Process and Apparatus for Roasting Pulverulent Materials.
Year: 1893

page_text: Date of Application, 11th Feb., 1893—Accepted, 6th May 1893
COMPLETE SPECIFICATION.
Process and Apparatus for Roasting Pulverulent Materials.
I, CHARLES VATTIER of 185 Calle Moneda, Santiago, Chili, Engineer,
do hereby declare the nature of this invention and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement :-
Hitherto the roasting of ore dust has presented great difficulties occasioning
large expenditure for small results, requiring special skill on the part of the
foreman and workmen engaged on the operations and furnishing only products of
irregular quality for metallurgical treatment.
In order to attain some degree of perfection recourse must be had to very large
reverberatory furnaces or to special furnaces.
In the case of reverberatory furnaces, which in fact extract all but 2 or even
1 per cent. of the sulphur, there are required a large expenditure of fuel and great
skill and activity on the part of the workmen and the output is nevertheless only
moderate. Besides as the gases contain little sulphurous acid, they cannot be used
for the manufacture of sulphuric acid.
In the case of shelf and other furnaces, there is less consumption of fuel, the
sulphurous acid can be utilised, the roasting is very perfect, but the cost of
manipulation is great, the construction of the apparatus is difficult, complicated and
such as to require frequent repair, and finally the output very small for a plant
so large.
These processes must therefore be abandoned when the production has to be
rapid, when workmanship is costly and especially when the metallurgical establish-
ments are situated in districts where all the industrial conditions present great
difficulties.
Already recourse has been had to the following expedient: the ore dust
arriving directly from the mines or from the screening of blocks of various sizes
was moistened with clay water and formed into small bricks which were left to dry
in the open air. These bricks, when dried, were roasted in heaps. The progress
of the roasting had to be carefully watched, closing or opening the flues according
to the condition, the covers had often to be repaired, and all the known incon-
veniences of roasting in heaps had to be undergone.
As many of the bricks were broken they had to be made again by moistening,
forming again into bricks, drying them in the open air, and when dried, conveying
them again to the muffle. Dust was formed during their transport. Moreover, as
the roasting was very imperfect, the first melt of copper pyrites could only produce
a matte of very low grade in respect of copper.
The roasting being bad, naturally little iron oxide is formed and consequently
this in melting being insufficient to saturate the contained quartz so as to produce
slags not containing more than 50 per cent, of silica, it was necessary to add to the
charge up to 15 per cent. of the ore, carbonate of lime and a large proportion of
basic slags resulting from other metallurgical operations (working of the converters)
of the establishment. It was only after these additions that slags could be got
sufficiently fluid.
On account of the slow working of the muffle the output from each furnace was
very small.
Another cause of expense was the rapid wasting of the iron rakes with which the
roasted dust was stirred when moist, which is explained by the presence of a certain
quantity of sulphate of copper formed during the roasting.
It is for the purpose of obviating all these inconveniences that I have formed the

page_text: idea of employing compressed air, and devoted myself to experiments undertaken
in this direction.
As air when forced tends to follow the walls, that is to say the circumference of
the apparatus, this could only have a very small diameter otherwise the central
part would remain crude; on the other hand for a like reason the dust could only
be charged in small thickness. Thus only a small quantity of ore could be calcined
in each apparatus, and that very imperfectly.
But besides difficulties in carrying on the operations, manipulation, expenditure
of fuel, escape of gas &c. the chief inconvenience was the following.
The gases reaching the walls of the apparatus at the beginning, a very vivid
combination of the pyrites near the walls took place, and the mass became scarified
while the centre remained unaffected. Shortly a single block became formed and
the operation had to be stopped. The difficulty was to remove this block from the
apparatus already worn and eaten into by the combustion gases, and recourse had
to be had to wedges, levers, pincers, &c., and after a few operations the apparatus
was quite unfit for use even if its construction were attempted in pieces quite
separable.
Turning my attention to remedies for these inconveniences, I have endeavoured
to obtain a diffusion as uniform as possible of the gases in the whole mass treated
by arranging a partitioning within it so as to form in the furnace separate fractional
spaces through which the gases circulate so as to act as uniformly as possible on all
the mass.
To attain this result, 1 arrange the apparatus as 1 shall describe referring to the
annexed drawing.
Figures 1 and 2 are sections at right angles to each other and Figure 3 is a plan
of the apparatus. It consists of a quadrangular iron casing formed by four plates A
resting freely on a well stamped concrete floor B, which projects beyond the sides
of the casing and is raised 0.10 m. above the surrounding ground, having through
it a passage C for the compressed air from a fan; at its centre it has an opening D
communicating with a flue which leads the fumes to the principal flues connected
to the great chimney of the establishment. The dimensions of the casing may be
varied, suitable dimensions are length 2.40 m. breadth 2.20 m. height 0.90 m.
Each of the plates is fastened to the next by removable keys which are pushed
into iron lugs fixed to the other plate. Each of the plates is terminated on three
sides by an angle iron having some holes and connected by a simple bent iron
entering these holes. At the distance of a metre from one of the smaller sides
commences internally a small brick wall E carried by trough shaped irons dividing
the casing longitudinally into two almost equal parts. This wall does not rest
directly upon the floor but it rests at a distance of say 30 metre upon angle iron a
connected to the central sheet iron chimney F. It forms a horizontal projection
which serves as support to one of the sides of the double bottom G composed of
pieces of sheet iron irregularly perforated. This bottom G is carried, at about
30 metre from the floor, in the longitudinal direction upon the projection beyond
the wall and the sheet iron tube, and in the transverse direction upon a plate of
iron H placed on edge directly on the floor.
The air is introduced into the larger compartment at one of the sides of the wall
and circulates freely in the whole of the double bottom which unites the two
compartments and has no partition. At about 1 metre above the level of the outer
edges of the casing four iron brackets support a conical roof I of sheet iron, the
fixed edges of which are situated at about 5 metre above the level of the upper
edges of the casing and are slightly receding.
The division wall inclines in the longitudinal direction from each of the smaller
sides up to the central pipe at the level of the fixed edges of the roof. On each of
the edges of the roof is fixed a binged sheet iron plate K so as to be capable
of being raised or lowered at will. In the latter case when all the sheets are
lowered there is no communication between the apparatus and the surrounding
atmosphere and the whole of the gases escape through the central chimney F. An

page_text: admission valve for the air of the fan allows the intensity of the air supply to be
regulated and a damper placed on the discharge flue of the gas regulates the
strength of the draught.
The mode of operating and the action of the apparatus are as follows. The iron
plates of the apparatus being once placed in position and keyed, the double bottom
is formed by simply placing upon the angle irons which pass along the wall and
surround the central chimney, pieces of perforated sheet iron which at the other
edge simply rest upon the iron plates H placed on the floor. On these perforated
plates are then placed portions of old sacks which are covered with branches, twigs,
waste pieces of wood &c. and upon this the charge of material is placed.
In the first instance care is taken to make a mixture of crude material with a
strong proportion of roasted material in form of powder resulting from the
preceding operations of the same apparatus (debris resulting from the disintegration
of the blocks) or coming from the outer layer of the heap of roasted small ore. In
place of roasted ore fragments of crude pyrites may be mixed with fragments of
ores poor in sulphur and containing a large proportion of quartz such as those
coming from the residues of the washing of the gangue of the furnaces and the
converters. A thick mud is made of this mixture which is charged on to the sides
and against the wall. At the centre the larger pieces are placed and at the sides
the smaller pieces. At distances apart are placed small horizontal circular pieces
of wood.
As soon as the layer has attained a moderate height the branches are ignited
and the blowing fan is set in motion so as to act first with a very slight pressure
(about of a centimetre of mercury) and increasing the pressure up to 2 centi-
metres of mercury. The casings are then completely filled up to the top and the
material is then raised at a slight incline up to the central wall so as to increase
the charge as much as possible. Care must be taken during the whole time of
charging to cause mud containing a small proportion of pyrites to flow against the
iron sides of the apparatus, and the operation is terminated by covering with a
thick mud the whole surface of the charge which is stamped down with a stamper.
During these operations, in order to prevent the fumes given off from annoying
the operators, only sufficient openings are uncovered to allow of the charging, the
other sheet iron flaps being left closed.
After from 3 to 4 hours the charging operation is completed and it then only
remains to watch the action. Every time that an incandescent place shows itself
in the charge from which a blue flame issues, such place is filled with the thick mud
having a small amount of pyrites which is always kept prepared ready at hand, or
in other words, the rising of the fire is prevented as much as possible.
As soon as the active combustion is finished, the operation is allowed to complete
itself and the mass is cooled. At the end of about 16 hours after the commence-
ment of the charging, the removal of the charge may be effected.
For this purpose
the keys which hold the iron plates are removed as are also such plates, and by
means of tongs acting as a lever the two formed blocks which readily detach them-
selves are made to fall out of the apparatus. Water is then thrown on these blocks
and by means of the blows of a hammer the large block is readily broken
pieces of the desired size for introducing into the smelting furnace. The powder
which results from such breaking is placed on one side for being used as above
described, in the next operation.
up
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The small ores actually treated coming from the upper mines of "Las Condes
(of Messrs. Elguin and of the Compagnie d'Exploitation des Bronces) are composed
of copper and iron pyrites with a quartz gangue containing from 18 to 20 per cent.
of copper from 28 to 30 per cent. of sulphur and about 18 to 20 per cent. of quartz
the remainder being arsenical iron.
The mattes produced by the direct smelting of the roasted ores in the apparatus
give from 52 to 55 per cent. of copper and this percentage may be considerably
increased, but this would not be advantageous on account of the losses in copper

page_text: which would result in the slags of the casting. It is even necessary to add to the
charge of the smelting furnace a certain quantity of crude pyrites for reducing the
percentages of copper of the mattes coming from the smelting of these ores treated
by my process.
By conducting the roasting with the necessary precautions, a spongy blackish
and very light mass is produced consisting of copper oxide containing hardly any
sulphur.
In this apparatus may be roasted white mattes (70 per cent. of copper) coming
from the converters, and previously ground to powder and granules and mixed with
small ore, being the residues of the washed earths, or with debris from the
furnace &c.
In melting down in the furnaces these roasted white mattes (which thus regain
the necessary cohesion) there is obtained directly without admixture of oxidised
ore, very fine metallic copper and, of course, a certain proportion of white mattes,
collected outside the moulds of the copper bars.
Thus the simple and single roastings in the said apparatus can replace the
roastings with two, three and even four fires, which it is necessary to apply to
the mattes in certain cases.
The operation is of the simplest, and does not require special operatives; the
apparatus can be worked during the worst weather without fear of interruption.
No sulphate of copper is formed which could, as in the other methods of roasting
be carried along by the water, causing considerable losses of copper and attacking
all the iron tools.
The chemical reactions produced allow of the obtaining without the least
addition of oxidised copper ores, directly from a first smelting, mattes having
a yield of 50 per cent., and, if desired, much higher.
As the physical condition of the mass produced during the roasting fulfils the
best conditions as to porosity and cohesion, a quantity thereof can be melted down
in 24 hours in a smelting furnace, which is equal to double that melted by the
existing processes.
Figures 4 and 5 shew in vertical and horizontal sections, a modification of the
above described apparatus. The small sides L of the apparatus instead of being
of movable sheet metal are of brickwork, forming fixed walls.
A brick wall E forming the longitudinal partition is extended along the entire
length, connecting the two lateral walls L L of the small sides and dividing the
apparatus completely in two by being extended up to the roof. Of course the
lower communication of the double bottom remains open along the entire length.
The admission of air is effected at the middle of the apparatus at C.
The hinged sheet metal flaps partly resting on the side walls, allow of a more
complete closing during the operations. Each compartment has no longer a
rectangular but a trapezoidal form, the larger side being the outer one; by this
means the discharge of the blocks will be much more easy, and being raised up, their
removal is further facilitated.
The central chimney F is of brickwork and has side openings o near the top.
The movable outer sides A A are each made with two metal sheets connected
together and forming a jacket 2 cms. wide, through which cold water is made to
circulate, which is discharged when the contents of the furnace are removed, the
circulation being reestablished when the apparatus is put in operation again.
By this circulation of water the sheet iron sides are protected from injury.
As shewn on the drawing, two or more apparatus may be combined with each other;
they have one side wall in common, and the air supply is distributed to the two
apparatus by means of a lateral flue T, imbedded in the ground and provided with
distributing valves.
Chains with counterweights fixed to the walls allow of the ready raising, to a
certain height of the two jacketted walls of sheet iron forming the external sides
and of thus leaving a free space during the discharging of the furnace.

page_text: With a double apparatus arranged in this way there will be no stoppage of the
process; the one apparatus is in operation while the other is cooling, discharging
and recharging, so that a great saving of time and labour is thus effected.
For special roasting operations requiring a very perfect treatment, there are
introduced into the compartments movable partitions formed of old sheet iron
coated with clay, for insuring the perfect diffusion of the gases throughout the
mass.
'
When the ores to be roasted contain very little sulphur and other combustible
matter, coke, coal or other fuel can be readily added for producing the necessary
reactions, and steam or other gases may also be introduced in place of or together
with air, for facilitating special reactions.
Lastly, the gases given off can readily be collected on issuing from the central
chimney and be conducted either to lead chambers for the manufacture of sulphuric
acid, or into any other apparatus.
The admission of air can always be so regulated as to produce any desired
composition of gases.
With this arrangement as with the preceding one the air pressure required is
very slight; the quantity of air supplied is as small as possible, so that the
sulphurous acid fumes can be utilised for the manufacture of sulphuric acid.
The principal applications of the above described process are as follows:-
1. The roasting of small sulphurous ores of copper, lead, silver, and other metals
(contained in pyrites gangues).
2. The roasting of mattes of copper, lead, silver, speiss and other intermediate
sulphurous arsenical or antimonical products of metallurgy.
3. The roasting of auriferous iron pyrites.
4. The roasting of iron pyrites for extracting sulphurous acid serving for the
manufacture of sulphuric acid, and oxide of iron.
5. The roasting of bituminous schistes containing copper or other substances.
6. The roasting of all other pulverulent substances for which it is desired to use
small coal or coke as fuel.
Lastly, for industrial applications for which under analogous conditions it is
desired to realise the greatest advantage as to simplicity and economy in roasting
or otherwise producing reactions between gases or vapours and solid bodies, either
in granular or pulverulent form.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The herein described process of roasting ores and the like wherein the perfect
diffusion of the air supply at a low pressure and of the gases produced by the fuel
and the charge, is insured throughout the same by dividing the mass by means of
internal partitions which oblige the air and gases to spread throughout the charge
so as to effect the uniform treatment thereof substantially as described.
2. The herein described construction of apparatus enabling the ready charging
of the ores and the easy removal of the products without risking the breakage of
the principal parts of the apparatus.
3. In apparatus such as is referred to in the preceding claims the employment
of jacketted sides to the apparatus which are subject to heat and to the attack of
the gases given off in which a circulation of water is maintained so as to protect
such sides from destruction, substantially as described.
4. The construction of apparatus for roasting ores herein described with reference
to the accompanying drawings.
Dated this 11th day of Habru 1902
ABEL & IMRAY,
Agents for the Applicant.