Improvements in the Treatment of Certain Minerals or Slag Con- taining Phosphate of Lime for the Purpose of Obtaining the latter in a Concentrated Form with or without the Production of Alkali as a Bye-product, and in Apparatus therefor.
Year: 1890

page_text: Date of Application, 13th Aug., 1890
Complete Specification Left, 1st Nov., 1890-Accepted, 27th Dec., 1890
PROVISIONAL SPECIFICATION.
Improvements in the Treatment of Certain Minerals or Slag Con-
taining Phosphate of Lime for the Purpose of Obtaining the
latter in a Concentrated Form with or without the Production
of Alkali as a Bye-product, and in Apparatus therefor.
I JAMES SIMPSON of SA Rumford Place Liverpool in the County of Lancaster
Alkali Manufacturer do hereby declare the nature of this invention to be as
follows:-
It is well known that minerals or slag containing only a small percentage of
phosphate of lime command but a low price per unit in comparison with those of a
higher grade. For this reason low grade minerals or slags are generally unsaleable
unless at prices which scarcely pay the cost of putting them on the market.
My invention relates to the treatment of such low grade minerals or slags in a
cheap and efficient manner whereby the line not combined with phosphoric acid may
be removed, the phosphate of lime contained in the mineral being thereby obtained in
a sufficiently concentrated condition for economical treatment with vitriol.
I effect this recult by converting the carbonate of lime and oxide of calcium in the
mineral into a soluble compound, when the insoluble phosphate will subside and may
he separated from the solution by decanting the latter.
In carrying out my invention I first roast the mineral. in a reverberatory or other
suitable furnace in order to convert the carbonate of lime into caustic lime, or oxide
of calcium, I then mix the roasted mineral with water and force sulphuretted hydrogen
through it in a series of towers or vessels so arranged that the gas shall pass from one
to the other, the said towers or vessels being sufficient in number and height to cause
the lime in the vessel receiving the fresh gas to be converted into sulphydrate of
calcium (Ca S, H₁) before any sulphuretted hydrogen begins to be evolved at the
final tower of the series. The treatment with sulphuretted hydrogen is then stopped
and the insoluble phosphate of lime is allowed to settle. The sulphydrate of calcium
liquor is then drawn off, and the phosphate of lime is removed, washed, dried or
filtered for use as required.
1 then treat the sulphydrate of calcium liquor from which the insoluble phosphate
of lime has been removed with carbonic acid gas in another series of towers and
employ the sulphuretted hydrogen which is given off for the treatment of a further
quantity of roasted mineral, and the operations are repeated. If during this operation
lime kiln gas is used for liberating the H, S the nitrogen mixed with it is allowed to
escape into the air preferably through a scrubber and an oxide of iron bed in order to
arrest any traces of sulphur.
An alternative method of working may be adopted whereby carbonate of soda may
be obtained with very little inconvenience or expense in conducting the operations
above described. This method of working consists in mixing a solution of sulphate
of soda or salt cake with the sulphydrate of calcium solution (after the phosphate of
lime has been separated from it) in proper proportions and at a suitable temperaturo,
when sulphide of sodium will be formed (or a mixture of sulphide and sulphydrate of
sodium) and hydrated sulphate of lime will be precipitated. The latter is suitable for
the manufacture of pearl hardening, plaster of Paris, or gypsum for agricultural
purposes. The sulphide of sodium formed in this operation is then treated in a
suitable carbonating apparatus (such as Solvay's towers) with carbonic acid gas when
bicarbonate of soda will be precipitated and sulphuretted hydrogen evolved. The
former is removed and treated by the well known methods for the manufacture of
commercial alkali, while the sulphuretted hydrogen is employed for the treatment

page_text: of a further quantity of the roasted mineral as before described, and the operations
are repeated.
Theoretically no loss of sulphur is incurred in this process the quantity employed
being used over and over again, but in practice it will be impossible to avoid a small
loss.
The carbonic acid given off in roasting the mineral and in converting the bicarbonate
of soda into mono carbonate may be employed in the process, but as it would not be
quite free from oxygen it ought to be conducted to the lime kiln.
Suitable apparatus under my invention consists of three series of towers with three
series of filter beds in combination with appliances for roasting the mineral and for
producing carbonic acid gas.
121
Per pro J. T. KING,
J. Johnson,
Agent.
COMPLETE SPECIFICATION.
Improvements in the Treatment of Certain Minerals or Slag Con-
taining Phosphate of Lime for the Purpose of Obtaining the
latter in a Concentrated Form with or without the Production
of Alkali as a Bye-product, and in Apparatus therefor.
I JAMES SIMPSON of 8 Rumford Place Liverpool in the County of Lancaster
Alkali Manufacturer 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:-
It is well known that minerals or slags containing only a small percentage of
phosphate of lime command but a low price per unit in comparison with those of
higher grade. For this reason low grade phosphatic minerals or slags are generally
unsaleable except at prices that scarcely pay the cost of putting them on the
market.
My invention relates to the treatment of such low grade minerals or slags (especially
to a certain mineral of this class known in France and Belgium as
" Craie grise") in
a cheap and efficient manner whereby the lime not combined with the phosphoric acid
may be removed and the phosphate of lime existing in the mineral thereby obtained
in a sufficiently concentrated condition for commercial purposes.
I effect this result by converting the lime (existing in the mineral as carbonate or
oxide) into a soluble compound-when the insoluble phosphate of lime will subside
and may be separated from the solution by decanting the latter.
In carrying my invention into practice I first roast the mineral in a reverberatory
or other suitable furnace in order to convert the carbonate of lime into caustic lime or
oxide of calcium, but in the case of slags in which the calcium exists already as oxide
I omit the roasting. I then mix the roasted mineral or slag containing oxide of
calcium, with water, and force gas containing sulphuretted hydrogen through it in a
series of towers or vessels so arranged that the gas shall pass successively through the
charge in each tower-the said towers or vessels being sufficient in number and
height to cause the lime in the vessel receiving the fresh gas to be converted into
sulphydrate of calcium (Ca S, H₂) before any sulphuretted hydrogen begins to be
evolved at the final tower of the series. The absorption of the sulphuretted hydrogen
in the mixture of lime and water is facilitated by conducting the operation under a
pressure of say 20 lbs. per square inch or over. The treatment with sulphuretted
hydrogen is then stopped and the insoluble phosphate of lime is allowed to settle or
subside. The sulphydrate of calcium liquor is then drawn off and the phosphate of
lime is removed-washed, dried or filtered for use as required.
I then treat the sulphydrate of calcium liquor from which the insoluble phosphate of
lime has been removed, with carbonic acid gas in another series of towers and employ

page_text: the sulphuretted bydrogen which is given off-for the treatment of a further quantity
of roasted mineral-and the operations are repeated.
If during the operation lime kiln gas is used for liberating the sulphuretted
hydrogen the nitrogen which is mixed with it is allowed to escape into the air-
preferably through a milk of lime scrubber and an oxide of iron bed to eliminate any
trace of sulphur.
An alternative method of working inay be adopted whereby carbonate of soda and
sulphate of lime may be obtained as bye products with very little inconvenience or
extra expense-while conducting the treatment of the phosphate of lime as above
described.
This method consists in mixing a solution of sulphate of soda with the sulphydrate
of calcium solution (after the phosphate of lime has been separated from it) in proper
proportions and at a suitable temperature-when sulphide of sodium (or a mixture of
sulphide and sulphydrate of sodium) will be formed and sulphate of lime will be
precipitated.
The latter is suitable for the manufacture of plaster of Paris or pearl hardening
for paper manufacture-or as gypsum for agricultural purposes.
The sulphide or
sulphydrate of sodium formed in this operation is then treated in a suitable carbonating
apparatus (such as Solvay's towers) with carbonic acid gas, when bi-carbonate of soda
will be precipitated and sulphuretted hydrogen will be given off. The former is
removed and treated for the manufacture of commercial alkali by well known
methods while the sulphuretted hydrogen is employed for the treatment of a further
quantity of the roasted inineral in water, and the operation is repeated.
The reaction between the sulphate of soda and calcium sulphydrate may be
facilitated by conducting the same under steam of a pressure of 60 to 70 lbs. per
square inch as sulphate of lime is insoluble at the temperature corresponding to this
steam pressure-but in order to avoid reverse action it is advisable to maintain the
pressure while the sulphydrate liquor is being drawn off. Or the aforesaid reaction
may be conducted at ordinary temperature by mixing a saturated solution of sulphate
of soda with about three times its volume of sulphydrate of calcium of a strength
containing about 14 to 15 per cent. of sulphur.
The solution of sulphide or sulphydrate of sodium resulting from this reaction being
too weak for the efficient production of bi-carbonate of soda-it is preferably con-
centrated by evaporation to the extent of about 40 per cent. before being treated
with carbonic acid. Further concentrations are also necessary for the removal of
the whole of the alkali as bi-carbonate-as the removal of the latter reduces the
specific gravity of the solution.
The diagram herewith illustrates a combination of apparatus required in carrying
my invention into effect. a, a, represents a lime kiln and scrubber, b blowing
engine, c, d, e, three series of absorbing vessels in which the reactions between the
sulphide of sodium and (CO2), between the ground roasted mineral and sulphuretted
hydrogen, and between the sulphydrate of calcium and sulphate of soda respectively
are carried out, f, g, h, three sets of filter beds, i, furnaces, j, pipe and valve con-
nections. In the vessels c sulphide of sodium in solution is acted on by carbonic
acid gas from the kiln a, and bi-carbonate of soda is precipitated whilst sulphuretted
hydrogen is evolved. The bi-carbonate is run on the filter, whilst the sulphuretted
hydrogen passes through the series of vessels d, containing ground mineral mixed
with water after being roasted in the furnace i. Any nitrogen or inert gas passes
away from the vessels d, whilst the sulphydrate of calcium obtained is run into the
series of vessels e, the insoluble phosphate being left in the filter g. Salt-cake is
mixed with the sulphydrate of calcium in the vessels e, and sulphate of lime and
sulphide of sodium are formed which latter is run into the vessels c, whilst the
sulphate of lime is separated out on the filter h.
Theoretically no loss of sulphur is incurred in the above process, the quantity
employed being used over and over again, but in practice it will be impossible to
avoid a small loss, and a portion of the precip.tated sulphate of lime may be used to
compensate for the small loss of sulphuretted hydrogen (which is inevitable in

page_text: manufacture) by reducing it to sulphide by the well known method of roasting with
carbonaceous matter.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
First. The above described method of removing the lime existing as carbonate or
oxide in minerals or slags containing phosphate of lime from the said phosphate in the
form of sulphydrate of calcium in solution, or as a mixture of sulphydrate and
sulphide of calcium.
Second. In the above described method of obtaining sulphydrate of calcium
employing sulphuretted hydrogen under pressure substantially as set forth.
Third. In combination with the above described method of treating phosphatic
minerals or slags, the method of making carbonate or bi-carbonate of soda, sub-
stantially as set forth.
Fourth. The combination of apparatus substantially as and for the purpose set
forth.
Dated this Thirtieth day of October 1890.
Per pro J. T. KING,
W. B. Johnson,
Agent.