Aug., 1921
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
693
Action of Lime on Greensand''' By R. Norris Shreve 43 FIFTHAVENUE,NEW YORK, N. Y .
In the last few years a great deal of work has been done on the extraction of potash from various minerals, such as feldspar, leucite, mine tailings, greensand, etc. For the purpose of liberating the potash, treatment with lime or with a mixture containing lime has been employed rather extensively. This paper gives the results of close study of the action of lime in the presence of water upon greensand or glauconite. To show the importance of greensand, it may be mentioned that this raw material underlies the surface of hundreds of square miles of the State of New Jersey in beds of commercial value, and w'thin reach of a steam shovel. The process discussed herein has been in actual operation at a small manufacturing plant for several years, and in its early stages was described by H. W. Charlton.s I n outline, this process as now empioyed consists in heating a slurry made from 1 part of ground greensand, 1 part of lime, and 5 parts of water or weak washings in a digester for about 1 hr., a t a temperature around 470" F., and under sufficient pressure to keep the water in the liquid phase. This will be somewhat over 500 lbs. pressure. The chief reaction which takes place is that of the lime upon the greensand, which on the one hand liberates the potash in the form of a very pure caustic potash, and on the other h m d produces a material high in lime which possesses valuable cementitious and liming properties. An analysis of greensand that has been commercially used is given herewith: TYPICAL NEW JERSEYGREENSAND Silica . . . . . . . . . . . . . . . . . . Alumina . . . . . . . . . . . . . . . Iron (figured as ) . ...... Lime.. Magnesia Potash ................ Soda . . . . . . . . . . . . . . . . . Sulfuric acid Phosphoric acid.. Loss on ignition..
................ .............. ........... ....... ......
SiOz A1203 FetOa CaO MgO KzO NazO SO?
PzOs
...
TOTAL
Per cent 49.8 9.8 18.0 0.9 7.7 7.4 0.4 0.24
0.25 5.6
100.1
The action of the lime has been studied from the following aspects: 1-Effect of state of division of the greensand (Table I). 2-Effect of temperature of digestions (Table 11). 3-Effect of ratio of water used (Table 111). 4-Effect of substituting KOH solutions for the water (Table IV). 5-Effect of variations in lime used (Table V). 6-Effect of addition of various salts (Table VI).
APPARATUS The method of conducting the experimental work offered various difficulties, and a number of different types of apparatus or digesters were tried. Finally the writer had built a multiple digester somewhat similar to that described by H. D. Gibbs and Max Phillips,4 which gave very satisfactory results with a minimum of time and effort. This multiple 1 Presented before the Division of Industrial and Engineering Chemistry at the 61st Meeting of the American Chemical Society, Rochester, N. Y.,April 26 to 29, 1921. * The work described in this paper has been done in the laboratories of the Eastern Potash Corp., for the improvement of the process t o be used at the large plant now under construction at New Brunswick, N. J. This plant will treat 1000 tons of the greensand per day, with about 900tons of quicklime, and will produce about 65 tons of caustic potash per day, or an equivalent amount of other potash salts, e. g., nitrate. Inaddition to the potash salts, the plant will turn out several thousand tons per day of a high lime carrying material. * THISJOURNAL, 10 (1918),6. 4 "Alkali Fusions,'' Ibid., 12 (1920), 145.
digester consisted of a molten metal bath (tin and lead in equal parts) heated by gas burners, and a carriage, so arranged as to revolve in the molten metal. This carriage held six cylinders which were rotated while immersed in this hot metal. The whole moving parts were so arranged that a quick removal could be made in order to take out one or more cylinders for cooling in water and analysis. The individual cylinders measured about 3 in. in diameter by 12 in. long and were similar to those used for shipping nitrous oxide. Each cylinder took a typical charge of: Greensand................................ Quicklime ................................ Water ....................................
Grams 85 85 425
The control of temperature was within 5" to 10" F., a t around 475" F., which was considered very good; furthermore the initial heating of the cylinders when plunged into the hot metal was rapid, t'aking only a few minutes.
EXPERIMEKTAL DETAILS I n general the experimental work indicated that the most economical yields of potash were obtained by heating under agitation a slurry of Parts Finely ground greensand.. . . . . . . . . . . . . . . . . . . 1 . 0 Quicklime ................................ 0.9 Water or weak washings., . . . . . . . . . . . . . . . . . . 5 .O
a t a temperature of 470" F., under a pressure of about 550 Ibs., for 40 min. I n this case about 61 per cent of the potash in the greensand was converted into the soluble form. I n the presence of various accelerators, such as nitrates, the conversion was increased to 81 per cent. The details of the experimental work are given in the following tables: TABLEI-EFFECT OF STATE+ OF DIVISION OF GREENSAND Per cent Potash Converted EXPT. iV0. CONDITION OF GREENSAND 40 Min. at 47Oo-48O0F. B 58 Unground 16.8 B 61 Ground, 90% 200 mesh, calcined 76.6 B 66 Duplicate 72.3 B 67 Unground, calcined 17.5 R 19,
ji}
Ground, 90% 200 mesh
60 ( A v . )
B 26
Table I shows the importance of fine grinding, and this is to be expected, as the action of the lime can only be on the surface of the solid particles. Agitation during digestion increases the yields, and violent agitation is very effective; i t is, however, not practical to carry this out on a large scale, and we have secured the same result by allowing the digestion to proceed for a somewhat longer interval. OF DIGESTION TABLE 11-EFFECT OF TIGMPERATURE Potash PerConvel cent EXPT. Temperatux Time of Digestion :ted O F. No.
B B B B B B
29 28 36 33 32 35
M 19
M 20 M 21 M 22 M 23 M 24
400-414 398-412 389-397 398-402 389-401 389-398 470-480 470-480 470-480 470-480 470-480 470-480
Medium Temaeralure 10 40 60 60 120 120 High Temperature 20 40 BO 90 120 240
26.1 43.5 44.2 56.4 56.2 58.8 47.5 65.3 68.8 74.2 77.9 83.4
A great many experiments indicated that the yield a t 470" to 480" F. was very much higher than a t temperatures up to 425' F. The results shown in Table I1 indicate that the recovery of potash from a digestion of 40 min. at 470' to 480" F. (about 500 lbs. steam pressure) is higher than from a digestion of three times that interval at 390" to 400"F. (about
T H E JOURNAL O F INDUSTRIAL A N D EiLIGINEERING CHEMISTRY
694
225 lbs. steam pressure). The digesters for the large-scale plant are accordingly being built to work a t 500 lbs. pre,
