The PRODUCTION of SALT JOHN E. HYLER 501 Broadway Ave., Peoria, Illinois
A
LL COMMERCIAL salt comes originally from salt deposits in the earth, in many cases lying far underground, in many others very close to the surface, in some actually cropping out. Some deposits are very great, without a question the beds of prehistoric salt lakes or seas. These may have been covered by huge advancing glaciers, as many believe; no doubt some cataclysmic upheaval or series of upheavals is responsible for the wide,distribntion of salt deposits. At any rate, salt is found everywhereyand scientific men are unable to estimate how much of it may lie beneath the surface. But it is very plentiful. Salt springs are by no means uncommon, and many times salt gushers have been brought in whiie drilling for oil. A bed of salt extends from Lake Michigan to Lake Huron across the state of Michigan, at some points 4000 feet or more underground. One deposit in Texas has had shafts sunk into it for many thousands of feet without reaching the bottom, and the depth of salt there is still unknown. The great Wieliczka mine in Poland, worked for a t least the last seven centuries, has a maximum depth of more than two miles. Salinity of present-day bodies of water is due to these underground deposits. The oceans are constantly becoming more salty. Water flowing into them from rivers brings a deposit of salt. Water evaporated from them carries no salt with it, but is precipitated upon the earth, and again carries a salt deposit to the sea. The same is of course true of inland salt seas and lakes.
How and when man first appropriated salt for his use we can only conjecture, though it is highly probable that his first salt came from deposits left by evaporated sea water. Quoting from a little booklet, "The History of Salt," published by the Morton Salt Company, "The first written reference to salt occurs in that greatest and most glorious of all books-the Holy Bible. In the book of Job (6:6), which was written about 2250 years before the birth of Christ? is found the line 'Can that which is unsavory be eaten without salt?' The Bible also contains thirty-two other reierences to salt, perhaps the most familiar of which is the story of Lot's wife, . . . .8 , Study of such ancient salt history as is available is very interesting. We read of Csarean soldiers penetrating into Britain, and finding people engaged in making salt by pouring brine on charcoal fagots and scraping away the formation of crystals which resulted. It is evident that the greater portion of salt produced in Biblical times was made along the shores of the historic Dead Sea in Palestine in shallow salt basins, that it was rather highly laden with sand as well as other impurities, and that a common method of obtaining it pure for seasoning food was to dissolve it in water to form a strong brine, allow this to clear, and then use the clear brine for seasoning. Obviously, each time this was repeated, the "salt" became weaker, untii it "lost its savor" altogether, and was, according to the word of Christ, "henceforth good for nothing, but to be cast forth and trodden under the foot of men." Salt that
was highly impure, in fact, continued to be used until relatively recent years. As late as one hundred years ago, people in some sections of our own country were using a coarse brown salt, and when salt had been successfully refined, it was difficult to sell it to those who had been accustomed to using the discolored product. Soldiers of Rome often received a part of their remuneration in salt, and this portion of their wages was called their "salarium," from which word, in turn, our word "salary" is derived. Another interesting fact is the naming of certain English towns after a term having to do with salt. Quoting from "Salt and the Salt Industry," an English book written by Calvert, we have some of his findings, as follows: "In Camden's Britannia (published in Latin in 1607, and translated by Philemon Holland in 1610) we read that the word Wiccij may seeme to have beene derived of those salt pittes that the old Englishmen in their language named Wicks, and William Smith, a Cheshire man and author of a work which is known as King's Vale Royal (1656 edition) says, 'The house in which the salt is boiled is called the Wychhouse; whence may be guessed what v y c h signifies, and why all those towns where there are salt-springs or where salt is made are called by the name of wych, uiz., Namptwych, Northwych, Middlewych, Droitwych.' " From the same work, we extract one or two interesting old records-"At Northwich there is a deep and plentiful brine pit with stairs about it, by which, when they have drawn the water in their leathern buckets,
they ascend, half naked, to their troughs and fill them, from whence it is conveyed to the wich-houses about which there stand on every side many stakes and piles of wood." Again, we are told, of two wells of salt water at Middlewich, which are separated by a small brook, "one stands not open but at certain set times, because folke willingly steale the waters thereof, as being of great vertue and efficacie." Yet again, we select one of many regulations in force in those ancient days, which read: "40. Item. It is ordered that if any Waller [a term probably
L FIGURE 3.-SALT
WASEER AND
ELEVATOR
derived from the Anglo-Saxon weallere, a boiler; German wallen, to boil] he found making of Course Salt when they might make it better if they would, the Lead-lookers or Salt-viewers so finding them and making presentment thereof e'ry such Waller so offending shall h e to yr Lord for e'ry offence therein-2d." We of modern days usually think of salt as being mined. Much of it is mined. The Morton Salt Company has a huge mine at Grand Saline, Texas, not far from Dallas. This, as well as other mines in many places, is equipped with modem machinery comparable to that used in mining coal, etc. Compressed air drills, electric mine cars and elevators, dynamite, and the usual mine buildings called tipples play their part. Such salt is crushed and screened into various grades, except for the larger and better-conditioned lumps which are piled to seasan ahd are sold as lump rock salt. The degree of purity of such salt varies in different mines-that from the Morton mine mentioned is said to be exceptionally pure, averaging 9g1/2%. Salt from underground deposits is often brought to the surface by means of mater and compressed air. Drilling down into the bed of salt to form one of these modern salt wells, or "water mines" as they have been called, a dual pipe, one casing within the other, is put down, and to the outer one is attached a water pipe connection fed by high-capacity mechanical pumps. Water is forced down to the salt bed through the outer casing, and dissolves salt to form brine. The brine is heavier than the pure water coming in from above, and therefore tends to remain at the bottom, though because of the weight and pressure of the water coming in from above, it rises to a considerable height within the inner casing. A compressed air pipe is placed down inside the inner casing to a point just below the surface of the brine, and air is released to lift the brine the remainder of the way. This is a very good method for such deposits as are lacking in purity, for the only impurities that are brought up by such an arrangement are those which have gone into solution. Some method of getting rid of the excess water from the brine, so that it will crystallize, is then in order. In practically all instances, the water is eliminated by
evaporation, through the applicafion of heat. There is one interesting variation that has been practiced in some very cold countries where the production of heat for the purpose is very expensive. In such cases, much of the excess water is removed by putting the briue through freezing processes instead. That portion which freezes is free of salt, and when the ice is removed the brine is much more concentrated. By this method i t is possihle to bring the brine to a point where it can be processed by evaporation q t h far less expenditure of heat. Evaporation of brine to obtain sodium chloride is usually very carefully controlled, especially in cases where the briue is impure. By very careful regulation of the evaporation process, only the sodium chloride is crystallized out, leaving such other salts as may be present in solution. The supernatant liquid can then be drawn off and the salt reclaimed, or more of the original solution can be added, and the process continued. Salt obtained from underground deposits directly is only one part of the picture. The ancient custom of obtaining salt from the ocean and from inland salt seas still prevails, hut the process has been improved by modern methods of control, enabling full and skilful use to he made of natural economies. Two factors operate to govern the choice of salt-project locations of the solar-evaporation type. One is the necessity for flat ground adjacent to the sea, and of low or questionable value for other purposes. The
other requirement is a hot summer climate, with as little rainfall as possible, so that evaporation will not be retarded. The Morton Salt Company has a solar project a t Great Salt Lake in Utah.'' A region especially favored for this purpose is that around San Francisco Bay. Another is adjacent to the Mediterranean Sea. A project in California which has practically revolutionized the business by its own pat.ented method of harvesting is that of the Alviso Salt Company, which supplied several of the photos shown here. It is located on a 15,000-acre area of low marsh land, which has been divided off with a dredge by digging out canals and throwing up levees. Water is admitted into a large area from the hay a t high tide, and from there is transferred into "making vats" as the evaporation process continues. The canals running between these vats are deep enough to permit a hopper barge to operate in them, as is shown in Figure 1, where a barge is seen being towed by a tractor operating on the levee road. Considerable time is required, and considerable moving of the water from pond to pond, before the salt is finally left on the floors of the vats, in the form of a crust several inches thick, and ready to harvest. Alviso uses a Caterpillar tractor which they have fitted up according to their own patents and to serve their particnlar purpose. This specially fitted tractor is provided with cutters, machinery, and a pair of elevators which will convey the stream of salt to either right or left as desired. Moving along as shown in
Figure 2, it deposits the salt which it tears loose from the vat floor onto the sectional conveyor shown a t the right. The sections of this conveyor stretch completely across the floor of the vat, and may be moved as the harvesting continues. The delivery end of this sectional conveyor discharges at the hopper barge formerly mentioned. The barge has a capacity of 600 tons. It is towed,
when loaded, to a washimg plant appearing in the background of Figure 3, into which it is discharged by the elevator it carries. The. washer consists of screw conveyors, elevator baskets, and Yied equipment. It carries the salt through a brine solution and up an elevator, washing it free from mud and vegetable matter. Provision is made for discharging the salt from the washing plant into railroad cars by running them under the tower. When these pictures were taken, a Caterpillar tractor was employed to pull the cars into position under the tower, and from there to the storage or "great pile," shown in Figure 4, where a Link-Belt crawler crane was employed to move the salt onto the pile. From such a storage, salt may be packed and sold directly for snow melting, ice-cream packing, fish packing, and many other industrial uses not requiring a high degree of refinement. Salt for table use is taken from the pile, as a rule, and goes through added washings, screenings, etc., to produce a more highly refined article. Most of this salt is for Westem consumption, transportation charges largely barring i t from eastern markets, where most of the salt used is obtained from mines or salt wells. The picture on the
front cover of this number shows a view taken from the washing plant a t Alviso, of a Caterpillar tractor pulling a loaded car from the washing plant to the great pile. Elevators of belt-and-bucket type are much used for elevating salt to storage and the screw type of conveyor is used for moving either wet or dry salt. Figure 5 shows a line of screw conveyor moving moist salt to storage. Belt conveyors of horizontal type are also used. Where wet salt is handled, there is an equipment corrosion problem. Consequently, Monel metal is often used for wet handling installations. In one case with which the Link-Belt Company had to deal, i t was found wise to use "granitized" rollers in a belt conveyor handling salt. It will be understood that these rollers were simply coated with "granite" after the manner of so-called granite kitchenware. The rollers have fulfilled every expectation. There are other evaporation processes used in connection with brine obtained from salt wells that we can mention but briefly. One is the open-pan process,
and a quite similar one is the grainer process, in which the brine is run into shallow vats in the salt factory, the vats containing steam-pipe coils to drive off the moisture. As the salt crystallizes and settles to the bottom, it is pulled up an incline from the vats by mechanically powered rakes, the liquid draining back into the vats. Of greater importance is the vacuum pan, which has attained considerable popularity. These pans are like two big iron cones joined together a t their bases, are air-tight, and are operated under vacuum, the brine being caused to boil by the combination of the vacuum
and the application of steam around a so-called steam belt. Because of the vacuum, they boil with much less heat, and they may be arranged in series so that the vapors from the first pan are used as heat for the second, the vapors from the second as heat for the third, etc. The heat grows less each time, of course, but the vacuum is correspondingly increased in the succeeding pans. The salt settles to the bottom of these "pans," from where it is removed by a belt and bucket elevator operating in a "hydraulic leg," and carried upward to storage. From such vacuum pans comes the modern free-running salt. Various methods of drying salt are used. Some of the moisture is allowed to drain away. Centrifugal machimes are sometimes used to remove a large part of it. For final and thorough drying, the rotary, heated, nearhorizontal drum is much used, the salt working through it in one direction while a blast of heated air is forced through it in the other. A modem change in one large department of salt production has to do with salt blocks which are used in
large quantities by d a i i e n , stockmen, etc. These used to depend very largely on select blocks of rock salt as they came from the salt mine, but the picture has rapidly changed, because of the pmsibility of forming better and more enduring salt blocks by hydraulic pressure. A salt press engaged in converting lowgrade salt into blocks of extreme hardness and endurance for this purpose is shown in Figure 6. Since this picture was taken, the hydraulic block salt press has been further refined, until now it is a fully self-contained machine, motor, pump, and fluid storage all being located above the ram. The author wishes to acknowledge his indebtedness to the Caterpillar Tractor Company, of Peoria, Illinois, the Link-Belt Company of Chicago, and the Hydraulic Press Mfg. Co., of Mount Gilead, Ohio, for the use of photographs reproduced in this article. Acknowledgment is also made to the Morton Salt Company of Chicago and to the Manistee Iron Works Company of Manistee, Michigan, for supplying certain data upon which we have drawn.
