IL26076A

IL26076A - Method for the manufacture of phosphoric acid and calcium sulphate hemihydrate

Info

Publication number: IL26076A
Application number: IL26076A
Authority: IL
Original assignee: Prayon
Priority date: 1965-07-07
Filing date: 1966-07-01
Publication date: 1970-07-19
Also published as: LU49007A1; BE683739A; DK130955B; ES329179A1; SE336775B; GB1111078A; NO116287B; AT269064B; SU378002A3; DE1567821B1; NL6609093A; FR1485940A; FI47652B; DK130955C; OA02091A; BG20319A3; FI47652C

Description

FOR THE OF ACID AND 24851 The invention concerns the simultaneous manufacture of phosphoric acid and calcium sulphate hemihydrate for by the by the decomposition of rock phosphate by sulphuric or another acid in the presence of sulphate In the mostly used conventional process of this kind referred to the rock phosphate is reacted with sulphuric acid and recycled phosphoric acid under conditions of concentration and temperature such that the by the reaction crystallizes in the of and the phosphoric acid liquor is separated by decantation or the the The gypsum is washed and the acidic washing liquor together with a part of the phoric acid liquor is recycled to the rock phosphate This method produces phosphoric acid containing from to by or even of The separated and washed sum still contains a considerable amount of of rock or with the fixed in the crystalline lattice of the latter in the form of ions replacing As a the yield of this process calculated on the contents of the rock is below to the contained in the gypsum makes the latter unsuitable for certain the crystal shape of the gypsum the rate of tion of the hos horic In the case of man the shape of the gypsum crystals un affects the rate of filtration makes it to keep the decomposition in the reaction tanks a prolonged time in order to produce gypsum with good filtering any a very continuous control of all the physical and chemical factors within narrow limits is always with the conventional decomposition installation in order to tain the conditions required for obtaining a gypsum of suitable It is also possible to work under conditions of concentration and of temperature such that the crystallizes as hemihydrate as For higher teiaperatures and high tions of ion are By these 5 4 which are known as the hemihydrate and the hydrite it is possible to obtain a more concentrated phosphorie aeid under certain readily filterable calcium sulphate the yield of these methods is rather lower than that of the For some methods have been These proceed under conditions such that the formed in the decomposition crystallizes as After this crystallization the reaction mixture is cooled and diluted whereby such conditions are created that the hemihydrate originally formed is no longer stable and to form By content in a value that is distinctly lower than in the the obligatory presence of a siderable of phosphorie acid constitutes a and the itself is difficult to The method of the like the performs the decomposition of the rock phosphate under such conditions temperature and of concentration that the C crystallizes originally as the decomposition mixture will have a temperature of about to preferably to a content of about to by preferably to an ion content of about to preferably to and a content of solids of about to preferably to According to the the gypsum is continuously into by an operation in which the decomposition containing mainly phosphoric acid and is mixed continuously with sulphuric acid of 50 to preferably 80 to the mixture is at a temperature of 70 to preferably 75 to if necessary by external and at a in the of 15 to preferably 20 to of and 2 to preferably 10 to of in order to crystallize the gypsum into the latter is separated frora the ef phosphoric and sulphuric By one embodiment of the invention the product phosphoric acid is withdrawn from the operating cycle before the is converted to hemihydrat in that the decomposition mixture is subjected to separation in a suitable a static a filt centrifugal decanter or extractor working continuously or a hydroc or the residue containing all the solids is then subjected to the By another embodiment of the invention the entire decomposition mixture is directly submitted to the recrystallization treatment and a mixture of phosphoric and sulphuric acids is thereafter separated from the This acid mixture can be utilized many it is fed to a second stallation for the decomposition of rock in which the product phosphoric acid is recovered directly from the decomposition In the practice of the recrystallization of gypsum to the gypsum either in mixture with the product phosphoric acid or after separation is advantageously in a continuous to a reactor provided with agitator and containing permanently a slurry of hemihydrate already phosphoric acid and sulphuric fresh concentrated sulphuric acid is continuously fed to the and though the heat of dilution steam The temperature of the mixture is maintained at to preferably to the concentration of liquid at 15 to 35 preferably 20 to 30 the concentration of the liquid at 2 to preferably 10 to sulphuric acid supplied to the reactor contains 50 to of preferably 80 to The by continuous crystallization can readily be filtered off and It can easily be separated the panying liquid in any suitable separation preferably the hemihydrate sludge is filtered through a flat tilting pan filter and washed with The hemihydrate excels by its low content which is below calculated on the dry matter at The separated from the hemihydrate is a mixture of washing It can be recycled wholly or in part to the rock phosphate decomposition or it may be ferred or in part to another installation for the decomposition of rock It is an important feature of the invention that the continuous recrystallization of gypsum to hemihydrate proceeds in a medium constituted principally of hemihydrate and phosphoric acid which latter is supplied to the reaction in concentrated f under these conditions the formed tends to lose its water of crystallization and to form the though as the latter is the only stable form under these Accordingly the hemihydrate should have a short dwelling time in the For the tion speed will be expressed herein by the number of filled tanks treated per This figure is approximately to depending on the conditions in continuous a tank of given the volume of reaction mixture expressed as m can and should be to to the of the tank Under the conditions set out the gypsum is recrys to hemihydrate which forms coarse crystals easy to filter and wash and which does not give off its water of By its crystal shape and tow content the hemihydrate ie advantageously distinguished from the anhydrite which would form or instead the hemihydrate if the eet out were if the temperature the concentration were higher the contact were The invention inter the following advantagess The product phosphoric acid has a content of ions similar as in the or even For the recrystallization of neither the quality of the gypsum formed in the rock phosphate decomposition nor the recovery in the decomposition are of this fact simplifies the control of the conditions of the decomposition The hemihydrate recovered has a low which fact makes for a good calculated on the content of the rock The hemihydrate thus produced is suitable for the plaster Upon hydration it yields an excellent dihydrate for in the cement The hemihydrate filters better than the gypsum normally formed in the the method of the invention requires a smaller filtering surface than the The course of the phosphate decomposition stage becomes much less dependent on the shape of the gypsum crystals formed in that stage than in the In the dwelling time in the decomposition and accordingly the volume of the can be which means furthermore that a reater concentration of th in method the the rock phosphate decomposition can performed with a slight excess of while the atage is with a strong concentration of sulphuric A plant for carrying out the method of the invention is diagrammatieally illustrated in the accompanying The phosphate decomposition takes place in a or 1 which is of the type used in the This may he vat or a series of with a recirculation and a cooler for the reaction The rock phosphate is introduced at the sulphuric acid at and the recycled acid separated from the hemihydrate at The reaction mixture passes from the reactor 1 at least in a into a separator 6 from which the product phosphoric acid is recovered at 7 while the separated gypsum sludge passes through a conduit 8 into a reactor A part of the reaction mixture may be without directly into the reactor 1 through conduit The 9 is fed with concentrated sulphuric aeid at 11 and supplied with external by means of steam introduced at reactor 9 is fitted with a suitable From the reactor 9 the hemihydrate sludge is drawn through a 13 a separator 14 in which it is washed with warm water supplied at The wet hemihydrate is withdrawn from the cycle at 16 while the liquid is recycled from the separator 14 through conduit 4 to the reactor If product phosphoric acid is not withdrawn from the V discharged from the reactor mixture of acids can then be for to second phosphate decomposition where product phosphoric acid will be recovered the reaction mixture directly after the decomposition Or some amount of product phosphoric acid may be recovered in the pure state from the decomposition mixture discharged from the reactor and another part thereof mixed with sulphuric from the reaction mixture withdrawn from the reactor insufficientOCRQuality

Claims

1. CLAIMS A for the of phosphoric acid and by decomposition rock phos rock phosphate slurry containing phoric acid gypsum is eontiauously with acid of 50 to preferably 80 to mixture is at of 70 to preferably 75 to i necessary by external and in the of 15 to preferably 20 to and 2 to preferably 10 to of order to the gypsum into and latter is the of phosphoric and acids if washed A method claimed wherein the liquid is recycled wholly or in part to rock phosphate decomposition A method as in the product phosphoric acid is the rock before the tion of acid and the of gypsum to A method claimed in Claim in which the product phosphoric om containing slurry fey withdrawing a part of the mixture of and sulphuric acids er 11 A as claimed in Claim wherein the product phosphoric acid separated in the form of acid mixture is fed to another rock phosphate decomposition stage froaa which it is recovered by separation from the gypsum A as claimed in Claim the volume of gypsum sludge and sulphuric acid continuously fed to the reactor hour is equal to to times the reactor A method for the of phosphoric acid and calcium sulphate substantially as described above and illustrated in the the Applicants insufficientOCRQuality