INDUSTRIAL AND ENGINEERING CHEMISTRY
646
Nomenclature
= fluid density, grams/cc.
p
= viscosity, grams/(cm.)(sec.) = kinematic viscosity, s cm./sec. T = shearing stress, dynesjsq. em. T O = shearing stress at the wall, dynes/sq. cm. n- = 3 . 1 4 1 6 c p = Reynolds number, dimensionless
p
C C’
= mean concentration a t any position, gram moles/cc. = fluctuation concentration, gram moles/cc.
= concentration at the surface, gram moles/cc. CaV.= average concentration of the main fluid, gram moles/
cc. C,,,. = concentration at center of the conduit, gram moles/cc. C , = specific heat, gram cal./(gm.)( C). D = d s u s i v i t y of solute or effective diffusivity of electrolyte, sq. cm./sec. D 1 = diffusivity of ion species 1,sq. cm./sec. Dz = diffusivity of ion species 2, sq. cm./sec. d = diameter or equivalent diameter of the conduit, em. E = mass eddy diffusivity, sq. cm./sec. EH = heat eddy diffusivity, sq. cm./sec. f = friction factor, dimensionless G = mass velocity, grams/(sq. cm.)(sec.) h = heat transfer coefficient, gram cal./(sq. cm.)(sec.) ( ” C.) k = thermal conductivity, gram cal.,/(cm.)(sec.) k , = mass transfer coefficient, cm./sec. 1 = mixing length, em. AT = mass transfer rate, gram moles/(sq. cm.)(sec.) n1 = valence of ion species 1 n2 = valence of ion species 2 U = average velocity of the main fluid, cm./sec. u = mean velocity a t any position, cm./sec. u’ = fluctuation velocity parallel t o the direction of the flowing fluid, cm. /see. U. = velocity of fluid beyond the floiv boundary layer, cm./sec. u* = friction velocity, cm./sec. u u+ = -, dimensionless u* v‘ = fluctuation velocity normal to the direction of main flowing fluid, cm./sec. v’ = root mean square value of L ‘, cm./sec. TV = number of light waves AJV = number of light waves displaced a t any position ~ b r= ~number ~ ~ of. light waves displaced a t the surface z = distance downstream from the leading edge of plate, em. zo = length of plate preceding the leading edge of electrode, cm. 21 = distance from the surface, em. O
+ ;
=
6 6, -da
= = = = = =
6.’ 6, E
(:)
.
Y
C.
(y) d;,
dimensionless flow boundary layer thickness, cm. diffusion boundarv laver thickness, cni. sublaminar layer thickness, cm. diffusion sublayer thickness, cni. wall layer thickness, cm. eddy viscosity, sq. cm./sec.
Vol. 45, No. 3
P
-k = Schmidt group, dimensionless PD = Prandtl group, dimensionless
a IC
Literature Cited (1) Eckert. E., “Introduction to the Transfer of Heat and Mass,”
New York, hlcGraw-Hill Book Co., 1950. Hansen, G., 2.tech. P h y s i k , 1 2 , 4 3 6 (1931). Jakob, &I., “Heat Transfer,” 5’01. 1, pp. 45-64, Sew York, John Wiley & Sons, 1949. (4) Kennard. R. B., J. Research .VatZ. B u r . Standards, 8, 787-805 (2) (3)
(1932).
( 5 ) Kinder, TV., Optik, 1 , 413 (1946). ( 6 ) Kolthoff, I. M., and Lingane, J. J., “Polarography,” New York,
lnterscience Publishers. 1946.
(7) RlcAdams, \I7.H., Chem. Eng. Progr., 4 6 , 121 (1950). (8) Levich, B., A c t a Physicochim. U.R.S.S., 17, 256 (1942). (9) Lin, C . S., Ph.D. thesis in chemical engineering, University of (10)
Washington. 1952. Lin, C. S., Denton, E. E., Gaskill, H. 8.. and Putnam, G. L., IND.E m . CHEM.,4 3 , 2 1 3 6 (1951).
( 1 1 ) Lin, C. S., hloulton, R. TT‘., and Putnam, G. L., Ibid., 45, 636 (1953).
Lin, C. S., Moulton, R. W.,and Putnam, G. L., deposited with the American Documentation Institute, Xashington 25, D. C , Doc. 3845 (1952). (13) Linton, W . H., Jr., and Sherwood, T. K., Chem. E n g , Progr., (12)
46, 258 (1950).
Page, F., Jr., Corcoran, TV. H., Schlinger, TT‘. G., and Sage, B. H., IND.ENG.CHEX.,4 4 , 4 1 0 , 419 (1952). (15) Schardin, H., 2. Instrumentenk., 53; 3 9 6 , 4 2 4 (1933). (16) Sherwood, T. K., and Woetz, B. B., Trans. A m . I n s t . Chem. (14)
Engrs., 35, 517-40 (1939).
Weissberg, A., et al., “Physical Methods of Organic Chemistry,” 2nd ed., Vol. 1, Part 1, pp. 1150, New York, Interscience Publishers, 1949. (18) Winckler, J., Rev.Sci. Instr., 19,307-22 (1948). (17)
RECEIVED for review December 4, 1951. ACCEPTED October 23, 1952. For material supplementary t o this article order Document 3845 from American Documentation Institute, c/o Library of Congress, Washington 25, D. C . , remitting $1.75 for microfilm (images 1 inch high on standard 35-mm. motion picture film) or $2.50 for photostats readable without optical aid.
0 0 0
0 0
By Fusion with agnesium and Potassium Sulfates G. 1. BRIDGER
AND
D. R. BOYLAN
Deporfmenf of Chemical and Mining Engineering, lowu State College, Ames, lawa
OST of the phosphorus in phosphate rock is present aa fluorapatite, CaloFz(P04)a,a compound so stable that the phosphorus is not readily available as a murce of plant food. To make the phosphorus available, it is necessary t o destroy the fluorapatite structure of the phosphate rock and form compounds that are soluble in soil solutions. This may be accomplished by acid treatment or by thermal treatment.
Treatment of phosphate rock with acids such as sulfuric or phosphoric acid is widely used for production of normal or triple superphosphates. However, in view of the current shortage of sulfur, used for production of both these acids, interest in processes that do not require sulfur has been accentuated. Such a process is the electric furnace fusion of phosphate rock with magnesium silicates-for example, olivine and serpentine.
March 1953
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
647
The effectiveness of magnesium silicate when fused with phosphate rock in forming products of high phosphorus pentoxide availability without defluorination suggested that other magnesium compounds might also be effective as addition agents. I n the present investigation magnesium sulfate, langbeinite (KsS04.2MgSOr), polyhalite (K2SO~.MgS0,.2CaSO4.2H20), and mixtures of magnesium sulfate and potassium sulfate in varying proportions were fused with phosphate rock. An added objective was preparation of a single fertilizer material containing available phosphorus, potassium, and magnesium.
Previous Work #r
9
Fusion of phosphate rock with addition agents to make the phosphorus pentoxide content of the rock available has been the object of many investigators. I n 1903 Wiborgh ( 2 7 ) obtained a patent on a process for making fertilizer by melting furnace slag with phosphate rock. I n the same year Wolters (18)described a process for making a product of high phosphorus pentoxide availability by melting a mixture of natural phosphate, alkali silicatea, and alkaline earth silicates. I n 1912 he and Giese ( 8 ) obtained a patent on the preparation of an available phosphate by fusing phosphate rock with silicates and cooling the melt in a blast of air and steam. Prjanischnilroff (19) in 1923 used sodium carbonate as an addition agent and Heskett ( 9 ) reported in 1935 the use of silica, alumina, magnesia, or alkalies as addition agents in the preparation of products of high phosphorus pentoxide availability by fusion. About 1934 considerable interest began to be shown in the relation of fluorine content to phosphorus pentoxide solubility (12, 14, 16,20-21) and a number of studies were made on the defluorination of phosphate rock by calcination or fusion with silica and water vapor in various types of furnaces (6, 7 , 10, 24, 26). I n 1943 Walthall and Bridger (26) showed that a product having high phosphorus pentoxide availability could be obtained giithout substantial removal of fluorine by fusing phosphate rock with magnesium silicates such as olivine. These results were confirmed by additional laboratory and pilot plant work by Moulton and coworkers (17). Subsequently, commercial plants using this process have been operated in the United States ( I C ) , Japan (18,89), and Formosa. Recently, considerable interest in fused phosphates has also been shown in England (4) and Germany (IS).
Materials and Procedures Materials. The phosphate rock used in these studies was a Florida land ebble obtained from the International Minerals and Chemica? Corp. The langbeinite was obtained from the same company under the trade name of Sul-Po-Mag. The chemical composition and screen anal sis of these materials are iven in Table I. Langbeinite A and plosphate rock L were use8 in the small scale laboratory fusions. Langbeinite A was ground in a micropulverizer and phosphate rock L was ground in a disk mill to the size shown. Langbeinite B and phosphate rocks G and P were used in the pilot plant studies. Rock G was received ground; rock P was unground pebble phosphate. The phosphorus pentoxide in the langbeinite was an impurity in the material as received. Proper account was made for this impurity in all material balances and analyses and the results were verified by control mixtures of reagent grade potassium sulfate and magnesium sulfate in the same proportion as pure langbeinite.
Figure 1.
ability. Available magnesia was taken as its solubility in 2 7 , citric acid, and water-soluble magnesia was determined by the AOAC method. Available potash was determined by the A0.4C procedure for mixed fertilizers, which entails a 30-minute digestion in boiling ammonium oxalate solution. Total potash was determined from an aliquot of the acid extract of the total phosphorus pentoxide determination. Iron, alumina, and silica (as acid-insolubles) were determined according to the methods of the Association of Florida Phosphate Mining Chemists (1). Fluorine was determined by the method of Brabson, Smith, and Darrow (S), in which perchloric acid digestion alone is used. Calcium was determined by the method of Hoffman and Lundell (11). All samples were ground to pass an 80-mesh screen before analysis. Samples of the fused products ground t o screen sizes of 35-, 80-, and 200-mesh showed no difference with respect to available phosphorus pentoxide, available magnesia, or available potash. Crucibles. Crucibles suitable for the laboratory fusions had to be nonreactive with the melt, nonabsorbent with respect to
Table 1.
Composition and Screen Analyses of Raw Materials (%, dry basis) Langbeinite
Composition
B
P205
3.9
0.78
15'7 18 4
18.9 22.1
Fez08 .4120a
,.
,.
SiOz Mesh sizes -8 -14 -28 -48 -48 -65 -100 -100 -150
A
CaO MgO K20 F
coz
The methods of analyses as set forth by the Association of Official Agricultural Chemists ( 2 ) were used for total phosphorus pentoxide, carbon dioxide, and magnesia. Available phosphorus pentoxide was determined by the AOAC neutral ammonium citrate method, and by the modified 2% citric acid method proposed by MacIntire (13). These two methods ,gave essentially the same results at high phosphorus pentoxide availabilities (greater than %yo),but differed by as much as 10% in favor of the 2% citric acid method in the neighborhood of 5070 avail-
Laboratory Fusion Furnace
- 200
..
..
f65
... .. .. .. ... ,..
12 1 29 8 26 2 15 8
+8 +14 +28 4-48 4-100 4-100 4-150 f200 +200
...
10:7 b:9 1$:5
,..
16.1
Phosphate RockG P 32.5 33.6 30.7 48.8 46.9 43 9 0.32 0.42 0.30 ... ... 4 4 4.8 4.4 0 89 ... 0 81 .., ... ... 2 42 10 2 12:5 7.4
L
.. .. ... ... ... ...
2.6 11.0
4:4 2i:o 32.7
...
2.8
2419 61.5
... I . .
4 5 9.5
16.2 37.8 22.1 9.0
...
io'i
8.0
3i'5
4.6
44 4
2:3
...
...
... ...
648
INDUSTRIAL AND ENGINEERING CHEMISTRY
LANQBEINITE A ,
Figure 2.
X
Variation of Melting Points of Langbeinite Phosphate Rock L Mixtures with Composition
A-
the melt, resistant to thermal shock, resistant t o temperatures from 2000" to 2600O F., and resistant to oxidizing atmosphere of combustion products of gas or oil. Tungsten, molybdenum, and graphite were found t o be satisfactory at all temperatures but suffered some loss by oxidation. Porcelain crucibles were found t o be completely satisfactory at temperatures below 2400' F. Most of the langbeinite-phosphate fusions were made at temperatures below 2300" F. with porcelain crucibles. These crucibles showed no chemical attack and could be easily cleaned by overnight immersion in weak acid. Laboratory Furnace. A gas-fired refractory furnace was built for the laboratory work from A. P. Green No. G-32 high temperature insulating brick as shown in Figure 1. A combustion volume of about 120 cubic inches was provided by forming a circular interior 6 inches in diameter and three brick thicknesses high b y cutting the brick. A burner port was provided in the side of the furnace and an opening in the top for venting the combustion gases. One of the bricks in the front side of the furnace was cut so t h a t a portion could be removed for inserting and removing t h t crucibles. A mirror was mounted above the furnace a t a 45 angle, permitting visual inspection of the crucible contents throughout the fusion procedure through the opening in the top of the furnace. A gas-air laboratory blast burner was used. Temperatures in the furnace were measured by a platinum-platinum rhodium thermocouple in a sillimanite tube mounted above the crucibles and connected t o a portable potentiometer. Temperatures of 2600" F. could be obtained without preheating the air. Fusion Procedure. Phosphate rock was mixed with various proportions of addition agents in either 10- or 20-gram charges. The mixed charge was transferred t o a crucible or boat which was inserted into the furnace for melting. During the process of fusion, melting first took place near the walls of the crucible, and then proceeded toward the center. Bubbles appeared throughout the charge as i t melted. When evolution of bubbles ceased, the charge was left in the furnace from 2 t o 5 minutes longer t o ensure complete fusion, and was then removed by a pair of tongs and quenched by pouring into a cooling medium. The quenched product was filtered, dried, and analyzed.
Vol. 45, No. 3
defined as the inflection point of the time-temperature curve (6). The melting points for mixtures of langbeinite A and phosphate rock L have been plotted against composition in Figure 2. This curve shows a sharp increase in melting point with mixtures containing less than 70% langbeinite. Fusions were then made with mixtures of langbeinite A and phosphate rock L having compositions ranging from 50 t o 90% langbeinite. Good melts were obtained which could be easily poured. The melts were quenched in water, filtered immediately, dried, and analyzed for total and available phosphorus pentoxide. The results are given in Table I1 and Figure 3. High phosphorus pentoxide availabilities were obtained with mixtures containing more than 68% langbeinite. I n this composition range, phosphorus pentoxide availability (27, citric acid) was at least 9570. Compositions containing less than 50Y0 langbeinite could not be readily fused in the equipment used. Fusion of Phosphate Rock with Magnesium Sulfate and Potassium Sulfate. T o show t h e effect of potassium and magnesium sulfates separately, fusions were made of phosphate rock with magnesium sulfate, and phosphate rock with potassium sulfate. The furnace temperature was maintained a t about 2100" F. The molten products were quenched in water. A plot of the phosphorus pentoxide availability (2y0citric acid) against composition is shown in Figures 4 and 5. The availability curve of magnesium sulfate and phosphate rock, Figure 4, shows complete phosphorus pentoxide solubility in the product when mixtures containing 7570 or more magnesium sulfate were fused. The phosphorus pentoxide content in this range was less than S70, however. When mixtures containing less than 65pd magnesium sulfate were fused, phosphorus pentoxide availabilities were sometimes high and sometimes lorn, depending partially on the loss of sulfate by volatilization. In all these fusions extreme bubbling in the form of foam occurred and a good fluid melt was very difficult to obtain. When sulfate loss was high (up t o 7575), availabilities were low; with lower sulfate loss, higher availabilities were obtained.
Experimental Results Fusion of Phosphate Rock and Langbeinite. Melting points of various langbeinite-phosphate rock mixtures were determined by time-temperature curves to establish optimum operating conditions and t o prescribe materials of construction. These curves were obtained by inserting a thermocouple in the mixture of materials and noting the time-temperature relationship as the materials passed from the solid state t o the liquid state on slow heating. The melting point for any particular mixture was
LANQBEINITE
A.
X
Figure 3. Effect of Composition on Phosphorus Pentoxide Availability of Fused Products from Langbeinite APhosphate Rock L
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March 1953
649
Table II. Compositions of Products from Fusions of Phosphate Rock L with Langbeinite A Quenched in W a t e r Langbeinite A, yo
Fusion
Furnace Temp., F.
864 866 47-2
PZOS, % Available (2% .oitric Total acid)
67-1 67-2 68-1 68-2 68 59 69
%
8.4 8.8 10.0 11.0 12.7 12.9 12.2 13.3 14.1 11.9 13.5 14.1 11.2 12.1 10.7 11.7 8.2
...
67
Availability,
1965 1965 2040 2040
...
...
1995
43 45 60 65 77
81
82
-
d
20
I
I
I
K p 804
I
I
Y
Figure 5. Effect of Composition on Phosphorus Pentoxide Availability of Fused Products from Potassium SulfatePhosphate Rock L
phorus pentoxide. Available phosphorus pentoxide was determined by 2Y0citric acid solubility and also by neutral ammonium citrate solubility, Duplicate fusions were made at each composition. The results are given in Table 111. The 2Y0 citric acid availabilities are shown in Figure 6 at each composition as well as the availabilities for the two-component systems, phosphate rock-magnesium sulfate and phosphate rock-potas-
SO
80
eo
10
MgSO4
90
Figure 6 shows that compositions high in phosphate rock and low in magnesium resulted in low phosphorus pentoxide availability; these compositions were very difficult t o fuse, giving viscous melts. Compositions containing greater than 50% of phosphate rock could not readily be fused. Compositions high in magnesium gave very fluid meJts and products of high phosphorus pentoxide availability. I n the
100
, *A
Figure 4. Effect of Composition on Phosphorus Pentoxide Availability of Fused Products from Magnesium SulfatePhosphate Rock L
Figure 5 shows that poor availabilities resulted from fusion of phosphate rock with potassium sulfate, even with high proportions of potassium sulfate. These fusions were easilv made and very fluid. To extend the composition limits in which high phosphorus pentoxide availability can be obtained,
J
studies were made in which phosphate rock L was fused with potassium sulfate and magnesium sulfate in varying proportions. Sixteen compositions, covering the range of critical solubilities, were chosen as shown on the triangular diagram (Figure 6). Each composition was expressible as a mixture of a base composition of potassium sulfate and magnesium sulfate with varying proportions of phosphate rock, shown by the tie lines from the phosphate rock apex t o the magnesium sulfatepotassium sulfate base at compositions 1, 2, 3, and 4, Base composition 3 (58% magnesium sulfate) is equivalent to the composition of pure langbeinite. All the samples were fused under as nearly identical conditions as possible and quenched immediately in water. The quenched products were filtered, dried, and analyzed for available phos-
Table
111. Results o f Fusion Studies of Three-Component System, Phosphate Rock L-Potassium Sulfate-Magnesium Sulfate % PsOs in Product
Total
Available Neutral 2% amcitric monium acid citrate
13.1 9.8 16.4 13.1 9.8 9.8 6.5 6.5 16.4 13.1 13.1 9.8
13.1 7.8 12.0 12.4 10.3 10.3 8.0 7.9 16.8 13.8 13.6 11.2
4.4 4.0 5.6 7.5 8.2 8.5 7.9 7.4 7.8 13.3 13.2 11.9
6.5 16.4 13.1 13.1 9,s 9.8 6.5 6.5
7.2 17.0 14.6 13.4
7.0 16.9 14.6 13.5 10.3 10.0 7.6
%E1
F ~ - Charge Composition sion Rock L KsSOd MgSOa (Calod.) H-1 G-1 C-2 G-2
~ - 2
D-3 H-3 c-3
g;F-3:
E-4 D-4 H-4 C-4 G-4 B-4 F-4
40 30
2:
30 30 20 2o 50 40 40
30
i20g
50 40 40 30 30 20 20
48 56
2;
42 42 48 48 21 25.2 25.2 29.4
12 l4 2o 24 28 28 32 29 32 34.8 34.8 40.6
333.6 2:; 2;:: 46.4 12.6 15 15 17.5 17.5 20
20
37.5 45 45 52.5 52.5 60 60
z:: l:z '::: 10.8 10.0 7.2 8.1
8.0
3.3 3.0 2.6 4 2 7.8 7.0 7.6 7.2 6.9 13.3 13.5 11.8 l:::
7.0 16.5 14.5 13.4 9.6 9.2 7.5
8.0
Availability, % ' Neutral 2% amcitric inonium acid citrate 33 50 46
60
80 82 99 93 46 96 97
loo
98
97 99 100 100 96 100 100 100
25 38 22 34 75 68 95 91
41
96
99 100 97 100 97 97 100 100 89 92
100 100
INDUSTRIAL AND ENGINEERING CHEMISTRY
650
area bounded by the curve and the magnesium sulfate apex, product availabilities of 80% or higher were obtained. This area is shown as the shaded portion of Figure 6. Compositions outside this area gave availabilities considerably less than SOYo and the availability decreased markedly as the phosphate rock content was increased. PHOSPHATE ROCK
water, however, was 17.4 and 5.47&, respectively. T o minimize these losses a saturated solution was subsequently used for quenching. Table V indicates that the phosphorus in the product was not water-soluble. This was verified by determining the watersoluble phosphorus pentoxide according to the AOAC procedure. The water-soluble phosphorus pentoxide content was found to be negligible. Additional water solubility tests were made by allowing a n 80-mesh sample to stand in water at room temperature, with intermittent agitation. Analysis of the water after a 6-week period showed no phosphorus pentoxide solubility Aqueous quenching of the melts shattered the product into small fragments. After drying, the product was chalk white and rather soft. It required no further curing and was noncaking. The phosphate-langbeinite product contains in a n available form two primary nutrients, phosphorus and potassium, and three secondary nutrients, sulfur, calcium, and magnesium. The fusion products from compositions containing phosphate rock and a minimum of 70% langbeinite were a t least 97% available with respect to phosphorus pentoxide and magnesia and 92y0 available with respect to potash.
BO
'2"4
Figure 6.
I
e
3
Vol. 45, No. 3
t
I
I
I
I
4
L A N OB E l Nl TE
/I
I
I
Effect of Composition on Phosphorus Pentoxide Availability of Fused Products
From mixtures of phosphate rock L potassium rulkte and magnesium sulfate. Numben in parentheses are $ 2 0 5 availabilities b y 2% citric acid
Along the langbeinite-phosphate rock tie line phosphorus pentoxide availabilities greater than 96% occur a t compositions containing the equivalent of more than 6OY0 of langbeinite. In the langbeinite A-phosphate rock L fusions, nearly 70% of langbeinite was required for this availability. When account is takrn of the magnesia content of the langbeinite used, which was only 13.7% instead of the 19.470 required for the pure mineral, the results are in good agreement. Fusion of Phosphate Rock with Polyhalite. Because of the abundance of polyhalite (K~SOa.hIgS0~.2CaS04.2Hz0),its use as an addition agent for fusions with phosphate rock was also investigated. A polyhalite composition was made by mixing potassium sulfate, magnesium sulfate, and calcium sulfate dihydrate in the proper proportions. Mixtures containing up to polyhalite were fused with phosphate rock, but phosphorus pentoxide availabilities (2% citric acid) greater than SS% were not obtained, as shown in Figure 7 , and polyhalite was the1 efore not considered promising as an addition agent. Product Composition and Properties. Product compositions from typical fusions of a charge containing 70% langbeinite -4 and 307, phosphate rock L are given in Table IV, together with the solubilities of the major constituents and the mole ratios hIgO/P,O, and KzO/P,O$ in the products. These ratios were 3.14 and 1.60, respectively, in the charge for the laboratory fusions, The lower ratios for the water-quenched producta indicated a loss of magnesia and potash by volatilization or solution in the quench water. To determine the extent of these losses, material balances were made of the major constituents for fusions 1370 and 1470, and are presented in Table V. The figures represent average values for the fusions. Volatilization losses of potash and magnePia were small. The loss of potash and magnesia in the quench
I
/l
I
I
I
I
I
I
1
I
70
60
90
30 50
60
POLYHALITE
,
I
100
%
Figure 7. Effect of Composition on Phosphorus Pentoxide Availability of Fused Products from Polyhalite-Phosphate Rock L
X-ray powder patterns were taken of the raw materials and of typical phosphate-langbeinite fusion products by a Norelco Geiger counter x-ray spectrometer. The comparison of the xray patterns showed t h a t certain well defined crystalline lattices of the raw materials were greatly reduced or entirely eliminated in the product. The enlargement of the area under the peaks in the product pattern as well as the indistinct diffraction line indicated a transition t o a n amorphous structure. Quenching Media Studies. As a result of the solubilit,y of potassium and magnesium in the quench water, studies were undertaken to develop a quenching medium which would be applicable t o pilot plant or commercial processes and which would not result in losses by dissolution. Various media were tried,
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March 1953
65 L
tion. The lower or hearth section was lined with 6 inches of Table IV. Laclede chrome-ore plastic f ire clay. Copper cooling coils were placedadjacent tothe steel shell Mole Ratio of Productsa in thehearth section and burner Product Composition Available Availability, % nozzle. The purpose of these sion FUPros PtOs PrOsb KrO MgO PrOa K r 0 MgO coils was twofold: t o Drotect the steel, and t o counteract the Laboratory samples corrosion of the lining by “freez92 100 1170 Water 1 4 . 6 1 1 . 5 11.4 4 0 . 0 ... 1 . 1 7 2 . 7 4 14.6 10.6 11.4c 100 ing” a layer of melt on the sur94 98 1370 Water 15.7 11.6 11.8 39.9 1 . 6 1 . 1 1 2 . 6 3 1 5 . 4 10.9 11.5 98 100 95 15.6 11.5 11.9 40.3 1 . 6 1.11 2 . 6 8 15.1 10.9 11.9 97 1470 Water face of the lining. No water 100 95 14.5 1 3 . 0 11.9 ... ... 1.35 2.90 14.1 12.3 1 1 . 9 97 Q-21 KaSOtd cooling was used on the ex93 98 Q-22 KzSO4and MgSOdC 12.8 12.8 1 1 . 4 . . . 1.51 3.15 12.1 11.9 11.2 95 terior surface. Combustion gas 93 98 Q-23 K~SObandMgSOIC 1 2 . 4 1 2 . 8 11.3 .. . ... 1.56 3 . 1 4 1 2 . 0 1 1 . 9 1 1 . 1 96 from the furnace was discharged Pilot plant samples through a Binch. pipe extend92 94 1 0 . 1 13.1 11.8 4 0 . 0 1 . 6 1.95 4 . 1 0 9 . 5 1 2 . 0 11.2 95 PP-4 Langbeinited ing outside the building and 93 100 9 . 8 12.5 11.3 4 1 . 7 1 . 6 1.93 4 . 0 5 9 . 6 11.6 11.3 98 PP-5 Langbeinited 96 96 1 2 . 1 1 3 . 0 11.0 3 9 . 0 1 . 5 1 . 6 2 3 . 2 1 11.1 1 2 . 5 10.5 92 through a steam jet ejector t o a PP-8 Langbeinited point above the roof. T h e ejeca Mole ratios KaO/PzOa and MgO/P*Os in charge were 1.60 and 3.14, respectively, for laboratory fusions and 2.16 and 4.32 for pilot plant. tor provided an adjustable conb By 2% citric acid method. trol of furnace draft a t various C Water soluble MgO was also 11.4%. d Saturated solution. charge levels. A Hauck combination oil-gas burner was used, having a caTable V. Material Balances for Typical Laboratory Langpacity of 1000 cubic feet of beinite A-Phosphate L Fusions Quenched in Water gas per hour. Burner control was provided by pressure measurement a t the following points: % of Total PzOs Kz0 MgO SO4 F 1. Top of furnace in duct to stack In“ 2. Draft just inside burner port 3. Gas pressure a t burner Phosphate rock 73.5 0.0 1. o 0.0 96.5 26.5 100.0 99,O 100.0 3.5 Langbeinite A 4. Primary air pressure a t burner Total 100.0 100.0 100.0 100.0 100.0 The quenching system consisted of a spray head, discharge trough, product settling tank, and recirculating pump. The out spray head had 371/8-inch orifices. The quench solution was reProduct 98 5 78 3 94.5 82.1 100.0 circulated a t 65 gallons per minute at a 60-foot head. T h e Quench water 0.0 17.4 5 5 11 4 0.0 1 . 5 4 . 3 0 0 6 . 5 0 . 0 Volatilization settling tank had a wire screen basket which could be lifted out - - - - , Total 100.0 100.0 100.0 100.0 100 0 for product removal. Furnace feed was prepared b y agglomerating the mixed phosa Charge ratio: 30% phosphate rock L. 70% langbeinite A. phate rock and langbeinite into pellets to 3/4 inch in diameter, by tumbling in a 55-gallon steel drum with the ends removed. Table VI. Results of Tests of Various Quenching Media on The roper roportions of langbeinite B and phosphate rock were PzOj Availability of Fusions with Phosphate Rock L and weigEed an$ mixed in a motor-driven cement mixer for about 5 Lungbeinite A minutes, t o ensure uniformity. The mix was introduced slowly into the rotary drum and the moisture content was adjusted b y Product ComDosition. addition of water until the material in the drum rolled into balls Lang%’ PZOS from ‘/a t o 1 / ~inch in diameter. The balls were screened through AvaiIable Availabeina */8-inch mesh screen and allowed to air dry. (2% pitric bility. Composition of Typical Langbeinite-Phosphate Rock Fusion Products (%, dry basis)
ygy&fJ
...
x
Fusion 47-1 Q-12 47-2 Q-45 2-6 2-54 2-3 2-2 2-1 a Saturated
J
ite, % 70 70 70 70 50 60
65 68
70 solution.
€&egFhig
Total 13.1 14.6 14 1 14 5 19.3 16.2 14.7 13.9 12.6
acid) 10.4 11.6 14.1 14.2 6.1 15.0 13.7 13.0 12.1
%
74 .I
80
100
98 32 92 93 94 96
including air, steam, carbon tetrachloride, and saturated sulfate solutions. The results of these studies are given in Table VI. Only water or aqueous solutions gave satisfactory quenchiqg from the standpoint of high phosphorus pentoxide availability. The effect of water compared with saturated potassium sulfate and magnesium sulfate as a quenching media for the langbeinitephosphate fusions is shown in Figure 3, where the dotted line represents results obtained with a saturated potassium and magnesium sulfate quench. The potash and magnesia losses were small.
Pilot Plant Studies The results of the laboratory work on the langbeinite-phosphate rock fusion process were considered promising, and a pilot plant was built to demonstrate the feasibility of the process on a larger scale, and to develop process and design data. Figure 8 shows the pilot plant furnace and accessory equipment. The furnace was a gas-fired vertical shaft furnace with a steel shell 2 feet 6 inches in diameter and 8 feet 6 inches in over-all height. T h e u p er sections of the furnace were lined with 4.5 inches of firehricg backed by 1.5 inches of mineral wool insula-
Figure 8.
Pilot Plant for Fusion Process
Operating Procedure. T h e furnace was filled t o the desired charge depth with agglomerated feed, introduced through the charging hopper at the top of the furnace. Approximately 800 pounds of feed were required t o fill the furnace to the maximum depth of 8 feet. For the experimental runs, however, charge depths of from 2 t o 5 feet were maintained.
INDUSTRIAL AND ENGINEERING CHEMISTRY
652
After charging, the furnace was warmed up for 2 t o 4 hours a t a low heating rate, using from 50 t o 100 cubic feet of natural gas per hour. The gas rate was then gradually increased to 200 t o 300 cubic feet per hour. At this rate the hearth temperature was about 2000” F. and the charge began t o melt. As the melting occurred the gas rate was increased to 350 to 450 cubic feet per hour, and the hearth temperature maintained a t 2400” to 2600’ F.
Vol. 45, No. 3
phosphate would be especially adapted to soils with magnesium deficiencies. In areas where there is high rainfall, considerable loss of magnesium occurs by leaching, leaving the soil deficient in magnesium. I n addition, many groITing crops, such as alfalfa, soybeans, clover hay, tobacco, and cotton require large amounts of magnesium, which must be added as fertilizcr in the same way as phoephorus and potassium are added. Acknowledgment
This work was supported by the Ion-a Engineering Experiment Station. The advice of Fred Keating of the Keating Coal Co., Des Moines, Iowa, in connection with the selection of the pilot plant burner is acknonledged. Literature Cited
Association of Florida Phosphate Mining Chemists, “Florida Land Pebble Phosphate Industry, Methods Used and Adopted,” pp. 23-6, 1948. (2) Association of Official Agricultural Chemists, “Methods of Analysis,” 7th ed., pp, 6-25, 1950. (3) Brabson, J. A., Smith, J. P., and Darron, Anita, J . Assoc. O&. Agr.
(1) SHAFT
DRYER QUENCHING MEDIUM
Figure
9.
SETTLING
BAGGER
POND
Chemists, 33, 467-69 (1950).
Chemistyy Research Board, Report pp. 32-7, London, H.M. Stationaiy Office, 1950. (5) Curtis, H. A., Copson, R. L., Brown E. H., and Pole, G. R., INDEXG.
(4)
Flow Sheet for Large Scale Plant for Making Fertilizer from Fused PhosphateLangbeinite
The melt was either tapped intermittently or run out continuously. The molten product stream from either method of tapping was broken up by high-velocity water jets and discharged through a trough into a settling tank. The quench water had previously been saturated with langbeinite to prevent dissolution of potassium and magnesium from the melt. It was recirculated from the settling tank to the quenching sprays a t the furnace. The product was removed from the settling tank by means of a screen wire basket and dumped in a pile for drainage of solution. It was then dried and packaged in 100-pound paper bags. The product was finely divided, ranging in size from very fine sand t o a maximum of inch. The production rate was approximately 150 pounds of fused product per hour. Pilot Plant Results. The langbeinite-phosphate rock fusion process was demonstrated t o be feasible in the pilot plant. Ten experimental runs were made. T h e total operating time was approximately 105 hours. Typical product sample analyses given in Table IV indicate t h a t products essentially the same as those made in the laboratory studies can be made on a large scale. The product had excellent physical characteristics. It was granular, chalk-white in appearance when dry, and soft, and could be stored in open containers without caking. I n general, the equipment and materials of construction used in the pilot plant were satisfactory. T h e chrome-plastic lining used in the hearth section showed practically no corrosion by slag attack and withstood severe abrasion incurred in chipping out solidified melt between runs. T h e firebrick in the upper section of the furnace also showed no corrosion or slag attack. Fuel consumption was approximately 6,000,000 B.t.u. per ton of product. Conclusions
The phosphorus in phosphate rock can be made available by fusing i t with magnesium sulfate or mixtures of magnesium sulfate and potassium sulfate and immediately quenching the molten mass in a suitable medium, without substantial removal of the fluorine content of the phosphate rock. Langbeinite can be used instead of pure potassium sulfate and magnesium sulfate t o obtain high phosphorus pentoxide availabilities. A mixture of langbeinite and phosphate rock containing about 70% langbeinite must be used. Fusion of a mixture of this composition gave a product containing 13 yo phosphorus pentoxide, 13% potash, 115V0magnesia, and 1.6% fluorine. The availability of the phosphorus and magnesium was 97% and the availability of potassium was 95%. Pilot plant studies indicated t h a t this process could be carried out on a large scale in a vertical shaft furnace. Preliminary economic studies indicated t h a t the process would be competitive with other fertilizer processes. A flow sheet for a proposed fusion plant i s shown in Figure 9. Because of the magnesium content, the fused langbeinite-
CHEM.,29, 766-70 (1937).
(6) Day, A. L., and Allen, E. T , “The Isomorphism and Thermal Properties of Feldspars,” Washington, D. C., Carnegie Institution of Washington, 1905. (7) Elmore, K. C., Huffman, E. O., and Wolf, W. W.,IND.LSG. CHEM.,34, 40-8 (1942).
(8) Giese, F., and Wolters, W.,U. S. Patent 1,025,619 ( M a y 7, 1912).
Heskett, J. A., Brit. Patent 435,763 (Sept. 23, 1935); Australian Patent 16,704,134 (Oct. 15, 1934). (10) Hignett, T. P., and Hubbuch, T. N., IND.ENG.CHEM.,38, (9)
1208-16 (1946).
(11) Hoffman, J. I., and Lundell, G. E. F., < J . Research Natl. /17~1.. Standards, 20, 607-26 (1935). (12) Jacob, K. D., Reynolds, D. S., and Marshall, H. L., Am. I m t , Mining Met. Engr., Tech. Pub. 695 (1936). (13) MacIntire, W.H., Hardin, L. J., and Meyer, T. A , , J. Assoc. O.#ic. Ag?. Chemists, 30, 160-8 (1947). (14) Marshall, H. L., Reynolds, D. S., Jacob, K. D., and Rader, L. P., Jr., IND.ENQ.CHEM.,27, 205-9 (1935). (15) Marshall, H. L., Reynolds, D. S., Jacob, K. D., and Tremearne, T. H., Ibid., 29, 1294-8 (1937). (16) Moulton, R. W., Chem. Eng., 56, 102-4 (July 1949). (17) Moulton, R. W., Univ. Washington Expt’. Sta., Bull. 2, 16-21 (18)
(January 1950). Nagai, S., Kawazumi, Y., and Nahazan-a, T., J . Electrochcnz.
SOC.J a p a n , 18, 155-8, 261-5 (1950); 19, 26-30, 97-100, 1246 (1951). (19) Prjanischnikoff, D. N., “Die Dungerlehre,” p. 243, from 6th
Russian ed. by M. Von Wrangell, Berlin, P. Parey, 1928; Reviewed i n J . Ministry Agr., 31, 102 (1924). (20) Reynolds, D. S.,Jacob, K. D., Marshall, H. L., and Rader, L. F., Jr., IND. ENG.C H E M . 27, , 87-91 (1935): (21) Reynolds, D. S., Jacob, K. D., and Rader, L. F., Jr., Ibicl., 26, 406-12 (1934). (22)
Reynolds, D. S., Marshall, H. L., Jacob, K. D., and Rader,
(23) (24)
Schatzel, B., Chcm. Tech. (Berlin),3, 135 (1951). Schereschewsky, Ph., Ann. mines & carburants, Mem. 135, 61-
(25)
Walthall, J. H., and Bridger, G. L., IND.ENG.CHEX.,35, 774-7
(26)
Whitney, W. T., and Hollingsworth, C . A , , I b i d . , 41, 1325-7
L. F., Jr., Ibid., 28, 6i8-82 (1‘336). 75 (1946). (1943). (1949).
(27) Wiborgh, J. G., Swedish Patent 18,401 (Jan. 16, 1903). (28) Wolters, IT7., U. S.Patent 721,489 (Feb. 24, 1903). (29) Yashido, Yuketo, J . Chem. Soc. .Japan, 63, 439-51, 615-25 (1942). RECEIVED for review September 2, 1952. ACCEPTED hTovember 7, 1952. Presented before the Division of Fertilizer Chemistry a t the 122nd Meeting: of the AMERTCAK CHEnrxcAL SOCIETY, Atlantic City, N. J.
