Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a method of producing an adsorbent,
typically for animal excretions, from a bloating mineral and
calcium sulfate hemihydrate where expanded granular bloating
mineral and calcium sulfate hemihydrate are mixed to form a
granulated product, where the calcium sulfate hemihydrate is
converted by the addition of a surplus of water in toto into
calcium sulfate dihydrate and where free water is removed by
drying.
In a prior-art method (German Patent 30 21 377) of this type,
a weight ratio of calcium sulfate to perlite of 5 : 1 maximum
is recommended for the adsorbent and the mixing is effected
in a rotating granulating drum whereby substantially round
granules are produced with a perlite core and a calcium
sulfate dihydrate coating, the granulated product having a
total water content of about 18% by weight. The satisfactory
adsorption effect of this adsorbent is achieved by the use of
a relatively great amount of perlite which is expensive.
Also, adequate hardness and abrasion resistance of the
adsorbent manufactured according to the prior art method is
obtained bv the addition of polyalcohol.
The present invention provides a method of the type initially
referred to by means of which an adsorbent can be made where
the percentage of bloating mineral is reduced, the adsorption
performance is substantially maintained and its hardness is
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increased without any additive substance. The method
according to the present invention is characterized in that
calcium sulfate hemihydrate and bloating mineral are mixed in
such proportion that a weight ratio between calcium sulfate
and the bloating mineral > 5 : 1 and up to 10 : 1 exi.sts in
the adsorbent, in that the mixing is effected by calcium
sulfate hemihydrate and the bloating mineral being poured
toyether in a tank and stirred there in bulk by means of a
stirring mechanism to form a granulated mixture, in that the
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~i,
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granulated product mixture aEter adding the water and before
drying is allowed a retention time of at least 4 minutes, and in
that such a proportion of the dry calcium sulfite dihydrate is
converted by calcining at 120 - 200C into calcium sulfate hemi-
hydrate that the adsorbent has a total water content of 1 ~ by
weight to 16 % by weight.
The method according to the invention uses a reduced amount of
bloating mineral and represents an adsorbent which, on the one
hand, contains particles consisting o~ an bloating mineral core
with a calcium sulfate coating and, on the other hand, particle~
which consist only of calcium sulfate. The particles of the ad-
sorbent are substantially of a shape other than round and have an
open-pore surface. Despite the reduction in the amount of bloat-
ing minerals, the total adsorption effect of the adsorbent i~
maintained due to the additional adsorption effect of the cal-
cined calcium sulfate. A reduction in the total water content by
1 % by wéight increases the adsorption effect by abt. 3 %. Al-
though, in calcining calcium sulfate dihydrate lumps, the hard-
ness of the product normally decreases considerably, this is not
so in the case of the method according to the invention. The
hardness of the manufactured adsorbent is not less than the
hardness of the granulated material before calcining and greater
than that of the adsorbent made according to the prior art method
It is eespecially effective and advantageous if the calcium
sulfate hemihydrate and bloating mineral are ~tirred in such
proportion that a weight ratio of calcium sulfate to bloating
mineral of 6 : 1 to 8 : 1 exists in the adsorbent. ~7ith this
weight ratio, there is a favourable saving in the amount of
bloating mineral and the specific weight of the adsorbent is
still not too high. The granular expanded bloating mineral is
included in the adsorbent not only because of its adsorbent ac-
tion, but also in order to reduce the specific weight of the ad-
sorbent within certain lirnits. In many cases, for instance in
producing pet litter, a ratio of 5.5 : 1 - 6.5 : 1, for instance
6 : 1 is preEerred.
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Conservative calcining is important Eor the properties of the
adsorbent made by the method according to the invention. It i9
especially effective and advantayeous, thereEore, if calcining is
effected at 135 - 1~5C. At the~e calcining temperatures, im-
proved adsorption effect and hardnes~ are obtained.
A calcining temperature up to 150~C is in many cases sufficient.
A increase in the calcining temperature to, say, lg0C will ab-
breviate the time required for the calcining process. Calcining
temperatures of 120- 190C, preferably 160 - 180C have proved to
be especially effective and advanta0eous.
It i5 also especially effective and advantageous if the propor-
tion converted into calcium sulfate hemihydrate i9 such thak the
adsorbent has a total water content of 6 % by weight to 12 % by
weight. On the basis of such calcining, the adsorbent calcium
sulfate which, in addition to hemihydrate, also comprises di-
hydrate and anhydrite III develops an excellent adsorption effect
The retention time allowed for the granulated mixture produced
with the addition of water after making this granulated mixture
and before drying has proved to be specially important for its
hardness and abrasion resistance. It is especially effective and
advantageous if the granulated mixture i5 allowed a retention
time of up to 8 minutes before drying. During this period of
time, the reaction of the water with the calcium sulfate
hemihydrate can proceed completely without any disturbance. In
practice, a retention time of about ~ minutes is as a rule suf-
ficient in order to obtain a ~ufficiently hard granulated product
and one of up to 5 minutes is still practicable.
The adsorbent made according to the invention can be used for
liquids of inorganic or organic origin, e.g. as a binding agent
for acids, alkalies or oil which may also be mixed with water.
However, the adsorbent is preferably used as a binding agent for
animal excretions, e.g. aq pets litter.
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The e~pensive propor-tion o~ bloating minerals in the finlshed
product can be reduced by more than 50 % which amounts to a
distinct saving in cost. The adsorbent granulated product is of
the open-pore type and has a shape other than round which i3 im-
portant when used as a pets litter because the granulated product
will not roll. It is especially effective and advan-tageous if the
adsorbent is produced with A bulk weight of 0.35 - 0.6 kg/liter,
preferably 0.~ - 0.5 kg/liter because lighter products would be
scratched out by the cats from the litter box. The adsorbent
according to the invention is harder and will not powder so that
the cat after using the litter box will not leave any traces.
The bloating mineral used for the method according to the inven-
tion may, Eor instance, be vermiculite which, in the raw condi-
tion is a water-containing mineral in line with the bloating
minerals under consideration here. It is especially effective and
advantageous, however, if perlite is used as the bloating mineral
Perlite is not yellow or brown, but white and is superior in re-
spect of the properties which the adsorbent to be produced
according to the invention is desired to have.
The adsorbent manufactured according to the invention may be used
not only for adsorption purpo~es, but also for other applica-
tions, e.g. in the building industry as an aggregate in gypsum-
compatible mortar mixtures. It is especially effective and ad-
vantageous if the adsorbent made according to the invention is
used as granulated building material for filling. This is because
this product has positive properties in respect of bulk weight,
abrasion, consolidation and strength which ma}ce it suitable as a
filler.
The total water content can be reduced by calcining to 1 % by
weight, ~I decrease in the total water content improving the ad-
sorption effect. It is especially effective and advantageous if a
total water content of about 2 % by weight, but not above 8 % by
weight, or of a percentage between these two limits is adjusted
by calcining. In this case, strength, bulk weight and adsorption
capacity will be in a preferred relationship to each other.
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The size of the expanded granular bloating mineral used is 0 ~ 6
mm and at least 85 % of the granules in the finished adsorbent
have a size > 1.25 mm. In this manner, a granulated product i5
obtained with approximately 95 % > 0.8 mm up to 6 mm . As a rule,
the adsorbent comprises greater particles which are calcium 9ul-
fate-coated bloating mineral particles and smaller particles
which con~ist only of calcium sulfate.
~t least 90 ~ of the granules in the bloating mineral used
should h~ve a size of 1 - 6 mm, because ~maller dust fractions
are undesirable. In the ca~e of the calcium sulfate hemihydrate,
at least 80 %, preferably at least 90 %, should be < 63 ~m,
For instance, 143 kg of plaster of Paris would be mixed Eor G0
seconds with 20 kg of expanded perlite in size~ of 50 % 0 - 3 mm
and 5~ % 3 - 6 mm with 80 liter water added in an Eirich mixer. ~
surplus of water is added. ~s a rule, the water is poured into
the mixer as a solid stream or flush. The peripheral ~peed of the
stirring mechanism is 6.5 m/s. An open-pore type granulated ma-
terial is obtained. The moist granulated material is allowed a
retention time on a slow-running conveyor prior to drying and
calcining.
The drying and calcining equipment is so conceived that the
granulated material is subject to minimum friction movements.
This is important in order to prevent abrasion of the initially
moist material and to preserve the open-pore surface. Therefore,
a drum dryer is not suitable while a fluidized-bed drying and
calcining installation or a drying and calcining apparatus of the
grain dryer type is suitable. Excellent results have been ob-
tained with drying and calcining equipment using a belt dryer
comprising a screen-type perforated belt where the carrying run
on which the material is deposited has hot gas blown through from
below.
The drying and calcining equipment is of the two-stage type. In
the drying stage, the free moisture is removed at 80 - 100C,
typically 90C. In the ca]cining stage, the granulated material
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is treated with hot air at abt. 130C in order to reduce t~e wa-
ter of crystallization from abt. 20 ~ to abt. 8 ~. This step im-
proves the adsorption effect of the f inished adsorbent by up to
30 % without the hardness and, consequently, abrasion re~istance
of the f inished product being noticeably impaired.
Generally, any suitable mixing apparatus using a ~tirring tool
may be used. It is especially effective and advantageou~ i~ mix-
ing is carried out in a rotating container and with the stirring
tool arranged eccentrlcally and rotating in the opposite direc-
tion and if the stirring tool is ~ubstantially formed by a plu-
rality of wire-type rods which substantially e~tend in the di-
rection of the rotating a~i~ and are arranged about the rotating
axis at a distance from the latter. This configuration enables
improved mixing to be achieved in a reduced period of time with-
out too many particles of the material being disintegrated.
The following table is intended to illustrate the influence of
the calcination and the perlite proportion on adsorption:
Perlite Total HzO Adsorp- Bulk Fracture Abra-
content of content of tion density resistance sion
finished finished after
product product Heberlein
% ~ % HzO g/l N %
17.8 80 ~10 20 - 35 16
10.5 100 380 20 - 32 17
8 110 370 20 - 32 18
12 17.9 75 ~40 25 ~ ~8 7.5
12 10.1 95 ~30 25 - 46 8.5
12 8.6 105 410 25 - 45 10.~
For a comparison, the granulated product obtained according to
German Patent 30 21 377 i9 as follows:
32 13 109 250 5 - 10 54
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In order to determine the adsorption (water adsorption capacity),
110 ~ of the substance to be tested was filled in a cyllnder.
This cylinder was closed at the bottom with a sieve. 250 ml water
was poured onto the substance to be tested from the top. The
amount of water running out was measured in ml. The indication of
adsorption of, say, 100 % means that 1 kg of the granulated
product material is capable of absorbing 1 kg of water.
The fr~cture resi~tance teat is rnade with the Heberlein 10 type
tablet tester. ~ranules of the granulated material to be examirled
with diameters of 1.5 - 3.5 mm are tested for resistance to
fracture. A mean value is derived from the 10 values obtained and
stated in terms of fracture resistance in kgf or N.
Abrasion test:
1. 100 g granulated product material is screened on the aieve
rnachine (model Siebtechnik Muhlheim-Ruhr) on 20 cm circular
sieves for 5 minutes.
3.5 mm and 250 ~ sieve and pan material >3.5 mm and C 250
is rejected.
2. Of the screened material 250 ~ - 3.5 mm, 50 g plus 300 g
~teel balls of ~ mm dia are filled in the ~ieve pan and
shaken for 20 minute~ in the screening machine.
3. Subsequently, the contents of the pan are poured on a 3.5 mm
sieve and the steel balls are removed. The screened material
is then placed again on a 250 ~ sieve and screened for 5
minutes. The material passing through the 250 ~ sieve is
defined as abrasion or attrition.
Abrasion (attrition) = Passed ma erial (q) x_100 = x %
50 g
