Manganese Concentration from Low Grade Domestic Ore NOSSEN NITRIC ACID CYCLE ERNEST S. NOSSEN E. S. Nossen Laboratories, Inc., Paterson,
N.. I .
Manganese deposits in the U. S., if developed, are sufficient to provide the industry for a century or longer with this strategic .material. However, the manganese content of the ores is low-5 to 20%. In most of the ores the components are so intimately interlocked that classical ore dressing methods are not suitable for concentration to a marketable product with a t least 40% manganese. Even modern flotation methods are limited to certain kinds of ores. Several chemical processes have been developed to recover the manganese. Usually these are only economical if the chemicals used are recovered. None is suitable to produce manganese from the major domestic sources a t a competitive price in a peacetime economy. Therefore a new approach to this problem was made.
The nitric acid cycle developed by the E. S. Nossen Laboratories permits the separation of manganese from iron, silica, and other undesirable impurities and the decomposition of the formed manganese nitrate solution directly to manganese dioxide and nitric acid. Manganese recovery is satisfactory in many ores that formerly were inaccessible to treatment. A nitric acid recovery of more than 95% can be obtained. In the pilot plant the technology of the process in continuous operation was developed, and the data were determined for several ores for a commercial operation. The product, mainly manganese dioxide, is suitable for the chemical and dry-cell battery industries. Other metals combined in the ore may be recovered in an inexpensive way.
M
In addition to the amounts required by the steel industry 80,000 to 100,000tons of ore (85% manganese dioxide and special purity requirements) are used per year in the dry-cell battery industry, the chemical industry, and others. The best native material for dry cell manufacture is the ore from the Gold Coast of Africa. Domestic production is limited in spite of the fact that millions of tons of manganese-containing ores are available in the U. S., primarily in the following locations:
ANGANESE is a very important strategic material. It puts the starch in steel; a certain amount of it is necessary and cannot be replaced by any other metal. Thirteen pounds of manganese are required for 9. ton of steel. Annual consumption of manganese in the U. S. steel industry amounts to 1,500,000 short tons of ore which averages 48% manganese. These ores are manganese dioxide (pyrolusite, cryptomelane, ramsdellite, and psilomelane) or ores containing lower oxides of manganese such as manganite ( Mn203.H20),bixbyite (Mn,Os), and hausmannite (Mn30,). The manganese ores are converted in a blast furnace into manganese alloys with iron, either to spiegeleisen with 20% manganese and 80% iron or to ferromanganese with 80% manganese and 20% iron. A minimum manganese content of almost 50% is required for this metallurgical process. Furthermore the ore must meet other specifications-for example, iron Iess'than 77,, silica less than log,, and phosphorus less than 0.3'%. About 907, of U. S. manganese ore requirements are imported (9): India Gold Coast (Africa) South Africa Russia Cuba Chile Brazil hl exio o Others
Imports, Tons 1946 1949 321,000 383,000 280,000 332,000 244,000 242,000 73,000 316,000 159,000 55,000 144,000 7,000 86,000 135,000 40,000 53,000 2,000 95,000
Cuyuna Range, Minn. Aroostook County, Me. Chamberlain, S. D. Artillery Peak, Ariz. Batesville, Ark. Three Kids, Nev. Butte and Philipsburg, Mont. Olympic Peninsula, Wash. The manganese content of domestic ores is generally low (between 5% and 20%) and large tonnages are required for the production of 1 ton of concentrate (48% manganese). I n physical concentration by washing, jigging, and tabling, a high percentage of the manganese goes into tailings, and the operation is not very attractive commercially. It is relatively easy t o obtain a manganese concentrate with 20 t o 25% manganese, but a higher degree of concentration is often impossible with the classical methods of ore dressing.
1695
1696
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
Automatic Test Equipment for Batteries
Recently froth flotation ( 1 1 ) was applied successfully, but this treatment requires fine grinding of the ore, agglomeration of the concentrate, consumption of expensive chemicals and heat, and a rather high investment. The total processing costs of this treatment are of the same magnitude as the cost of applying an economical chemical process. Furthermore even froth flotation is not suitable for ores in which the components-for example, manganese and iron or ot,her ore minerals-are intimately interlocked with each other as they are i? the big deposits of the Cuyuna Range in Minnesota and Aroostook County, Me., and Chamberlain, S. D. Pyrometallurgical methods were tried in the past ( 2 ) and are now being tested again in Pittsburgh with slag and low grade ore. If and when these methods become successful, their application may be limited t o emergency periods because of costs of processing. Most of the chemical processes developed during the last decade also have high processing costs. Generally a chemical process can only be economical if the chemicals used can be recovered or if there is practically no consumption of chemicals, as in the Anaconda recovery process for carbonate ores. The Anaconda process is favored because the carbonate ores in Montana (8) are amenable to physical concentration and the high amount of volatile matter (carbon dioxide) makes possible the production of a concentrate with 6070 manganese by calcination. About 1070 of the total U. S. manganese need is ensured by this operation. Unfortunately the ores of all other deposits in the U. S. are not amenable to this process. Oxide ores with a low iron content and a satisfactory porosity could be handled by the pickle liquor process ( 4 ) . Pickle liquor, a dilute solution of ferrous sulfate and sulfuric acid is a waste material from the steel industry; it reduces the manganese dioxide t o manganous sulfate. The manganese, after separation from the iron salt, is precipitated as a hydrated oxide. There is high consumption of calcium carbonate and calciuni oxide, but the problem of shipping t.he pickle liquor to t,he mine is the most serious drawback. iZnother process using manganous sulfate as an intermediate has been in technical operation for about 10 years at the Electro Manganese Gorp. in Knoxville, Tenn., for the production of high priced electrolytic manganese metal ( 5 ) . The solubility of manganese monoxide in ammonium salts is the basis of the processes of Bradley ( I ) , Sweet, and Dean. Soluble manganese salts are formed while ammonia is liberated. Their
Vol. 43, No. 7
feasibilit,y depends on whether the amrnonia or ammonium salts can he recovered in an inrspeiisive way. Consiclerable work has becri done on gas processes, where marigariesc oxide is suspended in wat,er arid 1,reated with a gaseous reagent such as sulfur dioxide ( 7 , 10) or nitrogen dioxide (3)t o extract the manganese from the ore in the form of a soluble manganese compound that can he separated from the insoluble gangue by filtration, then concentrated and decomposed into a manganese oxide and the gaseous leaching agent. However, experirncc has shown that these three-phase reactions between thc solid manganese ore, the liquid, and the gaseous reagent never come u p to expectations. Undesirable side reactions take place leading to unexpected eomplications in the system. Substantial losses of valuable gascous reagent cannot be avoided. In one of the processes t'he reported loss of sulfur dioxide was 40%. Losses in industrial plants often surpassed this figure . .Furthermore, in a cyclic process wherein the dissolving gas is evolved in the decomposition, its consumption in the leaching step determines the speed of the process and the production capacity of the plant. This leads to variations in production capacity and may affect the entire procedure in shifting from one raw material to another. NOSSEN NITRIC ACID CYCLE
The Nossen nitric acid cycle (6) is the rcsull of 15 years of industrial experience in the treatment of manganese ores and production of manganese compounds; t'he process avoids many of the limitations of other processes. I t is applicable to carbonate and oxide ores and to several types of silicate ores. Stabilization of production conditions for a separation of manganese from iron, silica, and other impurities and for the recovery of the manganese in a conccntrate (60Yc manganese) and of the nitric acid was achieved. By magnetic separation an iron conccntrate (60yo iron) can be obtained. Economical recovery of other metals such as silver, iiickel, cobalt, and zinc is also possible. d
The process starts with grinding the ore to -60 mesh. ,4rcduction of the ore in a reducing atmosphere follows; the greater part of the manganese goes to manganous oxide, and the iron oxide is reduced to ferrosoferric oxide. In the following leaching operation with nitric acid, the ferrosoferric oxidc remains insoluble with silicon dioxide and aluminum oxide, Sulfuric acid added to the nitric acid takes care of the barium, calcium, and lead which remain as sulfates in the gangue. If, however, the ore contains an excess of calcium it would be more economical to work only with nitric acid and produce a calcium nitrate for fertilizer as a by-product. Phosphorus remains in the insoluble remainder. The solution of manganese nitrate is concentrated and decomposed in the presence of air at' a tcmpeiature of 200' C. : Mn(N03),.H20
+
1/202
=
ilInOz
+- 2HK03
'
Manganese dioxide and nitric acid leave the decomposition unit. The manganese dioxide is purified by washing, and then is dried. I t is nodulizcd if it is to be uaed for metallurgical purposes. The washed and dried manganese product contains 60% mangancse; its manganese dioxide content is 88%. The steps of the process are simple and do not require complicated or unusual operating conditions such as high pressures, high temperat,ures, or difficult gas reactions. The accumulation of impurities in the cycle is avoided and standard equipment as ueed in mining, metallurgical, and chemical operations is applicable. By using stainless steel in the leaching equipment and in the dcconiposition unit, corrosion problems can be avoided.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July 1951 ORE -60MESH
ezzl
I
REDUCTION KILN
(MAGNE:TIC IRON SEPARATION)
An EVAPOHATOR CONCENTRATION
RETURN TO LEACHING KETT
Figure 1. e
Flow Diagram of Pilot Plant Operation .
LABORATORY TESTS IN SMALL SCALE EQUIPMENT
1697
leaching equipment (vessel and stirrer) is made of stainless steel ; 200 pounds of ore may be handled in one operation. In the pilot plant the separation of the manganese nitrate solution from the gangue, from the insoluble ferrosoferric oxide formed in the reduction step, and from the sulfates of barium, calcium, and lead takes place in a filter press connected by a centrifugal pump with the leaching vessel (Figure 3). The insoluble remainder is repulped to the leaching vessel for washing. Iu a production plant the filter press will be replaced by a countercurrent thickener. The manganese nitrate solution containing some sodium, potassium, magnesium, and zinc as sulfates is concentrated in a n evaporator. Because of the high solubility of manganese nitrate no scaling takes place on the walls of the evaporator, and a high degree of heat efficiency can be expected in this part of the equipment. The hot concentrated solution enters the feed tank (Figure 4) beside the decomposition unit, which is also made of stainless steel. Inside the decomposition unit (Figure 5) an internally heated rotating drum dips continually into a pan filled with concentrated manganese nitrate solution and is covered with a layer of the solution. Heat effects the decomposition of the solution into'manganese dioxide which is removed from the drum by a knife and discharged on a chute to the outside. Nitric acid vapor is the other decomposition product. The vapor is partially condensed a t the inside surface of the enclosure and either leaves the unit as liquid through an opening a t the bottom or as a gas, with the air sucked through the system, to be condensed (Figure 6) and collected in a 5-gallon bottle as a liquid containing about 50y0 nitric acid. Water in a gas adsorption bottle of the same size frees the air from the nitric acid vapor which is enriched to a suitable nitric acid concentration.
The process was developed at the start in small scale equipment for batchwise operation, Reduction of the ground ore in a reducing atmosphere was effected in a small rotary kiln in batches of 5 t o 10 pounds each. Leaching took place first in 4-liter beakers and then in 5-gallon earthenware pots with a stainless steel stirrer. The solution was concentrated in enameled pails heated by gas burners, and the manganese nitrate solution was decomposed into manganese dioxide and nitric acid in equipment which is described later. PILOT PLANT
After thorough investigation with laboratory equipment a pilot plant was built in Paterson, N. J. The essential steps of the process occur in the same way, in continuous operation (Figure l), as designed for a contemplated commercial unit. The manganese ore, containing usually about 20% manganese, is crushed and ground t o -60 mesh and discharged into the hopper of the reducing kiln (Figure 2). From there it is moved by a screw conveyor into the kiln, a 10-foot rotating pipe, 1 foot in diameter. A heating chamber, where city gas is burned (regulated by an automatic valve and a thermocouple inside the kiln), surrounds half the pipe. The end of the pipe is cooled by running water and is connected with the discharge hopper. A gas pipe which delivers the reducing gas is inserted a t the end of the kiln. The speed, the slope of the kiln, and the temperature can be adjusted during operation. Temperature and detention times depend on the kind of ore to be handled, on its density (tight or porous material), and on other components of the ore such as iron. The capacity of the kiln is 40 to 50 pounds an hour. The reduced material leaving the kiln is leached with nitric acid diluted by the wash solution of the previous leach. Sulfuric acid is added in a quantity equivalent t o the amount of soluble impurities in the ore. The temperature rises to 80' to 90" C. and within an hour the leach is finished; it is controlled by the p H of the salt solution. The quantity of liquid is kept as small as possible in order to obtain concentrated solutions. The
Figure 2.
Reduction Kiln
On a drum surface of 5 square feet a production of 8 pounds of raw manganese dioxide per hour was reached, and this amount can be doubled by increasing the heat supply and the speed of operation. The temperature of the drum is controlled by a thermocouple. The speed is variable and can be adjusted according to the supply of heat. For a commercial plant several large decomposition units with two drums each are contemplated. When the manganese dioxide leaves the decomposition unit in the pilot plant it is washed in a ball mill batchwise; a t production scale this operation will be conducted in a countercurrent system. ' In this washing process, soluble impurities are removed from the manganese dioxide. T h e washed product settles easily and is ready for drying and nodulizing. RESULTS OF PILOT PLANT WORK
In small scale laboratory equipment (Figure 7 ) typical ores from all over the country are handled. and the proper treatment
INDUSTRIAL AND ENGINEERING CHEMISTRY
1698
Figure 3 .
Leaching Kettle and Filter Press
for most of these has been developed. For the work in the pilot plant only a few types of ore were selected because the method of treatment developed in the small scale investigation 11 as easily transferred to the larger scale operation which required tons instead of pounds of the raw material to be treated. A low grade manganese ore from Deming (New AIexieo) was used for the initial walk in the pilot plant. This is a wad ore, rathei porous, Rith a high content of alkali and alkaline earth metals, The ole contains 26.8y0 manganese; four fifths of this amount is manganese dioxide. The iron content is C1.37~. An average extraction of 9 5 r 0 of the total manganese present in the ore vias achieved in the pilot plant, and no iron went into the solution. The high content of other soluble metal oxides in this ore (12 to 13Yc) requires an additional amount of nitric acid in the leaching step. I n the decomposition, 987, of the manganese nit,rate was decomposed; the remainder was washed out, from the manganese dioxide v.-ith the alkaline salts. These nitrate salts can be recovered by evaporation of the wash water and crystallized and sold as fertilizer. Losses of nitric acid (497,) mere due only to incomplete washing of the tailings Leachings and of the finished product. Experimental data 1 2 are shown in Tables I and 11. Much experiment'al work was done on ores from the Cuyuna Range. This dense ore contains very lit,tle alkaline earth metals, but its iron content is high-sometimes four times as high as thc manganese content. Iron and manganese are so intimately interlocked that, in the past, all efforts toward separation and concentration of these metals have failed. h similar ore is found in Cuba and in Maine, and these deposits seem to be the largest in the U. S. In most of the work on this type ore (Cuyuna), ores containing 10 to 13% manganese, 25 to 40% iron, and 15 to silicon dioxide TTere treated. Ores with a manganese content as low as 7y0 and preconcentrates with 20YG manganese and 2070 iron were included in this investigation. The conditions for ore reduction and leaching were arranged in such a wag t h a t t,he iron was kept completely out, of the manganese nitrate solution and only traces of phosphorus could be detected in the solution. Furthermore, the insoluble remainder settled rapidly, yielding an easy separation of the solution from the gangue. The recovery of manganese in these types of ore runs from 85 t o 90%. The cost of sulfuric acid equivalent to the soluble inipurit#ies varies from $1.00 t'o $4.00 per ton of finished product with 60% manganese. The iron oxide, magnetic FedOl,may be extracted from the insoluble remainder yielding a marketable
3 4 Total
Vol. 43, No. 7
product wit.h 50 to 60% iron. Thc mangaiiex nitrat,c Polution is decomposed by the method described for the pilot plant, operat,ion. The lower grades of manganiferous ore8 v-it,h 5 to 8% manganese are preferably upgraded with a relatively small loss of mangancse to about 20% manganese; these then make an excellent material for this chemical process. In the U. S.there are several deposits of manganese ores cont,aining large itmounts of calcium oxide, n-hich cannot, be separated in a physical way from t,he ore-for example, the deposit,&in Chamberlain, S.D., and Aroostook, &IC. The amount of sulfuric acid needed to treat the calcium n.ould be pyohibitive for an economical process. Therefore calcium nitrate, C ~ L ( ? ; O ~ ) ~ . ~ H ~ O (Norivegian saltpeter),a useful fertilizer, should be produced as a by-product, using only nitric acid as leaching agent. The economic aspect for the by-product is favorable as the lime, which would be purchased, is free of cost, and a large part of the production cost is covered by t,he manganese production. I t bappens t,hat there is a market for fertilizers in the viciiiit,y of these deposits. The production of calcium nitrate, of course, requircs a rather large production of nitric acid and consequently a much higher invest,ment for this integrated industry. On the other hand, t,he cost of nitric acid produced on a large scale a t the plant is only a fraction of the price mentioned in Table 111. In the experimental work it was found that the production of cdcium nitrate is favored by the enormous difference in solubility in hot and cold water; this allows its crystallization out of the concmtrated wash solution from the manganese dioxide. THE PRODUCT AND ITS APPLICATION
The washed and dried product from the h-ossen process is a fine bluish black powder of the following analysis: P e r Cent hInOp MnO CaO
88.0 5.32 1.67 0.31. 0.04 0.91 3.44
xgo
Fez03
Sz (as Nos)
HzO ( a t 300' C.)
OF REDUCED ORE TABLE I. LEACHISG
Ore:
I-I?.;oI
15.7 S ) , liters 48.0 8.0 3.0 0.0 59.0
Cycles 1 a n d 2 , 2 8 . 9 % > I n = 19 65 kg. Cycles 3 and 4, 27 6% h l n = 18.8 kg.
Input Wash hIn., splugrams/ IIn, tion, kg. liter liters First Cycle 20.0 60.0 65,0 68.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
~
Solution, liters 51 0 68.0 69.0 68.5
output lln, liter
Mn, kg.
209 82.5 31.7 6 0
10.68 56'2 2.19 0.41 18.90
grams/
Extraction,
%
96.3
Second Cycle Leachings 1 2 3
38.0 17.0 6:0
4
0:0
5
0:0 61.0
Total
40.0 28.0 20.0 49.0 17.0 51.5 17.0 68.0
82.5 82.5 31.7 31.7 6.0 6.0 0.0 0.0
3.30 2.31 0.63 1.48 0.10 0.31
74:O
7Y.4
68'0
1Q.7
0.00 8.13
69:O
4.4
0.00
52.0 69.0
194 142
..
10.01 9.79
s.29 1'.34
0.30 26.73
94.5
Third Cycle Leachings 1 2
40.0 18.0
3
4:0
4
0:0
5
0:0
Total
6210
Leachings 1 2
39.0 19.0
3
4:0
4
0:0
5
0:0
Total
62:O
60.0 9.0 40.0 34.0 28.0 40.0 30.0 39.0 30.0
142 1:'2 (1.4 71.4 19.7 19.7 4.4 4.4 0.0
8.52 1.28 2.86 2.43 0.55 0.79 0.13 0.17 0.00 16.73 Fourt,h Cycle
60.0 8.0 43.0 27.0 39.0 32.0 38.0 32.0 38.0
159 159 93.5 93.5 19.3 19.3 5.5 5.0 0.0
9.55 1.27 4.02 2.53 0.75 0.62 0.21 0.17 0.00 19.12
76.0 68.0
204 169
70'0
9i.5
7i:o
Y9.3
70:O
..
i3 0 72.0
.. 5 ,5 ..
214 172
15.50 10.82 6.'55
