CA1084957A - Plaster made from ferrous sulphate - Google Patents
Plaster made from ferrous sulphateInfo
- Publication number
- CA1084957A CA1084957A CA286,718A CA286718A CA1084957A CA 1084957 A CA1084957 A CA 1084957A CA 286718 A CA286718 A CA 286718A CA 1084957 A CA1084957 A CA 1084957A
- Authority
- CA
- Canada
- Prior art keywords
- reaction mixture
- ferrous sulphate
- plaster
- calcium
- ground
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
ABSTRACT
A plaster for use in the production of surface coatings, moulds and moulded artifacts can be made from ferrous sulphate, for example industrial waste ferrous sulphate in the form of copperas. The process involves heating a slurry or solution of the ferrous sulphate and a suitable calcium compound, which may be ground limestone, ground chalk, slaked lime or quicklime, under elevated temperature and pressure. The resulting crystalline product can be formed into a powder or used directly as a slurry and gives properties similar to commercial gypsum based plasters.
A plaster for use in the production of surface coatings, moulds and moulded artifacts can be made from ferrous sulphate, for example industrial waste ferrous sulphate in the form of copperas. The process involves heating a slurry or solution of the ferrous sulphate and a suitable calcium compound, which may be ground limestone, ground chalk, slaked lime or quicklime, under elevated temperature and pressure. The resulting crystalline product can be formed into a powder or used directly as a slurry and gives properties similar to commercial gypsum based plasters.
Description
10849~7 T~ lnvention relates to fcrrous sulphate.
Ferrous sulphate, known as copperas in its heptahydrate crystalline form, is produced in considerable quantities as a by-product in certain major industrial processes. In the "sulphate" process for the production of titanium dioxide by-product ferrous sulphate is produced both as copperas and as waste liquors containing, for example, up to 300 g/l - ferrous sulphate and up to 300 g/l free sulphuric acid. In sulphuric acid pickling processes waste liquors are produced containing, for example, up to 460 g/l ferrous sulphate and up to 90 g/l free sulphuric acid. Liquors containing ferrous sulphate cannot legally be dlscharged as effluent in many countries and their disposal is a major problem.
The present invention relates to the alleviation of this problem by the utilisation of ferrous sulphate. More particularly the present invention relates to the production of a plaster utilising ferrous sulphate as raw material.
By plaster we mean a material comprising one or more at least partially dehydrated compounds which on contact with water recrystallise in a higher state of hydratlon thereby causing the material to set, said material being usable to form, for example, surface coatings on the interior walls and ceilings of buildings, moulds for use in the manufacture of articles or moulded artifacts. The most c~only used plaster consists essentially of calcium sulphate hemihydrate produced from gypsum and is a relatively cheap and abundant product.
Ferrous sulphate, known as copperas in its heptahydrate crystalline form, is produced in considerable quantities as a by-product in certain major industrial processes. In the "sulphate" process for the production of titanium dioxide by-product ferrous sulphate is produced both as copperas and as waste liquors containing, for example, up to 300 g/l - ferrous sulphate and up to 300 g/l free sulphuric acid. In sulphuric acid pickling processes waste liquors are produced containing, for example, up to 460 g/l ferrous sulphate and up to 90 g/l free sulphuric acid. Liquors containing ferrous sulphate cannot legally be dlscharged as effluent in many countries and their disposal is a major problem.
The present invention relates to the alleviation of this problem by the utilisation of ferrous sulphate. More particularly the present invention relates to the production of a plaster utilising ferrous sulphate as raw material.
By plaster we mean a material comprising one or more at least partially dehydrated compounds which on contact with water recrystallise in a higher state of hydratlon thereby causing the material to set, said material being usable to form, for example, surface coatings on the interior walls and ceilings of buildings, moulds for use in the manufacture of articles or moulded artifacts. The most c~only used plaster consists essentially of calcium sulphate hemihydrate produced from gypsum and is a relatively cheap and abundant product.
- 2 -oP76 ~084~7 The present invention provides a process for the manu$acture of a plaster from ferrous sulphate comprising forming a reaction mixture consisting essentially of ferrous sulphate, any free acid therein having been neutralised, and one or more calcium compounds selected from calcium carbonate, calcium hydroxide and calcium oxide, in an aqueous medium, heatiny the reaction mixture in the presence of steam at a temperature greater than 100C and under a pressure greater than atmospheric pressure to form a crystalline plaster product.
Preferably the ferrous sulpnate is ferrous sulphate heptahydrate.
The ferrous sulphate may be in the form of a l~quor produced as a by-product by an industrial process as above described and generally containiny a proportion of free sulphuric acid. According to the invention any such free acid is neutralised with, for example, a calcium compound, thereby forming calcium sulphate dihydrate or synthetic gypsum,when the free acid is sulphuric acid. The higher the proportion of the sulphuric acid in the ferrous sulphate the higher the proportion of synthetic gypsum formed.
Preferably any free acid present in the ferrous sulphate is neutralised by reaction with the one or more calcium compounds used to form the reaction mixture and in the course of the formation of the reaction mixture, sufficient additional calcium compound being added to ach~eve this, and the resulting acid salt remaining in the reaction mixture.
10t~45~S7 I~ is not necessary, however, in the present invention for any free sulphuric acid to be present, the neutralisation step merely being omitted if none is present.
In tenms of the properties of the product we can obtain S at least some benefit according to the present invention over a very wide range of ratios o~ ferrous sulphate to sulphuric acid. The preferred molar ratio of ferrous sulphate to free acid is from 1:0 to 1:6.
The present invention may involve a drying step and it may therefore be advantageous to ensure that as little water as is possible is present during the earlier stages of the process. L1quors resulting from industrial processes are generally dilute making necessary the use of a more extensive dewatering and drying plant than might otherwise be necessary.
lS Preferably, therefore, the ferrous sulphate is in the form of copperas which has been dissolved or slurried in a relatively small amount of water or,preIerably, dissolved in a ferrous sulphate containing liquor as above described. The amount of water added may be relatively small in view of the release of water of crystallisation from the copperas. Preferably the amount of water used apart from the water of crystallisation present in the ferrous sulphate heptahydrate is from 4 to 100 and particularly preferably from 20 to 50 ml/lOOg ferrous sulphate heptahydrate.
According to a preferred feature of this invention the ca,lcium compound is calcium carbonate in the form of ground limestone or ground chalk. Such forms of calcium carbonate 108~9~7 do not react to completion with ferrous sulphate under normal pressure and at temperatures below 100C, and what reaction there is is generally slower than the reaction between ferrous sulphate and calcium oxide (quicklime) or calcium hydroxide (slaked lime). Under conditions utilised in carrying out the present invention, as hereafter described, these forms of calcium carbonate may be made to react with ferrous sulphate sufficiently readily to represent an advantage in using such raw materials in comparison with using lime bearing in mind the relative raw material costs involved. Where the sole calcium compounds used are calcium o~ide and/or calcium hydroxide theyare preferably used in at least the amount required in theory to react with the sulphate ion present and in not more than 30% ex_ess over that amount.
Where the sole calcium compound used is calcium carbonate it is preferably used in excess over the amount required in theory to react with the sulphate ion present and particularly preferably is used in an excess over that amount of at least 5~ and, for exa~ple, up to 30% on a molar basis. When we refer to sulphate ion we include that derived from any free acid originally present.
The reaction mixture is suitably formed by adding the calcium compound to a mixture of the ferrous sulphate and water. The calcium compound will react fairly readily with any free sulphuric acid present and for this reason it may be desirable to control the rate of addition of the calcium compound so as to ensure that this initial reaation proceeds smoothly.
10~49S7 The reaction mixture is preferably maintained at the required t~nperature and pressure by heating it in an auto-clare, e.g. in the presence of water vapour at a temperature not greater than 175C and particularly preferably at a temperature of from 115C to 160C. The autoclave need not be vented. Preferably a vented autoclave is used controlled to give an internal pressure of from 10 to 50 pounds per square inch gauge (psig). The duration of treatment in the autoclave is that required for completion of the reaction ~etween the calcium compound and the ferrous sulphate hepta-hydrate and the formation of a product which on drying will give the required properties in use and this duration will depend on the particular temperature and pressure used.
Preferably the reaction in the autoclave is conducted for from 1 hour to 10 hours and particularly preferably from 2 hours to 6 hours in total.
To ensure a reasonable speed of reaction the particle size of the ground limestone or ground chalk is preferably such that at least 60% by weight and particularly preferably at least 95% by weight has a particle size below 53 microns.
Preferably as large a proportion as possible of the reaction between ferrous sulphate and the calcium compound occurs at a super-atmospheric pressure and a temperature greater than 100C. Prefera~ly~ therefore, the temperature of the reaction mixture is maintained at below 100C and preferably below 80C during the formation thereof, thereby ~inimising reaction until the required super-atmospheric 1()~4~7 pressule can be generated.
Even under the conditions used in carrying out the present invention the reaction between ferrous sulphate and calcium carbonate in the form of ground limestone or ground chalk will not normally go to completion.
It i5 preferred to ensure reaction of all of the ferrous sulphate since the p~esence of residual ferrous sulphate in the plaster product of the present invention may result in undesirable characteristics in said plaster caused, for example, by leaching of the ferrous sulphate from the plaster. Prefer-ably, therefore, to ensure reaction of all of the ferrous sulphate, a quantity of calcium oxide or hydroxide is added to the reaction mixture.
Preferably the quantity of added calcium hydroxide or oxide is sufficient in theory to react with between 5% and 40% and particularly preferably with ~rom 5% to 25% of the sulphate ion derived from the ferrous sulphate originally incorporated in the reaction mixture. In this case it is possible, to use less than the quantity of calcium carbonate required in theory to ~eact with the sulphate ion present although for economy it is still desirable to use re than 80%, preferably more than 95%, of that quantity. The ~eaction between the ferrous sulphate and the calcium hydroxide or calcium oxide is also preferably conducted under like conditions of temperature and pressure as the reaction with the calcium carbonate. The maintenance of a temperature of the reaction charge above 80C is important, to prevent undue deterioration of the properties of the final product, ~0~'3~7 while a reaction temperature above 100C is necessary for t'ne formation of that product. Any material added to the reaction charge, therefore, are desirably conducted so as to maintain the temperature thereafter to at least 80 C.
This may be achieved, for example, by preheating such material to at least 80C preferably to at least 95C.
Any water remaining in the product formed in the auto-clave may be removed by drying which may be conducted in air, for example in a tunnel drier. If a substantial proportion of the water originally present in the reaction mixture has not been removed by, for example, using a vented autoclave, it may be necessary to precede the drying step by a dewatering step including, for example, filtration or centrifuge treatment. Preferably, the temperature of the product is maintained at, at least, 80C to prevent deterioration thereof, e.g. at from 85C
to 125C and particularly preferably at a temperature of from 100C to 125C until the conclusion of any dewaterins or drying thereof. The duration of the dryin~ step may be, for example, up to 24 hours. ,-The dried product may be puIverised and mixed with appropriate additives known in the art for the control of the properties of plaster of Paris to form a plaster powder.
This powder material may be mixed with ~ater to form a settable plaster mixture which may be used as a wall surface covering or as a material for the construction of moulds or of moulded artifacts. Alternatively the plaster product formed by the said heating of the reaction mixture in the iO~'3~7 autoclave may be directly formed, with tlle addition or removal of the requiTed quantity of ~ater to obtain the correct consistency and of any appropTiate additives as described above, into a plaster mix and shaped into desired artifacts, for example, blocks, tubes, rods or sheets.
The product of the present invention shows some properties similar to those of conventional plaster~ However, despite the very high content of iron compounds in the said product, particularly where ferrous sulphate has been the sole, or substantially the sole, source of sulphate ion we have found that the product of the present invention may be either non-magnetic or only slightly magnetic. In contrast, the product obtained by forming the same reaction mixture and heating it in air is relatively highly magnetic.
We therefore believe that the restricted access of oxygen to the reaction mixture resulting from heating in an autoclave in the presence of water vapour prevents, or reduces, the formation of magnetic iron oxides. This is an important feature of the present invention since in many uses of a plaster the presence of magnetic materials would be undesirable. One way of limiting the contact between the autoclave charge and such oxygen as may be in the autoclave initially, or as may be admitted to it by opening the autoclave during processing is to arrange that the autoclave charge 2a presents a relatively small surface area to the atmosphere in the autoclave.
When the autoclave charge is spread on shallow rays a more magnetic product may be formed than when the autoclave charge is confined in a relatively deep layer.
~0~S7 The present invention will now be illustrated by means of the following Examples.
278g of copperas (10 moles) containing less than 2~ of free sulphuric acid was slurried in 1 1 water in a 5 1 beaker at a temperature of 60C. lOOOy of natural dry chalk (10 moles) was ground in a micropulveriser until at least 95% by weight of the particles had a greatest particle diameter of 53 microns. The ground chalk was added to the copperas slurry over 30 minutes the addition being conducted particularly carefully until the free acid had been neutralised. The slurry was then stirred in the neakér for 15 minutes while maintaining the temperature at 60C. The slurry was then placed in an unstirred autoclave for 3 hours at a temperature of 126C and an internal pressure of 22 psig.
After 3 hours the autoclave was vented off to atmospheric pressure and the contents stirred while the temperature remained at above 95 C.
137.5g calcium hydroxide was slurried in 400 ml boiling water and was added to the slurry over 15 seconds which slurry was then stirred vigorously for 4 minutes after which time it had a pH of 7.7. The slurry was then returned to the auto-clave for a further 1 hour at a temperature of 126C and a pressure of 22 psig. The autoclave was vented off to atmospheric pressure and the contents reslurried, and filtered at a temperature of 85 C over 4 minutes. The hot filter cake 10~4'~57 was discharged onto a steel tray, chopped into ~" lumps and dried in an air oven for 17 hours at a temperature of 120C.
The dried product was discharged, cooled and ground. It was substantially non-magnetic. The filtrate showed a content of less than 1 ppm of Fe 2 showing that substantially all of the iron content of the copperas had remained in the product. The resulting product, tested as a plaster, showed a setting time of 6.5 minutes and a water demand of 44 mls/
lOOg under standard conditions.
To 30g of the product was added 0.3g calcium hydroxide and 0.04g keratin and the resulting mixture having a pH of 10.0 was micropulverised. When tested as a plaster the product showed a setting time of 50 minutes under the same standard conditions.
A series of plasters manufactured by a process sub-stantially as in the above Example showed a water demand of from 30 to 48 ml/lOOg in comparison with a commercial plaster manufactured fro~ natural gypsum which showed a water demand of from 36-40 ml/lOOg. A 100 mm cube made from plaster manufactured substantially according to the above Example showed a compressive strength of 41 kN/100 mm2 in contrast to a similar cube made from the commercial plaster which showed a compressive strength of 37 kN/100 mm2. The density of the plaster manufactured from products manufactured substantially as in the above Example was from 1.2 to 1.8 g/cc.
10~57 122.5g copperas containing less than 2~ free sulphuric acid was slurried in 8.8 galls water in a stirred tank and the slurry agitated whilst live steam was sparged lnto the tank to raise the temperature of the slurry to 65C. 44.lg natural dry chalk of which at least 95~ by weight had a greate~t particle diameter of 53 microns was added to the tank from a vibrating hopper over ~ hour. This reduced the slurry temperature to 45C. The slurry was then pumped into a warmed 20 gall autoclave filled with a stirrer, a pressure control valve, an inlet port which could operate under pressure and a bottom drain exit port. The slurry was sparged with steam to raise its temperature to 70C after which the autoclave was sealed. The autoclave in~erior was raised to a temperature of 126C and a pressure of 40 psig over a time of 1 hour 10 minutes while stirring.
These conditions were maintained for 3~ hours maintaining stirring. The pressure was then vented down to a pressure of 22 psig stirring being continued. 6.2 lbs lime in 2 galls of near boiling water were pumped into the autoclave under a pressure of 25 psig over a time of 5 minutes 5 seconds.
The conditions in the autoclave were then maintained under stirring at a temperature of 126C and a pressure of 22 psig for a further time of 1 hour. The slurry was then pumped over a time of 5 minutes from the autoclave into a filter press, which had been prewarmed to 90C. The resulting hot filter cakes containing 59~ solids were transferred to an air o~en sufflciently quickly to prevent them cooling to 80C
- 12 ~
1084~'~57 and were dried at a temperature of 120C for 17 hours after which they were cooled and pulverised.
To 30g of the resulting plaster product was added 0.3g calcium hydroxide and 0.04g keratin and the resulting mixture was micropulverised.under the same standard conditions as used in Example 1 this plaster gave a setting time of 80 minutes. Tested in a similar manner to that used in Example 1 the plaster showed a water demand of 40 mls/lOOg and a similar compressive strength and density to that found in Example 1.
Preferably the ferrous sulpnate is ferrous sulphate heptahydrate.
The ferrous sulphate may be in the form of a l~quor produced as a by-product by an industrial process as above described and generally containiny a proportion of free sulphuric acid. According to the invention any such free acid is neutralised with, for example, a calcium compound, thereby forming calcium sulphate dihydrate or synthetic gypsum,when the free acid is sulphuric acid. The higher the proportion of the sulphuric acid in the ferrous sulphate the higher the proportion of synthetic gypsum formed.
Preferably any free acid present in the ferrous sulphate is neutralised by reaction with the one or more calcium compounds used to form the reaction mixture and in the course of the formation of the reaction mixture, sufficient additional calcium compound being added to ach~eve this, and the resulting acid salt remaining in the reaction mixture.
10t~45~S7 I~ is not necessary, however, in the present invention for any free sulphuric acid to be present, the neutralisation step merely being omitted if none is present.
In tenms of the properties of the product we can obtain S at least some benefit according to the present invention over a very wide range of ratios o~ ferrous sulphate to sulphuric acid. The preferred molar ratio of ferrous sulphate to free acid is from 1:0 to 1:6.
The present invention may involve a drying step and it may therefore be advantageous to ensure that as little water as is possible is present during the earlier stages of the process. L1quors resulting from industrial processes are generally dilute making necessary the use of a more extensive dewatering and drying plant than might otherwise be necessary.
lS Preferably, therefore, the ferrous sulphate is in the form of copperas which has been dissolved or slurried in a relatively small amount of water or,preIerably, dissolved in a ferrous sulphate containing liquor as above described. The amount of water added may be relatively small in view of the release of water of crystallisation from the copperas. Preferably the amount of water used apart from the water of crystallisation present in the ferrous sulphate heptahydrate is from 4 to 100 and particularly preferably from 20 to 50 ml/lOOg ferrous sulphate heptahydrate.
According to a preferred feature of this invention the ca,lcium compound is calcium carbonate in the form of ground limestone or ground chalk. Such forms of calcium carbonate 108~9~7 do not react to completion with ferrous sulphate under normal pressure and at temperatures below 100C, and what reaction there is is generally slower than the reaction between ferrous sulphate and calcium oxide (quicklime) or calcium hydroxide (slaked lime). Under conditions utilised in carrying out the present invention, as hereafter described, these forms of calcium carbonate may be made to react with ferrous sulphate sufficiently readily to represent an advantage in using such raw materials in comparison with using lime bearing in mind the relative raw material costs involved. Where the sole calcium compounds used are calcium o~ide and/or calcium hydroxide theyare preferably used in at least the amount required in theory to react with the sulphate ion present and in not more than 30% ex_ess over that amount.
Where the sole calcium compound used is calcium carbonate it is preferably used in excess over the amount required in theory to react with the sulphate ion present and particularly preferably is used in an excess over that amount of at least 5~ and, for exa~ple, up to 30% on a molar basis. When we refer to sulphate ion we include that derived from any free acid originally present.
The reaction mixture is suitably formed by adding the calcium compound to a mixture of the ferrous sulphate and water. The calcium compound will react fairly readily with any free sulphuric acid present and for this reason it may be desirable to control the rate of addition of the calcium compound so as to ensure that this initial reaation proceeds smoothly.
10~49S7 The reaction mixture is preferably maintained at the required t~nperature and pressure by heating it in an auto-clare, e.g. in the presence of water vapour at a temperature not greater than 175C and particularly preferably at a temperature of from 115C to 160C. The autoclave need not be vented. Preferably a vented autoclave is used controlled to give an internal pressure of from 10 to 50 pounds per square inch gauge (psig). The duration of treatment in the autoclave is that required for completion of the reaction ~etween the calcium compound and the ferrous sulphate hepta-hydrate and the formation of a product which on drying will give the required properties in use and this duration will depend on the particular temperature and pressure used.
Preferably the reaction in the autoclave is conducted for from 1 hour to 10 hours and particularly preferably from 2 hours to 6 hours in total.
To ensure a reasonable speed of reaction the particle size of the ground limestone or ground chalk is preferably such that at least 60% by weight and particularly preferably at least 95% by weight has a particle size below 53 microns.
Preferably as large a proportion as possible of the reaction between ferrous sulphate and the calcium compound occurs at a super-atmospheric pressure and a temperature greater than 100C. Prefera~ly~ therefore, the temperature of the reaction mixture is maintained at below 100C and preferably below 80C during the formation thereof, thereby ~inimising reaction until the required super-atmospheric 1()~4~7 pressule can be generated.
Even under the conditions used in carrying out the present invention the reaction between ferrous sulphate and calcium carbonate in the form of ground limestone or ground chalk will not normally go to completion.
It i5 preferred to ensure reaction of all of the ferrous sulphate since the p~esence of residual ferrous sulphate in the plaster product of the present invention may result in undesirable characteristics in said plaster caused, for example, by leaching of the ferrous sulphate from the plaster. Prefer-ably, therefore, to ensure reaction of all of the ferrous sulphate, a quantity of calcium oxide or hydroxide is added to the reaction mixture.
Preferably the quantity of added calcium hydroxide or oxide is sufficient in theory to react with between 5% and 40% and particularly preferably with ~rom 5% to 25% of the sulphate ion derived from the ferrous sulphate originally incorporated in the reaction mixture. In this case it is possible, to use less than the quantity of calcium carbonate required in theory to ~eact with the sulphate ion present although for economy it is still desirable to use re than 80%, preferably more than 95%, of that quantity. The ~eaction between the ferrous sulphate and the calcium hydroxide or calcium oxide is also preferably conducted under like conditions of temperature and pressure as the reaction with the calcium carbonate. The maintenance of a temperature of the reaction charge above 80C is important, to prevent undue deterioration of the properties of the final product, ~0~'3~7 while a reaction temperature above 100C is necessary for t'ne formation of that product. Any material added to the reaction charge, therefore, are desirably conducted so as to maintain the temperature thereafter to at least 80 C.
This may be achieved, for example, by preheating such material to at least 80C preferably to at least 95C.
Any water remaining in the product formed in the auto-clave may be removed by drying which may be conducted in air, for example in a tunnel drier. If a substantial proportion of the water originally present in the reaction mixture has not been removed by, for example, using a vented autoclave, it may be necessary to precede the drying step by a dewatering step including, for example, filtration or centrifuge treatment. Preferably, the temperature of the product is maintained at, at least, 80C to prevent deterioration thereof, e.g. at from 85C
to 125C and particularly preferably at a temperature of from 100C to 125C until the conclusion of any dewaterins or drying thereof. The duration of the dryin~ step may be, for example, up to 24 hours. ,-The dried product may be puIverised and mixed with appropriate additives known in the art for the control of the properties of plaster of Paris to form a plaster powder.
This powder material may be mixed with ~ater to form a settable plaster mixture which may be used as a wall surface covering or as a material for the construction of moulds or of moulded artifacts. Alternatively the plaster product formed by the said heating of the reaction mixture in the iO~'3~7 autoclave may be directly formed, with tlle addition or removal of the requiTed quantity of ~ater to obtain the correct consistency and of any appropTiate additives as described above, into a plaster mix and shaped into desired artifacts, for example, blocks, tubes, rods or sheets.
The product of the present invention shows some properties similar to those of conventional plaster~ However, despite the very high content of iron compounds in the said product, particularly where ferrous sulphate has been the sole, or substantially the sole, source of sulphate ion we have found that the product of the present invention may be either non-magnetic or only slightly magnetic. In contrast, the product obtained by forming the same reaction mixture and heating it in air is relatively highly magnetic.
We therefore believe that the restricted access of oxygen to the reaction mixture resulting from heating in an autoclave in the presence of water vapour prevents, or reduces, the formation of magnetic iron oxides. This is an important feature of the present invention since in many uses of a plaster the presence of magnetic materials would be undesirable. One way of limiting the contact between the autoclave charge and such oxygen as may be in the autoclave initially, or as may be admitted to it by opening the autoclave during processing is to arrange that the autoclave charge 2a presents a relatively small surface area to the atmosphere in the autoclave.
When the autoclave charge is spread on shallow rays a more magnetic product may be formed than when the autoclave charge is confined in a relatively deep layer.
~0~S7 The present invention will now be illustrated by means of the following Examples.
278g of copperas (10 moles) containing less than 2~ of free sulphuric acid was slurried in 1 1 water in a 5 1 beaker at a temperature of 60C. lOOOy of natural dry chalk (10 moles) was ground in a micropulveriser until at least 95% by weight of the particles had a greatest particle diameter of 53 microns. The ground chalk was added to the copperas slurry over 30 minutes the addition being conducted particularly carefully until the free acid had been neutralised. The slurry was then stirred in the neakér for 15 minutes while maintaining the temperature at 60C. The slurry was then placed in an unstirred autoclave for 3 hours at a temperature of 126C and an internal pressure of 22 psig.
After 3 hours the autoclave was vented off to atmospheric pressure and the contents stirred while the temperature remained at above 95 C.
137.5g calcium hydroxide was slurried in 400 ml boiling water and was added to the slurry over 15 seconds which slurry was then stirred vigorously for 4 minutes after which time it had a pH of 7.7. The slurry was then returned to the auto-clave for a further 1 hour at a temperature of 126C and a pressure of 22 psig. The autoclave was vented off to atmospheric pressure and the contents reslurried, and filtered at a temperature of 85 C over 4 minutes. The hot filter cake 10~4'~57 was discharged onto a steel tray, chopped into ~" lumps and dried in an air oven for 17 hours at a temperature of 120C.
The dried product was discharged, cooled and ground. It was substantially non-magnetic. The filtrate showed a content of less than 1 ppm of Fe 2 showing that substantially all of the iron content of the copperas had remained in the product. The resulting product, tested as a plaster, showed a setting time of 6.5 minutes and a water demand of 44 mls/
lOOg under standard conditions.
To 30g of the product was added 0.3g calcium hydroxide and 0.04g keratin and the resulting mixture having a pH of 10.0 was micropulverised. When tested as a plaster the product showed a setting time of 50 minutes under the same standard conditions.
A series of plasters manufactured by a process sub-stantially as in the above Example showed a water demand of from 30 to 48 ml/lOOg in comparison with a commercial plaster manufactured fro~ natural gypsum which showed a water demand of from 36-40 ml/lOOg. A 100 mm cube made from plaster manufactured substantially according to the above Example showed a compressive strength of 41 kN/100 mm2 in contrast to a similar cube made from the commercial plaster which showed a compressive strength of 37 kN/100 mm2. The density of the plaster manufactured from products manufactured substantially as in the above Example was from 1.2 to 1.8 g/cc.
10~57 122.5g copperas containing less than 2~ free sulphuric acid was slurried in 8.8 galls water in a stirred tank and the slurry agitated whilst live steam was sparged lnto the tank to raise the temperature of the slurry to 65C. 44.lg natural dry chalk of which at least 95~ by weight had a greate~t particle diameter of 53 microns was added to the tank from a vibrating hopper over ~ hour. This reduced the slurry temperature to 45C. The slurry was then pumped into a warmed 20 gall autoclave filled with a stirrer, a pressure control valve, an inlet port which could operate under pressure and a bottom drain exit port. The slurry was sparged with steam to raise its temperature to 70C after which the autoclave was sealed. The autoclave in~erior was raised to a temperature of 126C and a pressure of 40 psig over a time of 1 hour 10 minutes while stirring.
These conditions were maintained for 3~ hours maintaining stirring. The pressure was then vented down to a pressure of 22 psig stirring being continued. 6.2 lbs lime in 2 galls of near boiling water were pumped into the autoclave under a pressure of 25 psig over a time of 5 minutes 5 seconds.
The conditions in the autoclave were then maintained under stirring at a temperature of 126C and a pressure of 22 psig for a further time of 1 hour. The slurry was then pumped over a time of 5 minutes from the autoclave into a filter press, which had been prewarmed to 90C. The resulting hot filter cakes containing 59~ solids were transferred to an air o~en sufflciently quickly to prevent them cooling to 80C
- 12 ~
1084~'~57 and were dried at a temperature of 120C for 17 hours after which they were cooled and pulverised.
To 30g of the resulting plaster product was added 0.3g calcium hydroxide and 0.04g keratin and the resulting mixture was micropulverised.under the same standard conditions as used in Example 1 this plaster gave a setting time of 80 minutes. Tested in a similar manner to that used in Example 1 the plaster showed a water demand of 40 mls/lOOg and a similar compressive strength and density to that found in Example 1.
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the manufacture of a plaster from ferrous sulphate comprising forming a reaction mixture consisting essentially of ferrous sulphate, any free acid therein having been neutralised, and one or more calcium compounds selected from calcium carbonate, calcium hydroxide and calcium oxide, in an aqueous medium, heating the reaction mixture in the presence of steam at a temperature greater than 100°C and under a pressure greater than atmospheric pressure to form a crystalline plaster product.
2. A process as claimed in claim 1 wherein the ferrous sulphate is ferrous sulphate heptahydrate.
3. A process as claimed in claim 2 wherein the free acid is neutralised by reaction with the one or more calcium compounds in the course of the formation of the reaction mixture the resulting acid salt remaining in the reaction mixture
4. A process as claimed in any one of claims 1 to 3 wherein the molar ratio of ferrous sulphate to free acid is from 1:0 to 1:6.
5. A process as claimed in any of claims 1 to 3 wherein the amount of water used to form the reaction mixture is from 4 to 100 ml per 100g ferrous sulphate excluding any water of crystallisation present.
6. A process as claimed in any one of claims 1 to 3 wherein the calcium compound used to form the reaction mixture is calcium carbonate in the form of ground limestone or ground chalk.
7. A process as claimed in any one of claims 1 to 3 wherein the calcium compound used to form the reaction mixture is ground limestone or ground chalk and at least 60% by weight of the ground limestone or ground chalk has a particle size below 53 microns.
8. A process as claimed in any one of claims 1 to 3 wherein the calcium compound used to form the reaction mixture is ground limestone or ground chalk and the quantity of ground limestone or ground chalk is in excess over that required in theory to react with the quantity of sulphate ion present said excess being up to 30%.
9. A process as claimed in any one of claims 1 to 3 wherein the calcium compound used to form the reaction mixture is ground limestone or ground chalk and wherein calcium oxide or calcium hydroxide is added to the reaction mixture in a quantity sufficient in theory to react with from 5%
to 40% of the sulphate ion derived from the ferrous sulphate originally incorporated in the reaction mixture.
to 40% of the sulphate ion derived from the ferrous sulphate originally incorporated in the reaction mixture.
10. A process as claimed in any one of claims 1 to 3 wherein the said heating of the reaction mixture is conducted in an autoclave at a temperature not greater than 175°C.
11. A process as claimed in any one of claims 1 to 3 wherein the heating of the reaction mixture is conducted under a pressure of from 10 p.s.i.g. to 50 p.s.i.g, in a vented autoclave.
12. A process as claimed in any one of claims 1 to 3 wherein the heating of the reaction mixture is conducted for from 1 hour to 10 hours.
13. A process as claimed in any one of claims 1 to 3 wherein the temperature of the reaction mixture is maintained at below 80°C during the formation thereof.
14. A process as claimed in any one of claims 1 to 3 wherein the temperature of the product is maintained at at least 80°C until the con-clusion of any dewatering or drying thereof.
15. A process as claimed in any one of claims 1 to 3 wherein the plaster product is recovered from any residual aqueous medium and is dried and pulverised, with the addition of any appropriate additives, to produce a plaster powder.
16. A process as claimed in any one of claims 1 to 3 wherein the plaster product formed by the said heating of the reaction mixture is directly formed, with the addition of any appropriate extra quantity of water and of any appropriate additives, into a suitable plaster mix in the shape of a desired artifact.
17. A substantially non-magnetic plaster containing iron compounds whenever prepared by a process as claimed in any one of claims 1 to 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4165576A GB1581539A (en) | 1976-10-07 | 1976-10-07 | Making plaster from ferrous sulphate |
| GB41655/76 | 1976-10-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084957A true CA1084957A (en) | 1980-09-02 |
Family
ID=10420692
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA286,718A Expired CA1084957A (en) | 1976-10-07 | 1977-09-14 | Plaster made from ferrous sulphate |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5346498A (en) |
| AU (1) | AU506984B2 (en) |
| CA (1) | CA1084957A (en) |
| DE (1) | DE2745023A1 (en) |
| ES (1) | ES462972A1 (en) |
| FR (1) | FR2367030A1 (en) |
| GB (1) | GB1581539A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS593275Y2 (en) * | 1979-10-12 | 1984-01-28 | サンデン株式会社 | Heat exchanger |
| JPS5849502Y2 (en) * | 1979-10-12 | 1983-11-11 | サンデン株式会社 | Heat exchanger for frozen/refrigerated showcases |
| IS1443B6 (en) * | 1980-12-17 | 1990-12-14 | Aalborg Portland A/S | thurr cement mix |
| DE3743818C2 (en) * | 1987-12-23 | 1995-02-23 | Hoelter Heinz | Process for the production of a building material resistant to water leaching and its use |
| FI100966B (en) * | 1995-04-21 | 1998-03-31 | Kemira Pigments Oy | Process for the treatment of ferrous sulphate |
| CN113401938B (en) * | 2021-08-04 | 2023-05-16 | 苏州市宏丰钛业有限公司 | Titanium dioxide manufacturing method and system based on sulfur-iron-titanium co-production method |
-
1976
- 1976-10-07 GB GB4165576A patent/GB1581539A/en not_active Expired
-
1977
- 1977-09-14 CA CA286,718A patent/CA1084957A/en not_active Expired
- 1977-09-30 AU AU29263/77A patent/AU506984B2/en not_active Expired
- 1977-10-06 ES ES462972A patent/ES462972A1/en not_active Expired
- 1977-10-06 FR FR7730115A patent/FR2367030A1/en active Pending
- 1977-10-06 DE DE19772745023 patent/DE2745023A1/en not_active Withdrawn
- 1977-10-06 JP JP11955077A patent/JPS5346498A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2745023A1 (en) | 1978-04-20 |
| AU2926377A (en) | 1979-04-05 |
| ES462972A1 (en) | 1978-06-16 |
| GB1581539A (en) | 1980-12-17 |
| FR2367030A1 (en) | 1978-05-05 |
| AU506984B2 (en) | 1980-01-31 |
| JPS5346498A (en) | 1978-04-26 |
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