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ORIGINAL PAPERS RECOVERY OF POTASH FROM GREENSAND’ By H. W. CAARLTON
I n t h e original process as developed t h e material adopted was feldspar, b u t it was later found t h a t glauconite, commonly called greensand, in many respects possesses marked advantages, although carrying a smaller percentage of potash. It exists in almost unlimited quantities in t h e Eastern states, particularly in New Jersey, and, unlike feldspar, requires neither blasting nor crushing. It is an accepted fact t h a t any commercially successful process of liberating potash in rocks, etc., must include a method of profitably employing t h e residue. I n this case a building material is produced and has t h e advantages of an unlimited market, as well as being a superior product capable of being manufactured a t a remarkably reasonable figure. The method consists in digesting under pressure finely ground greensand with lime and water, thereby obtaining caustic potash of remarkable purity and a t t h e same time converting the residue into a material of value The reaction is carried out in large digesters or autoclaves, heated by introducing into t h e charge highpressure steam in sufficient quantity t o maintain t h e desired pressure of about 2 2 5 lbs. for a period of from 2 t o 4 hrs. To conserve t h e heat, at the completion of each digestion the steam is allowed t o escape and be condensed in t h e greensand-lime-water mixture next t o be treated, and t h e contents of the autoclave, which should have a cream-like appe%rance,is filtered t o separate t h e dissolved caustic potash from t h e insoluble residue. With sufficient lagging t h e unavoidable heat losses are very moderate, especially as t h e chemical action requires b u t little, if any, beyond t h e heat necessary t o raise the temperature of the mass t o the reaction point. For this reason t h e efficiency is largely dependent upon t h e thoroughness of t h e heat insulation. On filtering, t h e potash appears in t h e filtrate as potassium hydrate associated with so few impurities t h a t on concentration it may be sold as a high-grade product without further treatment. Following is a n analysis:
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KsO... SOP Cla Sios..... Ala08
Per cent 77.2 0.90 0.35 0.70 Free
From t h e origin of glauconite it would naturally be supposed t h a t the percentage of impurities would be higher and t h e variety greater than is found t o be the case. According t o standard works on mineralogy, it is a hydrous potassium iron silicate, but this conclusion was probably based on t h e simple analytical figures, and there are very strong recent d a t a t o show t h a t this is not its true composition. As greensand 1,Presented at the 55th Meeting of the American Chemical Society, BortOn, Mass., September 13. 1917.
is a t t h e present time being carefully investigated, i t will very probably be shown t o be a potassium iron compound enveloping free silica, but not a silicate. T h a t it is of marine origin is undoubted, and its rich green color is probably due largely, if not entirely, t o organic matter with which it is chemically combined. The solid remaining on t h e filter, which is t h e insoluble portion resulting from the digestion, is employed in the manufacture of steam-hardened brick, tile, artificial stone, etc. I t acts as a binding or cementing material and is incorporated with high silica sand, as is customary in t h e manufacture of steam-hardened products, b u t differs fundamentally in t h a t , whereas lime has always previously been employed as a binding agent, in this case a pre-formed self-cementing hydrous silicate performs this function. I n t h e past, steam-hardened brick, commonly known as Sand Lime Brick, have not been t h e success predicted. They are not able t o stand t h e weather without more or less crumbling, and the edges and corners are seldom perfect even in the freshly made brick. This is due primarily t o t h e fact t h a t all the binding power depends on t h e interaction of lime and sand during steaming, with the resulting formation of a surface coating of calcium silicate which binds the sand particles. If any one of the many factors governing this reaction are overlooked, the brick is faulty. Imperfect slaking of t h e lime, improper mixing, imperfect steaming, a deficiency or excess of moisture, or dull cornered sand, would each be sufficient in themselves t o ruin t h e product. I n fact, every detail has t o be rigidly observed and little leeway is permissible. It is also found t h a t !he adhesion between t h e sand and lime in the pressed b u t unsteamed brick is slight in every case and t h a t these “green brick” crumble unless handled with t h e greatest care. When employing t h e digestion solids as cementing material these troubles are largely overcome. The pre-formed cementing properties insure an unfailing bond in addition t o any chemical action t h a t may take place between the hydrous silicate and t h e sand during steaming. Any type, such as bank, sea or loamy sand is permissible. Ordinary ground rock will serve t h e purpose. One of t h e most convincing proofs of t h e self-cementing properties of t h e digestion material is its ability t o bond ground limestone, with which there could not be any chemical action. Sand and the cementing material may be mixed in widely varying proportions ranging from 98 and 2 t o 40 a n d 60. I n fact, i t is almost true t h a t the process is “fool-proof.” The chemical composition of the autoclave residue depends, of course, on t h e material treated. With feldspar i t is probably a complex calcium aluminum silicate, and with greensand a calcium iron silicate. I n both cases i t possesses remarkable properties, being t o a degree self-cementing but capable of acting,
Jan., 1918
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
when subjected t o steam pressure, as a powerful binding agent, cementing sand so firmly t h a t small enclosed quartz pebbles fracture before the bond gives way. The cementing material resulting from the digestion of feldspar is superior t o t h a t from greensand, although the latter possesses sufficient cementing power t o meet t h e most rigid requirements and produces a brick of a pleasing light green shade a t a greatly reduced cost. ’ The feldspar brick are of a marble-like creamy whiteness, entirely devoid of a lifeless milky tint, and have surfaces so smooth t h a t at a distance of a hundred feet they cannot be distinguished from marble. If colored brick are desired, inorganic pigments may be mixed with the binding material, and if an ochre color is t o be produced t h e coloring matter may be obtained as a by-product in the general process. It is necessary t o calcine only a portion of t h e greensand-lime digestion product, under which treatment it becomes a rich ochre, and add i t t o either the feldspar or greensand cementing material. The properties of these brick are best illustrated by tests on samples chosen from t h e general run b y an inspector from t h e Building Department of New York City. The actual tests were carried out a t Columbia University and Pittsburgh Testing Laboratory. Feldspar Brick Crushing Strength, lbs. per sq. in. 9267 Modulus of Rupture, lbs. per sqin 1060 Average Absorption.. 4 . 4 4 per cent ~~
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Required Standard
2000
450
Under 15 per cent
The low absorption may be explained partially a t least b y the voluminous, easily compressible, waterrepellent nature of t h e bonding material. On being mixed with sand and subjected t o the usual high pressure in brick presses it oozes in and completely fills all the interstices between t h e grains of sand. Another feature, and in some respects perhaps the most important, is t h e plastic nature of the binding material which adds a toughness t o the brick after compressing and before steaming. This makes possible t h e handling of the “green brick” without breaking O E t h e corners. While brick i s referred t o particularly, i t is not intended t o convey the impression t h a t this is the only marketable product. The particular advantage of brick is the immense market. I n investigating the various factors governing the yield of potash it was found t h a t a high pressure and a large excess of water were absolutely essential. I n treating feldspar i t is necessary t o use eight times its weight of water, and ten is a fair amount. This necessitated a great deal of evaporation, materially reducing the capacity of the plant and requiring a large outlay for initial heating. After a series of experiments it was determined by a process of elimination t h a t the alumina was the cause of t h e trouble, and this naturally could not be removed
7
in the case of feldspar, KzO.Al20a.6SiO2,as it is an essential element in its composition. The only remedy consisted in the adoption of an alumina-free material, or one in which this element was partially or wholly replaced by a non-injurious one. Greensand appeared very suitable and was tried. Although its true composition is in doubt, the results in this case were surprisingly satisfactory. It was found t h a t t h e concentration could be doubled or in fact the water could be reduced t o a point where it was just possible t o agitate the mixture. A difficulty t h a t has been met in every process of recovering potash from feldspar is the invariable liberation of soda a t the same time. This is always difficult and expensive t o separate, and especially so where both alkalies are liberated as hydrates. Theoretically potash feldspar is soda-free, but in practice it invariably contains from z t o 3 per cent. Greensand is almost soda-free, which is all t h e more remarkable from the fact t h a t i t is of marine origin, being formed on t h e ocean bed by t h e selective absorption of potash from sea water b y precipitated colloidal silica and ferric hydroxide. Another difficulty encountered in applying this process t o feldspar is t h e invariable presence of alumina in t h e digestion liquors. Efforts t o entirely overcome this b y adding more lime while reducing t h e amount do not in any case remove it entirely. I n the greensand-lime digestions there is not a trace. This is surprising from the fact t h a t t h e analysis of greensand always shows a little alumina present probably in adhering clayey matter. It must be present in some combination t h a t this process does not break up. This is extremely fortunate. Another important feature in t h e process is the employment of a high temperature and pressure in t h e digestion. The reactions are not only speeded up, as might be surmised, but are different. This is partially due a t least t o t h e production of a chemically active sub-hydrate of lime approximating t h e formula CaO.CaO.HzO, which is formed a t pressures of zoo lbs. and over. That C a 0 . H 2 0 should be partially dehydrated during digestion in a large excess of water, such as an amount equal t o ten times t h e weight of the lime, appears t o be paradoxical, b u t such is t h e case; and it supplies a plausible explanation of t h e increased activity of t h e lime in decomposing t h e feldspar at pressures above zoo lbs. and corresponding temperatures. It is found t h a t t h e digestion of feldspar with lime a t 1 5 0 lbs. pressure for any reasonable length of time scarcely liberates any potash, but above zoo lbs. pressure t h e reaction is rapid. Greensand, on the other hand, is less refractory and may be liberated at lower pressures, b u t it is not advisable t o employ them, as t h e yield is uncertain and t h e insoluble residue unsatisfactory. Considered from an economic standpoint, it is believed t h a t i t is quite feasible t o adapt this process t o either greensand or feldspar and, in conjunction with the production of a marketable by-product, t o
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operate a t a profit when selling the potash a t pre- for their toluol content. But, t o pass t h e sorely needed war prices. With feldspar, owing t o t h e invariable legislation, t o change from a candle power t o a heat presence of soda, t h e mixed hydrate required t o be standard will take time, unless t h e War Department, carbonated t o effect a separation. The potash is as a military necessity, commandeers or orders t h e erec. then sold as hydrated carbonate. Carbonating is not tion of gas scrubbers i n every commercial sized gas necessary in t$e case of greensand as high-grade caustic plant in this country. But it will take time t o build potash is o.btained in one operation. If potassium scrubbers for t h e various gas plants. T o quickly chloride is desired it is necessary only t o modify t h e add 2,000,000 gallons of toluol t o our supply, i t is digestion by adding calcium chloride t o t h e original proposed i n this communication t o suggest t h e use mixture. of water-gas machines t o crack solvent naphtha and It is found in t h e case of feldspar t h a t t h e percentage produce toluol in t h e presence of blue gas. It is calculated t h a t there will be produced in t h e potash content does not give reliable data as t o t h e possible yield, this being dependent on unknown fac- year 1917, 15,000,ooo gallons of solvent naphtha tors pertaining t o each individual deposit. Often from which, in round numbers, 2,000,000 gallons of feldspars t h a t are valueless in pottery manufacture, toluol can be made by cracking solvent naphtha in being weathered and mixed with mica, give t h e highest carbureted water-gas machines. A more t h a n suffiyield, in some cases up t o 9-0per cent, while some very cient number of carbureted water-gas machines are already installed throughout t h e country t o more t h a n high-grade samples yield as low as 30 per cent. Greensand contains usually from 6 t o 7 per cent t a k e care of t h e cracking of 15,000,000gallons of solKzO and i t may be almost completely recovered, b u t vent naphtha from which 2,000,000 gallons of toluol it is found t h a t 7 0 t o 80 per cent of t h e total potash can be quickly made. is a satisfactory yield after considering such factors as SOLVENT NAPHTHA USED dilution, time of digestion, etc. This means t h e proThe solvent naphtha used in t h e following experiduction of about roo lbs. of KzO, and binder material ment was derived from t h e thermal decomposition for from twenty t o thirty thousand brick from each of coal and analyzed, using a standard Engler flask t o n of greensand. for distillation and the Westphal balance for specific If artificial stone, building blocks, roof, floor or drain gravity. tile are manufactured, t h e resulting amount will vary DISTILLATION ANALYSIS Specific Gravity 0.867/15.5 O C. with t h e composition and weight of t h e products. If Temp. O C. Per cent by Vol. desired, t h e digestion material without admixture 135.5 1st drop 140.0 49.1 with sand may be molded in its plastic condition, 150.0 87.0 dried and employed as insulating fire-proof blocks. 160.0 91.5 170.0 96.3 On t h e other hand, i t is believed t h a t brick have t h e 180.0 98.5 183.5 Dry point most extensive market. The fact t h a t t h e greensand beds are usually overlaid with a high silica sand C R A C K I N G TEST lessens t h e cost of manufacture. The overburden, The following test of cracking solvent naphtha which has t o be removed in any case, supplies t h e was conducted upon a Lowe 6' carbureted water-gas necessary sand. set, over a period of 48 hrs. The operation of t h e T h e initial experiments and t h e commercial de- plant in cracking solvent naphtha in t h e presence of velopment of t h e process have been made possible by blue gas for toluol is practically t h e same as when the scientific interest exhibited in t h e undertaking by cracking gas oil in ordinary carbureted water-gas Mr. Richmond Levering, who has, himself, bornk t h e making, with t h e exception t h a t the gallonage per great expense entailed in its development. hour of solvent naphtha into t h e cracking zone is KAOLINPRODUCTS CORPORATION higher. The d a t a upon a 24-hr. basis averaged as 120 BROADWAY, NEW YORK follows for a carbureted water-gas set: TOLUOL BY CRACKING SOLVENT NAPHTHA IN THE PRESENCE OF BLUE GAS By GUSTAVEGLOPF Received November 20, 1917
All past estimates of the gallonage of toluol which would be required in this war have been far too low. May not t h e present estimate of Brigadier-General Crozier of 2 2 , 0 0 0 , 0 0 0 gallons of toluol1 required by September, 1918, also be far t o o low for our war needs? The cry is toluol, more toluol and more toluol! One of t h e fruitful fields for increasing our toluol yield is by stripping carbureted water gas,2 coal gas and oil gas, by means of suitable scrubbing towers, THISJOURNAL, 9 (1917), 1002. a Mel. and Chem. Eng., 16 (19171, 492; Moore and Egloff, l b i d . , 17 (1917), 297. 1
Make per 6' set per day of gas formed.. ............... Candle power of the gas Candle power of gas per of o i l . . Solvent naphtha cracked per 1,000 cu. ft. of gas formed.. Gas per gallon of solvent naphtha cracked.. Coke used per 1,000 cu. ft. gas.. Steam used per 1,000 cu. ft. gas.. ........ Temperature of superheater base.. .................... Temperature of condenser outlet.. .................... Length of run.. ..................................... Length of blow.. Rate per hour solvent naphtha.. Rate actual flow of solvent naphtha into system.. Total gallonage of solvent naphtha passing through set in 24-hr. d a y . . Light oils collected in drips and seals. Tar in gas holder..
500,000 cu. ft.
....................... 2 1 a t 2 1 " C. ................. 1 .I5 at 21' C. .. 12 .O gal. ............ 8 3 . 3 cu. ft. .........
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825' C.
15.5' C. 4 min. 4 min. 250 gal. 500 gal. 6,000 gal. 57 per cent 15 per cent
ANALYSIS O F LIGHT O I L
The light oil was distilled in a one-barrel still with steam t o a temperature of 170' C. This c u t was
