feasibility studies on a proposed 40-ton per day plant in the Las Vegas area.-
-E d ito rsP
r o d u c t i o n of metallurgical-grade manganese materials has depended largely on high-grade imported ore containing about 50 percent manganese. It is now economi
cally feasible to produce from low-grade domestic ores a liigh-purity (98.5 to 99.9 per
cent) manganese metal, acceptable to the
Electrolytic m anganese pilot plant at
Largely financed by th e government as an emergency war measure, Bureau of Mines engineers and metallurgists conducted ex
periments over a three-year period in a pilot treatm ent by the bureau’s electrolytic proc
ess. Small scale production by this method
Manganese metal has been produced elec-trolytically on an industrial scale since 1939 by Electro Manganese Corp. a t Knoxville, T enn. T h e latest reported production rate was about 135 tons monthly. T h e process is the same as th a t developed by the Bureau of Mines. Only other domestic production of electrolytic manganese is the small and
nese metal under the favorable conditions in the Las Vegas area, basing this estimate
diameter Skinner furnace containing four muffles, where th e manganese dioxide is re
Wash liquor with spent electrolyte from the cells contain
ing 13 g. of M n, 130-135 g. of ammonium current washing thickeners, which wash the leach residue free of manganese and am
monium sulphates. It is then pumped to the tailing pond. Overflow from the primary thickener contains metallic impurities such as As, M o, N i and C u which m ust be re
moved before the solution can be electro- lyzed. T h e overflow passes by gravity into a Turbo-absorber tank, where hydrogen sul
phide is added. Metallic impurities are precipitated as sulphides and removed by Table II— D etailed E stim ates on Leach T otal leaching and purification.. . . 2.0167 1 On th e b a sis o f 40 to n s o f m a n g a n ese d ally.
Alteration on an acidproof Shriver press.
T he filtrate is stored in a lead-lined tank.
T h e solution, after purification with hy
drogen sulphide, is essentially free of metallic impurities b u t contains colloidal sulphur and colloidal metallic sulphides which arc removed by the addition of ferrous sulphate solution, followed by oxidation and precipi
tation of ferric hydroxide. This precipitate absorbs the colloidal material and also re
moves any arsenic or molybdenum still pres
ent. Oxidation of iron is carried out con
tinuously in a series of three Turbo-absorbers.
After iron precipitation, the solution is al sulphate per liter. Detailed cost estimates are given in Table II.
CELL R O O M O PER A TIO N S T h e cell room in the proposed 40-ton plant contains 264 lead-lined wooden cells.
Each has a capacity of 22 anodes and 21 cathodes. T he anodes are lead, containing 1 percent silver and 0.5 percent arsenic; they are perforated so as to be 40 percent void.
T he cathodes are type 316 stainless steel.
A copper conductor bar is riveted and brazed along the top of the cathode. Each cell contains a false bottom , which serves as a reservoir for the manganese oxides th at form at the anode and spall off periodically. A canvas diaphragm-covered frame surrounds the anode. A diaphragm cell is necessary to prevent the acid at the anode from mix
ing with the solution surrounding the cathodes, which has a pH of
8
.2-8.4. T he manganese concentration of the catholyte is 13 g- per 1.; the feed solution is 35 g. per 1., four Ignitrón mercury arc rectifiers, each CHEMICAL & METALLURGICAL ENGINEERING • M A R C H 19 4 6 •Flow sheet show ing com plete process
supplying a current of 9,900 amp. at 346 v. I in bichromate solution to prevent oxidation of the manganese, the deposited manganese is washed and removed by flexing or striking with a rubber mallet. T h e finished product, in th e form of chips just as stripped, is packed in metal containers for shipment.
It contains up to 99.9 percent M n and does not require melting or casting into pigs in order to be suitable for industrial use.
T h e small quantity of manganese th a t
re-Feed solution
Duration of electrolysis 24 hrs.
DC kw-hr. per lb. M n. 3 .5 - 3 .8
T able VI— Estim ated Construction Costs o f 40-T on Electrolytic Plant*
Miscellaneous buildings ... 246,000 C h e m ic a ls ... 53,996 surface, which aids stripping. Every second day the cathodes are buffed before the sili solution becomes chilled, a complex sul
phate containing 4-5 percent manganese, 4-5 percent magnesium, 34-36 percent am monium sulphate, and 28-30 percent water crystallizes out.
These sulphate crystals are separated from the solution in a Bird continuous centri
fugal filter. Removal of the complex sul
phate is necessary to keep the magnesium concentration down to the point where the complex sulphate will not crystallize any
where else in the plant circuit. T h e crystals percentage losses distributed as follows:
M A R C H 1 9 4 6 • CHEMICAL & METALLURGICAL ENGINEERING
Crushing, 1.0; grinding, 1.98; roasting, 0.97; produce 1 ton of metal, th e cost would be leaching and washing, 3.67; sulphide, purifi- $141.11 per ton or 7.06 cents per lb. before cation 0.40; electrolysis, 0.88; magnesium, allowance for return of capital. T h e 40-ton removal 2.90. reduction plant is estimated to cost
$2,431,-Estimates of operating costs for mining 665 or $60,790 per ton of daily metal- (including stockpiling and reclaiming of ore output capacity.
from piles and delivery to plant bins) be- A summary of the costs of th e various
Dean, College of Engineering U niversity of Missouri, Columbia, Mo.
In August, 1945, the author took p art in a prelim inary survey to deter
mine which processes and plants in the American and British controlled zones should be subjected to fu rth er detailed investigation. One of the interesting projects uncovered was the Siemens and Halske research and pilot plant production of synthetic mica under the im mediate direction of Dr. Viktor Middel. This rep o rt outlines the process and highlights the critical
R
e s e a r c h on the production of synthetic mica had progressed well into th e pilot plant stage and the second and larger of two pilot plants was then in operation. This plant was built as a final step before designing a full scale production plant and followed a smaller pilot plant which had only been successful within the preceding year.
PR O C E SS D E S C R IP T IO N Raw materials used were technical grades of alumina, magnesia, kieselguhr and potas
sium fluosilicate. T h e proportion of these ingredients needed not be controlled very accurately. A typical mix used at the Siemens and Halske laboratory was: Al,Os, 11.6 per
cent; M gO, 32.6 percent; kieselguhr, 30.7 percent; K.SiF,, 25.1 percent.
These ingredients were finely ground, thoroughly mixed, and then formed into pellets about
20
mm . in diameter and6
mm.thick. T h e pellets were placed in a deep crucible which was fitted w ith a lid having a hole in the center. As the pellets were subsequently melted, additional pellets were added until eventually a crucible full of m elt was obtained. T h e weight of the final m elt in the smaller of the pilot plants was about
10
kg. and in th e larger plant about 100 kg. T he crucible used was made by the Stastliche Porzellan concern of Berlin (this plant had been wrecked by bombs b u t the kieselguhr content accounted for at least 80 percent of the weight. ' H e added that large cylindrical crucible having separate top, bottom , and cylindrical wall parts. T he of additional pellets during melting.Dr. M iddel claimed not to know the composition of the outer, three-piece, cru
cible, b u t thought th at it was 80 to 90 percent silicon carbide. T h e crucible was made by the Koppers concern at Düsseldorf from material called “ Carbomanite” which had the appearance of carborundum.
T h e crucible assembly was placed on a refractory stand (carborundum ) which was mounted on springs, th e springs serving to minimize vibration of th e assembly. T h e crucible assembly, support, etc., were m ounted over a hydraulic ram which served
to raise the whole assembly vertically until the crucibles were in position in a gas-fired furnace. Before elevating the crucible assem
bly into the gas-fired furnace, the crucible assembly was inclosed in a vertical, elec
trically-heated furnace and the tem perature brought up to about 900 deg. C. T his pre
heating was only adopted to reduce the time in the gas-fired furnace.
Two gas-fired furnaces were used. T he smaller furnace had six burners, entering tan- gentially, three at each of two levels. In the molten material. Thereafter th e furnace and crucible assembly in the furnace were allowed to cool very slowly. This slow cooling, and the avoidance of vibration dur
ing the crystallization range of temperature, are the only critical features of the process,