Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1941-05-10

Montana and oregon Whlcn are De
ing investigated as hereinafter de-
scribed can be concentrated by
gravity 10 the same grade metallur-
gical Cr2O3 as used during the last
emergency period. These concen-
trates have a chromium iron ra-
ito of II; high-grade Imported me
tallurgical ore has a ratio OF 20.
The following account of the IN
vestigation is as given with some
excision) in a paper presented by
r G. Kniek erbocker, M. b. Roger
and T. E Evans OF the starr OF the
Metallurgical Division of the U. ).
Bureau of Mines at the dedication
of the Bureaus new experiment
station in Salt Lake City Utah
on May 81, 1910.
This investigation was undertak-
en- to demonstrate in small electric
pilot furnaces: 1) the chromium
recovery, (2) the power consump-
ton, and CD the grades of chrom-
ium products possible by several
electrothermal methods of reduc-
ton as applied to domestic high-ir-
on chromium ores.
SIAlNOAhD fEhtNOC11hONhn r.
ELECTRIC FURNACE PRACTICE.
Ferrochromium, to 10 per cent
carbon. The chromite ore or concen-
trate used usually analyses 40 to
SIS per cent Cr2O3 and II to IS
per cent, FEC, the rest being prin-
cipally alumina, magnesia and 81
lica. This standard method of fer
rochromium smelling is carried out
in open-top. stationary short-shaft,
one or three-phase electric fur
naces. Electrodes are of the Sol
derIberg" or continuous baking
type. The charge is mixed dry and
fed into the top of the shaft
around the electrodes. The molten
ferroalloy and Stag are tapped into
cast-steel pots, and separated when
cold. The carbon content OF the pro-
duet is controlled $40 per cent O.
by varying the amount of carbona-
ceous reducing agent on the charge.
Power consumption and chrom-
ium recoYeries on high-carbon as
compared to medium-carbon ferro-
chrome are given in Table l. These
recoveries are based on the pro-
duction of a 65per cent chrOm-
ium ferroalloy The comparative
prices of Highland low-carbon all
Toys in July, 1884, are given in
Table II.
GRAVITY CONCENTRATION OF
HIGH-IRON MONTANA CHROM-
TIE. % Diaphram Jig Concentra-
ton: Minus 2O-mesh unsized, un-
classified ore was concentrated with
the results given in Table III
pilot plant table concentration: Re-
suits are given in Tables Nv and
V.
1t is evident that regardless of
the Cr/Fa. ratio in the heads the
ratio of chromium to iron in the
concentrates is approximately IT..
The recoveries in the pilot-mill
runs were above so per cent.
The term fines in Tables Nv
and V is used to designate sample
rejects received from the Reno sta
ton which were found to contain
81 per cent 20 mesh. Approximate
" 5000 h. of these concentrates
was produced for subsequent ell
ectrothermal Investigations.
ELECTRIC FURNACE SMELT-
ING OF MONTANA CHROMIUM
ORES. % Direct, no tluxes: sew
eral 2O0-lb. charges of Montana
chromite mine-run ore were smelted
in an electric furnace. The reduc-
ing agent used was petroleum coke
from a California oil refinery and
of the following composition; Tx
ed carbon, S7.S per cent; volatile
11.9: benzol soluble, IL; sulphur,
1.2; ash, O.3; H20, 1.9. The coke
on the charge was 20 per cent.
Ore and coke were crushed to min
us u in. Mixed thoroughly and bril-
quetted. No fluxes were added.
Charges were intermittent batch
smelts, i. e., the furnace was at
room temperature at the start OF
each run.
ELECTRIC FURNACE SMELT-
ING OF MONTANA CHROMIUM
CONCENTRATES. Electric furnace
smelling of these ores direct, with
out fluxes, produced waste slags
containing only 3 per cent Of the
chromium charged. Table VIII gives
the results of smelling the cOncen-
trates made from these ores in the
gravity concentrating pilot plant.
In the gravity concentration,
mAgnesia and silica are the prin-
cipal gangue minerals removed. The
concentrates produced then re-
auire 10 per cent OF their weight
of silica, to be added as a flux in
smelling. Hence, the rejection OF
magnesia is the principal advantage
gained by gravity concentration 9TH
er than the gain in tenor of chrO-
MUM.
Microscopic examination of the
concentrate by Cooke showed the
presence of quantities of chlorite,
surpentine, magnesite and siderite,
both locked and free. Examination
of a polished section showed that
the chromite was not zoned and
that no free magnetic was pres
ent.
by crushing through 15O-mesh
and carefully vanning the minus
$50 and plus 2OO-mesh materials,
a good separation was effected be-
tween the chromite and the gangue
srninerals. This cleaned chromite was