LA N
-7
SEIN
and Processing S
I X years ago langbeinite was practically unknown in the fertilizer industry. Today it takes 1% prominent place among the potash and magnesium base fertilizers. Production of langbeinite in the 1941-42 fiscal year was 28,672 tons, compared with 85,701 tons during 1945-46. Langbeinite is a double sulfate of potash and magnesia, with the formula KzS04.2MgS01, and is composed of 22.7% KnO, 19.401, MgO, and 57.9% SOs. It has a specific gravity of 2.825 and a hardness of 4.2. It crystallizes in the isometric system, usually as simple tetrahedrons, which show a triangular outline on the surface of the hand specimen or on the walls of the mine workings. It is more slowly soluble in cold water than either sylvite or halite, and much of the langbeinite present in samples can be recovered by quickly dissolving out the chloride minerals. It is the hardest of the saline minerals, and has a conchoidal or irregular fracture with no cleavage. The geology of the region in which langbeinite occurs is complex and not fully understood. Langbeinite is one of numerous salts deposited during the latter stages of evaporation of a large Permian sea. In the early part of the Permian period a shallow sea extended across New Mexico and western Texas, northward through Oklahoma and Kansas, and into southeastern Nebraska. The indications ape that the shore lines of this sea fluctuated over considerable areas. The sea was originally in open communication with the ocean by way of a channel extending through Mexico into the gulf. One theory is that, late in Permian time, the connections to the sea berame restricted because of the deposition of limestone reefs. The further growth of these barrier reefs, coupled with t$e subsidence of certain areas, led to the formation of large evaporating pans. The area defining one such pan is generally known as the Delaware Basin, and it is in the series of evaporites found in this basin that commercial deposits of potash salts occur.
6. T. Harley and 6. E. Atwood International Minerals & Chemical Corporation, Carlsbad, N. Mex. The Delaware Basin is a pear-shaped area occupying approximately 15,000 square miles. It covers portions of Eddy and Lea Counties in southeastern New Mexico and extends as far south as the Glass Mountains in Brewster County, Tex. It is a t the northernmost edge of the basin in a relatively small area approximately 25 miles east of Carlsbad, N. Mex., that potash salts are being mined. This region is the only portion of the Delaware Basin in which commercial deposits of potash salts have been found. The potassium minerals are the products of the last stages of evaporation; consequently the horizons at which they occur are found in the upper salt strata. The top of the salt is found a t an average depth of 400 feet below the surface, or an elevation of approximately 2800 feet above sea level. The bittern salts are interbedded with halite and occur at vertical intervals of approximately 50 feet. The uppermost bed is ‘found about 750 feet below the surface and contains carnallite (KCl.MgCL.6HzO). At depths of 800 and 850 feet beds of langbeinite occur, the lower being associated with considerable sylvite. At 900 feet a stratum of sylvite is found. The stratographic sequence of these beds indicates that the cycle of deposition was periodically interrupted
43
44
I N D U S T-RI A L A N D E N G I*N E E R I N G C H E M I S T R
T h e only commercial deposits of langbeinite known to exist in the United States are located a t Carlsbad, N. Mex. Mining is by room and pillar method, and operations are carried qut with the latest type of mechanical equipmynt. There are no tracks on the level, and haulage is by means of rubber-tired shuttle cars operated from a double overhead trolley system and cable reels. The "ore is undercut and drilled with electric augers in a manner similar to coal mining practice. The level is equipped with modern electrical and mechanical shops, which permit almost a complete repair and maintenance schedule without removal of equipment to the surface. The finished langbeinite is prepared by simple crushing and washing in fresh water to dissolve the halite and wash out the clay impurities. The solid langbeinite is then centrifuged, dried, and placed in a storage warehouse ready for market. By hydrating langbeinite and combining i t with sylvite in a so-called base exchange process, magnesium is eliminated with the substitution of potassium to make sulfate of potash, containing 90 to 95% potassium sulfate.
and renewed. However, the order in which the bittern salts occur follows a normal path predictable from available solubility data. When attempting to explain the formation of any individual bed, the theorist is immediately confronted with contradictory evidence, and no effort is made here to unravel the many structural irregularities which occur in the potash beds. The ultimate answer as to the genesis of the beds will be obtained only through intensive geological-geochemical studies, which have as yet made little progress.
Y
Vol. 39, No. 1
It is opened up by a large hoisting shaft and by a system of 2 to 4 parallel entries driven to connect the various working sections of the mine. The main set of entries on the level runs parallel and directly above the main haulage road on the 900-foot level of the mine. At the intersection of each wofking panel with this main entry a raise, or ore pass, connects the two levels. The ore varies in thickness from 4.5 to 6 feet, and about a foot of salt is mined underneath to give a working height of 6 to 7 feet. Mining is by the room and pillar system with pillars 32 X 32 feet in dimension and rooms and breakthroughs 32 feet wide. The first step in the mining operation is to undercut the face. This is done with a Goodman mining machine having a 9-foot cutter bar. The cut, which is 6 inches wide and about 8.5 feet deep, is made at the bottom of the face and across its full width. The purpose of this cut is twofold, first to provide an additional free face to improve the work of the explosives used, and second to provide a smooth floor upon which to operate the shuttle cars. The mining machine has a cutting speed of 5 to 6 inches per minute and is driven by a 60-horsepower alternating-current motor. Various types of bits have been used in the cutter chain; after a long series of tests, this mine standardized on a bit faced with a Carboloy tip. Each bit can be sharpened fifteen to seventeen times before it is discarded and will do two to five times as much cutting per sharpening as any bit previously used. Machines are transported by tractor trucks from one room to another. Each truck has mounted on it an Aerodyne midget fan for ventilation of the face while the men are a t work; The next step is the drilling of the face, with Jeffrey A6 electric auger drilIs. Drilling speed is 28 inches per minute, and steel and bit wear is not excessive. Three lengths of steel serve to drill holes up to 11 feet deep. Holes are drilled in the common toe-hole pattern in vertical rows 4 feet apart, each row containing three to four holes, depending on height of face. Such a round will pull the full depth, give satisfactory breakage, throw
PAN FEEDER AND CONVEYOR
MINING
Langbeinite is dug by standard coal mining methods, someu-hat modified to meet the physical character of the ore. Only the higher grade bed, lying at a depth of 800 feet, is being mined.
FER
I
ONE B'x 25' DEWATERING
FLED WATER
,
SANDS
4
,
ONEB'x 25' DEWATERING DORR CLASSIFIER
OVERFLOW
IS' j E T T L l N G CON; OVERFLOW
I L--
CENT'RIFUGAL PUMP
DIAPHRAGM PUMP
.
I
1
36"X 50" BIRD CONTINOUS CENTRIFUGE
1
TO USE IN TAILINGS
1 DISPOSAL
FLIGHT CDNVEYOR
PLANT
J
5'X 40' ROTARY K I L N
I BOT. STORAGE BIN
FINISHED SUL! P O - MAG 9 6 % Q S 0 4 . 2 MC SO4
Dorr Classifier, Final Stage in Langbeinite Washing
Figure 1. Flow Diagram of Langbeinite Washing Section
January 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY.
45
Raymond Pulverizer Preparing Langbeinite for Base Exchange
. '
the ore away from the rib, and leave little or no overhang in the face. Langbeinite is so hard that i t was drilled with wet jackhammer-type drills a t first. This was unsatisfactory because of solution of salt in the water used and the attendant danger of short circuits. Experimental work was done on alloy-tipped bits used with the Jeffrey auger drill; after nearly a year of work Carboloy-tipped bits were adopted for all drilling at a substantial saving in cost. Much care has to be exercised in spacing and pointing holes, but after some practice the drillers become proficient. General practice is for the face boss or shift boss to locate each one of the holes and the position of the post by actual measurement. Blasting is done at the end of each shift with primers which are assembled underground. The shot firer hauls powder and primer from the underground magazines to the faces in insulated boxes. Holes are fired electrically, and each round is connected in series. The shooting circuit is 220 volts of alternating current; it is taken off the transformer serving the section with power, but through a separate blasting line having locked switch boxes. Both Du Pont and Hercules powders are used; the DLIPont is extra D, 40% volume strength, and the Hercules powder is Hercomite 4X, 40% volume strength. Primers are made up with unperforated sticks of powder, all other powder being perforated for better tamping in the hole. Blasting caps are KO. 6, and delays through KO. 4 are used on this,level of the mine. Powder consumption is 0.6 pound per ton of langbeinite ore. The ore and waste are loaded by Joy 11-BU caterpillarmounted conveyor-type machines. These machines have universal application, and can load in narrow or wide headings.
They are electrically driven through a trailing cable connected with a junction box, which is kept within a short distance of the working faces. The current is 220 volts, alternating current. The Joy machine can load out boulders that weigh as much as 1500 pounds; with a good face of broken ore and a plentiful supply of cars to serve it, a mucking rate of 150 tons per hour can be maintained. Haulage on this level is entirely b y rubber-tired shuttle cars, which operate on a double overhead trolley. This is the first installation of its kind in a nonmetallic mine. The f i s t cars used were the 42D, holding 7 tons of broken ore. Later the 60Dtype cars holding 10 tons were introduced. The cars are loaded by a Joy loader and haul the ore to one of the raises; there the ore is discharged by a conveyor in the bottom of the car. Hauls as long as 3000 feet have been made by these cars with remarkably high efficiencies, but best practice is to keep the haul length down so that the loader can operate continuously. Under these circumstances the material handled on the level will average 30 tons per man-shift. In mining langbeinite, 15 to 20% of the material is classed as waste and left in the mine. This material is loaded onto shuttle cars by Joy loaders and transported to an abandoned part of the mine, where it is dumped in front of a second loader which stacks it in the face over the tail conveyer. The ore is drawn from a 800-foot level through raises into mine cars on the 900-foot level, and is hauled to the shaft station where it is crushed in a Jeffrey 56-inch single-roll crusher to a maximum of 5 inches in size. It is then passed through storage bins to an automatic skip loader into the hoisting skips for transfer to surface and the treatment plant.
,
46
.INDUSTRIAL AND ENGINEERING CHEMISTRY
from the washer runs consistently above 20% in sodium chloride, whereas the residual solid phase analyzes 96 to 98% langbeinite. The solids are centrifuged and kiln-dried. to become finished products. The washing section as outlined is shown on the flow diagram (Figure 1). The results being obtained with the countercurrent washer are illustrated graphically in Figures 2 and 3. Figure 2 shows the grade of the solid phase in its travel through the wash section; Figure 3, the loss in recovery due to the dissolution of langbeinite. The data for these curves were taken during treatment of an ore analyzing 40% langbeinite and rejection of a liquor containing 22% sodium chloride. Langbeinite production has risen from approximately 200 tons per day in 1941 to a current daily tonnage of 500. Of this amount, approximately, 225 tons are consumed in the manufacture of potassium sulfate, and 275 tons are sold under the name Sul-Po-Mag.
v)
W
c5
Vol. 39, No. 1
POTASSIUM SULFATE SECTION
60
W
u z
3 lL
50
-L
40
0.0
2 .o
WASHTIME
-
4.0 MINUTES
6 .O
Figure 2. Analysis of Solid Phase during Travel through Wash Section
-
REFINING
The beneficiation of langbeinite ore does not present a serious problem. This mine has been successful in the development of an efficient fresh-water washing process in which the chloride gangue salts are dissolved away and leave residual langbeinite. Although langbeinite is the most soluble salt in the system under discussion, the rate a t which it dissolves is very slow. This slow rate, coupled with the relatively fast rate for the gangue salts, furnishes the basis for the wash process. Since langbeinite is a soluble salt, the extraction efficiency in any fresh-water washing process is a function of the rapidity with which the wash is accomplished. The salt content of the rejected wash water is also a function of processing time, and, therefore, optimum performance is obtained only after a delicate balance is reached between water consumption, equipment capacity, and extraction efficiency. This mine utilizes a continuous countercurrent washer, which gives maximum solution of the gangue salts in minimum contact time. Briefly this process consists of the following steps: Minerun ore is dry ground by Jeffrey hammer mills operating in closed circuit with vibrating screens. The crushed product has the following average screen analysis: Mesh
Cumulative % Retained
Mesh
In the potassium sulfate or base exchange section langbeinite is reacted with sylvite and water to produce potassium sulfate, of a minimum grade of 90% K2S04, and a waste liquor rich in magnesium chloride. The process involves the reaction of liquid and solid phases in the reciprocal salt pair system magnesium chloride-potassium sulfate-water. The phase reactions are complicated and can be thoroughly understood only in the light of certain solubility data. Solubility data on this system have been obtained independently by d’Ans ( I ) . van’t Hoff @),.and others, and check within reasonable limits.
Cumulative % Retained
The crushed ore is then introduced into the wash section proper, which consists of 140 feet of open launder discharging into the first of two Dorr dewatering classifiers operating in series. The feed water is added to the second classifier with the sands from the first unit. The overflow from the second classifier is pumped to the feed launder, where it travels to the first classifier with the new feed. The overflow from this classifier is the spent liquor and is rejected as waste after a settling operation for removal of suspended fines, The liquor rejected
a L
:E
z-
i G
T R A V E L THROUGH SECOND CLASSI-
6.0
T R A V E L THROUGH
LAUNDER AN0 FIRST CLASS1 FI E R
0.0
2 .o WASHTIME
-
4.0
6 .O
MINUTES
Figure 3. Processing Loss Resulting from Dissolution of Langbeinite The base exchange process is a two-step batch operation. I n the first, referred to as the hydration step, the finely ground langbeinite is agitated with potassium sulfate mother liquor to produce schoenite (KzS04.MgS04.6HzO) or leonite (KzSO4.MgS04.4Hz0), depending upon temperature, and a waste liquor of high magnesium chloride content. I n the second step, filtered schoenite or leonite is agitated with sylvite and water to produce potassium sulfate as a solid and a mother liquor for use in the preceding step. The essential reactions, although possible in one step, are purposely split so as to yield a higher potassium recovery. In the two-step process the principal reactions are believed to progress as follows:
+
2(K2S04.2MgSO4) f 2KC1 18Hz0 + 3(KsSO,.MgSOb.6H20)
+ MgClt 3(KzSOd.MgSOa.6H20) + 6KC1+ 6K2S04+ 3MgCI2 + 18H20
(1) (2)
a
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1947 SYLVITE
T-
JEFFREY
TI
MEASURED
+
Q.ZffiSO4
--?-
RAYMOND PULVERIZER
t
Y
I
.
ceases in favor of the double salt, glaserite [K8Na(S04)d. The following analysis of the mother liquor reflects the maximum tolerance of sodium in production of potassium sulfate a t 25’ C. The stable solid phases are glaserite, sylvite, schoenite, and potassium sulfate.
LANGBEINITE K
4 HYDRATION TANKS WITH TURBO AGITATOR2
-
S’IDRAGE BIN
47
t
CENTRlFrGAL PUMP
CENTRIFUGAL
Moles/1000 Moles Wetet
BIRD CONTINUOUS CENTRIFUGALS 60%MUFllATE TO STORAGE
15.75 10.0 23.75 9.25 1000
LEONITE CAKE KaS04 * MG S 0 4 . 4 H2D
+
+-
Per Cent 5.92
4.75 13.97 4.27 71.09
FLIGHT CONVEYOR
I
The most outstanding of the variables influencing yields in the base exchange is temperature. The solubility of potassium rises CENTRIFUGAL PU P rapidly with any increase in operating temperature, and, consequently, yields suffer. The THICKENER extent to which temperature influences rem covery is seen in the fact that an increase in UNDERFLOW OVERFLOW t t operating temperature of 25” C., or a change QLIVER FILTER CFN TRlFUGAl RJMP from 25 to 50 C., results in a decrease in yield I I ARCANITE CAKE MOTHER Liauou of aDproximately 10%. The optimum operating temperature in the t I base exchange is believed to be 25’ Operation below this temperature would not t only introduce cooling costs but would also FINISFED POTASSIUM SULPHATE 00% u2 s 0, impair reaction rates. The best results thus far obtained in the base exchange process Figure 4. Base Exchange Flow Diagram show a yield of potassium sulfate, equivalent to 7301, of the total input. Available Reaction 1 (hydration step) will proceed to much higher magsolubility data indicate these results to be approximately 90% nesium chloride and lower potassium chloride concentrations of the possible yields in operation at 25” C. than will the second (reaction step). In this system potassium sulfate is stable only at relatively low concentrations of magLITERATURE CITED nesium chloride accompanied by high concentrations of potas(1) d’Ans, J., “Die Losungsgleichgewichte der Systeme der Salze sium chloride. Reaction 2 therefore furnishes an ideal liquor ozeanischer Salzablagerungen”, Berlin, 1933. for the hydration of langbeinite. (2) Hoff, J. H. van’t, “Zur Bildung der ozeanischen Salaablagerungen”, Berlin, 1905. The extent to which each of the reactions progresses in a sodium-free system is illustrated in a comparison of typical mother PRESENTED before t,he Division of Fertilizer Chemistry a t the 110th Meeting and waste liquors at 25’ C.: of the AXERICANCHEXICAL SOCIETY, Chicago, Ill. 3 REACTION TANKS WITH TURBO AGITAATORS
O
c.
7
Stable Bolid Phases
Mother Liquor Sohoenite, K~QOP, KCl
Waste Liquor Sohoenite 14.82 9.84 5.26 70.08
In the base exchange flow (Figure 4) the reactions progress so slowly that careful selection of equipment is necessary to keep processing time within practical limits. Raymond mills are used for the reduction of langbeinite. When the langbeinite is introduced into the hydration step, i t analyzes 98% -200 mesh. All slurry tanks are equipped with Turbo agitators for maximum intensity of agitation. Although the sylvite is more rapidly dissolved than langbeinite, it must also be kept within certain definite size limits to prevent interference with the rapidity of react,ion. The presence of sodium in the base exchange system quickly impairs results; beyond certain definite concentrations of sodium in the reaction step the precipitation of potassium sulfate
Dryer for-Langbeinite
I
