AN IMPROVED PROCESS FOR SEPARATING SUBSTANCES FROM PHOSPHATE OF LIME
Year: 1885

page_text: I, THOMAS RICHARD SHILLITO of 89 Chancery Lane, in the County of Middlesex,
Engineer, do hereby declare the nature of said invention for "AN IMPROVED
PROCESS FOR SEPARATING SUBSTANCES FROM PHOSPHATE OF LIME" a communica
tion to me from abroad by Emil Hänisch and Max Schroeder of the Village of
Neumühl-Hamborn near Oberhausen in the Kingdom of Prussia, Engineers, to be
as follows:-
21
The process of this invention is based on the known property of sulphurous
acid of dissolving basic phosphate of lime in the cold state, when acid phosphate
of lime and acid sulphite of lime is produced, as also on the property possessed by.
phosphoric acid at boiling heat to again expel the sulphurous acid from the bodies
formed by the dissolution of the said sulphurous acid, and to become precipitated
as basic phosphate. By this means, the phosphate of lime may be separated from
those substances or bodies accompanying it which are insoluble in sulphurous acid.
In order to separate the substances soluble in sulphurous acid a special treatment
is requisite for which purpose the lime is converted into gypsum by adding to the
pulverised material the quantity of sulphuric acid necessary for binding the excess
lime, an intimate mixture being obtained by stirring. This composition is formed
into blocks and, heated to red heat, giving a porous material which is broken up
into pieces and treated with sulphurous acid as hereinafter described. Bones from
which the fat has been removed, or the substances prepared as before mentioned,
from which phosphate of lime is to be obtained are placed in vats arranged on the
contrary current principle and supplied with watery sulphurous acid, the latter
being introduced in the form of a concentrated gas into a reservoir charged with
water or lye. Then the lye is heated in lead pans up to from 60 to 70 degrees
Celsius, first by direct fire and later by means of a steam blast. The phosphate of
lime now becomes precipitated whilst the SO, gases together, with the water
vapours are absorbed in absorbing chambers.
"
The phosphate of lime precipitate is heated in a calcining furnace. The lye still
containing the remainder of the phosphate of lime is passed into a tower where it
is caused to flow against a current of SO, gases in order to saturate it with
SO, gases.

page_text: -
I, THOMAS RICHARD SHILLITO of 89 Chancery Lane, in the County of Middlesex,
Engineer, do hereby declare the nature of said invention for "AN IMPROVED
PROCESS FOR SEPARATING BUBSTANCES FROM PHOSPHATE OF LIME" a communica-
tion to me from abroad by Emil Hänisch and Max Schroeder of the Village of
Neumühl-Hamborn, near Oberhausen, in the Kingdom of Prussia, Engineers, and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
The process of this invention is based on the known property possessed by
sulphurous acid of dissolving basic phosphate of lime in the cold state, whereupon
acid phosphate of lime, and acid sulphite of lime is produced, as also on the
property possessed by phosphoric acid at boiling heat to again expel the sulphurous
acid therefrom, and become precipitated as basic phosphate. It differs from other
processes having the same object in view, in that it aims at reducing the loss in
acid used for disaggregating the phosphate of lime and at preventing the formation
of waste lye.
For dissolving, and separating the neutral phosphate of lime from the other
substances accompanying it, watery sulphurous acid is exclusively employed.
By the aforesaid means phosphate of lime may be separated from all those
substances which are insoluble in sulphurous acid, but not from substances which
sulphurous acid is capable of dissolving, as these latter upon the expulsion of the
sulphurous acid would also pass over into the insoluble state and consequently
remain mixed with the precipitated phosphate of lime. In order to be. able to
apply this process also to these substances, they require a special preliminary
treatment. All substances containing phosphate of lime, are, with reference to this
process, divided into two classes, the one comprising such substances, which,
consisting mainly of phosphate of lime only contain in addition, substances that are
insoluble in sulphurous acid; to this class belong bones, and phosphate of lime
poor in excess lime, chiefly containing insoluble gangue, the other comprising such
substances which besides phosphate of lime, further contain substances soluble in
sulphurous acid, such as Thomas" slag and phosphate of lime (phosphorite) rich
in excess lime. Of all the substances comprised in the second class, which are
disadvantageous to this process, excess free or also carbonate of lime is the more so.
As this lime together with the phosphate of lime present, becomes similarly
dissolved in the sulphurous acid, but cannot be fixed upon the expulsion of the
sulphurous acid by the phosphoric acid, it must yield a neutral sulphurous lime
and lower the percentage of the phosphoric acid contents of the precipitate
obtained, the object of the process thus not being effected. Thus, taking this as
an example, it is not possible in this way to obtain any increase in phosphoric acid
66

page_text: contents from "Thomas" slag which on an average contains with 16 per cent of
phosphoric acid about 50 per cent of lime. As the 16 per cent of phosphoric acid
can only bind about 19 per cent of lime in the state of the tri-basic salt, whilst
the other 31 per cent of lime is precipitated as neutral sulphurous lime with about
34 per cent of sulphurous acid, and remains mixed with the phosphate of lime,
the precipitate received will thus contain no more phosphoric acid than the original
Thomas" slag, quite apart from the iron and manganese compounds which
similarly pass over into the precipitate. The excess lime must therefore in the case
of the substances of the second class, be carried over into a compound in which it
is not soluble in sulphurous acid.
"
For this purpose the lime is converted into gypsum by adding to the pulverised
material the quantity of sulphuric acid necessary for binding the excess lime an
intimate mixture thereof being obtained by stirring. This pasty composition is
formed into blocks and then heated to red heat in a calcining furnace, in order, on
the one hand, to form a porous body by driving out the water from the formed
gypsum, and, on the other hand, to decompose the iron and manganese sulphates
formed at the same time, so that the whole of the sulphuric acid bound by these
bases into soluble sulphate exceeds the lime, and the said metal salts are again
converted into oxide. The porous substance so produced is broken into pieces and
treated with sulphurous acid, to which end I employ apparatus such as shewn in
the accompanying drawings in which Fig. 1 is a plan of the same and Figs. 2, 3, 4, 5,
6, 7, 8 sections taken respectively through the lines A B.C D—E F—Ĩ K―GH—
LM-NO of Fig. 1.
Bones from which the fat has been removed, or the aforesaid specially preprepared
substances are placed in air tight vessels a, and here systematically lixiviated with
watery sulphurous acid on the contrary current principle, the previously enriched
lye always acting on the freshly charged material. In order to obtain for the
purposes of this process a sufficiently concentrated watery sulphurous acid I employ
liquid compressed sulphurous acid, which by its own pressure within the vessel b is
forced to pass out of this latter through the pipe 6 into the coil b2 and thence
into the reservoir c supplied with water or lye, a strong solution being produced
under immediate cold producing gasification. The flow of this solution to the
extracting vessels a placed lower down takes place through the pipe d and the
overflow of the lye from one extracting vessel to the succeeding one through
pipe 6. The saturated lye after passing through the extracting vessels a passes by.
air pressure through pipe f to the higher placed covered collecting vessel g and
thence to the air tight closed lead pans h in which the lye is heated up to from 60
to 70 degrees Celsius. In this case the heating is effected by the waste heat
coming from the calcining furnace. The further heating is effected by blowing in
steam, as owing to the formation of a heavy precipitate, more direct firing is
unsuitable and would cause violent shocks. To this end the lye is drawn off
through the pipe i into the precipitating cylinder k (see Figs. 6 and 7) and high
pressure steam blown into the same through pipe 7, by which SO² is generated
this resulting in the phosphate of lime freed from its dissolving medium becoming
again separated as tri-basic salt in the form of a heavy crystalline precipitate,
whilst the generated S O' gases are conveyed with the water steam through the
cooling worm m immediately above, and thence in a cooled state through pipe n
to the air tight absorbing chests o where they are absorbed.
'
In this way from 85 to 90 per cent of the phosphate of lime may be conveniently
precipitated from the lye. The lye still retaining the remainder of the phosphate
of lime is after rapid clarification drawn off through cocks into the cooler q.
Seeing, as before mentioned, that the material most lixiviated, is at its last
lixiviation treated with the richest SO* solution, it occurs that when this solution
has been drawn off, a portion of the same remains mechanically held in the material.
In order that this portion may not be allowed to run to waste with the washing
waters, the cooled precipitating lye is used for the first or second washing. For

page_text: this purpose the said lye is conveyed by means of a pump through pipe 8 to
the corresponding extracting vessel and then carried back through pipe t up into
the reservoir u of the absorbing tower, thence it flows down into the tower V
charged with a suitable material (see Fig. 5) passing out of the same into the
aforesaid absorbing chests o, whilst the SO2 gases generated in the precipitating
cylinder flow against it in an opposite direction through pipe w and effect a
saturation of the lye with SO. From o, the lye passes through cock into the
reservoir c to commence over again its circulation through the extracting vessels a.
If, in this process no loss in SO' took place it would not be necessary to make
any addition thereto. As, however; both in the precipitation of the phosphate
of lime, some sulphurous lime is always taken down with it, and some loss of
the same may take place in the absorbing chests o and tower V, through a not
thoroughly complete absorbing action, such loss must be made good. This is done
in the reservoir c, by causing concentrated gases from the SO container b to
enter into the liquid until it again possesses the same quantity thereof as before,
when it commenced its circulation through the apparatus. From o the enriched SO
solution passes again through pipe d into the extracting vessels a and performs the
same circuit until it is so loaded with foreign impure substances that it is deemed
advisable to replace it with fresh water.
The precipitate formed in the precipitating cylinder k is, after the liquid has
been drawn off, removed through the door y and passed on to the calcining furnace z.
The heating operation in this furnace has for object not only to dry the precipitate
but to oxidise and convert the sulphurous lime-which it has taken down with
it in small quantities into gypsum, so that upon disaggregating the phosphate
with sulphuric acid no SO2 gases which are troublesome to the operatives, are
evolved, and also, further, so that these S O³ contents are at the same time
favourable to the disaggregating process.
The solution of phosphate of lime in watery sulphurous acid received after the
main process, would, for expelling the SO and for precipitating the phosphate of
lime, according to the usual method, be heated by means of steam to boiling
temperature and then drawn off direct from the precipitating vessel, for filtration,
but as the sulphurous acid, down to the last traces, cannot be removed from the
solution by the application of steam, some of this, laden with sulphurous acid
escapes in the passage and filtration of the boiling hot solution, and annoyingly
pervades the works. On the other hand, it is only with difficulty that the lye
mixed with the phosphate precipitate can be cooled in closed cooling apparatus
by indirect water cooling previous to filtration, because the phosphate precipitate
causes obstruction and also because the cooling surfaces soon become incrusted with
phosphate of lime and therefore ineffective..
By the process of this invention, the lye treated with steam is cooled in the
precipitating cylinder itself before filtering off the phosphate precipitate, and in
effect, when the steam is turned off a strong stream of cold air is blown therein,
which both by reason of its own low temperature, and of the cutting off of the
steam soon cools the lye. At the same time it carries with it traces of sulphurous
acid, so that in this way a liquid is obtained which not only possesses less SO, but
this latter owing to the low temperature is less freely liberated than from the lye
drawn off directly after blowing steam into it.
For carrying out this combined precipitating and cooling process we prefer the
arrangement shewn in Figs. 9, 10, and 11 which consists of three precipitating
cylinders lined with lead, in connection with each other. through pipes. The steam
blown into cylinder I for precipitating the phosphate, passes in so far as it is not
condensed, mixed with the S O' drawn from the lye, at once to cylinder II in order
that the fresh lye present in this latter may be previously warmed by the waste
heat coming from cylinder I. From the cylinder II the S O' now fairly free from
steam is conducted to the absorbing chests for regeneration. At the same time as
the heating and precipitating operations are effected in cylinders I and II the lye
'

page_text: already heated and precipitated in such operations is, in cylinder III cooled again
by blowing in air. For this purpose the same lead worm is used which has pre-
viously served for blowing in the steam. The vapours evolved, and air containing
traces of sulphurous acid, are carried into the chimney through a special pipe.
When these operations have been carried out, the process is proceeded with by
drawing the cooled lye off from cylinder III through valve k (Fig. 11) into
filtering chests and then filling this cylinder with fresh phosphate lye. In the
operations now to be carried out the valves are so arranged that direct steam is let
into cylinder II charged with previously warmed lye, and into the freshly charged
cylinder III the waste steam from cylinder II, whilst cylinder I charged with lye
is subjected to the air cooling process. The arrangement of the several pipes
and valves which is alike for the several cylinders is clearly shewn in the drawings
and to an enlarged scale in Fig. 11 with reference to which latter their relative
positions may be described. Of the six horizontal pipes which are in connection
with the cylinders I, II, III, by means of branches and valves, a serves for supplying
the fresh lye; b for steam, and c for air; d is the pipe for carrying off the
evolved SO to the absorbing chests; e for conducting away the air mixed with
vapour which escapes in the cooling process; f connects the several cylinders
together. When the cylinder I has been freshly charged with lye through valve
and pipe a steam is blown into the same by opening the valve on b and permitting
it to pass through pipe and worm g. The steam heats the lye and causes the S 0°
to escape therefrom and flow past valve h into the common connecting pipe f. All
the valves except 6 and.h are at this time closed to the cylinder I. The SO2 still
containing much steam passes along the pipe f to the cylinder II, entering it
through the opened valve i and pipe and worm g penetrating through the fresh lye
in the cylinder and at the same time losing steam until nearly free therefrom
whereupon it passes through valve and pipe d to the absorbing chests. During
this interval all the valves other than i and d are closed to this cylinder. The
third cylinder, whilst steam is being blown into cylinders I and II serves for
cooling the hot lye still mixed with the precipitate which remains behind in the
said cylinder. It is closed to all the valves except the air supply valve c and the
discharge valve. When these respective portions of the process are finished,
the cylinder III is emptied by opening the valve k, and is then charged with fresh
lye, whereupon by reversing the position of the several valves the operations are
so conducted, that now cylinder I is cooled by air blast; II heated by steam blast
and III preliminarily heated by waste steam and so on over again.
.
The lye discharged through valve k is drawn off into the filtering chest 7 for the
purpose of separating the precipitate therefrom, thence, for its complete refrige-
ration, it is conducted into the lye cooler m acting by indirect water cooling,
after which it passes into a collecting vessel n and from here is raised to the
absorbing chests for re-use.
Having now particularly described and ascertained the nature of said inven-
tion and in what manner the same is to be performed, I declare that what
I claim is :
1. The process of fixing with sulphuric acid the excess lime present in substances
containing phosphate of lime with the object of rendering it insoluble in watery
sulphurous acid, substantially as described and shewn.
2. The separation of the phosphate of lime from its solutions in sulphurous acid
by heat and application of steam blast, substantially as described and shewn.
3.. The re-use of the cooled liquid drawn off from the phosphate of lime for the
purpose of absorbing the sulphurous acid substantially as described and shewn.
4. The application of liquid compressed S O' to compensate for the loss in SO*
which may occur in the process, substantially as described and shewn.
5. The roasting of the precipitate for the purpose of oxidising the sulphurous
lime contained in it, substantially as described and shewn,

page_text: 6. The process of cooling in the precipitating vessel itself, by means of a blast
of cold air, the solution of lime phosphate in watery sulphurous acid which has
been heated to boiling temperature by steam blast-previous to filtering off the
separate precipitate substantially as described and shewn.
7. The combination of the precipitating vessels with each other in the manner
that the operations of preliminarily heating, of blowing in steam, and of cooling by
means of air may be carried out and transferred from one of the said vessels to
the other in progressive order continuously, substantially as shewn and described.
Dated this 20th day of September 1886