Process for the manufacture of zeolites 4A having a high crystallinity and a fine granulometry and being particularly suitable for the formulation of detergent compositions

The synthesis of zeolites 4A having a high crystallinity and a fine granulometry is disclosed, by the addition in a first stage of a sodium silicate solution to a sodium aluminate solution (containing an excess of NaOH and heated to a temperature of from 50.degree. to 100.degree. C.), and by the crystallization in a second stage at a temperature of from 70.degree. to 105.degree. C., characterized in that the temperature of the sodium silicate solution is lower by at least twenty Centigrade degrees than that of the sodium aluminate solution, the molar ratios SiO.sub.2 :H.sub.2 O and SiO.sub.2 :Na.sub.2 O in the sodium silicate solution being respectively from 0.030 to 0.150 and from 1.95 to 2.30, and the weight ratio between the reaction mother liquor and the zeolite thus formed being from 6.5 to 20.

This invention relates to a process for the manufacture of zeolites 4A 
having a high degree of crystallinity and a fine granulometry, and 
particularly suitable for the formulation of detergent compositions. 
Belgian Pat. No. 860,757 describes preparing zeolites of this type by 
adding to a hot (70.degree. C.) solution of a particular sodium silicate, 
a hot (70.degree. C.) solution of sodium aluminate containing an excess of 
NaOH. The silicate solution is prepared by mixing together, under 
stirring, an aqueous water-glass solution, in which the molar ratio 
SiO.sub.2 :Na.sub.2 O is 3.46, with an aqueous solution of NaOH, whereby 
the molar ratio drops to 1.65. French Pat. No. 2,096,360, on the contrary, 
describes pouring the hot silicate solution into the hot aluminate 
solution, previously placed into a reactor, while another Belgian Patent 
(No. 862,740) describes mixing the two solutions both at low temperature. 
According to these patents it is possible to obtain particles with a high 
degree of crystallinity and fine granulometry; however, the statistical 
particle size distribution is not fully satisfactory. In fact it is known 
that for the purposes of detergency, the zeolite particles must show a 
granulometric distribution completely between 1 and 10 .mu.m. The 
particles above 10 .mu.m display slow exchange kinetics with calcium and 
especially with magnesium, leave residues on the fabrics, and clog the 
discharge pipes; particles below 1 .mu.m penetrate deeply into the mesh of 
the fabrics, thereby causing a progressive matting of the same, and 
require too long a settling time in the ecological vats for the treatment 
of waste water. Experience teaches that best results, in the way of good 
detergency without ecological problems, are reached only when the 
granulometric modulation index is sufficiently high and the coarse 
fraction is negligible. By the term "granulometric modulation index" 
(.omega.) is to be understood the percentage by weight of particles the 
size of which is from 3 to 8 .mu.m, when the granulometric analysis is 
carried out with a Coulter Counter, as indicated in the Belgian Pat. No. 
860,757. By the term "coarse fraction" (.alpha.) is to be understood the 
percentage by weight of particles with a size greater than 10 .mu.m 
(Coulter Counter analysis). Another drawback of the prior art process is 
the complexity and the slow rate of the reaction. 
Thus, one object of the present invention is that of providing a simpler, 
faster, and more flexible process that will lead to a product of the same 
or even superior quality, and more particularly to a product that will 
have a greater softening power on waters made hard by the presence of 
magnesium ions. Still other objects will become evident in the following 
description. 
In its more general form, this invention provides a process for the 
manufacture of zeolites 4A, having a high degree of crystallinity and a 
fine granulometry, by the addition, in a first stage, of an aqueous sodium 
silicate solution to an aqueous sodium aluminate solution, containing an 
excess of NaOH and preheated to a temperature from 50.degree. to 
100.degree. C., and by the crystallization, in a second stage, at a 
temperature from 70.degree. to 105.degree. C., characterized in that the 
temperature of the sodium silicate solution is lower by at least twenty 
Centrigrade degrees than that of the sodium aluminate solution, the molar 
ratios SiO.sub.2 :H.sub.2 O and SiO.sub.2 :Na.sub.2 O in the sodium 
silicate solution being respectively from 0.030 to 0.150 and from 1.95 to 
2.30, and the weight ratio (.tau.) between the reaction mother liquor and 
the zeolite thus formed (understood as containing 22% by weight of water 
of crystallization) being from 6.5 to 20, but preferably from 8 to 15. 
The ratio (.tau.) may be defined in a precise way by the equation: 
##EQU1## 
wherein the symbols g Na.sub.2 O, g Al.sub.2 O.sub.3, etc., represent the 
quantities in grams of the fed-in reactants. 
By the process of this invention it is possible to obtain zeolites 4A with 
a high degree of crystallinity and a fine granulometry, having a 
granulometric modulation index (.omega.) equal to or greater than 85 and a 
coarse fraction (.alpha.) equal to or less than 1 (even down to zero). 
The products obtained by the process according to the invention have a very 
high exchange power, even with respect to waters made hard by the presence 
of magnesium ions. The exchange with magnesium can in fact attain (in 
equivalent terms) the level of 45 mg CaO/g (and even 50, in some cases), 
measured according to the method described below. 
This invention becomes even more significant if one considers that 
water-glass in which the molar ratio SiO.sub.2 :Na.sub.2 O is about 3.46 
(a product used in most of the other synthesis processes) is prepared by 
heating in a smelting furnace a mixture of siliceous sand and sodium 
carbonate, with a waste of energy, while the sodium disilicate (Na.sub.2 
Si.sub.2 O.sub.5) and the other silicates, according to the present 
invention are obtainable in a much less complex way, i.e., directly in 
solution, by the hot digestion of the silica in a solution of NaOH. 
The rate of formation of the desired zeolite is very fast and the process 
shows quite a high degree of flexibility with regard to the operative 
conditions such as temperature and time, a flexibility that in general is 
not obtained with processes involving too high SiO.sub.2 :Na.sub.2 O 
ratios. 
Zeolites obtained according to the present invention have been tested in 
some of the formulations described in Belgian Pat. No. 860,757, Italian 
Pat. No. 1,009,446, and U.S. Pat. No. 4,083,793, always obtaining 
excellent results. 
There are various possible ways of carrying out the invention. Thus, for 
instance, it is convenient that the silicate solution be added within a 
time equal to or below 15 minutes and that the temperature of the mixture 
during the first stage of the synthesis be maintained equal to that of the 
sodium aluminate solution, this latter being preferably between 70.degree. 
and 75.degree. C. Moreover, it is also convenient to subdivide the second 
stage into 3 sub-stages, the first sub-stage being characterized by a 
temperature equal to the temperature of the first stage, the second by a 
temperature rising from 70.degree. to 105.degree. C., and the third by a 
constant temperature between 95.degree. and 105.degree. C. 
The time of the sub-stages is respectively between 30 and 60 minutes 
(preferably between 40 and 50) for the first, between 10 and 80 minutes 
(preferably between 15 and 40) for the second, and between 10 and 90 
minutes (preferably between 15 and 60) for the third. 
For making the reaction mixture homogeneous a bland or mild stirring is 
sufficient. 
The reaction slurry may be conveniently filtered to centrifuged in order to 
obtain the separation of the microcrystals, and the mother liquor, after 
separation, may be discharged or recycled for the preparation of the 
sodium aluminate solution. 
Still another variant consists in preparing, separately, a new sodium 
aluminate charge while the reactor is in operation. 
The process may be conducted either in a continuous or in batch manner.

According to FIG. 1, into a reactor A are introduced, in the given order 
(lines 1, 2 and 3) NaOH, alumina and deionized water. The resulting sodium 
aluminate solution is thereupon made to react with a solution of sodium 
disilicate 4 in A and the reaction mixture 5 is then separated by 
centrifugation in B from the mother liquor 6 which is then conveyed into 
the collecting tank C. When the soda-rich mother liquor is re-cycled in 
partial substitution for the deionized water and the NaOH, it is fed into 
reactor A through line 7. The centrifuged micro crystals are washed with 
de-ionized water (line 8) and then conveyed into tank D where the cake 9 
is repulped with further de-ionized water (line 10). The resulting slurry 
11 is then conveyed into a spray dryer E and the resulting dry zeolite 12 
is stored in F. In the case of dryers of a different type, i.e., other 
than a spray dryer, cake 9 is conveyed directly to dryer E and then to 
storage F. 
The meaning of the remaining figures is readily deducible from the 
following examples that illustrate the invention without however limiting 
in any way of scope of the same. 
EXAMPLE 1 
Into a stainless steel reactor [reactor A in FIG. 1], having a holding 
capacity of 1200 liters, provided with a thermostatically controlled 
heating system and a reflux condenser and a stirrer revolving at about 120 
rpm, were introduced 239 kg of an aqueous solution of NaOH containing 
34.3% by weight of Na.sub.2 O, 67 kg of hydrated aluminum oxide, at 60% by 
weight of Al.sub.2 O.sub.3, and 585 kg of deionized water. 
This reacton mixture was maintained at 100.degree. C., for about 1 hour 
until a clear sodium aluminate solution was obtaned whose molar ratio 
Na.sub.2 O:Al.sub.2 O.sub.3 is 3.35, and in which the percentage of 
Na.sub.2 O is 9.2% by weight. 
This solution was cooled to 70.degree. C., and during 13 minutes it was 
fed, under stirring, with 209 kg of a second aqueous solution at 7.degree. 
C., containing 8.7% by weight of Na.sub.2 O and 18.4% by weight of 
SiO.sub.2. The molar ratio SiO.sub.2 :Na.sub.2 O is 2.2, a value that is 
near that of the stoichiometric composition of the disilicate (Na.sub.2 
Si.sub.2 O.sub.5). The quantities involved were such as to bring the 
weight ratios between the components of the reaction mixture to the 
values: Na.sub.2 O:Al.sub.2 O.sub.3 =2.49, Na.sub.2 O:SiO.sub.2 =2.60, 
H.sub.2 O:SiO.sub.2 =23.94. 
Passing now to the second stage, that is, to the crystallization of the 
alumino-silicate, at first the mixture is maintained, in a first 
sub-stage, at 70.degree. C. for 45 minutes, after which the temperature is 
slowly brought up from 70.degree. to 100.degree. C. within 15 minutes. At 
last, the mixture was heated for 90 minutes at 100.degree. C., under 
atmospheric pressure and with mild stirring. 
The resulting solid was separated from the mother liquor by means of a 
conventional basket-type centrifuge revolving about a vertical axis 
[centrifuge B in FIG. 1] and the resulting cake was then washed with 
deionized water until a pH value of 11.3 was attained in the wash waters. 
An aqueous suspension containing 54 kg of zeolite per 100 liters of 
suspension was dried in a spray dryer [apparatus E in FIG. 1] thereby 
obtaining a crystalline 4A zeolite of the following composition: 
1.01Na.sub.2 O.Al.sub.2 O.sub.3.1.98SiO.sub.2.4.51H.sub.2 O. 
The exchange power of this zeolite with calcium was determined according to 
the following method: 
An aqueous 0.005 molar solution of tetrahydrated calcium nitrate, that is, 
having a hardness of 50 French degrees, was prepared by dissolving 1.181 g 
of Ca(NO.sub.3).sub.2.4H.sub.2 O in deionized H.sub.2 O and then bringing 
the solution to a volume of 1 liter with more deionized H.sub.2 O. To this 
solution was then added 1 g of hydrated zeolite undergoing test and the 
ensuing suspension was subjected to vigorous stirring for 15 minutes by 
means of a magnetic stirrer, at a temperature of 22.degree..+-.2.degree. 
C. 100 cm.sup.3 of this soluton were then filtered on a porous septum 
(degree of porosity=4) and its residual concentration of Ca.sup.++ was 
determined by titration with the bisodium salt of centinormal (0.01 
Normal) ethylenediaminetetraacetic acid (EDTA). 
The exchange power of the hydrated zeolite was first calculated in mg of 
CaO per 1 g of zeolite, according to the following formula: 
PS(Ca)=(50-cm.sup.3 EDTA).times.5.6, wherein by "cm.sup.3 EDTA" is 
indicated the number of cm.sup.3 of EDTA N/100 consumed in the titration 
and wherein by hydrated zeolite is meant a zeolite product in equilibrium 
with a relative atmospheric moisture not below 50% at room temperature 
(between 15.degree. and 30.degree. C.). The "hydrated" zeolite was 
obtained by placing the filtered and washed zeolite product into an oven 
for 5 hours at 105.degree. C. The dried material was then ground in a 
mortar and then exposed to air for not less than 3 hours, under the above 
indicated temperature and humidity conditions. Then, by determining the 
moisture content of the hydrated zeolite by calcining at 800.degree. C. 
for 1 hour, one goes back to the exchanging power per gram of "anhydrous" 
product. The values indicated on Tables I to V below refer to an 
"anhydrous" zeolite. 
The exchanging power of the zeolite in respect of magnesium is determined 
in a similar way by using a 0.005 molar solution of MgSO.sub.4 containing 
1.232 g of MgSO.sub.4.7H.sub.2 O per liter. The exchanging power towards 
magnesium is calculated first in mg of CaO per gram of hydrated zeolite by 
means of the formula PS(Mg)=(50-cm.sup.3 EDTA).times.5.6, and then one 
determines the exchanging power with reference to the "anhydrous" product 
(referred to Tables I to V) exactly as described above for calcium. 
In order to evaluate the speed with which the exchange takes place, the 
tests were repeated with calcium and magnesium, by lowering the stirring 
time from b 15 to 2 minutes. The kinetics of the exchange is an important 
datum inasmuch as the sequestering action of the zeolite is exerted in the 
conventional washing machines in a short stretch of time of just a few 
minutes. The high exchanging power in the presence of magnesium-containing 
waters, as reported on Table I, represents a significant step forward in 
the art with respect to results obtained heretofore. 
The granulometric analysis (on Coulter Counter) yielded the results 
recorded on Table I and reported also in FIGS. 3 and 4. 
The diffractometric X-ray analysis showed a pure crystalline 4A zeolite. 
Below are reported the interplanary distances with the corresponding 
indexes and intensities for the diffractogrammic peaks: 
______________________________________ 
hkl d (.ANG.) I/Io hkl d (.ANG.) 
I/Io 
______________________________________ 
100 12.29 100 221.3 4.11 36.5 
110 8.71 69.5 311 3.714 53 
111 7.11 34.5 320 3.417 16.5 
210 5.51 25.5 321 3.293 46.5 
211 5.03 2 410 2.988 55.5 
220 4.36 6 
______________________________________ 
EXAMPLE 2 
Referring to FIG. 2, into a reactor C' identical to reactor A of FIG. 2 and 
which is similar to the reactor A of Example 1, were fed in 898 kg of a 
recycle of mother liquor 6 consisting of a solution containing 7.99% by 
weight of Na.sub.2 O and 0.85% by weight of Al.sub.2 O.sub.3. To this 
solution were then added under stirring (lines 1 and 2), 30 kg of a 34.3% 
by weight solution of Na.sub.2 O and 55 kg of hydrated aluminum oxide at 
60.87% of Al.sub.2 O.sub.3. 
The solution was then cooled down to 70.degree. C. and transferred into 
reactor A. Into the reactor A were then fed, in 15 minutes and under 
stirring, 155 kg of an aqueous solution of sodium silicate at 10.degree. 
C., containing 11.74% by weight of Na.sub.2 O and 24.82% by weight of 
SiO.sub.2 (molar ratio SiO.sub.2 :Na.sub.2 O=2.18). The ponderal or weight 
ratios between the components of the mixture corresponded to the following 
value: Na.sub.2 O:Al.sub.2 O.sub.3 =2.44; Na.sub.2 O:SiO.sub.2 =2.61; 
H.sub.2 O:SiO.sub.2 =24.36. 
Thereupon followed crystallization, centrifugation, and drying, just as in 
Example 1 (see Table V). 
EXAMPLE 3 (A Comparison Example) 
Into the reactor A indicated in Example 1 were loaded 307 kg of a solution 
containing 29% by weight of Na.sub.2 O, 67.2 kg of hydrated aluminum oxide 
at 60.38% of Al.sub.2 O.sub.3, and 591.5 kg of deionized water. 
The temperature was kept at 100.degree. C. for about 1 hour, until a clear 
solution was obtained in which the molar ratio Na.sub.2 O:Al.sub.2 O.sub.3 
was 3.61 and in which the percentage of Na.sub.2 O was 9.22% by weight. 
The reaction mass was then cooled to 70.degree. C. and into the reactor A 
were fed, in 15 minutes, under stirring, 134.3 kg of a water-glass 
solution at 8.degree. C., containing 8.24% by weight of Na.sub.2 O and 
28.69% by weight of SiO.sub.2, and in which the molar ratio SiO.sub.2 
:Na.sub.2 O was 3.6. The ratios between the components of the mixture are 
indicated below in Table I. 
Then followed crystallization, centrifugation, and a drying as in Example 
1, thereby obtaining poor results that are recorded in Table I below. 
This proves that it is advisable to avoid too high SiO.sub.2 /Na.sub.2 O 
ratios in the silicate solution. 
In the X-ray spectrum, the peaks have a mean intensity that is lower by 10% 
in comparison with that of Example 1, and the presence of no other 
crystalline compounds could be noted. 
EXAMPLE 4 
Into the same reactor A of Example 1 were loaded 243.3 kg of a solution 
containing 35.3% by weight of Na.sub.2 O, 67.2 kg of hydrated aluminum 
oxide at 60.38% by weight of Al.sub.2 O.sub.3, and 646.2 kg of deionized 
water. The reaction mixture was maintained for about 1 hour at 100.degree. 
C. until a clear solution was obtained whose molar ratio of Na.sub.2 
O:Al.sub.2 O.sub.3 is 3.48 and in which the percentage of Na.sub.2 O 
amounted to 8.98% by weight. 
The reaction mixture was cooled to 70.degree. C. and in 15 minutes, under 
stirring, there were admixed 143.3 kg of a sodium silicate solution at 
8.degree. C. containing 9.93% by weight of Na.sub.2 O and 26.90% by weight 
of SiO.sub.2, and in which the SiO.sub.2 :Na.sub.2 O molar ratio was 2.8. 
The ponderal or weight ratios of the components of the reaction mixture are 
recorded in Table I below. 
Thereafter followed crystallization, centrifugation, and drying as in 
Example 1. 
The results are recorded in Table I. These results, depending on a 
SiO.sub.2 :Na.sub.2 O=2.8 ratio which is lower than that of Example 3, are 
slightly better (with respect to Example 3), but are still below the 
excellent results in Example 1. 
EXAMPLE 5: (Na.sub.2 Si.sub.2 O.sub.5) 
Into the reactor A of Example 1 were loaded 227.6 kg of a solution 
containing 35.05% by weight of Na.sub.2 O, 67.2 kg of hydrated aluminum 
oxide at 60.38% by weight of Al.sub.2 O.sub.3, and 637.9 kg of deionized 
water. This mixture was maintained at a temperature of 100.degree. C. for 
about 1 hour until a clear solution was obtained in which the Na.sub.2 
O:Al.sub.2 O.sub.3 molar ratio was 3.23 and in which the Na.sub.2 O was 
8.55% by weight. 
Thereupon the reaction mass was cooled to 70.degree. C. and in 15 minutes, 
under stirring, it was additioned with 167.4 kg of a sodium disilicate 
solution at 8.degree. C., containing 34.9% by weight of sodium disilicate 
(Na.sub.2 Si.sub.2 O.sub.5), in which the molar ratio SiO.sub.2 :Na.sub.2 
O was 2. 
The ponderal or weight ratios between the components of the reaction 
mixture are recorded in Table I. 
Thereupon followed crystallization, centrifugation, and drying as in 
Example 1, thereby obtaining the results indicated in Table I below. 
EXAMPLE 6 
Into the reactor A of Example 1 were loaded 218 kg of a solution containing 
35.05% by weight of Na.sub.2 O, 67.2 kg of hydrated aluminum oxide at 
60.38% by weight of Al.sub.2 O.sub.3, and 636.6 kg of deionized water. 
This reaction mixture was maintained at 100.degree. C. for about 1 hour 
until a clear solution was obtained in which the molar ratio Na.sub.2 
O:Al.sub.2 O.sub.3 is 3.11 and where the Na.sub.2 O amounts to 8.31% by 
weight. 
The reaction mixture was cooled to 70.degree. C., and into the reactor were 
then fed during 15 minutes, under stirring, 177.5 kg of a sodium silicate 
solution at 8.degree. C., containing 13.20% by weight of Na.sub.2 O and 
21.71% by weight of SiO.sub.2, in which the molar ratio SiO.sub.2 
:Na.sub.2 O is 1.7. 
The ponderal or weight ratios between the components of the reaction 
mixture are recorded in Table II. 
Then followed crystallization, centrifugation, and drying as in Example 1, 
thereby obtaining the results indicated below in Table II. 
EXAMPLE 7 
In this instance Example 1 was repeated, leaving unchanged the global or 
overall composition of the reaction mixture (see Table II), but altering 
the composition of the starting solutions so that in the sodium silicate 
solution the ratio SiO.sub.2 O:Na.sub.2 O is equal to 2.5. 
The results are recorded below in Table II. 
EXAMPLES 8 A Comparison Example) and 9 
Example 1 was repeated, varying only the time of the addition of the sodium 
silicate to the sodium aluminate. 
Instead of 13 minutes as in Example 1, it was 45 minutes in Example 8 and 5 
minutes in Example 9. 
The results are recorded below in Table II. 
EXAMPLE 10 
Into the reactor A of Example 1 were loaded 250 kg of a solution at 35% by 
weight of Na.sub.2 O, 71.5 kg of hydrated aluminum oxide at 63.2% by 
weight of Al.sub.2 O.sub.3, and 633 kg of deionized water. The reaction 
mixture was heated at 100.degree. C., until the hydrated aluminum oxide 
passed into solution. 
This solution was then cooled to 70.degree. C. and into it were fed, in 15 
minutes and under stirring, 246 kg of an aqueous solution at 65.degree. 
C., containing 17.1% by weight of SiO.sub.2 and 8.83% by weight of 
Na.sub.2 O, according to a molar ratio SiO.sub.2 :Na.sub.2 O=2. 
The ratios between the components of the reaction mixture are as indicated 
in Table III below, which also reports the results obtained after 
crystallization, centrifugation, and drying as in Example 1. 
The high coarse fraction (.alpha.), equal to 2% by weight of particles 
above 10 micrometers, is a sign of poor product (and any way less valuable 
in comparison with that of Example 1) and shows the necessity for 
maintaining the temperature of the sodium silicate solution below the 
reaction temperature. 
EXAMPLE 11 
Example 10 was repeated, changing only the temperature of the sodium 
silicate solution from 65.degree. to 50.degree. C. From Table III, which 
shows data and results, there will be perceived a clear improvement 
connected with the lowering of the temperature as indicated above. 
The influence of temperature becomes even more evident if one compares the 
results of Example 10 (temperature=65.degree. C.) with the excellent 
results of Example 1 (temperature=7.degree. C.). 
EXAMPLE 12 
Example 10 was repeated, with the following variations: 
(a) the temperature of the sodium silicate solution was lowered to 
23.degree. C.; 
(b) after the addition of the sodium silicate to the sodium aluminate 
(first stage) there was carried out the crystallization (second stage), 
while maintaining the temperature at 70.degree. C. for 45 minutes. Then 
the temperature was gradually brought from 70.degree. to 100.degree. C. in 
60 minutes and it was maintained at 100.degree. C. for 90 minutes. 
From Table III it will be seen that, in spite of the low modulation index 
(.omega.), the exchanging power is very high and that the coarse fraction 
(.alpha.) is completely absent. 
EXAMPLE 13 
Example 10 was repeated, except for the following variations: 
(a) the temperature of the sodium silicate solution was lowered to 
23.degree. C.; 
(b) the sodium aluminate solution contained 90.8 kg of water more while the 
sodium silicate solution contained 90.8 kg less of water. In other words, 
the global or overall ratios between the components (Na.sub.2 O, Al.sub.2 
O.sub.3, SiO.sub.2, H.sub.2 O) were kept unchanged but the procedure was 
started from a more concentrated sodium silicate solution in which the 
molar ratio SiO.sub.2 :H.sub.2 O rose up to 0.138 (in Example 10 the ratio 
equals 0.069). 
The results recorded in Table III show a satisfactory exchange power and an 
excellent modulation index with a coarse fraction (.alpha.=1) at the limit 
of acceptability. 
EXAMPLE 14 
Example 10 was repeated, with the following variations: 
(a) the temperature of the sodium silicate solution was lowered to 
25.degree. C.; 
(b) the solution of sodium aluminate contained 103 kg more of water, while 
the sodium silicate solution contained 103 kg less of water, whereby the 
molar ratio SiO.sub.2 :H.sub.2 O, in the silicate solution rose to 0.159. 
The very poor results (Table IV) show that a low concentration of silica in 
the feeding solution, is an indispensable condition for the synthesis of 
zeolites of high quality. 
EXAMPLE 15 
Example 14 was repeated, but bringing the temperature of the sodium 
silicate solution up to 65.degree. C., whereby the viscosity drops to 
about one fourth of the starting value (to 25.degree. C.). Instead of 
obtaining better and acceptable results, as was to be expected, there was 
encountered (Table IV) a power of exchange with calcium inferior to that 
of Example 14, and granulometric parameters almost as poor as those of the 
preceding examples. 
This proves the criticality of the dilution of the sodium silicate solution 
and excludes the possibility that the poor results depend on phenomena 
purely bound to the viscosity of the solution itself. 
EXAMPLE 16 
Example 15 shows that the dilution of the sodium silicate solution is a 
critical and necessary factor. The present example shows that the dilution 
nevertheless is not also a "sufficient" factor, unless it is accompanied 
by SiO.sub.2 :Na.sub.2 O ratios sufficiently low. To this purpose, a 
sodium aluminate solution, prepared with 276.6 kg of a 35% by weight 
solution of Na.sub.2 O, 71.5 kg of hydrated aluminum oxide at 63.2% by 
weight of Al.sub.2 O.sub.3, and 640.4 kg of deionized H.sub.2 O, was 
heated up to 70.degree. C. an to it were additioned, during 15 minutes and 
under stirring, 211.2 kg of a sodium silicate solution at 23.degree. C., 
containing 19.9% by weight of SiO.sub.2 and 5.9% by weight of Na.sub.2 O, 
the molar ratio SiO.sub.2 :Na.sub.2 O amounting to 3.5. 
This was then processed as in Example 1 and thus was obtained a definitely 
poor product that showed a high coarse fraction (.alpha.)=4; (see Table 
IV). 
EXAMPLE 17 
Into a heat-insulated reactor with a holding capacity of 70 m.sup.3, and 
fitted with a stirrer and an external heating (by means of a recycle pump 
and an exchanger), were introduced 12,320 kg of a 35.5% by weight solution 
of Na.sub.2 O, 3,680 kg of hydrated aluminum oxide at 61.3% by weight of 
Al.sub.2 O.sub.3, and 17,120 kg of deionized H.sub.2 O. This reaction 
mixture was heated up to 100.degree. C. until dissolution of the alumina 
took place. 
Thereupon 14,620 kg of deionized H.sub.2 O were fed and the temperature 
dropped thus to 75.degree. C. At this point there were fed, in 15 minutes 
and under stirring, 12,240 kg of an aqueous solution of sodium silicate 
containing 17.16% by weight of SiO.sub.2 and 8.61% by weight of Na.sub.2 
O, at 22.degree. C. 
The temperature was maintained for 45 minutes at 75.degree. C. and was then 
gradually brought up in 60 minutes to 98.degree. C. Thereupon upon the 
mixture was kept at 98.degree. C. for 1 hour after which it was filtered, 
washed, and dried, the product thus obtained having the properties 
reported in Table IV. 
EXAMPLE 18 
Into the reactor described in Example 17 were introduced 12,700 kg of a 
solution at 35.5% by weight of Na.sub.2 O, 3.610 kg of hydrated aluminum 
oxide at 61.3% by weight of Al.sub.2 O.sub.3, and 17,760 kg of deionized 
H.sub.2 O, and the whole mixture was heated up to 100.degree. C., until 
the dissolution of the alumina took piece. 
Then were fed 14,940 kg of deionized H.sub.2 O, in consequence whereof the 
temperature dropped to 75.degree. C. 
At this point there were fed, during 15 minutes, 11,500 kg of a silicate 
solution containing 18.40% by weight of SiO.sub.2 and 8.70% by weight of 
Na.sub.2 O, at 23.degree. C. 
The temperature was maintained at 75.degree. C. for a period of 45 minutes 
and was then gradually brought up to 98.degree. C. in 20 minutes. 
The reaction mixture was then left for 30 minutes at 98.degree. C. after 
which it was filtered, and the product was then washed and dried. 
The excellent results thus obtained are recorded in Table V. 
EXAMPLE 19 
Example 10 was repeated except for the following variations: 
(a) the temperature of the sodium silicate solution was reduced to 
22.degree. C.; 
(b) the solution of the sodium aluminate contained 150 kg less of H.sub.2 O 
while the silicate contained 150 kg more of H.sub.2 O, wherefore the 
degree of dilution of the sodium silicate solution reached a high level 
(in fact the molar ratio SiO.sub.2 :H.sub.2 O amounts to only 0.038). 
The not altogether satisfactory results reported in Table V shows that if a 
too restrained dilution is detrimental for the purposes of this synthesis 
(Examples 13 and 14) it is also true that a dilution pushed too much 
forward must likewise be avoided. Thus, it is advisable to maintain the 
molar ratio SiO.sub.2 :H.sub.2 O in the sodium silicate solution within 
the limits indicated by the experimental practice, of course with due 
respect to the other critical parameters. 
EXAMPLE 20 
Into the reactor of Example 1 were loaded 255 kg of a solution containing 
35.5% by weight of Na.sub.2 O, 72.8 kg of hydrated aluminum oxide at 
63.12% by weight of Al.sub.2 O.sub.3, and 740 kg of deionized water. The 
whole mixture was then heated up to 100.degree. C. until complete 
dissolution. 
The mixture was then cooled to 70.degree. C. and then, in 15 minutes, it 
was additioned with 148 kg of a solution containing 28.76% by weight of 
SiO.sub.2 and 14% by weight of Na.sub.2 O, corresponding to a molar ratio 
SiO.sub.2 :Na.sub.2 O=2.1, at 21.degree. C. Other relevant data and 
results are reported in Table V. 
TABLE I 
______________________________________ 
Characteristics 
Ex. 1 Ex. 3 Ex. 4 Ex. 5 
______________________________________ 
SiO.sub.2 :Na.sub.2 O in the sili- 
2.2 3.6 2.8 2.0 
cate solution 
mixing time (in minutes) 
13' 15' 15' 15' 
ratios in the: Na.sub.2 O:Al.sub.2 O.sub.3 
2.49 2.47 2.47 2.47 
reaction mix- Na.sub.2 O:SiO.sub.2 
2.60 2.60 2.60 2.59 
ture H.sub.2 O:SiO.sub.2 
23.94 23.89 23.89 23.91 
Power of exchange: 
stirr. for 15 min. Ca.sup.++ 
177 163 173 175 
stirr. for 15 min. Mg.sup.++ 
45 29.5 28 45 
stirr. for 2 min. Ca.sup.++ 
145 123 137 145.5 
stirr. for 2 min. Mg.sup.++ 
16 13.5 14 24 
granulometry: 
&lt;2 .mu.m 2.5% 1% 1.5% 3% 
&lt;3 .mu.m 13% 4% 8.5% 21.5% 
&lt;5 .mu.m 68% 26% 50% 89% 
&lt;8 .mu.m 98.5% 69% 85% 98% 
&lt;10 .mu.m 100% 83% 90% 99% 
Coarse Fraction (.alpha.) 
0 17 10 1 
Modulation (.omega.) 
85.5 65 76.5 76.5 
______________________________________ 
TABLE II 
______________________________________ 
Characteristics Ex. 6 Ex. 7 Ex. 8 Ex. 9 
______________________________________ 
SiO.sub.2 :Na.sub.2 O in the silicate 
1.7 2.5 2.2 2.2 
solution 
mixing time (in minutes) 
15' 13' 45' 5' 
Ratios in the: Na.sub.2 O:Al.sub.2 O.sub.3 
2.47 2.49 2.49 2.49 
reaction mix. Na.sub.2 O:SiO.sub.2 
2.60 2.60 2.60 2.60 
H.sub.2 O:SiO.sub.2 
23.90 23.94 23.94 23.94 
Exchange power: 
stirr. 15 minutes Ca.sup.++ 
175.5 175 166 172.5 
stirr. 15 minutes Mg.sup.++ 
45.5 45 42.5 50 
stirr. 2 minutes Ca.sup.++ 
148.5 145.5 140 152 
stirr. 2 minutes Mg.sup.++ 
20.5 20.5 17 22.5 
granulometry: 
&lt;2 .mu.m 3% 2% 1% 2.5% 
&lt;3 .mu.m 28% 14% 9% 17% 
&lt;5 .mu.m 83% 80% 72% 85% 
&lt;8 .mu.m 97.5% 97% 98% 97% 
&lt;10 .mu.m 98.5% 98% 99% 98% 
Coarse fraction (.alpha.) 
1.5 2 1 2 
Modulation (.omega.) 
69.5 83 89 80 
______________________________________ 
TABLE III 
______________________________________ 
Characteristics 
Ex. 10 Ex. 11 Ex. 12 Ex. 13 
______________________________________ 
SiO.sub.2 :Na.sub.2 O (silicate solut.) 
2.0 2.0 2.0 2.0 
SiO.sub.2 :H.sub.2 O (silicate solut.) 
0.069 0.069 0.069 0.138 
Temp. (silicate solut.) 
65.degree. C. 
50.degree. C. 
23.degree. C. 
23.degree. C. 
Mixing time (in minutes) 
15' 15' 15' 15' 
Ratios in the: Na.sub.2 O:Al.sub.2 O.sub.3 
2.42 see see see 
reaction mix- Na.sub.2 O:SiO.sub.2 
2.60 Example Example 
Exam- 
ture H.sub.2 O:SiO.sub.2 
23.87 10 10 ple 10 
Duration of second 
15' 15' 60' see Ex. 
sub-stage 10 
Power of exchange: 
stirr. for 15 min. Ca.sup.++ 
170 175 175.5 172.5 
stirr. for 15 min. Mg.sup.++ 
44 47 52 42 
stirr. for 2 min. Ca.sup.++ 
132.5 137.5 158 129 
stirr. for 2 min. Mg.sup.++ 
3.5 3.5 23 3.5 
granulometry: 
&lt;2 .mu.m 2.5% 4% 4% 0.5% 
&lt;3 .mu.m 16% 16% 28% 6.5% 
&lt;5 .mu.m 71.5% 87% 92.5% 41% 
&lt;8 .mu.m 96% 97% 99.5% 94% 
&lt;10 .mu.m 98% 98.5% 100% 99% 
Coarse fraction (.alpha.) 
2 1.5 0 1 
Modulation (.omega.) 
80 81 71.5 87.5 
______________________________________ 
TABLE IV 
______________________________________ 
Characteristics 
Ex. 14 Ex. 15 Ex. 16 
Ex. 17 
______________________________________ 
SiO.sub.2 :Na.sub.2 O (silicate solut.) 
2.0 2.0 3.5 2.1 
SiO.sub.2 :H.sub.2 O (silicate solut.) 
0.159 0.159 0.080 0.069 
Temp. (silicate solut.) 
25.degree. C. 
65.degree. C. 
23.degree. C. 
22.degree. C. 
Mixing time (in minutes) 
15' 15' 15' 15' 
Ratios in the: Na.sub.2 O:Al.sub.2 O.sub.3 
see see 2.42 2.41 
reaction mix- Na.sub.2 O:SiO.sub.2 
Example Example 2.60 2.58 
ture H.sub.2 O:SiO.sub.2 
10 10 23.87 23.90 
Duration of second 
see Ex. see Ex. see Ex. 
60' 
sub-stage 10 10 10 
Power of exchange: 
stirr. 15 minutes: Ca.sup.++ 
170 168 174.5 175 
stirr. 15 minutes: Mg.sup.++ 
21 38 42 51 
stirr. 2 minutes Ca.sup.++ 
123.5 125.5 126 156 
stirr. 2 minutes Mg.sup.++ 
0 0.5 14 20 
granulometry: 
&lt;2 .mu.m 1% 1% 1.5% 3% 
&lt;3 .mu.m 4% 3.5% 15% 28.5% 
&lt;5 .mu.m 25.5% 23.5% 74% 91.5% 
&lt;8 .mu. m 68% 71.5% 94% 99.0% 
&lt;10 .mu.m 86% 89.5% 96% 100% 
Coarse fraction (.alpha.) 
14 10.5 4 0 
Modulation (.omega.) 
64 68 79 70.5 
______________________________________ 
TABLE V 
______________________________________ 
Characteristics 
Ex. 18 Ex. 19 Ex. 20 
Ex. 2 
______________________________________ 
SiO.sub.2 :Na.sub.2 O (silicate solut.) 
2.2 2.0 2.1 2.18 
SiO.sub.2 :H.sub.2 O (silicate solut.) 
0.076 0.038 0.151 0.117 
Temp. (silicate solut.) 
23.degree. C. 
22.degree. C. 
21.degree. C. 
10.degree. C. 
Mixing time (in minutes) 
15' 15' 15' 15' 
Ratios in the: Na.sub.2 O:Al.sub.2 O.sub.3 
2.49 see 2.42 2.44 
reaction mix- Na.sub.2 O:SiO.sub.2 
2.60 Example 2.61 2.61 
ture H.sub.2 O:SiO.sub.2 
23.95 10 23.87 24.36 
Duration of the second 
20' 15' 60' 15' 
sub-stage 
Power of exchange: 
stirr. 15 minutes: Ca.sup.++ 
176 167 174 176 
stirr. 15 minutes: Mg.sup.++ 
46 31 41 43 
stirr. 2 minutes: Ca.sup.++ 
142 121 147.5 144 
stirr. 2 minutes: Mg.sup.++ 
14 13.5 15 21.5 
granulometry: 
&lt;2 .mu.m 3% 1% 3% 1.5% 
&lt;3 .mu.m 14% 3.5% 11% 9% 
&lt;5 .mu.m 70% 37% 47.5% 71% 
&lt;8 .mu.m 99% 89% 94% 98% 
&lt;10 .mu.m 100% 96.5% 98.5% 99% 
Coarse fraction (.alpha.) 
0 3.5 1.5 1 
Modulation (.omega.) 
85 85.5 83 89 
______________________________________