Note: Descriptions are shown in the official language in which they were submitted.
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
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.
o li
h
Lq ~ ) r1 r~l O
r~l I .~ In o ~
H ~ I r~ .D r-l
O ~
~ U
~1 ra
U~ C
~ W ll
~1 ll r~
~1)
i A~
Qll ~,A~t~t~
~)l r-l ~ ~
0 l ~V
O ~r I OD U~ U7 ,-1 ~:: C~
~. I . ~ . ~ ~rl
U~ w~ r~ ~1 1 ~ ~ O ~ ~
~ ~ ,A~ I ~1 h
O ~ ~ l 11
H r rl ~) i
A ~ ~ ~ ~1
s~ ~ c l a
~ l ~ ta
~--¦ ~Or~ AW U~
~O I 11-) ~r) O O J_)
A ~ i l ~ O
Ol ~ ~
~_) i ~) ~ O l_ 1")
l ~rl ~ ~ O ~
i ~ ~) P~; C~
~i
U~ ~ i O CO ~) C5~
I
AW L~--~ I r~ O ~
~1 ~iI ~r Lll Ui
h I ~ ~i
O i o~
~ Ui
.) h 1
~1 ~ ll~
w~~ir~ ra
U~ h
~ ~ ~t ~t rl ~1
O I r~ ~ 1~
~1 ~rl O ~ '~ ~ O
~A;~ U7
a~
dP I ~ dP ~P ~ ~ a
