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INDUSTRIAL AND ENGINEERING CHEMISTRY
sulfate. A burner with a high-velocity nozzle formed by a '/r-inch (0.64-cm.) close nipple (upper part of Figure 4, Part 111) soon plugged with a hard scale about. 1/8 inch (0.32cm.) inside the burner nozzle. The scale was not more than l/82 inch (0.8 mm.) thick and had built out from the circular opening. This type of nozzle was replaced by a cap, H , drilled to give a sharp-edged orifice, I (Figure 4, lower part). This burner was found to give continuous operation; however, the pressure in the mixing chamber fluctuated continually, indicating that scale was forming a t the orifice and being blown Off.
Potassium chloride has a rising solubility curve. Conditions for evaporation were found to be identical with those of sodium chloride. Pressure fluctuations covered the same range but were a little more rapid, undoubtedly because of the more concentrated solution.
Potassium Chloride from Sylvinite A saturated solution of sylvinite a t room temperature was made as the original leaching liquor. This was placed in a cone-bottom evaporator (Figure 3, Part 111), the lighted burner placed in the solution, and the calculated amount of sylvinite added to saturate the solution with potassium chloride. The agitation of the hot gases from the burner bubbling through the solution was sufficient to keep the sylvinite crystals suspended in the solution. The solution came to a boiling point of 90" C. ; because of the partial pressure of the products of combustion, the boiling point was below 100" C. After a short time a t the boiling point the burner was removed, the sodium chloride crystals were allowed to settle, and the solution was removed to a crystallizing tank. A pale pink mass of crystals of potassium chloride separated out as the solution cooled. Two modifications can be made in the process ( 2 ) when submerged combustion heating is used, The submerged combustion of natural gas replaces steam for the heating. The steam digester has a liquor circulating pump, which will be unnecessary with submerged combustion heating. The burners can be placed directly in the digester and thus give excellent agitation of liquor, or they can be placed in a side tube connecting the bottom and top of the digester. The release of the products of combustion will give the same effect as an air lift and circulate the liquor in the digester. The yield of potassium chloride per unit of solution will not be as great with submerged combustion heating as with steam heat. With the latter the boiling point of the solution is 108' C.; with the former it is reduced to 90' C. Reference to the solubility isotherms of Blasdale (1) shows that this will decrease the amount of potassium ahloride in solution from 37 pounds potassium chloride per 100 pounds water a t 108" C. to 32.5 pounds potassium chloride per 100 pounds water a t 90" C. If the solution is cooled to 20' C., the recovery in the latter case is only 80 per cent of the former. This indicates that the capacity of the plant is theoretically reduced by 20 per cent when submerged combustion is used. Actual reduction in capacity cannot be predicted, since certain features of submerged combustion might offset the lowered solubility by giving greater rate of solution.
Acknowledgment The writers wish to thank the U. S. Potash Company for supplying the sylvinite used in this investigation.
Literature Cited (1) Blasdale, W. C., J. IND.ENG.CHEX.,10,347-8 (1918). (2) Chem. & Met. Eng., 41, Supplement t o May issue, No.33 (1934).
(3) Kobe, K.A.,Zbid., 41,300-2 (1934). (4) Ward, C.A., Ibid., 40,172-6 (1933). R E C ~ I V EMarch D 4, 1936. Presented before the Division of Industrial and Engineering Chemistry a t the 90th Meeting of the American Chemical Society, San Francisco, Calif., August 19 to 23, 1935.
VOL. 28, NO. 5
V. Sodium Carbonate Decahydrate KENNETH A. KOBE
AND
ROBERT P. GRAHAM
Q T
HE natural deposits of sodium carbonate in the western states differ, as do the deposits of sodium sulfate, from those in the southern and northern parts. The California deposits are trona (NanCOgNaHC03,2Hz0) which may readily be calcined to give sodium carbonate. The Oregon and Washington deposits are sodium carbonate decahydrate. This hydrate contains 63 per cent water and must be dehydrated before shipping. The methods are almost the same as those used for sodium sulfate, since both salts are so similar in their physical properties. Both have transition temperatures a t 32" to 35" C., and both have inverted solubility curves above the transition temperature, although the stable phase for sodium carbonate is the monohydrate whereas the sodium sulfate is anhydrous.
Submerged Combustion Cycle In order to study the dehydration of sodium carbonate decahydrate by the cycle of operations proposed for sodium sulfate decahydrate (Part 111), similar calculations were made. When sodium carbonate decahydrate is melted, sodium carbonate monohydrate and saturated solution are formed. When the NazC03.10Hz0 is introduced into a saturated solution a t 40", 18.6 per cent of the sodium carbonate precipitates as Na%C03.H20,and if the temperature is increased to 90" C., 25 per cent of the sodium carbonate precipitates. This is much smaller than the corresponding values for sodium sulfate from Na2SO4.10HzO. If one gram mole NazC03.10HzO is introduced a t A (Figure 6, Part 111) into a saturated solution a t 90" C., 25 per cent of the sodium carbonate will precipitate as the monohydrate (31 grams) leaving 75 per cent of the sodium carbonate in solution (79.5 grams sodium carbonate and 175.5 grams water). When this is pumped to the outdoor crystallizing pond a t an assumed temperature of 20" C., 61.3 per cent of the sodium carbonate crystallizes as the decahydrate (175 grams), leaving 13.7 per cent to be discarded (14.5 grams sodium carbonate and 65 grams water). Compared to sodium sulfate decahydrate, the sodium carbonate decahydrate gives a smaller recovery in the cycle, but less salt is discarded from the crystallizing pond so that more decahydrate is recycled. The data in the literature are insufficient to calculate a thermal comparison with the evaporation method, although the same general conclusions for sodium sulfate decahydrate hold for sodium carbonate decahydrate. The type of burner used for sodium sulfate solutions (Figure 4,upper part) was found tJooperate most satisfactorily. The salt that precipitated on the burner formed a chalklike mass and did not cake hard as did the sodium sulfate. Cone formation was very small and crumbly, and a large-size cone could not be formed with this type of nozzle. The formation was not even of sufficient strength to cause fluctuations in the gas-air pressure gage. The explanation is that the monohydrate first precipitated is dehydrated by higher temperature of the flame and leaves a crumbly mass easily blown off. The sodium carbonate does not fuse as does the sodium sulfate, for sodium carbonate taken off the burner combustion chamber dissolved readily, which is not the case for the sodium sulfate burner scale. RECEIVED hlarch
4, 1936.
