the products proved of unsatisfactory composition through the persistence of a portion of the lead sulfate and in all cases were of unsatisfactory color and tinctorial strength. Digestion with sodium hydrate and carbonate as a preliminary step gave but slightly better results as it proved practically impossible to convert all the lead sulfate present. As the amount of residual sulfate appeared larger when a coarsely pulverized cinder was employed, a microscopic examination of the digested fume was made, and this showed plainly that the residual sulfate mas encysted by crusts of hydrate, the complex particles having much the structure of a nut with a kernel of unchanged sulfate and a shell of hydrate. This observation naturally suggested trituration as a means of effecting complete conversion and the employment of a closed ball mill entirely obviated this difficulty, conversion being rapidly and completely accomplished. Up to this point little attention had been paid to the amount of reagents employed but for commercial application i t was manifestly necessary that the treatment be systematized and the chemicals reduced to the minimum amount. “Soda lye” had been selected as the most generally desirable reagent for decomposition of the lead sulfate, both because of its low cost and because b y adding i t in dry form its, heat of solution within the mill obviated any necessity for the employment of extraneous heat to accelerate reaction. In order t o obtain a sufficiently high temperature and also t o yield a sodium hydrate solution of sufficient concentration the water was proportionately reduced. A mechanical difficulty appeared in the first test: the solution of sodium sulfate resultant from the decomposition was supersaturated and the crystals of sodium sulfate interlaced the paste of lead hydrate converting the entire mass into a tough, coherent cake which had t o be broken out of the mill b y hand. From a practical standpoint it was impossible to remove it b y solution of the sodium sulfate b y treatment with water, for the cake, was almost impermeable b y water. I t was noted t h a t this solidifying action did not take place so long as the mill was in motion, but immediately after i t came t o rest the setting occurred. Repeated efforts were made to introduce water immediately after grinding had stopped, but in every instance the “setting” had taken place. The solution of this difficulty was effected by intro-
.
264
T H E JOURNAL OF I N D U S T R I A L AND E N G I N E E R I N G C H E M I S T R Y .
ducing a new pattern in double cone ball-mills which permitted of the introduction of water and washing out of the charge without stopping the mill. The body of the mill was of the familiar type employed in horizontal mills, but the outlet was made considerably wider than the charging hole so that when the level of water within the mill was raised i t would overflow a t the outlet only. This proved of the greatest convenience and value in operating. After conversion was completed a jet of water was turned into the charging hole and the rotation of the mill continued. The hydrate in the form of an impalpable sludge was, of course, kept continually stirred up and was rapidly floated through the outlet into a washing vat. This water-floating action had the additional advantage that by no possibility could any portion of the charge escape from the mill before it was reduced to extreme fineness. Washing was effected b y decantation and the hydrate was then ready for conversion into other compounds. For conversion into chromate i t was dropped from the washing vat into a large percipitating vat and treated with the theoretical amount of acetic or nitric acid required for its conversion into a basic salt; water was added and the necessary solution of an alkaline chromate or bichromate. The extreme reactivity of the hydrate enabled the conversion to be effected without heating and with no more than the theoretical amount of acid. For the production of oxides the hydrate was pumped into a filter press and the cakes furnaced without previous drying. I t was found possible t o produce a good lead arsenate a t a considerably lower cost than obtains with present processes by mixing the freshly made hydrate with a solution of arsenic acid obtained by oxidation of arsenious anhydride with nitric acid, and boiling. The reaction was a little slow but the product most satisfactory. Other instances of easily obtainable compounds might be cited but the possibilities of lead hydrate are manifest. While the method offers absolutely nothing new from a chemical standpoint, it promises to have a very considerable influence upon the lead pigment business on account of the great economy over present methods which it entails. The degree of saving effected by using a by-product such as “blue fume” and thus saving both the smelting cost of producing pig lead and the additional cost of furnacing the pig lead to litharge and pulverizing the litharge is apparent from the following tables : The cost of producing chrome by present methods varies somewhat according to the market rates for litharge, acetic acid, nitric acid and sodium bichromate; the following figures represent usual costs in manufacturing on a large scale: Cost per cwt. 69 pounds litharge a t 5 % c . . ..$3.i9 43 34 pounds 56y0 acetic ac . . 1.38 46 pounds sodium bichromate a t 5 % c . . . . . . . . . . 2.53 Labor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 Water and fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.05 Packages and packing. . . . . . . . . . . . . . . . . . . . . . . . 0.25
$8.25
April,
1912
To this must be added freight and selling expense. These figures are based on good practice without waste. Most manufacturers compute their cost of production a t from $8.50-$8.75. For small producers who have to buy in small lots and a t higher prices the cost is*much higher. COST
OF
PRODUCING
CHROME
UNDER
NEW
PROCESS.
Using the same basis of prices as before. the cost per cwt. is:
.................. ............. ........... ........
11 pounds caustic soda a t 2 c. 80 pounds burned fume a t 2 % c.. 29 pounds 56% acetic acid a t 3 34 c.. 46 pounds sodium bichromate a t 5 34 c.. Labor ...................................... Water and fuel. ............................ Packages and packing.
.......................
$0.22 2 .OO 1.38 2.53 0.25 0 .OS 0.25
$6.68
To this must be added freight and selling expense. It will be observed that less acid is used than in the former statement. This is because of the much greater reactivity of lead hydrate as compared with litharge. The burned fume is valueless except as a smelting material: its value is therefore the value of the metal which can be recovered from it, less the smelting cost and freight.
A METHOD FOR TESTING OUT PROBLEMS I N ACID PHOSPHATE MANUFACTURE.’ By F. B. PORTER. Received Jan. 12, 1912.
The process of manufacturing acid phosphate is, like many other factory processes, very hard to carry out on a laboratory scale. The writer has a t vaqious times made attempts to do this on 1000 or more grams of rock dust. It has so far been practically impossible to stir sufficimtly and control the temperature well enough with the limited apparatus available to get satisfactory results. This being the case we recently devised the plan of using the quantities of acid and rock required t o make 2 grams of finished acid phosphate, stirring them together with a stirring rod in a test tube and using the entire product for the insoluble test. The following is the method in detail: Weigh 1.100grams of rock dust into a 5” X . 5 / / test tube, add the quantity of acid required from a small bore I cc. Mohr’s pipette, allowing the pipette to run empty and draining for a definite length of time ( I minute). The acid required and used is determined by titrating amounts delivered in the same way with halfnormal alkali. Stir the acid and rock together for 3 minutes, being careful to see that the dust is all wetted by the acid in the first half-minute of the stirring period. The test tubes thus prepared, without removing the stirPresented a t the forty-fifth meeting, American Chemical Society, XVashington. December. 1911.
