Page 2
Two other methods of preparing anhydrous rare-earth fluorides are described in the literature. One method is precipitation from aqueous solution with hydrofluoric acid and dehydration 6. The principal difficulties are in the mechanics of washing and drying the hydrated fluoride to prepare anhydrous cerous fluoride consistently free from oxyfluorides. Another method is the gaseous fluorination of ceric oxide with HF or ClF3 (21). According to Von Wartenberg, CeF3 was made by passing anhydrous HF over CeO2 in a platinum tube at temperatures above 400° C. Popov and Knudson describe the fluorination of the oxides lanthanum to samarium with C1F3 (16).
The ammonium-bifluoride method used at Reno does not require the handling of a gelatinous precipitate and is simpler than either of the above methods for preparing small laboratory batches of anhydrous cerous fluoride.
Details of Reno Ammonium Bifluoride Method
Ceric oxide, obtained from a commercial company or from other work at the Reno station, was pulverized in a porcelain mortar with approximately 10 percent excess of the stoichiometric quantity of commercial anmonium bifluoride flakes. The mixture was placed in a platinum dish or CeF3 boat in a laboratory muffle open to the air. The muffle was maintained at 500° to 600° C. for 2 hours before the product was removed. Some ammonium fluoride collected on the inside of the muffle.
The purity of cerous fluoride batches was determined by the X-ray and spectrographic analytical laboratories. A typical spectrographic analysis indicated that aluminum, calcium, iron, lithium, magnesium, nickel, platinum, silicon, and zinc were not detected. An X-ray diffraction pattern showed
No ceric oxide or cerium oxy fluoride was detected. A sample of the Cef3 was reported by the Bureau of Mines Boulder City station to contain 0.004 percent nitrogen.
One-hundred-and-fifty grams of cerous fluoride made by this method was sent to K. K. Kelly, Chief, Berkeley Thermodynamics Research Laboratory, at Berkeley, Calif. Analyses in the Berkeley station laboratory showed:
In order to prepare larger batches of cerous fluoride without contamination and to eliminate the use of platinum ware, sintered cerous fluoride boats were developed. Cerous fluoride, prepared in platinum dishes as described, was mixed with Carbowax and pressed at 56,000 p.s.i. into 1-13/16inch, i.d. cylinders. The cylinders were cut in half longitudinally and the resulting boats placed in a 2-9/16-inch i.d. vitrified alumina tube within a horizontal tube furnace. The boats were heated in air at 250° C. for 2 hours to remove the Carbowax and sintered by bringing them to 530° C. in 15 hours.
The sintered cerous fluoride boats were loaded with the ammonium bifluoride-ceric oxide mixture (proportions as previously given), and the
tube furnace was brought from room temperature to 500° C. in 4 hours. The charge was maintained at 500° to 600° C. in the air for 2 hours. Eighthundred-gram batches of cerous fluoride were made by this method.
In a typical spectrographic analysis no aluminum, calcium, iron, lithium, magnesium, nickel, platinum, silicon, and zinc were detected. X-ray diffraction showed no CeOF2 or Ce02
High-temperature heat-content measurements were made at the Berkeley Thermodynamics Research Laboratory, Berkeley, Calif., on samples of cerous fluoride prepared by the ammonium bifluoride method in platinum dishes and in sintered CeF3 boats at the Reno station.
A prime requisite of a successful molten-salt electrowinning process is a suitable electrolyte. Such factors as cathode, anode, and cell construction materials, composition of the atmosphere surrounding the cell, and voltage and current requirements are also essential but are largely contingent on characteristics of the electrolyte. Accordingly, the electrolyte might be considered the heart of the high-purity-metal electrowinning process.
Surprisingly little basic data have been published on fluoride electrolytes. Because of the key function they perform and the dearth of information on them, considerable effort is being applied to basic studies of electrolytes--the preliminary of cell-box electrowinning investigations. The electrolyte experimentation is on a much smaller scale than the electrowinning studies; its purpose is to define the physical, chemical, and electrochemical characteristics of combinations of fluoride solvent-phase constituents and of electrolytic baths.
Measurements desired and phenomena about which better understanding are needed concern melting points, viscosity, density, vapor pressure, tendency to wet graphite, solubility of solute in solvent, ionization, transfer of ions, equilibria, polarization, and effects of anode gases.
These investigations on electrolytes require special measuring devices for use with melting and atmosphere-control equipment. Obtaining accurate data is complicated by the extremely corrosive nature of the molten fluorides. Many of these studies are in a formative stage, and a search is still in progress for instruments suitable for making some measurements. However, during the period covered by this report, melting points, conductivities, and solubilities of components were measured, and preliminary electrolyses were conducted on several fluoride baths. The small scale of the operations conserved time and materials in developing suitable electrolytes for trial in the larger cerium electrowinning cells.
Several types of small-scale cells were used for fluoride melting point determinations and electrolysis of short duration. One cell comprised a carbon pot (welding-rod carbon) 5/8 inch i.d. and 2-3/4 inches deep, set inside a 1- by 7.9-inch Vycor glass tube. The anode (a carbon rod 1/8-inch
in diameter) and the cathode (a molybdenum strip 1/32 inch wide and 0.01 inch thick) were attached to a 3/16-inch-diameter brass rod and insulated from each other with sheet mica. The brass rod served as the electrical lead to the anode, and a copper wire served as the lead to the cathode. The electrical assembly was introduced into the cell through rubber sleeves set over nipples in a Pyrex glass head. The glass head also had outlets, permitting evacuation and flushing with argon and introduction of a thermocouple protection tube, and was sealed in place in the mouth of the Vycor glass test tube with Apiezon wax. The wax was kept cool with a jet of air.
Neidrach and Dearing (13) have suggested that adding small amounts of chlorides to molten fluoride solvents increases fluidity and electrical conductivity. The described apparatus was used in investigating the effect of adding 5 percent by weight of MgCl2 to part of a CeF 3-LiF-BaF 2 bath from the Reno cerium electrowinning cell. The MgCl2 lowered the bath melting point from 740° to 690° C., but chlorine gas was produced during electrolysis and anode effect was noted.
The loss of lithium from the CeF3-LiF-BaF2 bath during electrolysis suggested the investigation of a new bath containing less Lif. With the previously described apparatus and the electrode assembly removed, a series of melting points was measured on various CeF-LiF-BaF2 mixtures by the thermalanalysis techniques and visual observations. A bath having a satisfactory melting point of 735° C. was prepared, comprising 77.3 percent CeF3, 12.7 percent Bar
21
and 10.0 percent LiF by weight. P. M. J. Gray's bath (4) contained 26.9 weight-percent LiF.
MgF2 was investigated as a substitute for Lif in the CeF 3-LiF-BaF2 bath because it has a lower vapor pressure. The melting points of various CeF3MgF2-BaF2 mixtures were measured. As the lowest melting point was 930° C., no mixture investigated was suitable as a solvent-phase electrolyte for electrowinning of cerium. However, MgF2 may serve as a bath constituent for electrowinning of uranium ingot and the rare-earth metals melting above 1,000° C.
Using a KF-LiF-NaF solvent-phase electrolyte and adding CeF3, the authors carried out electrolysis in a tantalum cell within a controlled-atmosphere glove box. A pool of molten alkali was noticed around the cathode at the top of the bath during electrolysis. X-ray diffraction patterns of cell products showed that no cerium metal had been produced. With a BaCl2-CaCl2-CeF3 bath, electrolysis in a Vycor cell within the controlled-atmosphere glove box produced massive cerium metal and chlorine gas. Spectrographic analysis showed 0.01 to 0.1 percent calcium in the cerium metal.
Several small-scale cells were designed and investigated to measure the electrical conductivity of molten fluoride systems with alternating current. The fabrication of a suitable cell has been hampered by lack of a nonconducting material resistant to fluoride corrosion.
A cell requiring about 75 grams of bath material was built and gave results in good agreement with values in the literature for the electrical conductivities of molten KCl and NaCl. All parts of the cell in contact with
the molten bath were made of graphite or molybdenum, except a Vycor glass tube that provided an insulated electrolyte path between the two molybdenum electrodes. Fluoride corrosion of the Vycor glass prevented good reproducibility in electrical-conductivity measurements of molten fluoride systems with this cell. A new cell is being developed in which the Vycor glass tube is replaced by a hot-pressed boron nitride tube. Data obtained in this laboratory and by other workers (22) have indicated that boron nitride is resistant enough to corrosion by molten fluorides for short periods to serve these experimental purposes.
The constituents for the solvent phase of the cerium electrolyte, that is, CeF3, BaF2 (reagent-grade), and Lif powder (reagent-grade), were mixed in air in the proper proportions. The mixture was placed in a glass-stopcocked Pyrex flask within a wire-wound resistance furnace. The flask was evacuated to about 10 microns, and the furnace turned on. All vacuum readings were taken with a Pirani gage. As the furnace heated, the flask was pumped out continuously by a mechanical high-vacuum pump with a dry-ice-acetone trap. A furnace temperature of approximately 280° C. and about 15 hours were necessary for the mixture to reach a vacuum of 10 to 15 microns. The powder mixture was then tested for moisture as follows: Moisture removed after dehydration of the electrolyte components was captured in a dry ice-acetone cold trap for 5 to 10 minutes. The trap was then warmed to room temperature and flushed with dry argon through a sensitive moisture-determining instrument, the moisture monitor. When no moisture was detected above the level of the argon blank, the sample was considered dry.
The powder, comprising 73 percent CeF3, 15 percent Lif, and 12 percent BaF2, contained approximately 1 percent moisture before vacuum drying. This mixture will be referred to in this report as the Reno fluoride solvent-phase electrolyte, or the Reno fluoride electrolyte. The procedure removed about 70 percent of the moisture. An experiment indicated that most of the remaining moisture was removed as the temperature was increased to the melting point of the bath. Ce02, the solute phase of this electrolyte, was vacuumdried in a similar manner.
Laboratory-Cell Development
A carbon cell 8 inches high by 4 inches i.d. was designed. P. M. J. Gray (4) used a similar cell. This cell, made of grade CS-31 carbon, was heated externally by a wire-wound resistance furnace through a type-316 stainless-steel can; the inside bottom of the carbon cell was covered with molybdenum sheet that extended 1 inch up the sides. A small 1- by 1-3/16inch-diameter molybdenum crucible for holding the molten cerium product was placed under the 0.2-inch-diameter molybdenum cathode. The cathode was protected to 1 inch above the bath by a carbon sheath, which also served as an
entrance tube for the argon gas that continuously purged the space above the bath. The small molybdenum crucible was suspended from the carbon sheath with molybdenum ribbons so that it could be raised above the molten bath when electrolysis was complete. No evacuation of contained air or occluded gases in the carbon or charge was possible in a cell of this type. A 0.625-inchdiameter, grade CS-31 carbon anode was used with l-inch spacing between electrodes. The cell was covered with a water-cooled carbon lid, and the lid was covered with 2 inches of transite insulation.
In a cell of this type ceric oxide cannot be added continuously during electrolysis, thus the operation was of short duration or a batch-type one. It is doubtful whether the data obtained can be compared with continuousoperation data in which the oxide feed is added during electrolysis.
A fluoride electrolyte composed of 60.8 percent by weight of CeF3, 26.9 percent Lif, and 12.3 percent BaF 2 was used. This mixture was reported to be capable of dissolving 3 to 5 percent by weight of CeO2 at 850° C. The density of the mixture was approximately 4.0 grams per cubic centimeter. The dry-powder mixture required to form a bath 2 inches deep in the cell was calculated to be of the following weight composition:
The cerous fluoride (99.8 percent pure) used in this experiment was prepared from ceric oxide purchased from a commercial source and mixed with ceric oxide prepared from bastnasite in the Extraction Section of the Reno laboratory. The mixture was fluorinated with ammonium bifluoride, as already described. The lithium fluoride powder was reagent grade; spectrographic analysis showing less than 0.1 percent barium, 0.001 percent magnesium, and other metallic and nonmetallic elements as traces. The barium fluoride was also reagent grade, spectrographic analysis showing less than 0.01 percent calcium, 0.001 percent magnesium, 0.001 percent silicon, 0.1 percent strontium, and 0.001 percent titanium.
The mixed charge was made into briquets in a laboratory hydraulic press at 20 tons per square inch. This permitted charging the complete 1,760 grams of mixture into the carbon cell where the charge was dried for 16 hours at 140° C. After the briquets were charged and the cell was covered, purified argon was passed through the cell for 30 minutes before initial heating.
While the purified argon continued to flow through the cell, the furnace temperature was raised. The time required for melting was 4 hours, and the
Page 3
In one experiment with the Reno fluoride solvent-phase electrolyte, a sintered cerous fluoride disk was placed in the cell bottom. The disk prevented the cerium metal from contacting the graphite cell, and no evidence of carbide formation was noted. However, the CeF3 disk dissolved slowly in the bath.
In another experiment (CE-30), an air-cooled copper coil was placed under the graphite cell bottom and a frozen layer of electrolyte maintained. Two hundred grams of massive cerium metal was deposited and held above the cell bottom. Analysis of a nodule of CE-30 cerium metal by the Boulder City station showed 0.01 percent carbon. Table 1 gives analyses of this nodule for metallic and nonmetallic impurities.
1 0.04 (27) 0.02 0.02 0.01 0.001 0.001-.01 0.02 1 (27) (27) (27) .04 (27) .01 (27)
.02 2 .01 0.03 (27) .04 .006 .01 (27)
.02 3 (27) .06 (21) .06 (21) .01 (27)
.05 25 (2) .03 (27) (27) (2)
.01 (27) (27) 2T (27) .06 (27) .08 (27) .01
(2/)
.05 is (27) .04 .01 .03 .001 (27) (27)
.04 Total impuri-
Temperature, °C. ties, Bath
Anode Cell bottom Run Nodule Elements pop.m. weight, Aver- Maxi-Aver- Maxi-Aver- Maxi- No. С 0 N H percent age
age mum
age
CE-301/ 1 100 20
15
3 0.125 820 850 780 818
622 749 CE-413/ 1
34 523 5 5 .126 845 932 785 822 675 728 2 (47) (47) (47) (4/7)
3 (47) (47) (47) (47)
CE-423) 25 207 569 6 9
.119
878 920 817 869 605 683 2T 55 594 6 4 .266
is (47) (47) (47) (47)
1/
Cell type 4.
2/ Not detected.
3/ Cell type 5.
4/ Not determined.
A mixture comprising 1,178 grams of the Reno fluoride electrolyte and 1,622 grams of old bath was dried using the procedure described under vacuum drying, page 9.
This bath was melted in a 4-inch-i.d. by 4-5/8-inch-deep graphite cell, using a wire-wound resistance furnace within the controlled atmosphere and temperature cell box. A bath temperature of 772° to 850° C. and a cellbottom temperature of 590° to 749° C. were maintained during electrolysis.
Page 4
The electrode assembly consists of an adjustable three anode- three cathode triagonal system. (See fig. 1.) A thermocouple well is drilled longitudinally in a carbon anode within 1 inch of the bottom. A chromelalumel thermocouple in a sillimanite protection tube is placed in the anode thermocouple well.
Two copper power-conductor rods from the anode and cathode holder pass through a transite block that is raised and lowered on a steel frame by operating an adjusting screw to position the electrodes vertically.
Rubber-insulated power cables carry the current to the conductors from power feedthroughs, which are vacuum-sealed in a rubber-gasketed Micarta plate on the end of the glove box. Rubber-insulated power cables carry current from the a.c.-d.c. rectifier and a.c. welder heater to the ends of the power feedthroughs outside the steel glove box.
The electrode assembly and graphite cell are centrally located in the controlled atmosphere-temperature-pressure (C.A.T.P.) steel glove box. The glove box and air-lock enclosures are made of welded 1/4-inch mild-steel plate. (See figs. 1 and 2.) The inside dimensions of the glove box are 24 inches wide by 36 inches long by 26 inches high. The air-lock inside diaensions are 12 inches wide by 12 inches high by 18 inches long. The room airlock door and the glove box-air lock access door are sealed with flat rubber gaskets. A 10- by 18-inch mild steel door is sealed to the rear side of the glove box with a flat rubber gasket. This glove-box access door is removed for setting up and dismantling the electrowinning cell and electrode assembly.
The inside of the glove box and air lock were sandblasted and painted with a water solution of l-percent "Siliclad." No noticeable corrosion had taken place on the inside surfaces of the mild steel glove box after exposure to vapors from various melting and electrolytic experiments with fluoride baths over a period of 9 months.
The l-inch-thick, laminated, safety-glass viewing ports were slightly etched after several electrolytic runs and were removed and buffed to restore transparency. A 100-watt light bulb within the box was used for illumination.
Replacing Air With Inert Atmosphere
Figure 2 shows the oil-diffusion pump, a welded-steel cold trap, and a mechanical fore pump connected to the end of the glove box opposite the air lock. The 6-inch-diameter oil-diffusion pump and the mechanical fore pump can be used to evacuate the glove box through a 6-inch steel pipe and the air lock through a 4-inch steel pipe. The box and air lock can also be evacuated through a 2-inch pipe attached directly to the mechanical pump.
Argon or helium is admitted to the glove box through the 1/4-inch copper tube shown in figure 1. Box atmosphere pressures were measured through this
tube using a mercury manometer. Samples of box and air-lock atmospheres for gas master tests and Orsat gas analyses were obtained through the 1/4-inch valve shown in figure 1. Box atmosphere samples for moisture determinations were transferred into the moisture monitor through a copper Teflon tube system connected to a vacuum pump.
FIGURE 2. - Electrowinning Gloved Cell Box and Accessories.
Electrocerium fluoride charges were melted by passing direct current through the graphite resistors contacting the bottoms of the electrodes. The 40-volt 300-ampere, silicon, a.c.-d.c. rectifier unit was the d.-c. source. Arcing was noted with erratic voltage and current conditions. Moreover, cerium carbides were formed, as cerium-metal deposition began with the initial melting of the charge when graphite resistors were present. Analysis of
a cerium metal sample, where part of a graphite resistor remained in the bath during electrolysis, showed 5,200 p.p.m. carbon.
Several attempts were made to use cerium metal strips as resistors in melting with direct current. In all instances the cerium metal melted, breaking the circuit before enough molten bath had been obtained to carry the cur
Additional work on this problem is planned in the future.
Cerium Electrowinning Run (CE-42)
A cerium electrowinning run was made using the Reno fluoride solvent phase of the electrolyte and CeO2 solute with a.-c. internal meltdown in the type No. 5 cell.
The C. A. T. P. glove box containing the triagonal electrode assembly and the 6-inch-diameter insulated graphite cell described previously were pumped down to 75 microns. High-purity tank argon was run into the glove box to 3/4-p.s.i. The box atmosphere and high-purity tank argon were compared with the gas master and found to have equal thermal conductivities.
Three thousand one hundred and thirty grams of minus-10-mesh charge, made from the old bath of a previous electrowinning run and vacuum dried, were loaded into the cell. Two graphite half-ring resistors, 3/16 inch thick by 3-3/4 inches o.d. by 3/8 inch wide, were placed on top of the minus-10-mesh charge. The electrodes were lowered to contact the resistors. The resistors were placed 1-3/4 inches from the top of the cell, and 1 inch of vacuum-dried, Reno fluoride, solvent-phase electrolyte powder was placed on top of the resistors. When the graphite resistors were placed on fresh powder, arcing was caused by shrinkage of the bath.
Alternating current at an average of 7 volts and 300 amperes was passed through the graphite resistors for 2 hours using the 40-volt 300-ampere arcwelding unit. About 1,500 grams of Reno fluoride solvent-phase electrolyte was added to the cell by the gloved operator through the feed tube during the alternating-current meltdown. No arcing was noted. When a fluoride bath was obtained around the electrodes and the bath temperature was 750° C., the graphite resistors were removed, using molybdenum tongs.
The current was then switched from a.c. on the welding unit to d.c. on the 40-volt, 200-ampere silicon rectifier. Ceric oxide (Ce02) powder was charged into the molten bath by the gloved operator through the sillimanite feed tube, using a calibrated glass spoon. A ceric oxide feed rate of 2 grams per minute was maintained during the 146 minutes of electrolysis.
An average direct-current voltage of 6.7 and an average amperage of 203 were maintained during electrolysis. The electrodes were immersed in the bath three-quarters inch, giving an initial cathode current density of 11.3 a. per sq. cm. and an initial anode current density of 4.5 a. per sq. cm. Adjoining cathodes and anodes were 0.75 inch apart and 1.25 inches from the cell wall.
During electrolysis the temperature of the anode having the thermocouple well averaged 817° C. and the cell-bottom temperature 605° C.
Samples of the cell-box atmosphere were taken for Orsat gas analysis at approximately 15-minute intervals. At intermittent intervals the box was partly pumped down, and high-purity argon was introduced to maintain the box atmosphere at about 66° C. which enabled the operator to work in the box. A maximum of 17.6 percent CO2 and 1.8 percent Co was reached in the box atmosphere. Usually, the pump downs and introduction of argon maintained the box atmosphere below 12 percent Co2 and 1 percent co. Qualitative tests of boxatmosphere samples for fluoride ion, using zirconium alizarin solution, were negative.
Some of the bath foamed over the side of the graphite cell during this run. A small amount of a white, powdery sublimate collected on the anodes above the bath. Previous X-ray diffraction patterns indicated that this sublimate was chiefly Lif. The glass viewing ports were also coated with a white, powdery sublimate and were slightly etched.
The bath with immersed electrodes was allowed to freeze in the cell-box atmosphere upon completion of the run and remained there for 15 hours. The frozen bath was then readily lifted from the graphite cell by means of the electrodes. The graphite cell was not visibly corroded.
Six hundred and six grams of massive cerium metal nodules, mostly 1/2by 1/2- by l-inch, were found scattered in the frozen bath beneath the electrodes. None of the cerium nodules touched the electrodes, walls, or bottom of the graphite cell. Only a very small amount of cerium metal adhered to the molybdenum cathodes.
Each cerium metal nodule under molybdenum cathode No. 2 in electrolytic run CE-42 was filed in the air to obtain one or two bright surfaces. The filed surfaces were examined megascopically after the nodules had remained in air 40 hours. Some nodules were tarnished and others remained silvery. Table 2 compares a silvery-surfaced nodule, 2s, with a tarnished-surfaced nodule, 2T.
,
Analytical comparison of two cerium nodules from run CE-42
Elements, weight-percent
Elements, Run Nodule
Ca+
Pop.m. No. No. Fe Si Al Mg Ba Li Мо С 0 N
CE-42 2S 0.03(1/) (1/) (1/) (1/) 0.01 (18) 207 569 6 9
CE-42 2T .06 (1/)| 0.08 (1/) (1/) .01 0.05 55 594 6 4
1/ Not detected.
Total impurities, weight, percent
0.12
.27
This method has been used to classify low- and high-grade cerium metal nodules from several electrolytic runs. Generally, nodules with silvery surfaces are higher grade than those with tarnished surfaces. Investigation of the air-corrosion classification method is being continued.
Current efficiency, computed from massive cerium metal produced, was 94 percent. Current efficiencies ranged from 70 to 94 percent, depending upon the amount of old bath reused in the charge and other factors inherent to small research cells and short electrolyzing periods.
Analyses of Cell-Box Gases
Gas analyses were performed during each run in cell type Nos. 3, 4, and 5. Gas samples were removed from the cell box by means of an evacuated gassample bottle 10 inches long and 1-1/2 inches in diameter with a stopcock at both ends. The sample bottle was evacuated to 20 microns pressure or less, then attached with a short piece of rubber tubing to a valve near the top center of the glove box. After the tubing was flushed with argon to remove any air, the valve and stopcock were opened and a sample of the glove-box atmosphere was sucked into the sample tube. The sample was then transferred to an Orsat apparatus and analyzed for CO2, co, and 02 by standard Orsat procedure. The Orsat apparatus had a capacity of 50 ml., and gas volumes could be measured to 0.1 ml. or 0.2 percent of the total gas volume. Qualitative tests were also made for HF and F2 by bubbling samples of the box gas through a zirconium-alizarin solution prepared according to Feigl (2).
The major gaseous product of the electrolysis was CO2, and small amounts of co were present. In this respect the current cerium cell is similar to the aluminum cell, in which coz is known to be the principal anode gas and co is formed by the reduction of CO2 by anode carbon or by metal fog (18, 14). The amount of co seldom exceeded 2 percent of the total volume of the gas in the glove box and usually remained within a range of 0.8 to 1.6 percent, despite the length of the runs. The concentration of CO2 continued to build up as the runs proceeded. By partly evacuating the glove box and adding pure argon at intervals, the operator diluted the CO2 and co and controlled the box atmosphere. The maximum concentration oĒ CO2 permitted in
of any run was 18 percent. The correlation between CO2 content of the box atmosphere and metal purity is to be investigated. Possibly, a greater CO2 concentration may be tolerated.
CF4 has been reported in the off gases of both aluminum (5) and uranium
. cells (13) and would be expected to be present in preference to F2 in any electrolysis of a fluoride bath using a carbon anode at temperatures greater than 450° C. (10) .
In the uranium cell the CF4 was usually present in concentrations of 0.19 percent or less, and in the aluminum cell the gas was detected only during an anode effect caused by depletion of Al203 in the cell.
There are no convenient chemical tests for the fluorocarbons, because of their extreme inertness. It is planned to have mass spectrometric analyses made of the cerium cell gas. Attempts to trap out CF4 by means of liquid oxygen traps did not indicate the presence of the gas in detectable quantities. It is believed that some CF4 and possibly other higher fluorocarbons may be present in the off gases of the cell but in too small amounts to be detected by available procedures.
Page 5
20 grams of cerium was melted in each crucible, and temperatures of approximately 1,000° C. were attained. The cerium adhered to the crucible walls and bottom, and spectrographic analysis indicated contamination of the cerium with titanium at an approximate weight-percent of 0.1 to 0.01 titanium.
Elements, weight percent Total
rare earths,
Ca
Ta weight
+
or Type of cerium
percent
Fe Si Α1 Mg Li Ba Mo I Reno bomb cerium regulus 0.05 0.05 0.06
0.06 0.01 (17) 1.00 (17) 0.20 0.31 (
( Reno bomb cerium regulus, refined...... .01 .05 .06 (1/) (1/) .01 (1/) .30 (17)
1/ Reno electrocerium..
.04 (17) .02 .02 .01 .001.005 .02 (17) Commercial cerium metal3/ 3.1 .12 .05 .01 .16 (1/) (1/) (17) .05
Total Elements Pop.m.
impurities, Type of cerium
C 0 H N
percent Reno bomb cerium regulus (27) (27) (21) (27)
1.68 Reno bomb cerium regulus, refined...... (27) (21) (21) (27)
.42 Reno electrocerium..
100 20 3 15
.12 Commercial cerium metal3/ 36
147 11 15
3.49 1/ Not detected. 2/ Not determined. 3 Commercial metal is prepared from an intermediate chloride salt, which may
account for the high concentration of other rare-earth metals.
In summarizing his experimental results, Foster (3) states that Ces is in no way superior to TiN or ZrN for melting cerium.
Some grades of graphite have proved satisfactory as cell construction materials at 810° C. in the Reno cerium electrowinning runs. Unlike Vycor glass and iron they were not attacked by the molten fluoride electrolyte. As the graphite surface was not wet with the Reno fluoride electrolyte, the frozen electrolytes could be easily removed, making possible reuse of the graphite cells.
In cerium electrowinning runs using cells of a certain grade of carbon, carbides were formed and the cells cracked when molten cerium contacted the carbon, resulting in loss of the molten electrolyte. Under parallel conditions in graphite cells, the molten cerium formed carbides on contacting the graphite, but no cracking took place at temperatures of 810° C.
When a frozen layer of electrolyte is maintained next to the graphite, as in cell type No. 5, electrocerium low in carbon impurity can be prepared in a graphite cell under properly controlled atmosphere and temperature conditions.
Page 6
resistance measurements in assessing the relative purity of metals,
since it is felt that the method may have more general utility as
a criterion of purity than is generally recognized.
The importance of obtaining the true electrical conductivity of cerium, is evident from examining the atomic structure of the rare-earth elements. They have similar electronic structures, although their nuclear structures differ. As the atomic weight of the series increases there is, with few exceptions, a regular decrease in atomic volume.
The chemical reactivities of the rare-earth elements, which are a function of their electronic structures, are quite similar. Their physical properties, which depend on their nuclear structures as well as other factors, show significant differences. Thus, they offer an excellent opportunity for checking present theories of metals and possible correlation of the properties of the metals and their structures. However, as they are extremely reactive and small amounts of impurities can drastically change their properties, accurate reproducible measurements of their characteristics are generally lacking.
Investigations With Chamber No. 1
The first chamber was fabricated from 3-inch-i.d. by 7-inch-long steel pipe, welded shut at the bottom, and a 3-inch-i.d., 5-inch-o.d. O-ring flange welded to the top.
The cover was a 5-inch-diameter Bakelite disk 1/2 inch thick, to which the entire bridge circuit was rigidly attached. The bridge comprised separate current and potential contacts with a copper-constantan thermocouple at either end of the sample. The sample was held tightly against the contacting edges by a spring-loaded Bakelite sheet. The cover also contained an outlet for evacuating the test chamber and a 1/2-inchdiameter brass rod for supporting the chamber in the Dewar of liquid oxygen. Vacuum-tight electrical connections were made by sealing the leads in a coldsetting plastic where they pass through the Bakelite cover.
Temperature of the sample was controlled by variable electric heaters, one in a thin-walled copper tube connecting the sample block to the bottom of the test chamber and another between the O-ring flange and the Bakelite cover.
A Kelvin bridge circuit was chosen to measure the resistivity, because the null detector method of measuring would eliminate errors due to contact resistances. These resistances will be present when working with reactive metals such as cerium, and because the total resistance of the sample is small the errors would be large.
The bridge consists of separate current and potential contacts to the sample.
The potential drop across the sample is measured by a Rubicon typeB precision potentiometer; the current, which is supplied by five 6-volt, low-discharge-type storage batteries, is measured by the potential drop across a standard resistance of 1 ohm.
The resistance, R, of the sample is given by Ohm's law as the quotient of the potential drop and current. The resistivity, P, of specimens is
RA then computed from the relation p =
where A is the cross-sectional
L area and L the distance between potential contacts. The temperature of the sample is indicated by two copper-constantan thermocouples, one at either end of the sample.
Specimens for comparing electrical conductivity were made originally as follows: Samples of Reno electrolytic and bomb cerium metals and commercial cerium metals were vacuum-melted in degassed, 1/2-inch-i.d. tantalum cans. Then these samples were prepared in an argon atmosphere in the glove box for X-ray lattice constant and electrical conductivity measurements. Disks 1/4 inch thick were cut with bolt cutters from the 1/2-inch-diameter cerium cylinders. The disks were cold-rolled into strips 1/8 inch thick with a hand rolling mill. The strips were squared into approximately 0.2 by 0.1 by 1-inch samples with a steel file and polished on grit 1/0 emery paper. All machining, rolling, polishing, and sample preparation were performed in an argon atmosphere.
Conductivity values obtained in chamber No. 1 on samples of cerium produced by three methods showed a distinct correlation with purity. (See table 4.)
TABLE 4. - Electrical conductivity and purity comparisons of vacuum
refined, cold-rolled cerium metal samples at 0° C.
Metal, type Reno electrolytic cerium... Reno lithiothermic cerium.. Commercial cerium..
8.3 x 104 2.7 x 104 2.5 x 104
Cerium, percent
99.8 98.5 95.8
The apparatus, although useful in gathering preliminary data, had several disadvantages: (1) It was extremely difficult to achieve zero flow of heat at the start of the run without considerable fluctuation in temperature. the resistivity of cerium is a function of the thermal history of the metal, it would be necessary to duplicate this cycle every run. (2) The temperature gradient across the sample could not be held at the desired maximum of 1/2° C., because the heat was being exchanged primarily from either end of the sample. (3) The danger of thermoelectric effects was present, as the bridge circuit was not in an isothermal region. (4) Finally, it was very difficult to reproduce the thermal cycles.
After some effort was made to eliminate these faults from the equipment, it became apparent that a drastic change was needed in the basic design, and chamber No. 2, was designed and constructed.
This chamber proved very successful.
Investigations With Chamber No. 2
Chamber No. 2 was fabricated from high-conductivity copper and has provisions for running three samples simultaneously. The chamber is surrounded by several inches of polystyrene foam, and temperature is controlled by circulating gases at various temperatures through coils soldered to the outside of the container. The same bridge circuit used with chamber No. 1 was also used with chamber No. 2. A technical paper, describing the equipment in detail, is being prepared for publication. The use of a small jeweler's lathe in making the samples did not introduce as many dislocations as rolling.
As it is impossible at present to remelt cerium without introducing impurities, the length of the conductivity samples is limited to that of the nodules. The average conductivity sample is approximately 0.125 inch in diameter and 1 inch long; thus, uniformity of cross section and measurement of the 0.8 inch between potential edges represent the largest uncertainties in the computed conductivity, being plus or minus 1.5 percent.
An axis is chosen through the longest dimension of the irregular nodule so that the finished sample will be as long as possible. A cold-setting plastic is cast around the nodule in a 3/4-inch cylindrical tube with the chosen axis of the nodule coinciding with the axis of the cylinder. cylinder is mounted in a jeweler's lathe and machined under vacuum oil to approximately 0.135 inch in the section containing the metal, leaving plastic knobs on the ends for mounting for the final cut. The semifinished samples are then stored in a desiccator. Just before measurement they are mounted again in the lathe and machined to 0.125 inch plus or minus 0.0005 inch, then mounted in the inert-atmosphere test chamber. Although much work remains to be done on controlling grain size, orientation, stress level, and dislocations the polycrystalline samples, preliminary investigations indicate that these factors were approximately constant in the samples used in this investigation.
By means of chamber No. 2 it was possible to compare Reno electrocerium with commercial cerium at liquid-oxygen temperatures. Samples for the comparison were machined, then measured simultaneously. A constant temperature rate of 0.2° C. per minute was used throughout the experiment, and the samples were held at the low point for 36 hours to insure equilibrium before the return cycle was begun. As was true with chamber No. 1, the conductivities with chamber No. 2 were greater for the purer metal. (See table 5.)
Metal, type Reno electrolytic cerium (Sample No.
CE-42-25)..... Commercial cerium..
No direct comparison can be made between the data from experiments in chamber Nos. 1 and 2 because of differences in temperature and sample fabrication. The large temperature gradient in the bridge circuit of chamber No. 1 probably affected the values obtained.
No low-temperature transition was evidenced in the commercial metal, nor was there any hysteresis. Reno electrolytic cerium (CE-42-2S) showed a normal transition and hysteresis pattern with the curves rejoining at minus 90° C. The measurement given for CE-42-25 is valid only for this sample, as the nodules produced in the same rup vary. For example, another sample, CE-42-2, had a conductivity of 18.0 x 102, ohm.-1.-cm.-1.
High-purity cerium ingot was prepared in Nos. 4 and 5 cells by maintaining a cell liner of frozen electrolyte and a controlled argon-carbon dioxidecarbon monoxide cell atmosphere. Control of the anode and cell-bottom temperatures in the cerium electrowinning runs given in tables 1 and 6 prevented molten cerium from contacting the graphite.
Analyses for metallic, nonmetallic, and gaseous impurities show that the cerium nodules from the same electrowinning run, as well as those from different runs, vary widely in composition. (See table 1.) Each set of analyses represents only the nodule sampled and illustrates the extreme reactivity of cerium metal.
The authors believe that the carbon in the cerium comes from the CO2 released at the anode. The variation in carbon content of the nodules shows the need for careful control of the composition of the cell-box atmosphere and the temperature and viscosity of the electrolyte. For example, samples of cerium metal nodules from CE-30 were analyzed for carbon at the Rolla (Mo.) station of the Federal Bureau of Mines, using the conductometric carbon analyzer. Ten determinations averaged 1,590 p.p.m. carbon with a low of 20 p.p.m. and a high of 6,200 pop.m. The nodules were exposed to the atmosphere, and pieces picked from nodules having the least surface corrosion on four determinations averaged 35 p.p.m. carbon with a low of 20 pop.m. and a high of 50 p.p.m.
The aluminum, silicon, and iron impurities in electro-cerium are attributed mainly to the fire-clay-brick cell cover and the carbon-welding-rod anodes. Iron also may be introduced in crushing old electrolytes for reuse. Lithium and barium impurities in cerium are low, although their fluorides are solvent-phase electrolyte constituents. Molybdenum cathodes and a molybdenum tool used to remove the graphite resistors after meltdown are the sources of molybdenum contamination of the electrocerium.
During the 3.65 hours of electrolysis it is doubtful whether the electrolyte reached a state of equilibrium, regarding either oxyfluoride content or cation versus anion balance. The considerable difference in the analysis of separate cerium nodules indicates that the selective purification of the electrolyte did not proceed to completion.
Before bath temperatures, cell-box-atmosphere temperatures, pressures, bath equilibrium, and compositions can be correlated with the amounts of impurities in the electrocerium, electrolytic runs of 72 hours or more are believed necessary. A cerium electrowinning cell has been designed for semicontinuous operation of 72 hours or more. A mechanical feeder for CeO2 will be used in operating this cell.
Coalescence depends upon the surface condition of the metal and upon surface tension, viscosity, and relative density of metal and electrolyte, manner of feeding ceric oxide, and possibly other factors. The authors believe that longer runs in a larger cell, with a deeper zone of electrolyte at a temperature above the cerium melting point, would aid in nodule coalescence.
The work in the Reno laboratories has been confined solely to fluoride electrolytes, the electrowinning of cerium from CeO2, and the lithiothermic reduction of CeF3. The problem of rare-earth metal coalescence in chloride systems has been reported by other workers.
P. M. J. Gray (4) reported on the metallothermic reduction of cerous chloride with lithium metal:
This reaction was carried out in a manner very similar to
that for the reduction of the trifluoride but was not nearly so successful. In every run a reaction took place satisfactorily
but the metal produced would not coalesce and remained finely
dispersed throughout the reaction cake * * * The failure
of the metal globules to coalesce is almost certainly due to
the presence of oxide or oxychloride which forms an infusible
skin on the surface of the metal.
Table 6 compares the apparent current efficiencies of three cerium electrowinning runs. The short duration of the runs, the presence of old electrolyte, lack of information as to the exact valence of the cerium in the compound being electrolyzed, and other cell conditions prevented calculation of actual current efficiencies. For example, in run CE-30 the bath was kept molten by external heating with alternating current, whereas in runs CE-41 and CE-42 direct current was used both for electrolytic and thermal energy.
Apparent current efficiencies, calculated on the basis of total direct current and a valence of 4 for cerium, although useful in comparing one electrolytic run with another, should not be regarded as absolute values.
Average and maximum CO2 and co in the cell-box atmospheres for runs CE30, 41, and 42 show no correlation with the amounts of carbon and oxygen in the cerium metal nodules. (See table 7.)
The present work indicates that the 73 percent CeF3, 15 percent LiF, 12 percent BaF2 mixture is satisfactory for the solvent phase of the electrolyte. With longer runs, however, loss by volatilization may necessitate finding a substitute for LiF.
Page 7
Typical data and results of electrowinning
cerium from Reno electrolyte
Electrolyte composition, Apparent weight-percent
Current current Fresh Reno
density solvent-phase old Run No.
electrolyte electrolyte Anode Cathode CE-303/..
85 48
52
1.5 4.8 CE-4147.
78 80
20
4.1 10.0 CE-424/.
94 37
63
4.5 11.3 CeO2 added
Electrode
Ampere- Amount, Rate, immersion,
minutes Run No.
8. g./min.
inch CE-303/
227 0.6 1.00
10.0 CE-414/.
444 1.8
.75
43.4 CE-4241
575 2.2
.75
32.4 1 Calculated using the weight of cerium ingot recovered, the ampere-minute
value of the run, and a valence of 4 for cerium. 2) Calculated using the weighted average amperage for the run and the start
ing electrode curved surface areas. 3/ Cell type No. 4. 4 Cell type No. 5.
Considerable cerium and misch metals are prepared commercially by electrowinning from cerous chloride in the air, using the frozen electrolyte as a cell cover. At present, cerous chloride is reported to be cheaper than ceric oxide because it is an intermediate product from the processing of monazite concentrates for thorium. Future electrowinning investigations using cerous chloride as the source of high-purity cerium metal, under controlled atmospheric and temperature conditions similar to those described in this paper, might be worthwhile.
Although there are many important points of similarity between the basic electrochemistry and mechanics of transfer of ions in the commercial aluminum cell and the electrowinning of cerium at the Reno laboratories, two essential differences are apparent to the laboratory investigator.
Page 8
RECOVERING IRON CONCENTRATES FROM THE PEA RIDGE
DEPOSIT, CENTRAL MISSOURI”
D. W. Frommer/ and M. M. Fine 3
Mineral dressing research was conducted by the Federal Bureau of Mines under a cooperative agreement with the St. Joseph Lead Co., on three samples of iron ore from the Pea Ridge deposit in central Missouri. The objective was to provide information on how to upgrade these submarginal ores and produce marketable concentrates.
Samples were prepared from drill-hole cores of similar composition and character to produce (1) a medium-grade mixed hematite and magnetite, (2) a
) high-grade mixed hematite and magnetite, and (3) a high-grade magnetite. In all three ores phosphorus and sulfur constituted objectionable impurities; excessive amounts of silica were also present in the medium-grade ore.
Low-intensity magnetic separation of high-grade magnetite ore readily produced acceptable concentrates analyzing 71.4 percent iron with an accompanying recovery of 97.1 percent. Magnetic separation made only a partial recovery on the mixed ores, as natural hematite is not concentrated by this treatment.
Flotation was one process applicable to all three samples. With the high-grade ores, it merely involved floating apatite and the sulfides, but with the medium-grade ore an additional step was required in which the iron oxides were floated away from the silica. Flotation produced concentrates containing at least 60 percent iron at recoveries of 89.9 to 97.6 percent of the contained iron. In all instances the iron-to-phosphorus ratio was in excess of 292, which was considered to be a minimum acceptable value.
A third method was considered but was not fully developed because of time limitations. This method combined magnetic separation as the basic step with flotation of the nonmagnetic fractions. Acceptable concentrates containing more than 64 percent iron with satisfactory iron-to-phosphorus ratios were
1/ Work on manuscript completed June 1959. 2/ Supervising metallurgist (Mineral Dressing), Region V, Minneapolis, Minn. 3/ Supervising extractive metallurgist, Bureau of Mines, Region IV, Rolla, Mo. made by this dual treatment, but additional research would be required to achieve recoveries comparable to those obtained by straight flotation.
In early 1957 discovery of a large iron ore deposit at Pea Ridge, in east central Missouri, was reported.4 5/ The discovery was an indirect result of exploratory drilling for base metals. In 1956, as part of an exploration program, St. Joseph Lead Co. drilled holes at the Pea Ridge magnetic anomaly (high). After failing to find base metals at normal depths, a hole was drilled into the Pre-Cambrian porphyry to determine the cause of the anomaly. This hole penetrated a deposit rich in magnetite.
The geophysical surveys establishing the location of magnetic anomalies in east central Missouri were begun by the Missouri Geol. Survey in 1931.61
At that time an area in Crawford County known as the Bourbon Magnetic Anomaly was located and detailed. A similar anomaly, discovered about 6 miles northwest in Franklin County, became known as the Sullivan Magnetic Anomaly. The latter was not studied in detail until the early 1940's but was similar in size and intensity to the one near Bourbon, Mo. From the known geology of the area it was suspected that iron-ore deposits were responsible for these phenomena. To establish the cause of the anomalies, in 1943-44 the Bureau of Mines?) drilled four holes at the Bourbon site. The most productive hole penetrated four mineralized zones --a total thickness of 127.5 feet--and these contained magnetite occurring in a rhyolite porphyry at depths between 1,600 and 2,000 feet. Additional iron ore below 2,000 feet was considered a possibility at the time.
In 1947 an airborne magnetometer survey conducted by the Federal Geological Survey and others located the third anomaly at Pea Ridge, Washington County (Mo.) about 8 miles from the other two mentioned. At Pea Ridge, the St. Joseph Lead Co. located a deposit of iron ore estimated to contain between 50 and 100 million tons. The company has drilled in other areas, and while these areas are of definite interest, the main attention is focused on the Pea Ridge deposit.8/
Current with the announcement of the ore discovery, the St. Joseph Lead Co. and the Bethlehem Steel Co., revealed plans to exploit the deposit. These two companies formed the Meramec Mining Co.9/ (a corporation under joint ownership) and set 1962 as the date for completing the physical plant. An
4/ Engineering and Mining Journal, This Month in Mining: Vol. 158, April
1957, p. 72. 5/ Mining World, International Panorama: May 1957, p. 35. 6/ Grohskopf, J. G., Reinoehl, C. 0., Magnetic Surveys: Missouri Bureau of
Geology and Mines, 57th Biennial Rept., 1933, app. 4, pp. 5-20. 7/ McMillan, W. D., Exploration of the Bourbon Magnetic Anomaly, Crawford
County, Mo.: Bureau of Mines Rept. of Investigations 3961, 1946, 9 pp. 8/ Work cited in footnote 4. / 9/ Kohlmeier, Louis, Mountain is Being Moved to Get a Missouri's Iron Ore;
St. Louis Globe Democrat, Nov. 17, 1957.
annual production goal of 2 million tons of beneficiated and pelletized iron ore was proposed. Preparation of the site and sinking of the shaft were begun in September 1957.
Acknowledgments are made to the St. Joseph Lead Co., which furnish the ore samples, chemical analyses, and funds for this cooperative work.
Iron ore destined as feed to the blast furnace must meet certain chemical specifications,10 11; which may be influenced by subsequent steelmaking processes, that is, basic open hearth or acid bessemer. In actual practice a certain latitude is permitted, as lower grade ores are blended with ores of higher purity to produce a feed with a composition averaging within the accepted limits. The average iron content of blast-furnace ores used in the United States is 50 to 51 percent. Successful operation of the blast furnace requires slag-producing constituents in the feed; therefore, high-iron-content ores are usually diluted with leaner ores to bring the average iron content down to 50 to 51 percent. In past practice, blast-furnace ores have rarely averaged more than 55 percent iron. An ore usable as a blast-furnace feed without blending should fall within the specifications listed in table 1.12/
In research on the Pea Ridge samples, an arbitrary standard with respect to phosphorus was devised. This standard had an iron-to-phosphorus ratio of 292 minimum rather than an absolute value. This ratio was based on a median iron content of 52.5 percent, and a maximum phosphorus content of 0.18 percent for iron ores (figures from table 1).
Size specifications were not considered, as it was anticipated that fine grinding and pelletizing of the concentrates would be required.
10/ Bureau of Mines, Materials Survey--Iron Ore: Sec. 7, May 1956, pp. 2-3. 11/ Camp, J. M. , and Francis, C. B., The Making, Shaping, and Treating of
Steel: Carnegie-Illinois Steel Corp., Pittsburgh, Pa., 5th ed., 1940,
pp. 71-74. 12/ Work cited in footnote 10.
Page 9
Sample 1: Medium-grade hematite and magnetite
Percent of total in indicated size range -65 +100 -100 +150 -100 +200 -150 +200 -200 +325 -325
Total 20.6 29.6
12.8 37.0
100.0 12.9
13.0
19.6 54.5
100.0 17.6
20.9 61.5
100.0
Sample 2: High-grade hematite and magnetite
Percent of total in indicated size range -48 +65 -65 +100 -65 +200 -100 +150-100 +200-150 +200 -200 +325
-325 Total 8.8 32.8
15.7 42.7 100.0 9.2
21.6
17.7 51.5 100.0 12.0
12.6
19.3 56.1 100.0 14.1
20.4 65.5 100.0 Sample 3: High-grade magnetite
Percent of total in indicated size range -48 +65 -65 +100 -65 +200 -100 +150-100 +200 - 150 +200 -200 +325 -325 Total 10.1 36.2
11.7 42.0 100.0 12.2
25.1
17.2 45.5 100.0 17.0
17.7
15.8 49.5 100.0 19.0
24.0 57.0 100.0
Page 10
Weight- Analysis, percent Percent of total Product
percent Fe P Si02
s Fe
P Apatite concentrate. 6.6 8.6 11.5
1.4 83.0 Apatite middling... 3.0 33.0 .47
2.5 1.5 Sulfide concentrate.
.9 37.3 .44
.5 Sulfide middling.. 1.2 26.3 .31
.8 .5 Iron concentrate..
58.9 60.0
9.8 0.075
89.9 12.1 Iron middling...,
6.6 10.0 .06
1.7 .3 Tailing...
20.2
4.0 .04
2.0 .9 2.6 11.8 .42
.8 1.2 Composite. 100.0 39.3 .91
100.0 100.0 Operating data, apatite and sulfide flotation
Pounds per ton of crude ore
Apatite Conditioners
Sulfide Reagents
1 2 Rougher Cleaner Conditioner Rougher Cleaner Sodium carbonate 2.0 Sodium silicate. 2.0
A C 7101/....
0.5 Secondary butyl xanthate..
0.10
Aerofroth 652/..
.02 pH..
10.2 Time. minutes 5
5 5 5
5
5 Operating data, iron flotation
Pounds per ton of crude ore Conditioners
Cleaner Reagents
1 2 Rougher 1
2 Sulfuric acid..
0.67
0.20 0.20 Sodium fluoride.
.25
.08 .08 Pamak No. 137
0.90 pH....
7.5 Time.
.minutes 5
10
5
5
5
1 2/ American Cyanamid Co., 30 Rockefeller Plaza, New York 20, N. Y.
3/ Hercules Powder Co., Wilmington 99, Del.
Sample 2 also was a mixed ore containing magnetite and hematite, and it analyzed 59.6 percent iron, 1.14 percent phosphorus, 5.3 percent silica, and 0.52 percent sulfur. As with the medium-grade sample, sample 2 was ground to minus-65-mesh in a pebble mill, and the apatite and sulfides were floated in succession while depressing the iron. Table 8 summarizes the results of these operations.
Table 8 shows that the nonfloat fraction constituted an iron concentrate meeting chemical specifications, It recovered 95.0 percent of the total iron in the sample, at a grade of 65.5 percent iron, 0.18 percent phosphorus, 6.4 percent silica, and 0.067 percent sulfur. The iron-to-phosphorus ratio is 364, which also is above the minimum goal of 292.
Page 11
These results illustrate the possibility of producing high-grade concentrates by a combination of magnetic separation and flotation. In this instance the combined concentrates analyzed 64.7 percent iron, 0.15 percent phosphorus, 7.6 percent silica, and 0.075 percent sulfur. The iron-tophosphorus ratio was a favorable 431. The recovery of iron by the dual process was 77.8 percent. This was less than desired, but a continued study to achieve optimum reagent balance should remedy this deficiency. In the test described, considerable iron oxides were collected with the apatite, and this was the primary factor contributing to lowering of recovery values.
Similarly, sample 2, containing magnetite and hematite, was ground through minus-150-mesh, magnetically separated, and the nonmagnetics routed to flotation. The nonmagnetic fraction was given a flotation treatment identical to that described in table 8, except quantities of reagents were halved. The results of this magnetic-flotation treatment are presented in table 11.
The iron concentrates analyzed 65.4 percent iron, 0.19 percent phosphorus, 6.0 percent silica, and 0.05 percent sulfur. The recovery, 91.8 percent of the total iron, was considered highly acceptable, as was the iron-to-phos phorus ratio of 344.
As a sidelight of the research on flotation it was discovered that by upgrading the iron, the apatite probably could be recovered as a byproduct of commercial value. In some tests recoveries of 75 to 80 percent of the phosphorus were effected at grades of 66 to 71 percent bone phosphate of lime (BPL). The Pea Ridge iron ore deposit, as announced, will be brought into production within the next 5 years at an annual output of 2 million tons. At that rate, Pea Ridge could also be the source of approximately 100,000 tons annually of apatite concentrate. Although apatite is, reportedly, not competitive with phosphate rock for the production of wet-process superphosphate because of its lower reactivity, it should be a satisfactory raw material for electric-furnace elemental phosphorus.
INTE-BU.OF MINE S P GH..PA. 913