CA1184046A - Method for the preparation of potassium fertilizer salts by electrostatic separation - Google Patents
Method for the preparation of potassium fertilizer salts by electrostatic separationInfo
- Publication number
- CA1184046A CA1184046A CA000427125A CA427125A CA1184046A CA 1184046 A CA1184046 A CA 1184046A CA 000427125 A CA000427125 A CA 000427125A CA 427125 A CA427125 A CA 427125A CA 1184046 A CA1184046 A CA 1184046A
- Authority
- CA
- Canada
- Prior art keywords
- separator
- fraction
- percent
- concentrate
- clay
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C7/00—Separating solids from solids by electrostatic effect
- B03C7/003—Pretreatment of the solids prior to electrostatic separation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C7/00—Separating solids from solids by electrostatic effect
- B03C7/006—Charging without electricity supply, e.g. by tribo-electricity, pyroelectricity
Abstract
ABSTRACT
A method for electrostatic separation of clay-containing sylvinitic crude potassium salts in several separation steps is described. According to this method a potassium fertilizer salt having a K2O content of at least 60 percent by weight is obtained in a 3-step separation in free-fall separators, and fractions from which valuable potassium compounds are recover-able are obtained by way of dissolving processes or conductivity separation.
A method for electrostatic separation of clay-containing sylvinitic crude potassium salts in several separation steps is described. According to this method a potassium fertilizer salt having a K2O content of at least 60 percent by weight is obtained in a 3-step separation in free-fall separators, and fractions from which valuable potassium compounds are recover-able are obtained by way of dissolving processes or conductivity separation.
Description
Numerous methods for the separation of crude pota~sium salts in free-fall separators are known. According to these methods crude potassium salt, which is ground to a grain size of >0 to 3 mm and which is treated with ~arious different conditioning agents, is triboelectrically charged at predeter-mined temperatures and relative atmospheric humidities and fed into an electric free-fall separator in which an electrostatic field of 3 to 9 kV/cm is maintained. Due to the different charges of the various components of the crude potassium salt, these components are deflected differently from the free falling stream of the crude potassium salt particles in the electro-static field of the free-fall separator towards one or the other electrode and can be collected as concentrates of the various components at the foot of the separator close to the electrodes. However, these methods, in particular the separa~
tion of potassium chloride from sylvinitic crude potassi~m salts, can only be performed successfully, if the crude potassium salts do not contain more than a maximum of two per-cent by weight of clay. Lower clay concentrations in the crude potassium salt do not considerably interfere with its electro-static separation. But even then reactions go on which in the case of crude potassium salt with clay-concentration of more than the maximum of 2 percent by weiyht do not allow the recovery of a potassium chloride concentrate with a K2O~content of 60 percent by weight or more from such crude potassium salts by way of electrostatic separation in the ree-fall separator.
In previous tests it has been determined that the clay ~2-contained in the crude potassium sal~s as well as the potassIum chloride becomes negati~ely charged and~or prevents or at least strongly reduces the selective triboelectrical charging of the various components of the crude potassium salt.
In the first case, the clay together wi~h the potassium chloride i5 deflected to the positive electrode and remains in the potassium chloride concentrate~ In the second case, electro-static separation of the crude potassium salt in the electric free-fall separator does not occur at all or only to a very unsatisfactory extent. For this reason, many attempts were made in the past to electrostatically separate the clay from crude potassium salts, which have a clay-content of 2 percent by weight or more, in a separate process step.
Thus, German Auslegeschrift 10 52 921 describes a method for the separation of clay from crude potassium salts by electrostatic separation. The clay-containing crude potassium salt, which is ground to a grain size of at most 3 mm, is first dried to such an extent that the salt-like components loose their moisture while the clay retains sufficient moisture so that its electrical conductivity is not affected. The clay is separated from the dried crude potassium salt by means o~ a drum separator with a spray electrode. As in this process the total quantity of crude potassium salt has to be heated prior to the recovery of the valuable components and as drum separa-tors generally ha~e only a small hourly throughput of 0.4 to0.6 t/m drum width, this process requires considerable expenditure in energy and technical equipment.
~3~
From German patent 11 9~ 342 a further mehtod of electrostatic separation of crude potassium salts is known, according to which clay~containing crude potassium salts can be treate~. From ground and conditioned crude potassium salts a potassium chloride concen~rate having a K20-content of ~ to 59 percent by weight is produced in two electrostatic separation steps, whereby one step is performed on a drum separator with spray electrode and the other in a free-fall separator~ In a further electrostatic separation step in a free-fall separator the thus obtained potassium chloride concentrate can be conver-ted into a concentrate with a K2O-content of over 60 percent by weight. The quantity of the latter amounts, however, to only 66 percent of the material introduced into this additional separation step, while 34 percent have a K2O-content of only 40 percent.
German patent 10 95 762 also describes a method of electrostatic separation of clav-containing crude potassium salts accordin~ to which the qround crude potassium salts are treated with polyvalent materials and anionic conditioning agents prior to the triboelectric charging. Due to the polyvalent materials the electric conducti~ity of the clay is compensated for and, accordingly, its accumulation in the potassium chloride concentrate is prevented in the same way as its separate recovery in the following separation in a free-fall separator.
In this process the clay remains in the concentrate which predominantly consists of rook salt and/or kieserite.
A further process and an apparatus for electrostatic -4~
separation of clay from crude potassi,~m salts is described in German Patent 19 ~7 464. Aceording to this proeess the ground crude potassium salts, after having been conditioned with organic and/or inorganic eonditioning agents which are capable of splitting off one or several hydrogen or metal ions to form negatively charged molecule rest, are heated and treated with air having a relative humidity of 5 to 30 percent.
In a special elay separation step, the elay is then separated solely for the reason that the material to be separated under-goes repeated contact charging while passing through theeleetrostatie field. This process is performed in an apparatus in whieh a vertieally arranged electrode of large area is spaced fxom a pluralit~ of horizontally arranged eounter electrcdes of small surfaee and from inserts of non-conducting material which are inclined downwardly towards the large surface electrode. Due to these inserts the material to be separated eomes repeatedly into contact with the large surface eleetrode, whereby the elay particles become eharged and are then repelled by the large surfaee electrode. The particles then enter the inhomogeneous electrostatic field with a high magnetic flux at the counter electrodes between whieh the elay partieles, having been eharged by the large surfaee eleetrode, pass through without a ehange in charge. After passing at least twice thxough the separator, the potassium salt concentrate has a low clay content and is recoyered elose to the large surfaee eleetrode at the ~oot of the separator and ean then be processed electrostati-eally like a clay-free'erude'potassium salt~ In this proeess, too, the total amount of erude potassium salt whieh is to be 4(~
~-5~
separated must be pre-treated in a specially equipped apparatus, thus requirin~ considerable technical resources.
A further development of the electrostatic separation of clay-containing crude potassium salts is described in German patent 20 07 677~ Accordin~ to this process the ground crude potassium salts, which are cond~tioned with lactic acid and chloroacetic acid, are heated in an atmosphere of 2 to 20 percent relative humidity to temperatures of 20 to 65C and - triboelectrically charged fed into a free-fall separator. At l~ the foot of the separator a clay-rich crude potassium salt concentrate is collected close to the positive electrode and a practically clay-fxee crude potassium salt concentrate is collected close to the negative electrode. The middlings obtained are recirculated through the separator.
According to German patent 20 52 993 the ground clay containing crude potassium salt can also be conditioned with
tion of potassium chloride from sylvinitic crude potassi~m salts, can only be performed successfully, if the crude potassium salts do not contain more than a maximum of two per-cent by weight of clay. Lower clay concentrations in the crude potassium salt do not considerably interfere with its electro-static separation. But even then reactions go on which in the case of crude potassium salt with clay-concentration of more than the maximum of 2 percent by weiyht do not allow the recovery of a potassium chloride concentrate with a K2O~content of 60 percent by weight or more from such crude potassium salts by way of electrostatic separation in the ree-fall separator.
In previous tests it has been determined that the clay ~2-contained in the crude potassium sal~s as well as the potassIum chloride becomes negati~ely charged and~or prevents or at least strongly reduces the selective triboelectrical charging of the various components of the crude potassium salt.
In the first case, the clay together wi~h the potassium chloride i5 deflected to the positive electrode and remains in the potassium chloride concentrate~ In the second case, electro-static separation of the crude potassium salt in the electric free-fall separator does not occur at all or only to a very unsatisfactory extent. For this reason, many attempts were made in the past to electrostatically separate the clay from crude potassium salts, which have a clay-content of 2 percent by weight or more, in a separate process step.
Thus, German Auslegeschrift 10 52 921 describes a method for the separation of clay from crude potassium salts by electrostatic separation. The clay-containing crude potassium salt, which is ground to a grain size of at most 3 mm, is first dried to such an extent that the salt-like components loose their moisture while the clay retains sufficient moisture so that its electrical conductivity is not affected. The clay is separated from the dried crude potassium salt by means o~ a drum separator with a spray electrode. As in this process the total quantity of crude potassium salt has to be heated prior to the recovery of the valuable components and as drum separa-tors generally ha~e only a small hourly throughput of 0.4 to0.6 t/m drum width, this process requires considerable expenditure in energy and technical equipment.
~3~
From German patent 11 9~ 342 a further mehtod of electrostatic separation of crude potassium salts is known, according to which clay~containing crude potassium salts can be treate~. From ground and conditioned crude potassium salts a potassium chloride concen~rate having a K20-content of ~ to 59 percent by weight is produced in two electrostatic separation steps, whereby one step is performed on a drum separator with spray electrode and the other in a free-fall separator~ In a further electrostatic separation step in a free-fall separator the thus obtained potassium chloride concentrate can be conver-ted into a concentrate with a K2O-content of over 60 percent by weight. The quantity of the latter amounts, however, to only 66 percent of the material introduced into this additional separation step, while 34 percent have a K2O-content of only 40 percent.
German patent 10 95 762 also describes a method of electrostatic separation of clav-containing crude potassium salts accordin~ to which the qround crude potassium salts are treated with polyvalent materials and anionic conditioning agents prior to the triboelectric charging. Due to the polyvalent materials the electric conducti~ity of the clay is compensated for and, accordingly, its accumulation in the potassium chloride concentrate is prevented in the same way as its separate recovery in the following separation in a free-fall separator.
In this process the clay remains in the concentrate which predominantly consists of rook salt and/or kieserite.
A further process and an apparatus for electrostatic -4~
separation of clay from crude potassi,~m salts is described in German Patent 19 ~7 464. Aceording to this proeess the ground crude potassium salts, after having been conditioned with organic and/or inorganic eonditioning agents which are capable of splitting off one or several hydrogen or metal ions to form negatively charged molecule rest, are heated and treated with air having a relative humidity of 5 to 30 percent.
In a special elay separation step, the elay is then separated solely for the reason that the material to be separated under-goes repeated contact charging while passing through theeleetrostatie field. This process is performed in an apparatus in whieh a vertieally arranged electrode of large area is spaced fxom a pluralit~ of horizontally arranged eounter electrcdes of small surfaee and from inserts of non-conducting material which are inclined downwardly towards the large surface electrode. Due to these inserts the material to be separated eomes repeatedly into contact with the large surface eleetrode, whereby the elay particles become eharged and are then repelled by the large surfaee electrode. The particles then enter the inhomogeneous electrostatic field with a high magnetic flux at the counter electrodes between whieh the elay partieles, having been eharged by the large surfaee eleetrode, pass through without a ehange in charge. After passing at least twice thxough the separator, the potassium salt concentrate has a low clay content and is recoyered elose to the large surfaee eleetrode at the ~oot of the separator and ean then be processed electrostati-eally like a clay-free'erude'potassium salt~ In this proeess, too, the total amount of erude potassium salt whieh is to be 4(~
~-5~
separated must be pre-treated in a specially equipped apparatus, thus requirin~ considerable technical resources.
A further development of the electrostatic separation of clay-containing crude potassium salts is described in German patent 20 07 677~ Accordin~ to this process the ground crude potassium salts, which are cond~tioned with lactic acid and chloroacetic acid, are heated in an atmosphere of 2 to 20 percent relative humidity to temperatures of 20 to 65C and - triboelectrically charged fed into a free-fall separator. At l~ the foot of the separator a clay-rich crude potassium salt concentrate is collected close to the positive electrode and a practically clay-fxee crude potassium salt concentrate is collected close to the negative electrode. The middlings obtained are recirculated through the separator.
According to German patent 20 52 993 the ground clay containing crude potassium salt can also be conditioned with
2, 6-dinitrophenol, halogen carbonic acid and water andl after being triboelectrically charged, can be separated with con-siderable success in an electrostatic free-fall separator into a rock salt-clay concentrate and a sylvite-kieserite concentrate.
The clay-specific conditioning agents used in the two last mentioned processes, however, impede the subsequently necessary triboelectric charging of the sylvite against the other components of the sylvite-containing concentrate and therefore complicate the further electrostatic treatment of these concentrates. For this reason, investigations were di--rected towards finding a method for obtaining component~
concentrates from clay containing sylvinitic crude potassium -6~
salts b~ way of a simple electrostatic separation process without the use of clay~spec~fic condàtioning agents, whereby the resulting concentrate can ~e further processed without difficulty or can be employed for utility purposes.
It has now been found that potassium fertilizer salts having a K2O~content of at least 60 percent can be obtained by a method comprising a multistep electrostatic separation of ground conditioned and triboelectrically charged, sylvinitic crude potassium salts, which contain clay, at predetermined relative atmospheric humidity and elevated temperatures in electrostatic free-fall separators with an electric field intensity of above 3 kV/cm. Accordingly, the method comprises:
a) conditioning crude potassium salts, which are ground to a grain size of about 1 to 2 mm depending on the lS degree of inter~rowth, with about 50 to 100 g/t oE a mixture of fatty acids and about 50 to 100 g/t salicylic acid and feeding the conditioned raw potassium salts in an atmosphere having a relative humidity of about 5 to 12.5 percent triboelectrically charged into an electrostatic free-fall separator in which the middlings are recirculated, at the foot of the separator collecting close to the positive electrode a residue to be discarded and close to the negative electrode a pre-concentrate of valuable material;
b) conditioning the pre~concentrate of step a~ with about 100 to 300 g/t silica and feeding said conditioned pre-concentrate in an atmosphere having a reIative humidity of bout 5 to 10 percent triboelectrically charged into an electro-static free-fall separator without recirculation of middlings, at the foot of the separato~ collectin~ close to the positi~e electrode a residue to be discarded, close to the negative electrode a first concentrate of ~aluable material, and in the centre between the two electrodes a medium friction;
c~ feeding the first concentrate of step b) into an electrostatic ~ree-fall separator in which the middlings are circulated, at the foot of the separator collecting close to the positive electrode a residual fraction and close to the negative electrode a potass.ium fertilizer salt product having a X2O-content of at least 60 percent by weight; and d) recovering valuable potassium material from the mQdium fraction of step b) and the residual fraction of step c).
The method according to the invention is particularly directed to the recovery of a concentrate of potassium fertilizer salt having a K2O-content of 60 percent by weight or more from sylvinitic crude potassium salts having a clay-content of 2 percent by weight or more by way of electrostatic separation in free-fall separators. Such a crude potassium salt can, for example, have the following composition:
41.0 % by weight KCl 55.8 ~ by weight NaCl 0.3 % by weight CaSO4 2.9 ~ by weight Clay or 24,5 % by weight KC1 Q..5 % by weight MgSO4 H2 72.3 % by weig~t NaCl 2.7 % ~y welght Clay.
According to the in~enti~e method the crude potassium ~3~
salt is first ground to an average grain size of preferably 2 mm.
The ground crude potassium salt is then thoroughly mixed with 50 to 100 g/t of a mixture oE fatty acids and with 50 to 100 g/t salicylic acid. Thereafter this mixture is supplied to a fluidized bed which is exposed to an air stream having a relative humidity of from 5 to 12O5 percent and a respective temperature. In the fluidized bed the particles of the ground crude potassium salt become charged triboelectrically.
Following this the crude potassium salt is fed into a free fall separator between the electrodes of which a high voltage field having a field intensity of 3 to 5 kV/cm is maintained and which is provided with e~uipment for the recirculation of the middlings produced in the separator. At the foot of the separator close to the positive electrode a residue accumulates which besides containing considerable amounts of roek salt also contains elay and sulfate as well as relatively small amounts of potassium chloride. This residue is discarded.
Close to the negative eleetrode a pre-concentrate of valuable material enriehed in potassium chloride is obtained. In the eenter between these collecting stations a residue accumulates which is reeireulated and, in admixture with crude potassium salt, again fed into the free-fall separator.
The pre eoneentrate of valuable materi~l obtained in this step is then mixed thoroughly ~ith 100 to 300 g/t finely divided siliea and in an atmosphere ha~in~ a relative humidity of 5 to 10 pereent tr~boelectrieally charged by brisk move~
ment of the particles relative to each other, preferably in a fluidi,zed bed~ Following this the'pre ~oncentrate is again fed into a free~~all separator in which an electrostatic field with an intensity of 3 to 5 kV/cm is maintained~ This free~fall separator is not provided with equipment which allows recirculation of middlings or, is such equipment is available, it remains idle during this step.
At the foot of the free-fall separator close to the positive electrode a residue which mainly consists of rock salt and contains clay and small amounts of potassium chloride accumulates and is discarded. Close to the negative electrode a first valuable concentrate is collected which already has a K2O~content of more than 50 percent by weight. The medium fraction accumulating between the two electxodes of the free fall separator is collected and can, according to procedures described hereafter, be used to recover valuable potassium compounds since the K2O-content of the fraction is above 25 percent by weight but due to its relatively high clay-content the fraction cannot be recirculated.
The first concentrate of valuable material is, without renewed conditioning and triboelectric charging fed into an electric ~ree-fall separator in which an electrostatic high voltage field of 3 to 5 kV/cm is maintained. This free-fall separator has to be provided with equipment which allows recirculation of the middlings obtained in the separator. At the foot of this separator close to the positi~e electrode a residu~l fraction is collected wh~ch is ~ixed ~ith the medium fraction of the preceding separation step, Close to the 4~)~6 '`10--`
negative electrode a potassium fertilizer salt product having a K2O~content of at least 60 pe~cent b~ weight is recovered in a yield of at least 65 percent, prefexably over 67 percent, of the K2O-content of the crude potassium salt.
The clay content of this prGduct is below 1.0% by weight. The middlings accumulated in the free~fall separator are reintro-duced into the separator.
From the medium fraction collected in the preceding separating step and the residual fraction obtained in the last mentioned separation step valuable potassium compound concen-trates can be recovered in known manner according to dissolving processes, preferably hot dissolving processes such as, for example, described in "Ullmanns Encyklopadie der technischen Chemie" 3rd Edition, Vol. 9, p. 185 (1957). It is also possible to feed a mixture of the medium fraction and residual fraction into a conductivity separator in the form of a drum separator and to separate the mixture into a salt fraction low in clay and a residue rich in clay, whereby the latter is discarded.
Such a process is; for example, described in German patent 10 52 921. The salt fraction obtained by this separation process is mixed with the crude pota9sium salt which is pro-cessed according to the invention.
In accordance ~ith the in~entive process, the clay is stepwise charged against the potassium chloride and remo~ed at the appropriate locations in the process. To this effect it is important that the reIative humidity in the charging atmosphere of the first process step lies between about 5 and ~11~
12.5 percent and that the crude potassium salt to be separated is conditioned with fatty and salicylic acid. Under these conditions the clay does not become charged together with the sylvite~ According to the inventive procedures distribution of the clay in about equal amounts over the residue to be dis-carded and the pre-concentrate of valuable material can be achieved already in the ~irst SeparatiQn step. In the second separation step the medium ~raction also contains a consider-able portion of clay. For this reason this fraction is not recirculated into the free-fall separator. The residue obtained in this separation step also contains a considerable portion of clay.
The residues of the first and second separation step contain already about 80 percent of the clay introduced with the crude potassium salt, but contain at mos-t 7 percent of the s~lvite, so that the residues can be discarded without consid-erable loss. This does not apply to the medium fraction of the second and the residual fraction of the third separating step which also contain clay, but include additionally about 23 percent of the sylvite contained in the crude potassium salt which is introduced into the inventive process. The mixture of these fractions therefore has to be treated to recover valuable potassium compounds. This recovery can be effected according to known dissolving processes~ preferably a hot dis-solving proce$s~ Particularly advantageously this recovery isperformed by ~ay of conductivity separation in a drum separator.
The xesulting concentrate of valuable material, which contains -12~
only very small amounts of clay~ is added to the crude potassium salts which are to be treated in accordance with the inventive process. Due to the particular combination of pro-cedures, the process according to the invention allows for the first time the direct production of a potassium fertilizer salt having a K2O~content of at least 60 percent by weight in a yield of about 70 percent from clay-containing sylvinitic crude potassium salts without requiring technically complicated pretreatments to separate the clay and without the resulting disadvantages regarding the electrostatic separation. Moreover, when a drum separator, the throughput capacity of which is considerably smaller than the capacity of a free-fall separator, is used in accordance with the invention, the drum separator can be loaded with only as much material as is commensurate with its capacity without thereby affecting the operation of the free-fall separators which o~erate with a considerably larger throughput.
Example 100 t/h of a crude potassium salt ground to an average grain size of 2 mm and containing 41.0% by weight Sylvite 55.8% by weight Rock Salt 0.3~ by weight Anhydrite 2.9~ by weight Clay were mixed with 75 g~t ea`ch of salicylic acid and a mixture of fatty acids having 10 to 15 carbon atoms per molecule, and ~ere fed into a fluidized bed dryer which was exposed to air ~13~
of 10 percent relative humidity~ The mixture which ~as drawn off the dryer was directl~ fed ~nto a free~fall separator provided with circulation equipment, in which an electro-static high voltage field of 4 to 4.5 kV~cm was maintained.
Such a free-fall separator is described in German patent 11 54 052. At the foot of this separator close ~o the positive electrode a residue which was discarded was obtained. The produced middlings were circulated through the separa~or. At the negative electrode a concentration of valuable material was obtained which, after having been mixed with 200 g/t finely divided silica, was triboelectrically charged in a fluidized bed dryer which was exposed to air of 9 percent relative humidity. Following this, the concentrate was fed into an electrostatic free-fall separator (4 to 4.5 kV/cm field intensity). At the foot of this separator close to the positive electrode a residue which was discarded was obtained. This residue and the residue from the irst separation step were obtained in an amount of 52.9 t/h having a K2O-content of 2.4 percent by weight and a clay content of 3.1 percent by~,weight (see Table I).
Xn the center between the two electrodes of the second separation step a medium fraction was obtained, while close to the negative electrode the concentrate of valuable material was collected. The latter was fed into an electrostatic free ~fall separator (4 to 4.5 kY/c~ fieId intensity) provided with circul~tion equipment. ~t the negative electrode at the foot of this separator a potassium fertilizer salt ha~ing a K2O~content of 60,4 percent by weight and a clay content of 0.5 pexcent by wei~ht was obtained as reaction product in an amount of 38.9 t/h (see Table Il. Close to the postive elec-trode a residual fraction was obtained. This residual frac-tion was mixed with the medium fraction and, after the mixturewas recharged at a relative humidity of 15 to 25 percent, it was fed into a drum separator of known construction having a field intensity of 4 to 5 kV/em.
From this separator were collected 8.2 t/h of a residue to be discarded whieh had a K2O-content of 13.8 per-cent by weight and a elay eontent of 13.0 percent by weight (see Table I). The valuable material fraction obtained from this separator was returned to the start of the first separation step.
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The clay-specific conditioning agents used in the two last mentioned processes, however, impede the subsequently necessary triboelectric charging of the sylvite against the other components of the sylvite-containing concentrate and therefore complicate the further electrostatic treatment of these concentrates. For this reason, investigations were di--rected towards finding a method for obtaining component~
concentrates from clay containing sylvinitic crude potassium -6~
salts b~ way of a simple electrostatic separation process without the use of clay~spec~fic condàtioning agents, whereby the resulting concentrate can ~e further processed without difficulty or can be employed for utility purposes.
It has now been found that potassium fertilizer salts having a K2O~content of at least 60 percent can be obtained by a method comprising a multistep electrostatic separation of ground conditioned and triboelectrically charged, sylvinitic crude potassium salts, which contain clay, at predetermined relative atmospheric humidity and elevated temperatures in electrostatic free-fall separators with an electric field intensity of above 3 kV/cm. Accordingly, the method comprises:
a) conditioning crude potassium salts, which are ground to a grain size of about 1 to 2 mm depending on the lS degree of inter~rowth, with about 50 to 100 g/t oE a mixture of fatty acids and about 50 to 100 g/t salicylic acid and feeding the conditioned raw potassium salts in an atmosphere having a relative humidity of about 5 to 12.5 percent triboelectrically charged into an electrostatic free-fall separator in which the middlings are recirculated, at the foot of the separator collecting close to the positive electrode a residue to be discarded and close to the negative electrode a pre-concentrate of valuable material;
b) conditioning the pre~concentrate of step a~ with about 100 to 300 g/t silica and feeding said conditioned pre-concentrate in an atmosphere having a reIative humidity of bout 5 to 10 percent triboelectrically charged into an electro-static free-fall separator without recirculation of middlings, at the foot of the separato~ collectin~ close to the positi~e electrode a residue to be discarded, close to the negative electrode a first concentrate of ~aluable material, and in the centre between the two electrodes a medium friction;
c~ feeding the first concentrate of step b) into an electrostatic ~ree-fall separator in which the middlings are circulated, at the foot of the separator collecting close to the positive electrode a residual fraction and close to the negative electrode a potass.ium fertilizer salt product having a X2O-content of at least 60 percent by weight; and d) recovering valuable potassium material from the mQdium fraction of step b) and the residual fraction of step c).
The method according to the invention is particularly directed to the recovery of a concentrate of potassium fertilizer salt having a K2O-content of 60 percent by weight or more from sylvinitic crude potassium salts having a clay-content of 2 percent by weight or more by way of electrostatic separation in free-fall separators. Such a crude potassium salt can, for example, have the following composition:
41.0 % by weight KCl 55.8 ~ by weight NaCl 0.3 % by weight CaSO4 2.9 ~ by weight Clay or 24,5 % by weight KC1 Q..5 % by weight MgSO4 H2 72.3 % by weig~t NaCl 2.7 % ~y welght Clay.
According to the in~enti~e method the crude potassium ~3~
salt is first ground to an average grain size of preferably 2 mm.
The ground crude potassium salt is then thoroughly mixed with 50 to 100 g/t of a mixture oE fatty acids and with 50 to 100 g/t salicylic acid. Thereafter this mixture is supplied to a fluidized bed which is exposed to an air stream having a relative humidity of from 5 to 12O5 percent and a respective temperature. In the fluidized bed the particles of the ground crude potassium salt become charged triboelectrically.
Following this the crude potassium salt is fed into a free fall separator between the electrodes of which a high voltage field having a field intensity of 3 to 5 kV/cm is maintained and which is provided with e~uipment for the recirculation of the middlings produced in the separator. At the foot of the separator close to the positive electrode a residue accumulates which besides containing considerable amounts of roek salt also contains elay and sulfate as well as relatively small amounts of potassium chloride. This residue is discarded.
Close to the negative eleetrode a pre-concentrate of valuable material enriehed in potassium chloride is obtained. In the eenter between these collecting stations a residue accumulates which is reeireulated and, in admixture with crude potassium salt, again fed into the free-fall separator.
The pre eoneentrate of valuable materi~l obtained in this step is then mixed thoroughly ~ith 100 to 300 g/t finely divided siliea and in an atmosphere ha~in~ a relative humidity of 5 to 10 pereent tr~boelectrieally charged by brisk move~
ment of the particles relative to each other, preferably in a fluidi,zed bed~ Following this the'pre ~oncentrate is again fed into a free~~all separator in which an electrostatic field with an intensity of 3 to 5 kV/cm is maintained~ This free~fall separator is not provided with equipment which allows recirculation of middlings or, is such equipment is available, it remains idle during this step.
At the foot of the free-fall separator close to the positive electrode a residue which mainly consists of rock salt and contains clay and small amounts of potassium chloride accumulates and is discarded. Close to the negative electrode a first valuable concentrate is collected which already has a K2O~content of more than 50 percent by weight. The medium fraction accumulating between the two electxodes of the free fall separator is collected and can, according to procedures described hereafter, be used to recover valuable potassium compounds since the K2O-content of the fraction is above 25 percent by weight but due to its relatively high clay-content the fraction cannot be recirculated.
The first concentrate of valuable material is, without renewed conditioning and triboelectric charging fed into an electric ~ree-fall separator in which an electrostatic high voltage field of 3 to 5 kV/cm is maintained. This free-fall separator has to be provided with equipment which allows recirculation of the middlings obtained in the separator. At the foot of this separator close to the positi~e electrode a residu~l fraction is collected wh~ch is ~ixed ~ith the medium fraction of the preceding separation step, Close to the 4~)~6 '`10--`
negative electrode a potassium fertilizer salt product having a K2O~content of at least 60 pe~cent b~ weight is recovered in a yield of at least 65 percent, prefexably over 67 percent, of the K2O-content of the crude potassium salt.
The clay content of this prGduct is below 1.0% by weight. The middlings accumulated in the free~fall separator are reintro-duced into the separator.
From the medium fraction collected in the preceding separating step and the residual fraction obtained in the last mentioned separation step valuable potassium compound concen-trates can be recovered in known manner according to dissolving processes, preferably hot dissolving processes such as, for example, described in "Ullmanns Encyklopadie der technischen Chemie" 3rd Edition, Vol. 9, p. 185 (1957). It is also possible to feed a mixture of the medium fraction and residual fraction into a conductivity separator in the form of a drum separator and to separate the mixture into a salt fraction low in clay and a residue rich in clay, whereby the latter is discarded.
Such a process is; for example, described in German patent 10 52 921. The salt fraction obtained by this separation process is mixed with the crude pota9sium salt which is pro-cessed according to the invention.
In accordance ~ith the in~entive process, the clay is stepwise charged against the potassium chloride and remo~ed at the appropriate locations in the process. To this effect it is important that the reIative humidity in the charging atmosphere of the first process step lies between about 5 and ~11~
12.5 percent and that the crude potassium salt to be separated is conditioned with fatty and salicylic acid. Under these conditions the clay does not become charged together with the sylvite~ According to the inventive procedures distribution of the clay in about equal amounts over the residue to be dis-carded and the pre-concentrate of valuable material can be achieved already in the ~irst SeparatiQn step. In the second separation step the medium ~raction also contains a consider-able portion of clay. For this reason this fraction is not recirculated into the free-fall separator. The residue obtained in this separation step also contains a considerable portion of clay.
The residues of the first and second separation step contain already about 80 percent of the clay introduced with the crude potassium salt, but contain at mos-t 7 percent of the s~lvite, so that the residues can be discarded without consid-erable loss. This does not apply to the medium fraction of the second and the residual fraction of the third separating step which also contain clay, but include additionally about 23 percent of the sylvite contained in the crude potassium salt which is introduced into the inventive process. The mixture of these fractions therefore has to be treated to recover valuable potassium compounds. This recovery can be effected according to known dissolving processes~ preferably a hot dis-solving proce$s~ Particularly advantageously this recovery isperformed by ~ay of conductivity separation in a drum separator.
The xesulting concentrate of valuable material, which contains -12~
only very small amounts of clay~ is added to the crude potassium salts which are to be treated in accordance with the inventive process. Due to the particular combination of pro-cedures, the process according to the invention allows for the first time the direct production of a potassium fertilizer salt having a K2O~content of at least 60 percent by weight in a yield of about 70 percent from clay-containing sylvinitic crude potassium salts without requiring technically complicated pretreatments to separate the clay and without the resulting disadvantages regarding the electrostatic separation. Moreover, when a drum separator, the throughput capacity of which is considerably smaller than the capacity of a free-fall separator, is used in accordance with the invention, the drum separator can be loaded with only as much material as is commensurate with its capacity without thereby affecting the operation of the free-fall separators which o~erate with a considerably larger throughput.
Example 100 t/h of a crude potassium salt ground to an average grain size of 2 mm and containing 41.0% by weight Sylvite 55.8% by weight Rock Salt 0.3~ by weight Anhydrite 2.9~ by weight Clay were mixed with 75 g~t ea`ch of salicylic acid and a mixture of fatty acids having 10 to 15 carbon atoms per molecule, and ~ere fed into a fluidized bed dryer which was exposed to air ~13~
of 10 percent relative humidity~ The mixture which ~as drawn off the dryer was directl~ fed ~nto a free~fall separator provided with circulation equipment, in which an electro-static high voltage field of 4 to 4.5 kV~cm was maintained.
Such a free-fall separator is described in German patent 11 54 052. At the foot of this separator close ~o the positive electrode a residue which was discarded was obtained. The produced middlings were circulated through the separa~or. At the negative electrode a concentration of valuable material was obtained which, after having been mixed with 200 g/t finely divided silica, was triboelectrically charged in a fluidized bed dryer which was exposed to air of 9 percent relative humidity. Following this, the concentrate was fed into an electrostatic free-fall separator (4 to 4.5 kV/cm field intensity). At the foot of this separator close to the positive electrode a residue which was discarded was obtained. This residue and the residue from the irst separation step were obtained in an amount of 52.9 t/h having a K2O-content of 2.4 percent by weight and a clay content of 3.1 percent by~,weight (see Table I).
Xn the center between the two electrodes of the second separation step a medium fraction was obtained, while close to the negative electrode the concentrate of valuable material was collected. The latter was fed into an electrostatic free ~fall separator (4 to 4.5 kY/c~ fieId intensity) provided with circul~tion equipment. ~t the negative electrode at the foot of this separator a potassium fertilizer salt ha~ing a K2O~content of 60,4 percent by weight and a clay content of 0.5 pexcent by wei~ht was obtained as reaction product in an amount of 38.9 t/h (see Table Il. Close to the postive elec-trode a residual fraction was obtained. This residual frac-tion was mixed with the medium fraction and, after the mixturewas recharged at a relative humidity of 15 to 25 percent, it was fed into a drum separator of known construction having a field intensity of 4 to 5 kV/em.
From this separator were collected 8.2 t/h of a residue to be discarded whieh had a K2O-content of 13.8 per-cent by weight and a elay eontent of 13.0 percent by weight (see Table I). The valuable material fraction obtained from this separator was returned to the start of the first separation step.
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Claims (3)
1. A method for the preparation of potassium fertilizer salt having a K2O-content of at least 60 percent by way of a multistep electrostatic separation of ground, conditioned and triboelectrically charged, sylvinitic crude potassium salts, which contain clay, at predetermined relative atmospheric humidity and elevated temperatures in electrostatic free-fall separators with an electric field intensity of above 3 kV/cm, comprising:
a) conditioning crude potassium salts, which are ground to a grain size of about 1 to 2 mm depending on the degree of intergrowth, with about 50 to 100 g/t of a mixture of fatty acids and about 50 to 100 g/t salicylic acid and feeding said conditioned raw potassium salts in an atmosphere having a relative humidity of about 5 to 12.5 percent triboelectrically charged into an electrostatic free-fall separator in which middlings are recirculated, at the foot of said separator collecting close to the positive electrode a residue to be discarded and close to the negative electrode a pre-concentrate of valuable material;
b) conditioning the pre-concentrate of step a) with about 100 to 300 g/t silica and feeding said conditioned pre-concentrate in an atmosphere having a relative humidity of about 5 to 10 percent triboelectrically charged into an electrostatic free-fall separator without recirculation of middlings, at the foot of said separator collecting close to the positive electrode a residue to be discarded, close to the negative electrode a first concentrate of valuable material, and in the center between the two electrodes a medium fraction;
c) feeding the first concentrate of step b) into an electrostatic free-fall separator in which the middlings are recirculated, at the foot of said separator collecting close to the positive electrode a residual fraction and close to the negative electrode a potassium fertilizer salt product having a K2O-content of at least 60 percent by weight; and d) recovering valuable potassium material from the medium fraction of step b) and the residual fraction of step c).
a) conditioning crude potassium salts, which are ground to a grain size of about 1 to 2 mm depending on the degree of intergrowth, with about 50 to 100 g/t of a mixture of fatty acids and about 50 to 100 g/t salicylic acid and feeding said conditioned raw potassium salts in an atmosphere having a relative humidity of about 5 to 12.5 percent triboelectrically charged into an electrostatic free-fall separator in which middlings are recirculated, at the foot of said separator collecting close to the positive electrode a residue to be discarded and close to the negative electrode a pre-concentrate of valuable material;
b) conditioning the pre-concentrate of step a) with about 100 to 300 g/t silica and feeding said conditioned pre-concentrate in an atmosphere having a relative humidity of about 5 to 10 percent triboelectrically charged into an electrostatic free-fall separator without recirculation of middlings, at the foot of said separator collecting close to the positive electrode a residue to be discarded, close to the negative electrode a first concentrate of valuable material, and in the center between the two electrodes a medium fraction;
c) feeding the first concentrate of step b) into an electrostatic free-fall separator in which the middlings are recirculated, at the foot of said separator collecting close to the positive electrode a residual fraction and close to the negative electrode a potassium fertilizer salt product having a K2O-content of at least 60 percent by weight; and d) recovering valuable potassium material from the medium fraction of step b) and the residual fraction of step c).
2. A method according to claim 1 wherein the medium fraction of step b) and the residual fraction of step c) are converted to crude potassium salts by a dissolving process.
3. A method according to claim 1 wherein the medium fraction of step b) and the residual fraction of step c) in admixture are fed into a conductivity separator in the form of a drum separator where the mixture is separated into a residue having a high clay content, said residue being discarded, and into a salt fraction having a low clay content, said fraction being mixed with the crude salt of step a).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19823216735 DE3216735C1 (en) | 1982-05-05 | 1982-05-05 | Process for the production of potash fertiliser salt with a K2O content of at least 60 % by weight, by multistage electrostatic separation |
| DEP3216735.0-24 | 1982-05-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184046A true CA1184046A (en) | 1985-03-19 |
Family
ID=6162724
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000427125A Expired CA1184046A (en) | 1982-05-05 | 1983-05-02 | Method for the preparation of potassium fertilizer salts by electrostatic separation |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1184046A (en) |
| DD (1) | DD209181A5 (en) |
| DE (1) | DE3216735C1 (en) |
| ES (1) | ES522077A0 (en) |
| FR (1) | FR2526417B1 (en) |
| SU (1) | SU1329613A3 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3439042A1 (en) * | 1984-10-25 | 1986-04-30 | Kali Und Salz Ag, 3500 Kassel | METHOD FOR THE ELECTROSTATIC TREATMENT OF GROUND POTASSIUM SALTS CONTAINING KIESERITE |
| DE3825461A1 (en) * | 1988-07-27 | 1990-02-01 | Kali & Salz Ag | Process for the electrostatic processing of clay-containing crude salts |
| DE102007049182B3 (en) * | 2007-10-13 | 2009-05-14 | Kali-Umwelttechnik Gmbh | Producing potassium-magnesium-fertilizer and filling material, from polymineralic raw potassium salt, comprises e.g. fragmenting dry raw salt by sieving to different fractions and separating to magnetic and non-magnetic fractions |
| RU2555906C1 (en) * | 2014-02-11 | 2015-07-10 | Закрытое акционерное общество ВНИИ Галургии (ЗАО ВНИИ Галургии) | Method of processing potassium-containing ores |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1390910A (en) * | 1962-08-24 | 1965-03-05 | Kali Forschungsanstalt Gmbh | Process for the electrostatic treatment of crude salts containing carnallite |
| DE1953534C3 (en) * | 1969-10-24 | 1974-03-14 | Kali Und Salz Ag, 3500 Kassel | Process for the electrostatic treatment of crude potash salts containing Kiesent |
-
1982
- 1982-05-05 DE DE19823216735 patent/DE3216735C1/en not_active Expired
-
1983
- 1983-04-27 SU SU833584517A patent/SU1329613A3/en active
- 1983-04-29 FR FR8307124A patent/FR2526417B1/en not_active Expired - Fee Related
- 1983-05-02 CA CA000427125A patent/CA1184046A/en not_active Expired
- 1983-05-02 DD DD25050583A patent/DD209181A5/en not_active IP Right Cessation
- 1983-05-04 ES ES522077A patent/ES522077A0/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| SU1329613A3 (en) | 1987-08-07 |
| ES8402516A1 (en) | 1984-02-01 |
| DE3216735C1 (en) | 1983-08-25 |
| FR2526417A1 (en) | 1983-11-10 |
| FR2526417B1 (en) | 1990-06-01 |
| ES522077A0 (en) | 1984-02-01 |
| DD209181A5 (en) | 1984-04-25 |
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