IMPROVEMENTS COLLECTION AND TREATMENT OF FLUE-DUST
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
We HUGH BARCLAY Metallurgical Chemist and ROBERT SIMPSON Chemical
Engineer, both of Harrington Iron Works, in the county of Cumberland do
hereby declare the nature of the said invention for "IMPROVEMENTS
COLLECTION AND TREATMENT OF FLUE-DUST" to be as follows:-
IN THE
The substance commonly known as flue dust is formed at a high temperature in
the blast furnace carried off in the vaporous condition with the ascending gases
and afterwards deposited in the solid state in the "down-comer," gas mains,
culverts, heaters, boilers and other flues.
It is generally considered a nuisance and hitherto has been treated as a waste
product.
The object of our invention is to collect this flue-dust, and treat it by the process
hereafter to be described for the extraction of Chloride sulphate, and carbonate of
Potassium and other alkaline salts. We also adopt a more systematic method of
collecting the flue-dust; this we effect by means of trays made of suitable material
placed vertically and horizontally in the flues and gas conduits by erecting dust
chambers, and trapsat various points; and by direct washing of the waste gases
with water, to extract any vapours not otherwise condensed.
Our process for the extraction of the alkaline salts is as follows: We place the flue-
dust in vessels constructed of wood, or other suitable material, fitted with stirrers and
steam pipes for stirring and beating the contents as occasion demands: Water is then
added to the vessels and contents stirred to effect complete solution of the alkaline
salts. The liquor obtained by washing the gases with water can be used for this
treatinent of the flue-dust. After some time we allow the insoluble residue to subside,
the supernatant liquor is then decanted off, filtered if very turbid; and passed by the
aid of a syphon or other ready means into vessels of suitable construction, where
it is evaporated to complete dryness. By this evaporation silica and silicates are
rendered insoluble, the residue is now treated with hot water, which dissolves the
potassium salts, leaves the silica and silicates, together with calcium sulphate and
other salts sparingly soluble in water: the solution thus obtained containing the
maximum quantity of Potassium salts is run off to another vessel where it is
evaporated to the required degree of concentration to allow the sulphate and
chloride of Potassium to be crystallized out separately and removed: the mother
liquors remaining contain the carbonate of Potassium which is separated by further
evaporation.

page_text: During our process we make careful analysis of the flue-dust and the various
liquors, and modify our process if desirable: for example if we find the solution
obtained by treatment of the flue-dust, contains only traces of silica or calcium
sulphate, we dispense with the first evaporation to dryness, and proceed direct to
separate the salts of Potassium as above described.
But in all cases the principle of our process is the same, namely, lixiviation of
the flue-dust in suitable vessels with water and the subsequent concentration of the
solution thus obtained to extract the sulphate, chloride and carbonate of Potassium
and other alkaline salts.
Our evaporations are effected by the waste heat from boilers and heaters.
The residue from the flue-dust insoluble in water, usually contains oxide of Iron,
this being so, we dry it, compress it into bricks with pitch or coal slack, and smelt
these in the blast furnace.
This invention is applicable for the treatment of flue-dust, produced in any of
the ordinary industrial processes.

page_text: COMPLETE SPECIFICATION.
We, HUGH BARCLAY, Metallurgical Chemist, and ROBERT SIMPSON, Chemical
Engineer, both of Harrington Iron Works in the County of Cumberland do
hereby declare the nature of our invention for "IMPROVEMENTS IN THE COLLECTION
AND TREATMENT OF FLUE-DUST and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement:-
The substance commonly known as flue dust is formed at a high temperature in
the Blast Furnace, carried off in the vaporous condition with the ascending gases
and afterwards deposited in the solid state in the "downcomer" gas mains, culverts,
heaters, boiler and other flues.
This flue-dust is generally considered a nuisance and hitherto has been treated
as a waste product.
The object of our invention is to collect this flue-dust and treat it by the process
hereafter to be described for the extraction of Chloride, sulphate and carbonate of
Potassium and other alkaline salts.
We also adopt a more systematic method of collecting the flue-dust, this wo
effect by means of trays, made of suitable material, placed horizontally and
obliquely in the flues and gas conduits; by erecting dust chambers and traps at
various points; and by direct washing of the waste gases with water to extract
any vapours not otherwise condensed.
Our process for the extraction of the alkaline salts is as follows:-
Wo place the flue-dust in vessels constructed of wood or other suitable material,
water is then added and solution aided by stirring and by direct agitation with
steam. (When the waste gases are washed with water the liquor thus obtained can
be used for this treatment of the flue-dust.)
After some time we allow the insoluble residue to subside the supernatant liquor
is then decanted off settled, and filtered, if very turbid, and passed by the aid of a
syphon or other ready means into vessels of suitable construction where it is
evaporated to dryness.
By this evaporation silica and silicates are rendered insoluble. The residue is
now treated with hot water, which dissolves the potassium salts and leaves the
silica and silicates, with sulphate of lime and other salts sparingly soluble in water;
the solution thus obtained containing the maximum quantity of potassium salts is
run off to another vessel where it is evaporated to the required degree of concentra-
tion to allow the sulphate and chloride to be separated: the mother liquor remaining
contains the carbonate which is obtained by further evaporation. During the
process we make careful analysis of the fluc-dust and the various liquors, and
modify the method of procedure if desirable, for example if we find the solution
obtained by treatment of the flue dust contains only traces of silica and sulphate
of line, we dispense with the first evaporation to dryness, and proceed direct to
separate the salts of potassium The distinct novelty in this invention being the
extraction of potash salts from a new source we do not bind ourselves to adopt
the lixiviation process herein before described; for as is well known to chemical
experts, the extraction of the potash salts could be effected by different processes
all for the most part being based on the solubilities of the various salts, and in

page_text: cases where cyanides or oxide of zinc is present some slight deviation from our
usual process would be required. After thorough exhaustion of the flue dust with
water, there is left a large quantity of insoluble matter, which we find always
contains Oxide of Iron. This being so, we form this residue into "bricks" with
pitch or purple ore, and smelt these in the Blast Furnace. We have made a
valuable raw material for Iron Smelting by mixing this insoluble residue with
purple ore in the proportion of one to ten. We do not claim novelty for the
lixiviation process hereinbefore described; for in some cases when we find a larger
proportion of Potash Salts than usual; we use the Flue dust in its crude state; but
having now particularly described and ascertained the nature of our said invention
and in what manner the same is to be performed, we declare that what we
claim is
(1), The methods as set forth for the systematic collection of the waste product
known to Iron Smelters as "fume " or flue dust.
(2), Obtaining from this flue dust, Salts of Potash, Sulphate of Lime, and Oxide
of Iron substantially in the manner described.