DEPARTMENT of NATURAL RESOURCES 
ZAcK D. CRAVEY, Commissioner 
DIVISION OF MINES, MINING AND GEOLOGY 
425 State Capitol ATIANTA, GEORGIA 
GARLAND PEYTON, Director 
 
MAGNETIC ROASTING TESTS on 
CARTERSVILLE MANGANESE ORES 
(Preliminary Report) 
AUTHORS 
L. L. McMURRAY, Assistant Mining Engineer 
s. D. BROADHURST AND M. T. PAWEL 
In Collaboration with H. S. RANKIN, Senior Mining Engineer 
Under the General Qirection of W. HARRY VAUGHAN, Chief, &gional Products Research Division 
Tennessee Valley Authority 
Published in cooperation with the Tennessee Valley Authority 
 
INFORMATION CIRCULAR 13 
 
DECEMBER, 1941 
 
  DEPARTMENT of NATURAL RESOURCES 
ZAcK D. CRAVEY, Commissioner 
DIVISION OF MINES, MINING AND GEOLOGY 
42 5 State Capitol ATLANTA, GEORGIA 
GARLAND PEYTON, Director 
 
MAGNETIC ROASTING TESTS 
on 
CARTERSVILLE MANGANESE ORES 
(Preliminary Report) 
AUTHORS 
L. L. McMuRRAY, Assistant Mining Engineer 
s. D. BROADHURST AND M. T. PAWEL 
In Collaboration with H. S. RANKIN, Senior Mining Engineer 
Under the General Direction of W. HARRY VAUGHAN, Chief, Regional Products Research Division 
Tennessee Valley Auth&rity 
Published in cooperation with the Tennessee Valley Authority 
 
INFORMATION CIRCULAR 13 
 
DECEMBER, 1941 
 
  I 
FOREWORD 
This preliminary report concerns some research and tests in connection with magnetic roasting of Cartersville (Ga.) manganese ores. This work was done at the request of the Georgia Division of Mines, Mining and Geology, and was perfonned in cooperation with them at the Minerals Testing Laboratory of the Tennessee Valley Authority at Norris, Tennessee, between the months of Kay and November, 1941. It is believed that the results submitted herewith may be useful in connection with the urgent need for additional supplies of manganese during the present national emergency. 
This experimental work does not represent an exhaustive stuQy of the problem of the separation of manganese from manganese-iron ores. Instead, it represents a brief practical study of the problem of improving the quality of manganese from low grade manganese concentrates from the Cartersville district. It is reasonable to expect that further research into the subject would result in further improvements. However, it is believed that the results to date may warrant serious consideration and investigation by commercial interests. Moreover, it appears hardly likely that further research would result in diminishing the value of the work covered by this report. 
While this report does not present figures representing operating costs based on actual tests of full-sized commercial equipment, it does include sane data from which competent operators may fairly estimate such costs. 
Therefore, it is expected that those who are interested in the 
 
 II 
subject matter will draw their own conclusions concerning the value of the procedures outlined and the possible commercial application of the process. 
We wish to acknowledge the interest and assistance which has been received from the Division of Kines, Mining and Geology of the Georgia Department of Natural Resources and from several manganese producers in the Cartersville, Georgia, area. 
 
 l 
Preliminary Report 
MAGNETIC ROASTING TESTS ON CARTERSVILLE ~~GPJf.ESE ORE 
ABSTRACT OF RESULTS 
These tests were carried out on washed concentrate ore from the Cartersville (Ga.) district rhich had the following approximate analysis: manganese 21.4 per cent, iron 27.0 per cent, insoluble 11.2 per cent. The results of magnetic roasting and subsequent magnetic separation indicated that 61 per cent of the roasted ore can be separated into manganese and iron concentrates. 
The combined roast~d product constituted 85.7 per cent by weight of the original washed concentrate ore and analyzed as follows: manganese 25.42 per cent, iron 31.41 per cent, insoluble 12.0 per cent. 
B,y closely controlling the jigging of the manganese concentrate, we obtained the following three fractions: 
(1) Manganese concentrate after jigging 32.0 per cent by weight 
{loss in jigging 3.7 per cent by weight). This concentrate analyzed as follows: manganese 45.10 per cent, iron 6.41 per cent, insoluble material 12.0 per cent. 
(2) Iron concentrate 25.3 per cent by weight. This concentrate analyzed as follows: manganese 8.74 per cent, iron 55.1 per cent, insoluble material 8.1 per cent. 
(3) Middlings 39.0 per cent by weight. This concentrate analyzed as follows: manganese 23.3 per cent, iron 34.16 per cent, insoluble material 12.2 per cent. 
All of the products separated are believed to be marketable under 
 
 2 
present conditions. It must be understood that the foregoing represents the result 
of tests under one set of conditions. In order to evaluate the work cov1ered by this report in tenns of commercial application, the report must be studied in its entirety. 
Commercial Application The results represent conditions of roasting, magnetic separation 
and jigging of the manganese concentrate considered optimum, but not beyond the limits of ordinary mill operations. Commercially, close control of the several operations is imperative. '" Moreover, there are certain features whit::h require particular attention. Among these are: 
(1) The roasting furnace must have an air-tight reducing chamber. (2) Reasonably accurate control of the temperature and reducing agent are required. (3) The rate of processing must be carefully regulated by the ore discharge in order to allow sufficient time for heating and reducing the ore. (4) Means must be provided for cooling the roasted ore without contact with the atmosphere. This may be done by quenching in water. (5) Magnetic separators with controlled magnetic intensities must be provided, by the use of which the production of the middling product may be regulated. (6) The jigging of the feed to the furnace or the manganese 
concentrate must be closely controlled. By this operation, silica and 
iron, contained in the insoluble particles, are removed from the manganese concentrate. 
 
 3 
Estimated Costs and Profits It is estimated that the costs of magnetic roasting with a 
furnace of two tons per hour capacity should not exceed $1.50 per ton. It is not unreasonable, under present market conditions, to 
expect a profit of $2.00 per ton of ore processed by the method outlined 
in this report, assu!Jl:ing a steady processing of 90 per cent capacity in 
a furnace designed for the production of two tons per hour. 
Remarks This preliminary report will include some details and data by 
the examination of which the foregoing has been estimated. 
Substantiating Tests 2!!. Commercial Size Equipment The large scale tests on the manganese-iron ores were confined 
to the roasting step and only small-scale laboratory magnetic separation testing was applied. In order to check the results of the magnetic separation on commercial size equipment, roasted ore samples were sent to various manufacturers for testing on magnetic separation equipment. These results, while not canplete, indicate that the laboratory magnetic separations given herein can be equaled or improved on commercial separators. 
 
 4 
INTRODUCTION PJf.D DISCUSSION 
Ores of manganese containing iron in excessive amounts are not suitable for use in the production of ferro manganese. Many of the manganese ore~ deposits in the Cartersville district of Georgia contain iron as an ingredient which may be present in quantities up to 27 per cent. Economic separation of this iron from the manganese has been studied, and the principal results of this work, to date, are reduced in this report. 
Careful review of previous work performed Qy the United States Bureau of Mines indicated that magnetic roasting,with subsequent magnetic separation of the synthetic magnetite, offered promise of success. Preliminary small scale tests were made, and favorable separations of the manganese 
and iron, b.1 the method suggested, were indicated. 
reduction As a result of these studies, a pilot/roasting furnace, with a capacity of 500 pounds of ore per hour, was constructed. This furnace was of t he vertical shaft type, and was designed to provide complete control over the various phases of the roasting process. The furnace operating results indicate that 97 per cent of the iron in the material fed into the fUITtace was made magnetic. I!lving thus made the iron magnetic, the method of magnetic separation of the iron from the maganese in the product discharged from the pilot furnace was undertaken. In this operation it was discovered that this separation is by no means complete, e.nd that a large percente.ge of the manganese minerals are removed with the synthetic magnetite. However, the separation is partially complete, and it is possible that it is sufficiently 
 
 5 
complete to warrant the use of the process commercie.lly. Apparently the manganese, at least to some degree, develops magnetic characteristics during the roasting, and several reasons for this condition of the manganese minerals are discussed in this report. 
This report describes the work to date on magnPtic roasting of Cartersville, Georgia, manganese-iron ores v.rith a view to concentrating both the iron and manganese by subsequent magnetic separation. This 
Vlork has been performed during the period from May to November, 1941, at 
the Minerals Testing Laboratory of the Tennessee Valley Authority at Norris, Tennessee. 
Little or no separation of the two minerals in the crude state of pyrolusite (or psllomelane) and hematite (or limonite) is possible by magnetic means until magnetic roasting is performed. This roasting 
3 converts the iron oxide hematite (Fe2o .n~O) to magnetite (Fe3o4 , composed of .31.0% FeO and 69.0% Fe2o3 (1) )  The following table shows the relative 
magnetic strength of various minerals which might be associated with the Cartersville manganese ores in the crude state or after being roasted. 
 
 6 
TABLE I 
PEL.ATIVE MAGNETIC FORCE OF MINERALS VHITCH MIGHT BE M.ADE IN MAGNETIC ROASTING I!LAlfGJlJ'<TESE ORE (a) 
 
Mineral 
Iron M:e.gnetite Manganese Hausmannite Hematite Limonite Pyrolusite Manganite Manganosite 
 
Formula 
Fe 
Fe.304 
Mn 
Mn.304 
Fe2o3 3 Fe2o .2~0 
Mn02 
3 r.~o .F2o 
MnO 
 
Relative Force 
100.00 40.18 8.9.3 
0.88 * 
1.32 0.84 0.71 0.52 
0.65 * 
 
(a) Table from Catalogue No. 77, Dings Magnetic Manufacturing Company, Page 8. 
 
* Calculated from data given in International Critical Tables. 
 
These data are in specific susceptibilities; vlith Mn02 given as 69.0 and 
 
ll.m3o4 as 55.8 (both as 21 C). 
 
Thus: 
 
69.0 x 0 71 = 55.8 
 
0.88. 
 
 7 
 
Chemical Reactions 
 
Theoretically, the reactions, involved in roasting under various 
 
conditions of reducing agent and temperatures, are represented by the follow- 
 
ing equations: 1. 
 
===.. co 
 
2 Fe3o4 (Magnetite) 
 
(i.e. 2(3(F1.e0O%.F6e29.o03%)) t co2 
 
t 
 
3. 
 
Mno2 
 
(psilomelane} 
 
(pyrolueite) 
 
t . CO ----;- MnO (Manganosite) 
 
MnO 
 
-f HzO 
 
5. 3 Mn02 -+ 2 co 
 
6. Fe2o3 -+ co 
 
+ 7. 3 FeO 
 
~0 
 
s. FeO ... co 
 
9. MnO ... co 
 
. 10. 2 co 
 
~ 
02 
 
ll. 3 FeO t C02 
 
Mn304 
 
-+ 
 
( :&usmannit e } 
 
2 FeO 
 
-+ 
 
(FeiTous OXide) 
 
Fe3o4 
 
. 
 
. Fe 
 
co2 
 
"' Mn 
 
C02 
 
2 co2 
 
Fe o 
34 
 
t 
 
co 
 
2C02 C02 
 
Discussion of Reactions 
If equations 1, 2, 3, 4, and 5 are allowed to proceed to the right, 
magnetite and either manganosite or hausmannite are produced, the specific 
 
 8 
oxio_e depending upon roasting conditions. To allovr these equations to proceed to the right, two primary conditions are necessary: 
(1) Sufficient temperature for the reaction to take place. (2) Sufficient vapor pressure of reducing agent. The most satisfactory temperature limits were found to lie between 500 C. 
and 1000 C. At convenient ore sizing and temperatures below 500 C., 
reducing periods are too long to be practical. At temperatures above 
1000 c., sintering may be encountered, which is an undesirable condition. 
For all practical considerations, we have found the reduction of the iron o:x:i.des to magnetite may be accomplished at a temperature of 600 C. in one half hour, with the ore particles sized to 7/8 inch or smaller. Even though shorter reducing periods can be realized by higher temperatures than 600 C., the decrease in time is not wholly warranted due to added costs of operation and more difficult problems of furnace design. 
To maintain sufficient vapor pressure of reducing agent, it has been found practical to perform the reduction in a closed chamber and allow 
the gaseous products of reduction, co2 and H20, to escape. This may be done 
by passing the reducing gas over the ore. In addition, after the reduction has taken place, means to keep the reaction from reversing are necessary. This can be done by quenching the ore in water or passing the ore through a cool inert atmosphere. 
Means to control the reaction are also desirable. The reduction of hematite to magnetite, if continued, may produce ferrous oxide. The formation of this compound represents a loss of reducing agent and should be 
 
 9 
avoided. If the reaction continues after ferrous oxide is produced, metallic iron may be made, as shown in equation 8. The reduction to metallic iron, however, re~uires a more intense reducing action than that obtained using a reducing gas and temperatures around 6o0 C. For the production of sponge iron solid carbon plus a reducing gas and prolonged heating at approximately 950 C have been found necessary (2). Likewise, the production of metallic manganese as shovm in equation 9 is not possible under the conditions employed. 
To control the roast to yield magnetite of a composition approaching the reaction in 
the theoretical, conditions were controlled to utiliz~equation 7. The reaction in equation ll also allowed some oxidation of the ferrous iron, but design of the reducing furnace prevented this reaction from being very effective. The use of steam in connection with such roasting was suggested by Davis (3) and proved very effective in the Cartersville ore roasting tests. The steam required was obtained by quenching the hot ore upon discharge from the furnace. 
~Sizing 
The ore size is an important variable in roasting technique. Fine ore generally permits shorter reducing periods than coarse ore, but the Cartersville ores used in these tests were sufficiently porous to allow rapid and complete reduction at jig sizes. The use of coarse ore overcomes several difficulties in roasting and also produces finished concentrates not requiring sintering for furnace use. Particle liberation was found to be relatively complete at sizes of -1/4 inch, but was never entirely complete, 
 
 10 
 
even on grinding to -200 mesh. It appears ths.t some iron (3 per cent 
to 4 per cent) is intimately associated with the manganese and could not 
be liberat,ed at any practical sizing. 
 
Reducing .P.gent 
 
As a reducing agent, a gas is almost a necessity. Reduction 
 
can be obtained by intimately mixing carbon and ore, but this solid to 
 
solid reaction is poor. Generally, reduction ~ solid c~rbon is caused 
~ the presence of some air, thus forming co, which is a very effective 
 
reducing agent. Many types of reducing agents may be used, but their 
 
effectiveness depends wholly upon their available carbon monoxide or hydrogen. 
 
Producer gas and coke oven gas are particularly good as they are mixtures 
 
of both carbon monoxide and qydrogen. Efdrocarbon gases such as propane 
 
and methane are compounds of hydrogen and ce.rbon, and are not satisfactory 
 
reducing agents until th~ have been converted to carbon monoxide and 
 
eydrogen. Hot iron oxide is a fairly good catalytic agent for breaking 
 
down these compounds. Superheated steam converts the carbon to carbon 
 
monoxide: C .f. H:20 
 
.. ~ .f. CO. Thus, the steam aids effectively in 
 
producing a reducing agent as well as controlling the roasting. Ordinary 
 
fuel oil may be gasified at a temperature of about 375 C, and the gas 
 
tms produced is a mixture of eydrocarbons and can be made an effective 
 
reducing agent by the means described. The low cost of fuel oil, combined 
 
with its ease of handling and measuring, made it attractive for use in the 
 
pilot-furnace. 
 
 11 
The roasting furnace used in these tests, involving the scheme described above, proved efficient and practical, making over 95 per cent of the iron in the ore into magnetite. 
ROASTING 
Furnace Design end Operation After small batch preliminary testing had indicated promise for 
this method of treating the Cartersville ore, a pilot furnace for continuous roasting was constructed. Since it was not possible to control the roast in the preliminary tests, the results of magnetic separation wereof doubtful value and the process could not be evaluated Q1 these small tests. As a shaft-type furnace bad proved effective and economical in magnetic roasting 
of Mesabi hematite (3), this type was adopted for roasting these ores. 
Description and Operation of Furnace The accompanying sketches show the principles of construction of 
the pilot furnace erected at the laboratory. The essential details consist 
of a shaft or cupola made of circle fire brick surrounded qy a metal shell 
built in halves and fastened around the brickvmrk. A separate fire box of regular firebrick, in which the gaseous products from the oil burner were completely burned, adjoined the cupola. By means of an exhaust fan these hot gases were drawn through a bed of ore eighteen inches thick. The heat intake and exbaust pipes were of extra heavy cast iron pipe in the form of a 11T" with holes along the bottom of both for spreading the gases throughout the cupola cross-section to provide uniform heating. A skirt was provided 
 
 12 
 
over the exhaust pipe to prevent small ore particles from being drawn 
 
out through the exhaust. The reducing chamber was immediately below as a gas or in the form of gaseous 
the heating zone. The reducing agent/ crude oil was introduced into 
a l-inch cast iron ring, which distributed the reducing agent over the 
 
furnace area. A quenching hopper was located below the cupola proper, 
and the open end was sealed Q1 water to prevent air from entering the 
furnace. A rotary disc ore discharge was used to provide a uniform dis- 
 
charge from the furnace. As the normal furnace capacity of crude -7/8 
 
inch ore was 500 pounds per hour, an elevator was built to facilitate ore 
 
handling. Thermocouples were installed to permit accurate temperature 
 
measurements in the cupola. In operation, two defects in'the original furnace were noted: 
 
cupola. 
 
{1) Objectionable air leaks developed in the single brick 
 
(2) The reducing chamber should have been much longer, thus 
 
providing a greater furnace capacity at very little additional expense. 
 
To prevent the air leaks the furnace was rebuilt after a few 
 
tests. A layer of asbestos refractory cement was plastered on the out- 
 
side of the cupola, and the sheet iron shell was firmly fastened and all leaks pl~ged in the shell openings. This provided a good seal, but a 
 
double brick furnace with interspersed impervious cement is recommended. 
 
When the furnace was properly regulated, one men could carry out 
 
the operation easily. Fuel consumption and other pertinent data are given 
 
later in this report. 
 
 13 
Heating Unit The beat capacity required varied greatly with the ore moisture 
content, and thus a flexible heating unit was necessary. A Johnson Series 520 oil burner proved satisfactory. The capacity of this burner is from 0.65 gallons/hour to 7.5 gallons/hour, with an air blower furnishing air at from 100 to 350 cubic feet/minute at 10 ounces to 16 ounces pressure. This blower was arranged in series with a rheostat so that the air volume was variable at will. With a total moisture content of 10 per cent, the heat requirement was calculated to be 340 Btu/potmd; if the moisture content increased to 18 per cent, 445 Btu were required. The heat value of the fuel oil used was 18,000 Btu/pound so that with 10 per cent moisture, 9.5 pounds of oil/hour was required. In normal operation this amount was close to ll.6 pounds/hour due to radiation and other items not used in the calculations. The high coefficient of heat transfer of the ore should be noted. The fact that the heat of the gases could be dissipated in passing through 18 inches of ore in no small way affects the cost of such a roasting mheme. 
Exhaust Fan Due to resistance of gas flow, the horsepower required for the 
exhaust fan increases rapidly as the height of ore column is increased. The height of this ore column was determined from actual test data given by Davis (3) in heating Mesabi iron ores. The specific heats of the manganese and iron oxides are so nearly the same, and with tmiform size of 
 
 the ore, these values could be used directly. The hot gases entered at a temperature of approximately 950 C, and the exhaust temperature remained relatively near 90 C. 
As no test date. were available to determine the fan capacity required for drawing the correct amount of hot gases through the ore, a variable speed for the fan was provided and a gate valve was inserted in the exhaust line. By these means the correct amount of hot gases could be dra1m through the charge, and at the same time a suitable be.lance between the oil burner blower and the exhaust fan could be maintained. 
Reducin.. Oil The amount of reducing oil used was regulated by a needle valve 
which had been calibrated. The needle valve reading was checked qy direct 
measurement in the oil storage reservoir. This oil was introduced into the furnace in the raw state or vaporized. Generally a vacuum of 1/4 inch of water existed at the reducing oil entry level. Introduction of the raw oil absorbed heat during vaporization, but as the subsequent reaction was exothennic, very little total heat was lost by using the crude oil direct. 
Regulation of ~ Discharge The ore discharge was closely regulated by the ore discharge 
disc. The ore discharge rate determined the time the ore was in the heating and reducing zones. The quantity of ore discharged also determined the amount of steam made in quenching a.lthough the ratio of steam produced and ore discharged remained constant. By a study of the FeO-Fe304-H20 equilibrium 
 
 15 
 
conditions, Davis (3) determined that a temperature of 60o C it was 
 
desirable to have in excess of SO per cent by VIeight of steam in the 
 
atmosphere in the reducing chambel". OUr calculations indicate the.t this 
 
amount of steam was present at all times. A sample calculation will shOlr 
 
the following: 
 
At a feed rate of 500 pounds/hour, 42S pounds/hour were discharged, 
 
the difference being loss of moisture (50 pounds at 10 per cent 
 
water) and oxygen (22 pounds). With a heat capacity of 20S 
 
Btu/pound of ore (assuming specific heat of MnO ~nd Fe3o4ae 0.20 : Q  
 
(1112 F - 70 F) x 0.20 x 1 pound  20S Btu/pound). The heat 
 
. (lJJ20p- : 600 C) 
 
. 
 
= required was 20S x 42S pounds S9,000 Btu. Of this amount of heat 
 
11,500 Btu were required to heat 2200 pounds of water 5 F every 
 
hour in the quenching tank (2200 x 5 :a 11,500 Btu.). 89,200 - 
= 11,500 77,770 Btu available for steam production. To superheat 7 = steam tolll2 F, 1531 Btu. per pound are required. 77,770 1531 
 
50.7 pounds water. Generally it was shovn1 that the reducing oil 
= used amounted to 3.0 pounds/hour. Thus 50.7 ~ 3.0 53.7. + = 50.7 53.7 94.5 per cent steam. 
 
Losses due to radiation of heat by the ore were not included, 
 
buft is obvious that an excess of steam was available. This steam aided 
 
the thermal be.lance of the unit as the heat of this rising steam aided in 
 
beating the ore, but, as previously indicated, its main 1JllrPOSe was to crack 
 
the gases and prevent the formation of ferrous oxide. 
 
 16 
TESTS 
Preliminary Tests 
The Bureau of Mines, Report of Investigations 2936 (4), gives 
preliminary results of small batch tests made on roasting Cartersville ores and then magnetically separating the roasted product. The results of treating one Cartersville jig concentrate is shown in Table II. 
This ore was roasted in a batch revolving drum for thirty minutes. The nature of reducing gas was not disclosed. The ore was a clean jig CJncentrate between one inch and one-half inch in size. After roasting, the magnetic portion was removed with a hand magnet. While these test results are very good, it appears that this ore must have been quite different in character from the ore samples used in our tests. The results of the Bureau were limited in scope, and as no further work has been published by the Bureau in connection with these tests, performed in 1929, it may be assumed that the ore used in these tests was not representative of that now available in the field. The ore samples taken in this district for the roasting tests shown in this report have not allowed such complete separation as that shown in Table II. 
Batch testing on Cartersville ore covered in this report may be show in Table III, ;hich is typical of the results obtained. This ore was roasted in a crucible with 10 per cent -200 mesh coke at 600 C for one hour. 'rhe ore was crushed and passed through 1/4 inch screen. The products representing various magnetic susceptibilities were kept separate and combined for final products. The magnetic separator waB a Stearn's 
 
 17 T.ABLE II 
ROASTING OF CARTERSVILLE ORE * 
 
Product 
 
Per Cent Weight 
 
Analysis, Per Cent 
 
Per Cent total 
 
Mn 
 
Fe 
 
Insol. Mn 
 
Fe Insol. 
 
Unroasted Cone. 
 
1~gnetic Portion 
 
.38.7 
 
Nomag. Portion 
 
61.~ 
 
Composite (roasted) 100.00 
 
.32.8 17.9 7.1.:,. 12.4 45~5 12.2 51.7 2.3 5.0 .36.5 19.0 7.$ 
 
1.3.2 86.6 100.0 
 
92.6 60.7 7.4 .39.3 100.0 100.0 
 
* The Bureau of Mines, Report of Investigations 29.36 (4) 
 
 18 
TABLE III 
 
BATCH ROASTING TEST OF CARTERSVILLE MANGANESE 
 
Product 
 
- - - Per Cent Analysis, Per Cent Per cent Total Ma:giier- 
 
Weight M!!. 
 
Fe Insol. M!!. Fe Insol.Resistence 
 
Mag. Cone. #1 18.6 1.10 66.91 7.56 
Mag. Cone. #2 28.3 3.96 54.19 11.42 
 
71 000 ohms 
51 000 ohms 
 
Mag. Cone. #3 32.1 39.68 23.23 14-54 
 
2 1 000 ohms 
 
Mag. Cone. #4 14-4 45.80 6.08 15.04 
 
500 ohms 
 
Tails 
 
6.6 44.10 1.93 18.50 
 
Combined Cone. 46.9 2.82 59.3 
 
5.5 76.6 
 
Combined Midds 32.1 39.68 23.2 
 
54.0 20.5 
 
Combined Tails 21.0 45.20 4.S 
 
40.5 2.9 
 
Heads (Calc. } 100.0 23.53 36.4 
 
100.0 100.0 
 
 19 
 
Type "KS" d.c. separator (dry material required) and the resistance inserted in the magnet circuit was taken as the standard method of determining the magnet strengths. By assuming these standards of magnet strengths the tests could be compared as the same resistance produced the same magnet strength each time. In the batch using coke as the reducing agent, the roast was more intensely reducing than in the pilot furnace, and the results are not very reliable. 
 
Pilot Plant Tests 
 
In the pilot roasting furnace many test runs were made, and after 
 
the furnace was properly adjusted, all gs.ve very similar results. In order 
 
to avoid unnecessary duplication, only Test 12, typical of other results, 
 
is given in full. 
 
Conditions of Test: 
 
Test Number 12 
 
Sample Number, Feed-Sample No. 8a.. -7/8 inch Cartersville Ore, 
 
Jig Concentrate (See Screen .Analysis) 
 
Feed rate- 
 
500 pounds per hour 
 
Solids removed from furnace--428 pounds per hour 
 
Time of test-- 
 
12 hours. Samples collected over one-half 
 
hour periods after furnace running smoothly. 
 
12 samples collected. 
 
Temperature range of ore--585 C to 630 C. 
 
Reducing fuel oil, average--3.0 pounds per hour 
 
Heating fuel oil, average--1.0 gallon ger hour 
 
Temperature intake gas., average-960 C. 
 
Temperature exhaust gas., average 93 C. 
 
Vacuum in reducing chamber--1/4 inch water 
 
Vacuum in steam chamber--1/8 inch water 
 
Temperature rise in quenching water-5F, measured in first three 
 
hours after discharge of hot ore. 
 
 20 
 
TABLE IV 
 
SCREEN ANALYSIS OF PRODUCTS IN FURNACE; TEST NO. 1.2 
 
Screen Analysis of Feed 
 
-7/8" .J.3/4" 9.0 
 
-3/4TI .f.l/2" 16.1 
 
-1/2" U/4" 43.7 
 
-l/4TI .J.lO mesh 17.4 
 
-10 mesh .J.20 mesh 7.6 
 
-20 mesh +48 mesh 4.3 
 
-48 mesh 
 
1.9 
 
100.0 
 
Screen Analysis of Discharge 
 
-7/8" -3/4" -1/~" -1/4" -10 mesh -20 mesh 
-48 mesh 
 
.J.3/4" 
f.l/2" 
.J.l/4" flO mesh .J.20 mesh 
+48 mesh 
 
4.7 18.4 50.0 16.6 
4,..55 
0.3 
100.0 
 
Screen Analysis--Feed to Magnetic Separator 
Furnace Discharge Crushed to -4 Mesh 
 
-4 mesh 
-10 mesh -20 mesh -48 mesh 
 
++ 10 mesh 20 mesh i 48 mesh 
 
6o.5 21.9 
10.8 6.8 
100.0 
 
 21 
TABLE V 
RESULTS ON SEPARATION OF FURNACE DISCHARGE 
SAMPLES cmmiNED AND CRUSHED TO -4 MESH 
SEPARATED DRY ON "KS" MAGNETIC SEPARATOR 
 
Product 
 
J.QW_ Anal;:Lsis 1 Per Cent 
 
Weight Mn 
 
Fe Insol. 
 
Per Cent Total Ma.~et 
 
Mn 
 
Fe Insol.Re~istance 
 
Magnetic #1 
 
25.3 
 
Magnetic #2 
 
39.0 
 
Magnetic #3 
 
17.6 
 
Nonmagnetic 
 
18.1 
 
Heads (Calc. ) 
 
100.0 
 
Heads (Analysed) 100.0 
 
Combined Fe Cone. 25.3 
 
Combined Middling 56.6 
 
Combined Mn Cone. 18.1 
 
8.74 23.30 42.22 43.79 26.68 25.42 8.74 29.20 43.79 
 
55.10 8.1 34.16 12.2 12.95 14.8 
8.27 15.6 31.04 12.2 31.41 12.0 55.10 8.1 27.58 13.0 
8.27 15.6 
 
8.3 45.2 16.8 5,000 ohms 34.1 43.0 39.0 2,000 ohms 
27.7 7.4 21.1 ;oo ohms 
29.9 4-4 23.1 100.0 100.0 100.0 100.0 100.0 100.0 
8.3 45.2 16.8 5,000 ohms 61.8 40.4 60.1 500 ohms 29.9 44 23.1 
 
 22 TABLE VI 
RESULTS OBTAINED BY COMBINING MAGNETIC PRODUCT #3 AND 
NONMAGNETIC PRODUCT SHOWN IN TABLE V 
 
Product 
 
~Cent 
Weight 
 
Analysis, Per Cent ~Cent Total Magnet 
 
MD. 
 
Fe Insol. Mn Fe Insol. Resistance 
 
Combined Fe Cone. Combined Mdds Combined Mn Cone. Heads (Calc.) 
 
25.3 39.0 35.7 100.0 
 
8.74 23.30 43.10 26.68 
 
55.10 8.1 34.16 12.2 10.60 15.2 31.04 12.2 
 
8.3 45.2 16.8 34.1 430 39.0 57.6 11.8 44.2 100.0 100.0100.0 
 
5,000 ohms 
 
 23 
 
Table V shows that in Test No. 12, 45 per cent of the iron in the 
 
furne.ce discharge was recovered in an iron concentrate analyzing: 
 
55.10% Fe 
 
8.74% Mn 
 
8.1% Insoluble 
 
Also that 29.9 per cent of the manganese in the furnace discharge was recovered 
 
ina product analyzing: 
 
43.79% Mn 
 
8.2'7% Fe 
 
15.6% Insoluble 
 
By combining magnetic concentrate No. 3 with the non-me.gnetic. portion, t.he results 
 
would be as in Table VI, where the manganese concentrate has ananalysis of: 
 
43.10% Mn 
 
10.6()% Fe 
 
15.2% Insoluble; with a recovery 
 
of 57.6% of the mangs.nese in the ore. 
 
The total iron made magnetic {at the magnet strength existing when 
 
500 ohms resistance was inserted in the magnet circuit) was 95.6 per cent. The 
 
remaining 4.~ per cent iron, not magnetic, remained in the manganese concentrate. 
 
This iron has been found to be in the insoluble portion of the ore, and due to 
 
the impervious nature of this cherty insoluble material, it cannot be properly 
 
roasted in the pilot furnace. Tests have established that for each unit of 
 
insoluble material, present in the non-magnetic portion, 0.266 per cent iron 
 
oxide cannot be magnetically roasted. Applying this knowledge to the above results 
 
it shows that 97.5 per cent of the iron available for roasting was made magnetic. 
 
Thus the poor separation results obtained cannot be chargeable to poor furnace 
 
roasting. 
 
It should be noted that in the batch tests (Table III) the iron 
 
portion in the manganese concentrate lla.s much lower due, no doubt, to the 
 
more intense roast available with solid carbon and limited oxygen so that the 
 
 iron ass()Ciated. with the insolubles was roasted to the magnetic oxide. To determine if' this insoluble portion of the manganese concentrate 
could be effectively removed by jigging, a sample of ore -7/8 inch in size was jigged in the laboratory with an 8-inch by 12-inch jig. The results are tabulated in Table VII. 
These jigging results represent close regulation of the jig and of course this was necessary. in order to perform the task of removing only a 
small amotmt of tai 1ings from such a rich feed. App~ these results to the total recovery, the results of this 
process in separating the manganese from the iron are shown in Table IDI. 
 
 25 
TABLE VII 
JIGGING TEST ON MANGP..NESE CONCENTRATE 
 
Product 
 
.f!!: .9!m! 
 
Analzsi~ 1 Per Cent 
 
Weight !f!t 
 
~ 
 
Inso1. 
 
Per Cent Total 
 
!g. 
 
~ 
 
In~o1. 
 
Concentrate Tails (Calc.) 
Beads {Calc.) 
 
89.7 
10.3 100.0 
 
45.10 32.91 43.10 
 
6.41 
47.2 
10.60 
 
12.0 47.1 15.2 
 
92.2 7.8 
100.0 
 
54.2 68.9 45.8 31.1 100.0 100.0 
 
 26 
TABLE VIII TOTAL RECOVERY AND GRADE OF MANGANESE FROM PILOT FURNACE 
 
Product 
 
Per Cent Weight 
 
Analzsis 1 ~Per Cent 
 
Mn 
 
Fe 
 
Insol. 
 
Per Cent Total 
 
Mn 
 
Fe 
 
Insol. 
 
Feed to Furnace 100.0 
 
Roasted Product 85.7 
 
Magnetic Separation: 
 
Fe Concentrate 25.3 
 
Middlings 
 
.39.0 
 
Mn Concentrate .35.7 
 
Jigging: Jig Mn Concentrate 
Jig Mn Tails 
 
30.6 5.1 
 
21.40 25.42 
 
27.05 31.41 
 
11.18 12.0 
 
100.0 101.8 
 
1-00.0 100.0 99.5 92 .3* 
 
8.74 55.10 8.1 23.30 .34.16 12.2 43.10 10.6C 15.2 
 
8.3 45. 2 16.8 .34.1 43. 0 39.0 57.6 11.8 44.2 
 
45.10 6.41 12.0 
 
5.3.1 
 
6.4 .34.0 
 
32.91 47.2 47.1 
 
4-5 
 
5.4 10.2 
 
* Theoretically this should total 100 per cent. The discrepancy is 
due to error in weighing and sampling the ..many products to make up the furnace feed. For per cent totals of separations subsequent to roasting, 100 per cent 
was used. 
 
 27 
 
OPERATING COSTS 
 
Operating costs from which a commercial operator could draw 
 
any conclusions with reasonable certainty are not available. However, the 
 
following data are submitted, together with some comments, by the inter- 
 
pretation of which anyone familiar with the operations of roasting furnaces 
 
may compile reasonably accurate estimates which may apply to any specific 
 
condition. 
 
The cost of roasting in the laboratory furnace, not including 
 
the magnetic separation, crushing, and jigging, follow: 
 
Labor (one man @ $5.00/8 hour shift) Fuel Oil (heating and reducing 1.6 
gallon/hour @ 9) 
Power (2-1/4 H. P.) Miscellaneous 
 
$2.50 per ton 
 
14 
.04 
 
n 
" 
 
" n 
 
.04 It n 
 
Total 
 
$2.72 per ton 
 
The low pilot furnace capacity of two tons per eight hour shift 
 
makes the labor item badly out of proportion as compared with a furnace 
 
of larger capacity. Since one man can operate with equal ease a furnace 
 
with a capacity of two tons per hour, the labor cost would ?e reduced to 
 
32 per ton. 
In a report of the operation of the Mesabi Magnetic Roasting 
 
Furne.ce (.3), which was of shaft-type construction, the following costs 
 
are given: 
 
 28 
 
Number of operatiQg days (September, 1935) 30 
 
Opera,ting hours 
 
692 
 
Lost time, per cent 
 
3.89 
 
Tons of feed 
 
5,802 
 
Total gallons of oil 
 
55,182 
 
Number of men per shift 
 
1.3 
 
Electric power per ton or feed, 
 
kilowatt hours 
 
19,0SO 
 
Gallons oil per ton of feed 
 
9-5 
 
Electric power per ton or feed, 
 
kilowatt hours 
 
3-3 
 
Cost per ton of feed: 
ou 
 
$0.555 
 
Power 
 
0.050 
 
Labor 
 
0.072 
 
Total 
 
$0.677 
 
An operation at Anzau, South Manchuria, described in the same 
 
report, where 120 tons of iron oxides per day were magnetically roasted 
 
in a shaft-type furnace, showed the following costs: 
 
Cost per ton: Combustion fUel-pulverized coal 
Redaction fuel-coke oven gas Power and electricit.Y 
 
Total 
 
$0.634 
 
Both of the above furnaces are of a type applicable for roasting Cartersville 
 
manganese-iron ores. The magnetic roasting of iron ores is not essentially 
 
different from the roasting of manganese-iron ores, provided both lave the 
 
general p~sical characteristics required for shaft fUrnace operation. 
 
Therefore, these costs can be considered as representative of comparable 
 
operations on the Cartersville ore. Operating costs will vary with the 
 
capacity of the fUrnace. Computations based on the above large scale 
 
 29 commercial operations and the small pilot~furnace tests indicate that for a roasting furnace of two tons per hour capacity, the cost of operating would be less than $1.50 per ton. 
 
Additional Magnetic Separation Tests 
 
In an effort to improve the mapnetic separations , 
 
a large 
 
number of small scale laboratory separators were made using various ore 
 
sizings and alternating current as well as direct current separators. 
 
The results of some of these tests are given and discussed in this section of the report. 
 
The failure of the two metal oxides to completely separate is 
 
difficult to explain. The question of locked grains has been studied 
 
and the results show that good liberation is obtained even in sizes as 
coarse as one-half inch with 95 per cent liberation at -4 mesh. Co~plete liberation is not attained by grinding to very fine sizes and this 4 or 5 per cent of iron in the manganese is thought to be intimately associated 
 
with the manganese and not capable of being liberated at any practical ore size. 
 
Wet Tube Separator Tests 
A separation of the roast of pilot-furnace Test No. 4 (very 
similar to Test No. 12), which was ground to pass through a 200 mesh screen, is shown in Table IX. This separation was made in a modified Davis Tube Wet Separator (5). This separator consisted of an inclined tube filled with water with the poles of a strong magnet resting against the 
 
 30 
TABLE IX 
WET TUBE SEPARATION OF ROASTED ORE NO. 4 
 
Product 
 
Per Cent 
 
Analzsis 1 Per Cent 
 
Per Cent Total 
 
Weight ~ 
 
Fe 
 
Insol. Mn 
 
Fe 
 
Insol. 
 
Magnetic No. 1 12.4 
 
Magnetic No. 2 1.4.3 
 
Magnetic No. 3 23.8 
 
Magnetic No. 4 1.4.2 
 
Nonmagnetic 
 
35.3 
 
Combined Mag. Cone. 12.4 
 
Middlings 
 
38.1 
 
Combined Nonmag. 49.5 
 
Heads (Calc.) 100.0 
 
13.63 21.13 38.38 43.88 43.88 
 
47.07 35.71 18.94 10.82 14-34 
 
10.02 14-24 19.78 25.58 15.52 
 
13.63 32.2 43.8 35.8 
 
47.07 25.2 13.3 22.02 
 
10.02 17.6 18.2 17.10 
 
4.8 35.5 6o.7 100.0 
 
26.5 43.5 30.0 100.0 
 
7.8 39.0 53.2 100.0 
 
 31 
sides of the tube. The ore was made into a slurry and poured through 
the water-filled tube with the magnet at different intensities. In 
settling through the magnetic zone, the magnetic particles stick to the sides of the tube and the non-magnetic material settles to the bottom of the tube and is drawn off. By using sufficient magnet strength, the tube can be rotated, allowing the particles to roll over one another, liberating entrapped non-magnetic particles. Washing can also be performed. In this way clean separations are possible. This separator has been used with remarkable success qy many investigators and is especially valuable in testing fine ores. 
Note in Table IX that no greater selection in the separation is possible even in this fine size. It was also found that dry separations in the "KS" Separator at fine sizes did not improve the separation over 
dry separations at -4 mesh. Therefore, it appears that close sizing of the 
product does not improve the separations appreciably. 
Alternating Current Separator Test Two primary causes for the relatively poor separations have been 
advanced as a result of study of our test results: (1) The high permeability and high coercive force of the manganese 
minerals causes the manganese to be removed in the magnetic fractions. (2) The high permeability of the synthetic magnetite causes 
induced magnetism in the manganese and it is removed along with the iron. In many instances an alternating current separator bas given 
improved results over a direct current separator when separating minerals 
 
 32 
with high permeabilities (6), (7), and (8). To determine if an alternating current separator would allow 
improved results, a laboratory model was constructed. This separator consisted of an alternating current relay with a laminated core in series with a variable transformer which was in turn in series with a 120-volt, 60-cycle line. The separator permitted sufficiently accurate control to permit regulating the magnet intensity and the distance of the ore from the magnet, thus removing products of decreasing susceptibility. Table X shows the results of a typical separation with this alternating currentseparator. 
Roasted ore, -4 mesh, from furnace Test No. l2 was used as the feed. Three 
magnetic fractions were removed and the products were analyzed and combined without a middling product to give the results shown in Table X. 
To determine the influence of ~cle changes in using an alternating current magnet, the laboratory magnet and variable transformer were placed in series with a rotary converter and the results are tabulated in Table XI. No improvement in separation was apparent. 
Variations in Reducing Roast to Improve Separation A study of the possibilities of improving the separation by a 
more intense reducing roast with production of sponge iron was made. In 
. this test -4 mesh ore was roasted with 35 per cent of -200 mesh coke in a 
m.t.lffle furnace. The charge was heated for three hours at 9500 C. The results obtained by the magnetic separation of this product are shown in Table XII. 
 
 33 
TABLE X A.C. MAGNETIC SEPARATION 
 
Product 
 
~Cent 
We!ght 
 
Ana1~sis 1 Per Cent 
 
Ma 
 
l!. 
 
Inso1. 
 
Per Cent Total 
 
Ma 
 
Fe 
 
Inso1. 
 
Magnetic Nonmagnetic Heads (Calc.) 
 
59.9 40.1 100.0 
 
15.47 42-34 26.3 
 
42.98 10.47 30.00 
 
12.12 18.78 1.4.8 
 
35.3 64.7 100.0 
 
86.0 49.0 14.0 50.9 100.0 100.0 
 
 34 TABLE XI 
EFFECT OF CYCLE CHANGES ON A. C. SEPARATION 
 
Product 
A. Mag. Cone. No 1 Mag. Cone. No. 2 Mag. CoJo.c. No. 3 Tails 
B. Mag. Cone. No. 1 Mag. Cone. No. 2 Mag. Cone. No. 3 Mag. Cone. No. 4 Tails 
C. Mag. Con.c. No. 1 Mag. Cone. No. 2 Mag. Cone. No. 3 Taila 
 
Qzcles Voltage Per Cent Weight 
 
21 
 
20 
 
21 
 
45 
 
21 
 
40 
 
60 
 
55 
 
60 
 
70 
 
60 
 
100 
 
60 no 
 
114 
 
55 
 
114 
 
70 
 
114 
 
75 
 
18.9 20.0 14-9 46.2 22.5 19.5 12.0 17.2 28.8 20.9 16.4 17.2 45-5 
 
Anal~si~ 2 fer Cent 
 
Mn 
 
~ Inso1. 
 
5.28 6.60 24.42 38.50 5.38 10.08 25.42 37.41 40.88 6.16 6.93 23.42 38.72 
 
54.97 7.46 52.51 9.84 30.08 14.S2 9.30 18.S2 57.3 7.96 50.1 ll.36 31.4 13.98 16.5 16.66 7.4 20.40 55.52 7.26 51.97 9.78 31.73 14.20 9.85 20.20 
 
 35 
TABLE XII 
MAGNETIC SEPAP~TION OF SPONGE IRON ROAST 
 
Product 
 
Per Cent Weight 
 
Anal;y:sis 1 Per Cent Per Cent Total Ma~et 
Mn Fe. Insol. MB. E!t Insol. Resistance 
 
Magnetic No. 1 Magnetic No. 2 Magnetic No. 3 Magnetic No. 4 Nonmagiletic Heads (Calc. ) 
 
5.3 29.8 15.7 22.5 26.7 100.0 
 
4-03 6.94 27.33 43.12 47.26 28.9 
 
S2.79 9.04 0-7 12.5 2.6 10,000 ohms 72.18 14.15 7.2 61.3 21.9 5,000 ohms 32.51 21.50 14.8 145 17.7 2,000 ohme 13.78 19.50 33.5 8.9 22.9 500 obns 3.58 23.86 43.8 2.9 34.9 35.1 19.2 100.0 100.0 100.0 
 
 36 
Inspection of Table XII indicates that an appreciable amount of metallic iron was made. The amount of metallic iron here cannot be determined accurately due to the fact that analysis for metallic iron, ferrous oxide, and ferric oxide are confused by the oxidization effect of the manganese oxide present. In some attempts to make such an analysis, it was found that the amount of oxidization during volumetric analysis was dependent upon the amount and type of manganese oxide present in the sample. Metallic manganese had little or no effect. A study of other methods of analysis for these products revealed length;y and somewhat doubtful successes, so that further attempts were abandoned. 
A calculation of analytical percentages does reveal the metallic iron present. Calculating the manganese present as MnO and leaving the iron as metallic iron gives: Concentrate No. 1, 97.03; Concentrate No. 2, 95.28; Concentrate Mo. 3, 89.31. Assuming that the undetermined constituent of the concentrates is oxygen, it follows that the first two concentrates al'e almost wholly metallic iron, and the other concentrate probably contains an appreciable percentage of metallic iron. The charge is probably "over roasted." This intense reduction allowed no better selection in the magnetic separation than when only magnetite is made. The concentration was essentially the removal of oxygen from the iron. To proouce such a product commercially would be very expensive and would offer many difficulties. 
Magnetic Separation Teets ~ Hand-Picked Sample An interesting test was made ~ band picking manganese minerals 
from crude ore Sample No. Sa (feed to pilot-furnace Test No. 12) which were 
entirely free from iron viewed under the microscope. This sample was crushed 
 
 37 to -4 mesh and resampled. This material was given a roast with 10 per cent -200 mesh coke in a muffle furnace for a time of one hour. The results upon magnetic separation are shown in Table XIII. 
Note in Table XIII how the iron content of the manganese decreases 
with decreased magnetic susceptibility. This test indica.tes that 40 per cent of the manganese minerals are "magnetic. n Grinding this sample to -200 mesh and separating in the Davis Tube at very high magnet intensity 
gave the results shown in Table XIV. 
In Table XIV note that much more manganese was removed e.t the high 
magnet intensity than in Table XIII. Thus it ap!)ea.rs that only the very 
purest manganese minerals are "non-magnetic." However, caution should be exercised in stating that this iron content of the manganese alone is the cause of poor manganese-iron separations. It must be remembered that the liberated magnetite has a relative magnetic strength of at least forty times the relative magnetic strength of pure mangenese minerals (see Table I). The influence of this unliberated magnetite contained in the manganese minerals (without bringing other forces into play, such as permeability and coercive force) cannot influence the magnetism of the manganese greater than the extent of its iron content. To approximate the influence of the magnetite content of the manganese minerals, we can assume 
that the manganese containing 18.75 per cent Fe, or 25.8 per cent Fe3o4(of 
which only 5.2 per cent exists as shown in Table nii, Magnetic Concentrate No. 1) would have a relative magnetic strength of: 
40.18 x 25.$% or 10.3 (see Table I, where relative magnetic strength of magnetite is given as 40.18 and MnO as 0.65) 
10.3 plus (74.2% x 0.65) or 10.8 
 
 .38 TABLE XIII A. C. SEPARATION OF HAND-PICKJ!D :MANGANESE l..J!NERALS 
 
Product 
 
Cycles Vo1ta.rut Per Cent Weight 
 
Analzsis 1 Per Cent 
 
Mn 
 
Fe 
 
Insol. 
 
Mag. Cone. No. 1 60 
 
100 
 
Mag. Cone. No. 2 60 
 
70 
 
Mag. Cone. No. 3 60 
 
50 
 
Mag. Cone. No. 4 60 
 
40 
 
Non-magnetic 
 
5.2 41.72 18.73 6.92 
 
9.1 48.72 11.02 7.'36 
 
11.7 54.60 
 
6.06 6.02 
 
13.9 57.12 
 
4-a. 5-54 
 
60.1 59 .36 
 
1.65 5.38 
 
 
 
 39 
TABLE XIV 
WET SEPARATION OF -200 MESH HAND-PICKED MANGANESE MINERALS 
 
Product 
 
~Cent 
 
.Analysis, Per Cent 
 
Mg, 
 
~ 
 
Insol. 
 
Per Cent Total 
 
Mn 
 
Fe 
 
Insol. 
 
Magnetic Non-magnetic 
 
75.0 53-33 5.53 5.79 
 
93.7 90.7 
 
25.0 
 
61.05 
 
l.ll 
 
1.so 
 
27.6 
 
6.3 
 
 40 This value of relative magnetic strength is still only one-fourth as much as pure magnetite. If, however, the magnetite contained 75.2 per cent unliberated pure manganous oxide, its relative magnetic strength would be approxims.tely the same as the manganese oxide containing 25.8 per cent magnetite. It hardly seems probable that this is the cause of such poor seps.rations. As we have expressed, they are more due probably to the high permeability of the iron or the manganese minerals themselves. To determine this fact is quite out of the scope of our laboratory investigations. 
Various other schemes have been tried for improving the separations. Regrinding of the middling gives no improvement. Schemes involving the use of both alternating current and direct current magnets intermittently have not indicated a promising trend. To obtain improved results over those obtained at present, appears impossible until more information can be gathered so that the cause of poor separations will be pinned down to one known condition and a practical means adopted to overcome this condition. For instance, if it were definitely determined that the high permeability of the manganese minerals were the cause of the failure to make a clean separation, a study to either reduce this high permeability, inherent in the 
roasted product, or to nullify its effect b.1 using a specially designed 
magnetic separator might solve the problem. In reganl to the reduction of the effect of high permeability, it 
may be stated that the effect of temperature of roasting influences this condition and a study of temperature versus permeability might be enlightening. 
In regard to the type of magnetic separator adaptable, R. s. Dean 
 
 41 
and c. W. Davis (8) discuss the use of magnetic separators involving 
separation b.Y magnetic remanence alone. Because of the variable existing in such a stu.dy, a practical solution appears doubtful. 
 
 FOOTNOTE REFERENCES 
1. W. E. Ford, Dana's Textbook of Mineralogy, page 494 
2. C. E. Williams, E. P. Barrett, and B. M. Larsen, Production of Sponge Iron, U. S. Bureau of Mines, Bulletin 270, 1927 
3. E. W. Davis, Magnetic Roasting of Iron Ore, Bulletin No. 13, University of Minnesota, Mines Experiraent Station, 1937 
4. }i'. D. DeVaney and w. H. Coghill, Beneficiation of Oxidized Mangenese Ores by' Magnetic Separation of Roasted Jig Concentrates. U. s. Bureau 
of Mines, R. I. 2936, 1929 
5 Magnetic Mineralogy, Dings Magnetic Sepa.rator Company, page 6 
6. T. J. Martin, The Magnetic Concentration of Certain Natural and 
Artificial Manganese Oxides. Transactions American Electro-Chemical Society, Vol. 57, (1930) 
7. J.,. M. Gaudin, Principles of Mineral Dressing, page 456 
8. R. s. Dean and C. w. Davis, Magnetic Concentration of Ores, A.I.M.E. 
Transactions, Vol. 112 (1934) 
ADDITIONAL REFERENCES 
U. S. Bureau of Mines R. I. 6768, page 37 
W. H. Smith, Low Temperature Reduction of Ore, Transaction A.I.M.E. 91:419 (1930) 
C. W. Davis, Alternating-Current Magnetic Separation of Iron Ores. u. s. 
Bureau of Mines, Department of Investigations 3229:37 (1934) 
R. B. Sosman and J. C. Rostetter, The Ferrous Iron Content and Magnetic Susceptibility of Some Articifial and Natural Oxides of Iron, A.I.M.F.. 58:409-33 (1917) 
s. G. Frantz and G. W. Jarman, Magnetic Beneficia.tion of Nonmetallics 
Transactions of A.I.M.E. 102:122 (1932) 
0. Lee, B. w. Gandred and F. D. DeVaney, Magnetic Concentration of Iron Ores 
oi.. Alabama. U. S. Bureau of Mines Bulletin 278 (1927) 
 
 43 
ADDITIONAL REFERENCES (continued) 
S. Norton and s. LeFeure, The Magnetic Concentration of Law Grade Iron 
Ores, Transactions of A.I.M.E. 56:892-916 (1917) 
0. C. Ralston, Iron Oxide Reduction Equilibria, U. s. Bureau of llines 
Bulletin 296, 1929 
C. o. Hawk, P. L. Golden, H. H. Storch, and A. c. Fieldner, Conversion 
of MetlE.ne to Carbon Monoxide and }Vdrogen, Industrial and Engineering Chemistry 28;23-27 (19.32) 
 
 
 'i 
.. 
 
 EXHAUST PORT 
 
- - - -WATI!."' LEVI!.L- - - - - - - - - - - - QUENCHING lOX 
VERTICAL SECTION 
 
" iJ 
 
6 
 
f!' (} 
 
Q 
CJ 0 
0  
0 0 a 
 
q 0 
./> <J IJ 
0 
 
"' 
.0 " II 
 
-. - <)- 
 
<7 
 
<> 
 
d 
 
VERTICAL SECTION 2 
 
= SCALE r" I' 
DRAWING REDUCED TO APPROXIMATELY 1/2 
 
HEAT INTAKE 
1 
j 
REDUCING OIL RESERVOIR 
MANGANESE CONCENTRATION 
MAGNETIC ROASTING FURNACE 
TENNESSEE VALLEY AUTHORITY 
COMMERCE DEPARTMENT 
IIECOWW[NDED