AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS Technical Fblication No. aaqg
Class D, Metals Technology, December 1947 DISCUSSION OF THIS PAPER IS INVITED. It should preferably be presented by the conpibutor in
person at the New York Meeting. February 1948. when an abstract of the aper will be read. If this is impossible discussion in writing ( a copies) may be sent to the Secretary. American fnstitute of Mining and ~etallurgicai Engineers. 29 West 39th Street, New York 18, N. Y. Unless special arrangement is made, discussion of this paper will close April 1 , 1948. Any discussion offered thereafter should preferably be in the form of a new paper.
Roan Antelope Smelter, .Northern Rhodesia
BY R. J. STEVENS,* JUNIOR MEXBER AIME
(New ~ b r k Meeting. February 1948)
THE Roan Antelope Smelter commenced from this ore consists mainly of chalcocite operations in October, 1931. As originally and shale with-small proportions of other designed, its equipment consisted of one copper minerals. As mining operations ex- reverberatory furnace, 120 X 25 ft, two tend to the ~ o a n Extension orebody; the Peirce-Smith converters 12 X 20 ft, and proportions of bornite and chalcopyrite one straight line casting machine. Since in the concentrate will increase with a cor- that time the following additions have been responding decrease in the copper content made: of the concentrate. Because of the con- One reverberatory furnace 120 ft centrate grade the capacity of the rever-
X 28 ft (1934) beratory furnaces in terms of tons of One reverberatory furnace 95 ft copper produced per ton of coal burned is
X 28 ft (1943) high..This ratio is usuaUy over 2.2, and on Two 12 X 20 ft Peirce-Smith especially favourable runs has reached 2.6.
converters (1934 and 1938) Reference to Table I shows that the One 13 X 30 ft holdingfurnace i; (1938) iron content of the concentrate is unusually One straight line casting machine low. Only part of this iron is available for
and 2 ladle tilting quadrants (1934) slag formation, the balance going to the The metallurgy of the smelting process matte. To make up this deficiency in bases,
is comparatively simple. However, there limerock is added to the furnace charge. are several features .of operation which are This flux ensures a slag that is of the cof- uncommon to most copper smelters: (I) rect silicate degree, is sufficiently fluid, of The high grade of concentrate treated; this low specific gravity, and it counteracts the has always been about 50 pct copper. (2) thickening effect of the alumina present. The high flux burden on the charge. This is An ample supply of flux is obtainable from necessary because of the deficiency of Ndola, 22 miles distant by rail. Although bases ' in the concentrate and the high the reverberatory slag has a high copper alumina content of the concentrate. (3) content, the slag fall is low and the copper The frequent necessity of adding coal to loss in the slag now rarely exceeds 1.0 pct the furnace charge to control the matte of the total copper charged. grade. (4) The high grade of matte pro- The blister copper shipped is of such duced. This has led .to unusual converter purity that only one fire refining operation ~roblems. has been necessary to produce a wirebar r
From the commencement of 'operations, with properties comparable to electrolytic the ore mined has come from the Roan copper; Bismuth has always been the most Basin orebody. The concentrate produced- troublesome impurity and consequently
the problem of its control in the finished Manuscript received a t the office of the
Institute April 19. 1947 Printed without product has been of prime importance. author's corrections. Subject t o revision.
* Smelter Superintendent. Roan Antelope Practically none is removed in the rever- C o ~ ~ e r Mines. Ltd. Northern Rhodesia. beratory furnace. The bulk of the elimina- - * -
Copyright. 1947. by the American Institute of Mining and Metallurgical Engineers, Inc. Printed in USA
ROAN ANTELOPE SMELTER, NORTHERN RHODESIA 2
tion is accomplished in the converters. I t atmosphere in the furnace, the degree of was established i n 1934 that this removal oxidation of iron sulphide is minimised was, generally speaking, inversely propor- and a lower grade matte results. The effect tional to the grade of matte. Whether this of coal in reducing the grade is limited;
FIG I-GENERAL VIEW OF SNELTEK. TAILINGS DALI m BACI
R. J. STEVENS 3
matte produced coupled with the prob- hopper is automatically stopped when this lem of bismuth elimination has meant weight has been charged. The gross weight that the operation of blowing the con- is obtained and printed. The drum 'is ro- verters could not follow well-established tated 360' and dumps its contents into a
TABLE 2-Reverberatory Furnace Tonnages
*Includes a proportion of blister produced from the smelting of concentrate for the account of Mufulira Copper Mines. Ltd.. Northern Rhodesia. - practice. This problem is fully dealt with receiving bin below. When the drum re-
& under " converting." turns to the upright position, the tare weight is obtained and printed and charg-
CONCENTRATE C O ~ E Y I N G , WEIGHIXG AXD ing of the next batch of concentrate STORAGE mences. An automatic sampler and riffle
Concentrate is delivered from the Oliver chute are provided to sample the stream filters by belt conveyors to the three storage of concentrate as it discharges from the bins. Each of these has a capacity of 1 2 0 belt conveyor to the weigh-hopper. tons wet concentrate. From the bins the The concentrate in the receiving bin is concentrate is discharged by belt feeders discharged by belt feeder on to a zo-in. on to a zo-in. conveyor belt which delivers belt conveyor which delivers it to the it to the weigh-hopper. This machine con- charge bins. sists of a circular steel drum with dished The charge bins consist of 18 steel com- ends. An opening is provided in the shell partments, in two parallel rows of 9 each. for charging and discharging concentrate. Each bin has a capacity of zgoo cu ft. I t is carried on a horizontal shaft which is One row of bins is reserved for concentrate rotated by an electric motor through reduc- tion gears. The whole unit is carried on a frame set on knife edges. The capacity of the drum is 25 tons of wet concentrate.
, The operation of feeding conveyors, weigh- hopper and ticket printing mechanism are electrically interlocked and the weight cannot be printed unless the scalebeam is in
and the other for fluxes and plant reverts. Material is charged to the bins by two zo-in. belt conveyors and distributed to each compartment by travelling trippers, one over each row. The contents of each bin is taken as a unit lot and the weight and analysis are known before it is charged to the furnace.
balance. Any predetermined weight is set Each bin is equipped with a motor- on the steelyard and the feed into the driven apron feeder. This discharges on to
ROAN AHTELOPE SMELTER, NORTHERN RHODESIA
a 24411. belt conveyor which runs down contents on to a go-in. belt conveyor. This the centre line of the bins, delivering its discharges t o a 24 X 15-ib jaw crusher., contents to a 20-in. belt conveyor, 656 ft The product of the crusher is then delivered long, which carries the charge to the in turn to a gj$-tt standard Symons cone
smelter. Incorporated in this conveyor is a . Dennison weightometer which recordsfthe
weight of charge delivered to the furnace. Since the charge ingredients (concentrate, limerock, reverts and others) are fed on to the 24-in. belt simultaneously, they are well mixed after they have been discharged on to the four other belts which carry them to the furnace. All these conveyors and the apron feeder motors are operated by push button control on the feed floor of the furnace and are electrically interlocked.
The flux bins consist of six steel com- partments, each of 3550 cu ft capacity. A standard gauge (3 ft 6 in.) railroad track runs over the top of the bins so that cars which deliver fluxes can be directly off- loaded into the bins. Plant reverts are delivered to these bins in bottom dump cars of 15 tons capacity. A travelling feeder runs under the bins and delivers their
crusher and a 42 X 16-in. Allis-Chalmers rolls crusher which can operate either in open or closed circuit with 4 X 5-ft Hum- mer vibrating screens. All units are served by the necessary feeders and conveyors. The crushed product is delivered to the charge bins by a no-in. inclined belt conveyor.
Table 3 gives the dimensions of and in- formation about the three reverberatory furnaces. The sidewalls are 24-in. thick and built of firebrick throughout, except in the settling zone where they are faced with 12 in. of magnesite brick from the furnace bottom to above the normal bath level.
All three furnaces have slag bottoms. During construction of the furnaces, the concrete foundations were lined with fire-
R. J. STEVENS 5
brick and protected with a layer of crushed poured into place through launders. Ordi- -slag. Blast furnace slag from Bwana nary molten reverberatory slag from this Mkubwa was used for the bottom of No. I furnace was used to pour the bottoms of furnace. I t was melted in a cupola and Nos. 2 and 3 furnaces. Coal was burned in
TABLE 3-Reverberatory Fz~rnnce Data both furnaces during the slag pouring operation and only when the correct level of molten'slag had been transferred was the coal firing rate slowly reduced. This insured cooling of the bottom a t a slow even rate to minimise cracking. I n No. 3 furnace over 1300 tons of slag