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Calcination of Texas polyhalite
270
U.S.
BUREAU OF MINES NOTES.
[J. F. I.
within the furnace. The first phase of this work has been the laboratory study of the flow of gases through beds of broken solids. In so far as possible the results of the work have been formulated into general laws, but special attention has been paid to the particular materials entering into the blast-furnace processes. The data so far obtained from this study have been published in Bulletin 307, by C. C. Furnas. Two hundred and fifty-eight separate sets of data have been obtained and correlated in this work. In all instances the data have taken the form of the pressure required to force gas through a given system under given conditions. Definite laws have been formulated that make it possible to predict with a reasonable degree of accuracy the resistance to gaseous flow of a bed of broken solids of sized material. It has not been possible to formulate general laws for systems involving all mixtures of sizes, but many data have been taken and recorded for such systems and compiled into rules of somewhat limited application. The materials used have ranged in size from minus ioomesh dust to pieces 25 centimeters in diameter. D a t a have been taken on lead shot, various iron ores, limestone, coke, and roll scale. Most runs have been made with air: a few data have been taken on hydrogen and carbon dioxide. Temperatures have ranged from 20 ° to 66o ° C. These data are to be correlated in a later publication with data obtained for gas flow in commercial furnaces, thus affording a means of intelligently criticizing present blastfurnace practice and of suggesting and criticizing innovations. CALCINATION OF TEXAS POLYHALITE.
THE behavior of Texas polyhalite (a complex salt composed of potassium, magnesium, and calcium sulfates with 6 per cent. water of crystallization) upon calcination is one of the important factors involved in several processes for the extraction of potash from this material. A detailed investigation of the calcination of polyhalite has been made by the Non-metallic Minerals Station of the United States Bureau of Mines, Department of Commerce, in co6peration with Rutgers University at New Brunswick, N. J.
Feb., I93o.]
U.S.
BUREAU OF MINES NOTES.
27I
Polyhalite dissolves very slowly in water and requires a considerable volume of water for complete extraction of the potash salts. If, however, finely ground polyhalite is first calcined so that most of its water of crystallization is driven off, it is possible to obtain more than 9o per cent. extraction of the total potash by using 2.3 parts of boiling water. Upon heating powdered polyhalite, vigorous evolution of steam is observed at 30o ° C. and about 5° per cent. of the total water present is given off between 300 ° and 31o ° C. Subsequent heating for one-half hour in the temperature range between 43 °o and 45 °° C. results in the removal of an additional 48 per cent. of the water. The remaining 2 per cent. is tenaciously retained and requires a higher temperature or prolonged heating for its removal. The efficiency of the extraction of potash from calcined polyhalite (using boiling water), depends upon practically complete desiccation without sintering. Sintering is observed to start at about 475 ° C. and becomes very obvious at 500 ° C. while at 55 °0 C. the originally powdered polyhalite sinters forming a hard crystalline mass. This sintered material yields its potash to boiling water very much more slowly than the material calcined below 45 °o C. During calcination in the temperature range 3000-475 ° C. polyhalite is decomposed leaving an amorphous mixture of potassium, magnesium, and calcium sulfates. Above 475 ° C. and rapidly between 500 ° and 575 ° C., this amorphous powder sinters, forming a new compound, which is probably langbeinite (a double salt of potassium and magnesium sulfates, the calcium sulfate being held in solid solution in this new material). These changes are accompanied by marked variations in the refractive index, the determination of which may be used as a rapid method of controlling the calcination conditions. MICROSCOPIC INVESTIGATIONS OF COMPLEX ORES. MICROSCOPIC investigations of complex ores conducted at the Intermountain Experiment Station of the United States Bureau of Mines, Department of Commerce, Salt Lake City, Utah, in co6peration with the University of Utah, show that the microscope has an almost unlimited field of application
U.S.
BUREAU OF MINES NOTES.
[J. F. I.
within the furnace. The first phase of this work has been the laboratory study of the flow of gases through beds of broken solids. In so far as possible the results of the work have been formulated into general laws, but special attention has been paid to the particular materials entering into the blast-furnace processes. The data so far obtained from this study have been published in Bulletin 307, by C. C. Furnas. Two hundred and fifty-eight separate sets of data have been obtained and correlated in this work. In all instances the data have taken the form of the pressure required to force gas through a given system under given conditions. Definite laws have been formulated that make it possible to predict with a reasonable degree of accuracy the resistance to gaseous flow of a bed of broken solids of sized material. It has not been possible to formulate general laws for systems involving all mixtures of sizes, but many data have been taken and recorded for such systems and compiled into rules of somewhat limited application. The materials used have ranged in size from minus ioomesh dust to pieces 25 centimeters in diameter. D a t a have been taken on lead shot, various iron ores, limestone, coke, and roll scale. Most runs have been made with air: a few data have been taken on hydrogen and carbon dioxide. Temperatures have ranged from 20 ° to 66o ° C. These data are to be correlated in a later publication with data obtained for gas flow in commercial furnaces, thus affording a means of intelligently criticizing present blastfurnace practice and of suggesting and criticizing innovations. CALCINATION OF TEXAS POLYHALITE.
THE behavior of Texas polyhalite (a complex salt composed of potassium, magnesium, and calcium sulfates with 6 per cent. water of crystallization) upon calcination is one of the important factors involved in several processes for the extraction of potash from this material. A detailed investigation of the calcination of polyhalite has been made by the Non-metallic Minerals Station of the United States Bureau of Mines, Department of Commerce, in co6peration with Rutgers University at New Brunswick, N. J.
Feb., I93o.]
U.S.
BUREAU OF MINES NOTES.
27I
Polyhalite dissolves very slowly in water and requires a considerable volume of water for complete extraction of the potash salts. If, however, finely ground polyhalite is first calcined so that most of its water of crystallization is driven off, it is possible to obtain more than 9o per cent. extraction of the total potash by using 2.3 parts of boiling water. Upon heating powdered polyhalite, vigorous evolution of steam is observed at 30o ° C. and about 5° per cent. of the total water present is given off between 300 ° and 31o ° C. Subsequent heating for one-half hour in the temperature range between 43 °o and 45 °° C. results in the removal of an additional 48 per cent. of the water. The remaining 2 per cent. is tenaciously retained and requires a higher temperature or prolonged heating for its removal. The efficiency of the extraction of potash from calcined polyhalite (using boiling water), depends upon practically complete desiccation without sintering. Sintering is observed to start at about 475 ° C. and becomes very obvious at 500 ° C. while at 55 °0 C. the originally powdered polyhalite sinters forming a hard crystalline mass. This sintered material yields its potash to boiling water very much more slowly than the material calcined below 45 °o C. During calcination in the temperature range 3000-475 ° C. polyhalite is decomposed leaving an amorphous mixture of potassium, magnesium, and calcium sulfates. Above 475 ° C. and rapidly between 500 ° and 575 ° C., this amorphous powder sinters, forming a new compound, which is probably langbeinite (a double salt of potassium and magnesium sulfates, the calcium sulfate being held in solid solution in this new material). These changes are accompanied by marked variations in the refractive index, the determination of which may be used as a rapid method of controlling the calcination conditions. MICROSCOPIC INVESTIGATIONS OF COMPLEX ORES. MICROSCOPIC investigations of complex ores conducted at the Intermountain Experiment Station of the United States Bureau of Mines, Department of Commerce, Salt Lake City, Utah, in co6peration with the University of Utah, show that the microscope has an almost unlimited field of application