Salt Harvesting on Great Salt Lake.

Oamaru Mail, Volume XXXI, Issue 8835, 15 July 1905, Page 3 (Supplement)

Salt Harvesting on Great Salt Lake.

(By Edwin C. Eckel.)

In some respects the salt industry of Utah is of peculiar interest and picture:;qUesness, and a trip out to the saltworks at Saltair would well repay any visitor to Salt Lake City. For the "first few years the salt was obtained from the evaporation, during the summer; of the water contained in little lagoons or natural basins along the shore of the lake. The early settlers were supplied in this crude way until about I860; when some one conceived the idea of building eartheen dams in low places along the shore of the lake, which would hold back large quantities of water for evaporation.

If the lake water were evaporated just as it is pumped in, a number of undesirable impurities would be precipitated along with the salt. To avoid this, the water is passed through a series of ponds. The first of these is a large "stock" or "settling" pond, around which are grouped a series of shallow "harvesting" ponds, each about eight hundred feet wide and one thousand feet long. About May 1 the stock pond is pumped full of water from the lake, and this is allowed to stand until the iron and most other impurities have settled to the bottom as a reddish precipitate. The water is then permitted to flow into the harvesting ponds, which arc usually kept about six inches deep in brine. ' In an ordinary hot season the water will evaporate at the rate of about two inches a day, and this loss is made up from the stock pond, which in turn is kept full by pumping direct from the lake. A further purification is effected by the fact that one of the principal impurities contained in the brine, sodium sulphate, floats when formed, and is driven by the wind to the leeward sides of the ponds. The product from these parts is therefore impure, and is marketed for cattle and silvermill use, while that from the rest of the ponds is' very pure salt and is sent to the mill for further refining. Until about September 1 the ponds arn kept full of water, after which time pumping stops and the ponds are allowed to evaporate almost to dryness. They are not permitted to evaporate completely, for the last inch or so of brine contains impurities, and is therefore drained back into the lake. During the progress of this evaporation, the brine has deposited a layer of salt on the tanks. In average seasons this layer is about three inches thick, though as much as six inches has been obtained in particularly favorable (i.e., hot) years. After evaporation has emptied the ponds, the salt is ready for harvesting. It shows as an intensely white, level surface, clister.ing in the sun like a snowfield. Part of it is fine grained, but most is in the form of large crystals. Harvesting is commenced by shovelling the salt up into wheelbarrows, after the crust has been broken by ploughs. The crude salt is then heaped up into large stacks, and allowed to stand until needed. Rain has only the effect of purifying it, as the more soluble impurities are readily washed off flic stacks while the more resistant salt is left.

The mill of the Inland Crystal Salt Company, near Saltair, is constructed in two duplicate sections, each containing one dryer and six sets of rolls, fans, shaking sieves, etc. Each of these sections is operated as follows: The crude salt arrives at the mill in standard-size cars over a- switch from the tracks of the Saltair Railways. The saltfirst passes through a Hersey rotary drier. This consists of two concentric cylinders clamped together and rotating on bearings which support the outer cylinder. The inner cylinder, or steam drum, is fed with steam from the boiler. The outer cylinder is six feet in diameter and forty-five feetlong. Angle irons are fixed at intervals around its inner circumference. The drier is set at- a slight inclination, say about one-half inch to the foot. The salt is fed into the space between the two cylinders at- the- upper end of the drier, and as thedrier revolves the. salt travels slowly toward its lower end where it is discharged into a conveyor. This carries it to the second floor of the mill froth which it falls through a chute to the first set of a series of six rolls.

After passing through these the crushed material is again elevated to the second' floor and sent over a shaking sieve which acts as a separator, allowing the fine stuff to go to the bagging-room while the coarser material is again dropped through a chute to the second pair of rolls, which are set closer than the first set and therefore give a finer product. This is again sieved, separated and crushed in still finer rolls, the process continuing until the material has passed through six sets of rolls of increasing closeness, passing over sieves between each crushing. These sieves are of forty meshes to the inch at their upper ends and thirty meshes at their lower ends, thus giving a graded product which is fed into'different bins. The salt, thus prepared, is sold as table, salt and for other high-grade uses. During the crushing it lias been purified by fans', which are pla-jed in the roll casings and the dncrs also over the. top of each sieve. These fans take off the lightest and finest material, which contains most of the objectionable impurities, and their product is conveved into a room where it is pressed for cattle feed. Here the fine material is mixed with one-half to two per cent, of powdered sulphur, dampened slightly, and pressed into boxes or blocks. These are loaded on to little trucks and run into a drying tunnel where they are baked by direct heat;