TRONA VILLAGEAND PLANT FROM SEARLES LAKE
POTASSIUM CHLORIDE FROM THE BRINE
OF SEARLES LAKE R. W. MUMFORD American Potash & Chemical Corporation, Trona, Calif.
0
KE of the parties of "forty-niners," known to history as
The Setting
the Manly party, attempted to find a short cut .to California. It finally found itself stranded in Death Valley, exhausted and with no knowledge of the way out. Help was finally obtained and the party escaped on foot through the rugged mountains surrounding the valley. In the course of their journey they passed a salt lake, later to be known as Borax Flat and Searles Lake. To them in 1849 this lake meant only another one of the salt lakes which provided no water for their parched tongues. It was a thing to be avoided. Had they come in 1938 instead of 1849, they would have walked into Trona, a modern village containing everything to minister to their needs. The long journey on foot of nearly 200 miles would have been saved. They would have found, as the reason for existence of the town, a large plant for the production of chemicals from the lake whose waters were loathsome to them. The transformation of this lonely spot in the desert so repellent to the forty-niners into the modern industrial institution, with its equally modern village, will be presented in the following pages.
Searles Lake is in the extreme northwest corner of San Bernardino County, Calif., 190 miles north and east of Los Angeles in the Mohave Desert at an elevation of 1618 feet above sea level. The valley in which the lake is located is part of the Great Basin and is about 40 miles long and 25 miles wide. The plant of the American Potash & Chemical Corporation stands on the northwest shore of the lake at Trona. Trona is reached by the Trona Railway, which joins the Owenyo Branch of the Southern Pacific Company at Searles 30 miles distant. Good, paved highways lead to the modern town of Trona. It is a miniature urban community with a normal population of about 1800 people. The climate of Trona is healthful. I n winter it is bracing and exhilarating with averages from 55 O by day down to 25 O F. by night. In summer during the hottest months, July and August, the temperature range is from an average of 110" in the daytime to 75" a t night, but it is a dry heat leaving no permanent ill effects and only a mild temporary discomfort. Children seem to thrive on it. One official recording point in 872
AUGUST, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
an adjacent county showed a shade maximum last year of 124” while 118’ is Trona’s maximum. Annual rainfall averages 4 inches; last year an official station in nearby Inyo County had only 0.83 inch in 12 months, the same as another point in Imperial County. The average barometer is 28.4 inches of mercury.
The Problem Searles Lake is a “dry” lake containing a large mass of crystals a t its center. The exposed crystal body is surrounded by mud flats perhaps 100 square miles in area. It covers slightly less than 12 square miles and is a hard compact mass which will support automobiles, tractors, and other heavy rigs. It wns estimated by the United States Geological Survey to contain 25 per cent of voids. These voids are permeated by a saturated brine which forms the raw material for the op. erations a t Trona. The level of the brine stands close to the surface a t all times and varies from about 6 inches above the level of the crystal to about 6 inches below. This variation is largely due to flooding in the winter months and evaporation of this flood water during the dry summers. A typical analysis of the brine (see page 869) is expressed in terms of the materials which are recovered during the reduction of the brine. The brine itself consists mainly of the sulfates, chlorides, carbonates, and borates of sodium and potassium. There are several other acid radicals. Some lithium is present with only traces of calcium and magnesium. The minerals listed on page 869 have been identified as the main solid phases containedin the crystal mass. A number of others have been reported, but, a t present, they are mainly of academic interest; thenardite (Na2S04), burkeite (Na2CO3.2Na2S04, and sodium bicarbonate are found in the isolated strata in the surrounding mud, as well as numerous rare insolqble minerals.
which were hauled to San Pedro, a harbor near Los Angeles, or to the railroad for shipment to refineries. In 1878 this business was incorporated and operated as the San Bernardino Borax Mining Company. A small plant was erected and Searles produced a considerable tonnage of crude borax. Then deposits of colemanite were discovered, a material which so reduced costs of production of borax that competition was useless. I n 1895 Searles closed down as did all other plants which attempted to manufacture borax in this manner. In 1907 the California Trona Company was organized to produce soda ash and caustic soda from’the trona reefs which exist on the eastern shore of Searles Lake. I n 1908 the company went into a receivership, and the receiver, to keep the claims alive, sunk many drill holes to prospect the crystal body and to determine the recoverable values in the deposit. I n this period the presence of potash in the crystal body and the brine was well proved. In 1910 a strenuous search for potash began in the United States because contracts of American fertilizer manufacturers with German producers expired and subsequent negotiations were unsatisfactory; the Congress of the United States appropriated funds to make search for adequate domestic supplies. The Geological Survey and the Bureau of Soils were commissioned to conduct this search. Early in 1912 representatives of-these bureaus confirmed the presence of potash in commercial quantities in Searles Lake. Owing to the difficulties of mining solid salts and the necessity of dissolving them to separate the mass into marketable salts, attention was early focused upon the brine as the raw material for whatever process should be developed. It was an extremely complex solution, and a t once it became apparent
The History In the treatment of the history, only an exceedingly brief and cursory chronological recital is here possible. The colorful early chapters of the story are filled with intense drama as man, aided by science, struggled to overcome the obstacles of the elements, a contest providing material enough to fill a half dozen volumes. In 1849 the Manly party, craving only safety, hurried by this spot, probably thus marking the first visit of white man to the area. I n 1860 discovery of rich pockets of gold and silver in the arid mountains west of Death Valley did much to open this region in a preliminary way. In 1863 John W. Searles, a hardy prospector after whom this brine lake was named, passed through the basin. Noticing a similarity a t this point to a borax lake in western Nevada he staked out those areas of the mud flats which seemed to him most valuable. I n the 70’s Searles, joined by his brother, Dennis, and E. Merrill Skillings, utilized a method of scraping up the mud, hot leaching it to remove the borax, letting it settle, and decanting the clear liquor. This was cooled in open vats to form crude borax crystals
873
POTASH CENTRIFUGES
A
\
\
that an entirely new procedure would have to be devised. Nothing practical could be gleaned directly from the German production methods. Chemists and engineers were blazing entirely new trails. There were no precedents. Later in 1912 experimental work resulted in the Hornsey process, which seemed to offer considerable promise. I n 1913 the American Trona Corporation was organized. Its founders had the vision of a plant and process which would eventually produce and market on a large scale all the products that might be manufactured from the deposit. The path of development has never wavered from that objective. I n 1914 a plant to operate the Hornsey process was constructed, as well as a 30-mile standard-gage railroad, for Searles Lake was far from any city or town. A village sprang up, water was piped from the mountains, and then all the features necessary to make life modern were started. Today we have regular church services, both Catholic and Protestant; a ball park; a social club with bowling, pool, basketball, lounge, bar, card room, and reading room; an airport; a fine school; a motion picture theater where the latest releases are shown for 30 cents; a hospital; a cooperative general store; a library. All the utilities are present as well as a post office, telegraph office, tennis courts for night play, and a fine 18-hole sand golf course. The corporation participates jointly with the county to furnish the schools, library, and law enforcement, and it also cooperates with church organizs tions to provide church and Sunday school facilities. Later in 1914 the World War shut off the supply of potash from abroad and temporarily the efforts of the company were concentrated upon potash production problems. In the meantime the Hornsey process had been found impracticable and the Grimwood process was being developed. In 1915 a plant to operate the Grimwood process was begun, and in 1916 it was put in operation. In 1918 the first plant was duplicated and a considerable tonnage of potassium chloride was produced and marketed; this plant was one of the largest individual producers of potash during the war. period. This process produced a concentrated liquor high in potassium chloride and borax from which they could be separated by cooling. The cooling was done in open vats and sumps producing two crops, one high in potassium chloride but containing considerable borax. The second crop was high in borax and contained considerable potassium chloride. During 1918 and 1919 the Morse quick-cooling process was developed and put into operation, since a cleaner separation of the potassium chloride and borax was required to ensure a higher grade of final products. Prior to 1919 only potash was produced. Beginning with 1919 borax was added as a product. Economically the plant left much to be desired. An intensive study of the physical chemistry of the system was instituted. The mechanics of the process were begun, but several years elapsed before the process was proved and the equipment was sufficiently developed to produce potash and borax a t reasonable costs. In 1920 among the many barriers to necessary increased production of potash and borax were a poor condensing equipment on the evaporators and also serious foaming in the evaporators, which of necessity had to be overcome before sufficient evaporation could be accomplished. Barometric condensers and steam-jet vacuum pumps were installed in place of the rotary-jet condensers originally provided. A method of foam control, which is still in use, was devised. Between 1920 and 1924 vacuum coolers were developed and installed for part of the potash cooling and for crystallizing refined borax. Better centrifuges and conveying equipment were installed. The boiler plant was operated in a more ef-
R
-.__.__.-
874
AUGUST, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
--
875
---1
PROCESS c _
M.L.NO.2 FROM CRUDE BORAX PROCESS
POTASH PROCESS
,
STORAGE TANK
VIA HEAT EXCHANCERS
CRUDEBORAX PROCESS
ficient manner; an efficiency close to 80 per cent was finally obtained from boilers without heat recovery equipment. In 1926 the American Potash & Chemical Corporation was organized to take over the operations of American Trona Corporation. From 1925 to 1927 the plant a t Trona was completely rebuilt. Production was increased threefold. During this period the present type of evaporators with outside heaters and positive circulation was built. The salt removal system of the evaporators was improved by the installation of salt traps, clarifiers, and rotary vacuum filters. Secondary vacuum coolers were added to the potssh cooling plant. An entirely new crude borax cooling and crystallizing equipment was installed. Beginning in 1930, a construction campaign was started to increase the productive capacity of the plant. Continuing since then and through the depression years, there has been a general rearrangement of the plant, and the practice has been brought up to date. The steam required for process work is now produced from oil in modern boilers fully equipped with heat recovery and control equipment, operating a t an efficiency of 90 per cent. Prior to use for heating, the steam is passed through noncondensing turbines operating against a back pressure of 33 pounds per square inch to generate all the electric power required for the operations. After several years of phase-rule studies, a process was developed for producing soda ash and anhydrous sodium sul-
fate. This process was tested, a plant was built, and in 1934 production on a commercial scale was begun. The soda ash produced is chemically equal to the best Solvay process soda ash. Although physically different it has many characteristics which have caused the consumer to accept this material readily. The sodium sulfate produced finds ready market in the paper, glass, and dye industries.
The Trona Process The following discussion will deal only with that part of the operation which separates potassium chloride from the other salts occurring in Searles Lake brine. Brine is pumped from wells drilled in the crystal body of the lake by means of deepwell-type pumps. Booster pumps are installed in the pipe line leading to the storage tanks a t the plant to provide necessary flexibility in the quantity of brine delivered. The brine is pumped a t a temperature of 72" F. The pipe line is insulated against temperature changes by means of paper felt. Raw brine is used as a condensing medium for the potash vacuum coolers. It is also used for washing various filter cakes throughout the plant before it enters the evaporators. The evaporator feed consists of a mixture of end liquors from the crystallizing house and brine from the lake. The end liquors can be considered as a carrier which takes up the potash and borax resulting from the evaporation of all the
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 30, NO. 8
water from the raw brine entering the system. The resulting concentrated solution is then sent to the crystallizing plants for removal of the potash and borax, and the end liquor repeats the cycle. The evaporator feed enters the third effect of triple-effect e v a p o r a t o r s a n d passes through the effects counter to the steam flow. A partial concentration is effected in t h e t h i r d effect with t h e elimination of part of the water, sodium sulfate, sodium carbonate, and sodium chloride. The liquor then passes to the second effect where a similar further elimination of water and salts takes place. Final concentration of the liquor occurs in the first effect with further elimination of water and salts. The suspended salts are removed from the liquors of each effect by continuously circulating the liquor through cone s e t t l e r s called “ s a l t traps.’’ In the salt traps a separate cone is provided for each effect of the evaporators. The underflow from the firsteffect cone containing the salts passes through an orifice into the second-effect cone, receiving a countercurrent wash with clarified liquor from t h e second-
INDUSTRIAL AND ENGINEERING CHEMISTRY
AUGUST, 1938
effect cone. The combined salts from the first and second cones are given a countercurrent wash with liquor from the third cone as they pass through an orifice' into the third cone. The combined salts from the first, second, and third cones are given a countercurrent wash with raw brine as they leave the third-effect cone. The combined underflow is filtered on a rotary vacuum filter, the filtrate being returned to the evaporators. The cake is sent to the soda products plant. The settled liquor from each cone is returned partly to the same effect from which it was withdrawn and partly to the next hotter effect. The final concentrated liquor is withdrawn from the overflow of the first-effect cone to an auxiliary settler called a "clarifier." The overflow from the clarifier goes to storage a t the potash plant. The temperature of the liquor leaving the clarifier is 235" F. The underflow from the clarifier is filtered on a rotary vacuum filter, the filtrate returning to the evaporators and the cake going to the soda products plant. The quality of the concentrated liquor leaving the clarifier is controlled within narrow limits of concentration of potassium chloride. A chemist is on duty 24 hours per day and periodically samples and analyzes this liquor. In addition, all the information concerning physical conditions of the evaporators is assembled for the foreman and charted for his guidance. Experience has shown what variations in conditions are significant. The operation is varied according to the chemical and physical conditions observed. Steam is admitted to the heaters of the first effect a t 31 pounds per square inch gage pressure and 274" F. The liquor in the first effect is a t 240" F. The vapor temperature in the third effect is 101' F., which means a total temperature drop of 173" F. Boilingtemperature losses amount to 80' F., leaving a working drop of 93' F. The concentrated liquor leaving the clarifiers is essentially saturated with potassium chloride. Cooling to 100' F. to crystallize the potassium chloride is effected in three-stage vacuum coolers. Enough dilution water is added to replace the water which is evaporated to cool the liquor, thus holding the sodium chloride in solution. The suspension of solid potassium chloride in the mother liquor passes to a cone settler. Here a thickened sludge is obtained in the underflow which goes to a battery of Westontype sugar centrifuges. The overflow from the settlers is
PLANT OF
THE
877
combined with the filtrate from th centrifuges and is sent to the borax plant for the removal of orax. The solid potassium chloride ontaining a maximum of about 5 per cent free moisture is conveyed by pan and belt conveyors to oil-fired rotary dryers where its moisture is reduced to 0.3 per cent. The dried potash is then conveyed to storage or to the bagging machines or cars. The potash is reclaimed from storage by means of an electric or gasoline shovel. The shovel discharges to a pair of rolls, thence through an elevator to belt conveyors which feed the sacking machines and the bulk car loaders. Automatic samplers cut the stream of potash at regular intervals, and the samples are analyzed to control the quality of the product. Potash is sacked on automatic sacking machines, and the bags are sewed on power sewing machines. They are loaded to the cars by conveyor. The sacks are stacked in the cars by hand. Bulk potash is loaded into the cars by conveyors and a boxcar loader. The mother liquor from the potash plant is pumped to the crude borax vacuum crystallizers where it is cooled to 75" F. The cooling medium employed is liquid ammonia, which is expanded in helical coils in the head of the crystallizer. The water condensed is refluxed to the boiling liquid to avoid concentration of the solution and consequent precipitation of potassium chloride with the crude borax. The cooled liquor containing borax in suspension is sent t o a thickener. The underflow from this thickener goes to a rotary vacuum filter. The filtrate from this filter cdmbined with the overflow from the thickener is returned to the evaporator cycle as part of the evaporator feed. The cake from the crude borax filters is refined to produce commercial borax. This operation will not be discussed here as it has no direct bearing upon the separation of the potash from the other constituents of the brine.
I
Conclusion Today a modern plant is operating a t Trona to provide more than 40 per cent of all muriate of potash produced in the United States and averaging 97 per cent potassium chloride. Production of borax, soda ash, and sodium sulfate brings the total production of highest grade chemicals to about 400,000 tons annually. Trona pioneered in developing a United States potash industry. Today it continues its contribution of high-quality potassium chloride for the farmer and the chemical manufacturer.
AMERICANPOTASH & CHEMICAL CORPORATIOX AT TRONA, CALIF.
878
INDUSTRIAL AND ENGINEERING CHEMISTRY
The vision of the founders of American Potash & Chemical Corporation has been translated into reality. The management of the company has wisely and courageously utilized the money entrusted to it to develop this business. Its plant managers, chemists, engineers, and office workers, and its plant labor have each contributed to the building and operating of its plant. The product has been sold by its sales force. A freight rate structure which makes possible delivery to markets in competition with other producers has been negotiated by its traffic department. Cooperation has effected the cycle necessary for the development of a successful business.
VOL. 30, NO. 8
BiblioaraDhv Gale, H . S.,U. S. Geol. Survey, Bull. 580-L (1912). Manning, P. T.V., Chem. & M e t . Eng., 36, 268-72 (1929). Robertson, G. R . , IND. ENQ.CHEM.,21, 520-4 (1929). Ropp, Alfred de, Jr., Chem. & M e t . Eng., 19,425 (1918). Ropp, Alfred d;, Jr., J . IND.ENG.CHEM.,10,839-44 (1918). (6) Teeple, J. E., Industrial Development of Searles Lake Brine,” A. C. S. MononraDh 49. New York. Chemical Catalon Co.. 1929. (7) Teeple, J. E . , J.%D. EXQ.CHEM.,13, 249 (1921); 787, 904 (1922); 19,318 (1927). (8) Turrentine, J. W., “Potash,” pp. 74-82, New York, John Wiley & Sons, 1926.
(1) (2) (3) (4) (5)
14,
RECEIVED June 3, 1938.
POTASH IN T H E FERTILIZER INDUSTRY P.S. LODGE The National Fertilizer Association, Washington, D. C.
P
OTASSIUM is one of about fourteen chemical elements that have been shown to be essential to the growth of plants. Plants may obtain hydrogen, oxygen, carbon, and to some extent nitrogen, from air and water. The other necessary plant foods must be furnished by the soil. Some of them are needed only in minute quantities and are usually present in agricultural soils in sufficient amounts to support normal plant growth. Nitrogen, phosphorus, and potassium are the three elements most often contained in soils in insufficient quantities to produce optimum crops; consequently they are the elements usually added in commercial fertilizers. Although no one of these fourteen elements can be said to be more essential to plant growth than the others, the continued growing and removal of crops tend to remove some of them from soils faster than others. Potassium is notably one of the elements so removed and is found as one of the principal constituents in the ash of all plants. Credit for the discovery of the role of potassium in plant nutrition is given to Justus von Liebig ( 1 ) often called the father of agricultural chemistry; in 1840he said: “Since growing plants assimilated potassium this element must necessarily be resupplied t o the soil.” He is also generally credited (6) as the originator in 1840 of the process of acidulating phosphatic material in order to make its phosphorus available to plants. Escher (18), however, suggested the idea in 1835. Later Lawes (11), applying this process to phosphate rock, produced superphosphate, the most important single fertilizer material in America, quantitative!y considered. Liebig had analyzed the ash of many different species of plants and had noticed that certain elements, of which potassium was one, were always present to a greater or lesser degree. He evolved and announced the theory that such elements were those mineral elements essential to plant growth. His own and contemporary experiments of Lawes and Gilbert (6) and the slightly later work of Ville (200)demonstrated the correctness of the theory. It has become customary to speak of the potassium content of fertilizers and fertilizer materials in terms of potassium oxide and to use the word “potash” to represent this compound in all the forms in which the element potassium is used in agriculture.‘ 1 In this paper the chemists’ designations “potassium chloride,” “potassium sulfate,” and “potass~umoxide” have been used in preference to “muriate of potash,” “sulfate of potash,” and “KzO,” respectively, whlch are more familiar in the fertllizer industry where It is maintained that the
terms used convey a Bomewhat different meaning.
Sir John Russell (16), director of the Rothamsted Experiment Station a t Harpenden, England, founded by John Lawes, assigns to potash three distinct effectson the growth of plants: (a) It facilitates either the production or the translocation of sugars and starches from the leaf, hence its value for sugarand starch-making crops; (6) it stiffens the straw of cereal crops and the grass tribe generally; and ( c ) i t enables the plant to withstand adverse conditions of soil, climate, and disease, making it more resistant to drought, rust, and other diseases. By balancing the plant food ration, potash tends to counteract rankness of growth developed by abundant nitrogen. At the Fourth International Grassland Conference at Aberystwyth last year, Eckstein (4) reported upon a series of experiments to determine the influence of potash on the protein economy and the production of organic matter in the plant. He stated: “In our experiments the production of protein was definitely increased with increasing potash applications, provided always that sufficient amounts of nitrogen and phosphates were applied. . . . Increased application of potash favors growth, always provided that the other plant nutrients are present in ‘harmonious’ relation.” The effect of sufficient potash is readily seen in many crops. Cereal grains are plump and well filled, the stalks are strong and erect; root crops, such as sugar beets, turnips, and potatoes, are solid and well filled with starches and sugars; cotton is free from rust and productive; tobacco matures evenly with smooth leaves of satisfactory texture; and fruits are well colored and of good keeping quality. Conversely, potash starvation resu!ts in fallen cereal crops with shriveled grains; the foliage of root crops dies too soon to permit maximum storage of sugars and starches in the roots, and keeping quality is impaired as well as quantity reduced; cotton plants are subject to rust and the bolls fail to mature; tobacco leaves are curled and spotted; and fruits are of inferior color, flavor, and keeping quality. Harvested crops remove vast quantities of potash from the soil. Table I gives the pounds of potash removed from the soils by some important crops. Unless potash in available form is contained in the soil in sufficient amount to furnish crops with their requirements, crop yields will be reduced. However, under some harvesting practices a considerable portion of the potash removed from the soil by the crop while growing is returned to the soil in
