Process for the synthesis of a layered, clay-like material as well as its use

The invention relates to a process for the synthesis of a layered, clay-like material starting from a silicon oxide containing material in a finely divided state by reacting a glass phase containing material at a pH from 5 to 8, in the presence of water, with a source of layer-forming metal ions and an activator for the formation of clay under atmospheric conditions to obtain a material with a stable structure. Preferably aluminium and/or magnesium ions are employed as layer-forming metal ions. Furthermore, according to a suitable embodiment, boron glass or cullet is employed as a material containing silicon oxide. The conversion of the mixture of materials into a substance having an ordered structure takes place preferably at a pH of approximately 7 and a temperature of 30.degree.-45.degree. C., in which the starting materials appropriately have a particle size of approximately 100 microns. An activator for the formation of clay is added to accelerate the process of conversion. Moreover, if desired, a clay modifier can be added. As starting mixture, a hearth ash containing a glass fraction obtained by incinerating household and industrial waste can be employed; this hearth ash proves to be a useful secondary raw material. By means of the present process waste material, whether subjected to incineration or not, that has been polluted with inorganic material can be immobilized.

BACKGROUND OF THE INVENTION 
The invention relates to a process for the preparation of a layered, 
clay-like material using a silicon oxide containing material in a finely 
divided state as a starting material. 
It should be noted that the clay minerals occurring in nature are generated 
through the erosion of rocks and sediments. Such erosion processes appear 
to be accellerated under hydrothermal conditions. 
Thus, such a hydrothermal process is known from GB-A-1- 560 504, wherein by 
hydrothermal treatment of igneous rocks, clay-like materials are obtained. 
On the other hand, the synthesis of a layered material under hydrothermal 
conditions is also known. The Derwent abstract AN 91-183100, week 9125 & 
JP,A,3 112 808, disclose the hydrothermal synthesis of a layered silicate. 
More specifically, an amorphous silica-containing material, an alkali 
metal source, water and alcohol are according to these references reacted 
under hydrothermal conditions at at least 150.degree. C. A source of 
alumina or of magnesia can further also be present. 
Hydrothermal processes nevertheless require special equipments. 
Clay materials are responsible for many natural conversion processes, 
including reactions involving oxidation and hydrolysis. They can bind 
heavy metals because they have a net negative charge, which is compensated 
by interchangeable cations. In nature these are mainly the ions of 
alkaline earth metals. 
On the other hand, it is possible to modify clay minerals such that their 
original affinity will change from hydrophilic to hydrophobic. Because of 
that the clay becomes suitable for the adsorption of organic compounds 
which dissolve poorly in water. 
At the moment a very important application of clay, whether it has been 
modified or not, lies then in the field of the immobilization of polluted 
industrial waste material, in which the waste material is adsorbed by the 
clay and then isolated by incorporation into a cement matrix. 
Due to the growing amount of industrial waste material as well as the 
requirements, which are becoming more and more strict, concerning the 
amount of waste material allowed to be discharged into the environment, 
there is an increasing need for a clay-like material that also has the 
capacity to absorb different substances that clay inherently possesses. 
SUMMARY OF THE INVENTION 
Surprisingly, a process has now been found for the preparation of a 
layered, clay-like material in which it is not necessary to appeal to 
natural sources of clay, nor to appeal to a hydrothermal process. 
More specifically the process according to the invention comprises the 
formation of a layered, clay-like material by reacting a glass phase 
containing material at a pH from 5 to 8, in the presence of water with a 
source of layer-forming metal ions, and an activator for the formation of 
clay, under atmospheric conditions to obtain a material having a stable 
structure. 
It should be noted that the fineness of the various constituents may vary 
within a wide range of limits. However, it will be obvious that the 
smaller the size of the particles is, the faster the velocity of 
conversion will be. Actual practice has shown that a particle size of 
approximately 100 microns is very suitable. 
Preferably aluminium ions are employed as layer-forming metal ions. The 
source concerned of such ions may in that case consist of aluminum oxide. 
However, it may also be appropriate to employ magnesium ions as 
layer-forming metal ions. Advantageously, magnesium oxide is employed 
then. 
Preferably a clay-like material is formed using boron glass or waste glass 
as starting material. Boron glass has the advantage that in addition to 
boric oxide (B.sub.2 O.sub.3), both silicon dioxide and aluminum oxide are 
present, which also form the structural elements from which clay is built 
up. Waste glass is known in English-speaking countries as cullet. It is 
employed as a fluidizing agent in the manufacture of glass because it 
lowers the temperature at which the mixture employed for the manufacture 
of glass becomes fluid. Although the mechanism underlying the present 
invention is not entirely clear, it is assumed that it is this property of 
cullet that makes it possible for the conversion into a stable ordered 
structure, consequently the clay-like material, to take place relatively 
quickly. 
Preferably the transformation that occurs in the present process is allowed 
to take place at a pH of approximately 7 and at a temperature of 
approximately 35.degree.-40.degree. C. 
It should be noted that a pH of at least 5, and preferably 7, is fairly 
essential in the present process. The fact is that at a lower pH of, for 
example, 1 to 3 a silicate employed as a material containing silicon oxide 
will be converted into a silicic acid polymer, such as is disclosed in 
U.S. Pat. No. 4,404,105, from which it is no longer possible to form a 
material having a stable ordered structure with the characteristics of 
clay. 
The application of a temperature of 30.degree.-45.degree. C. is favourable 
for obtaining a fairly rapid conversion. Although this range is not very 
critical, it will be obvious that at a lower temperature the reaction 
velocity will also be lower, while at a temperature above 45.degree. C. 
the reaction velocity will indeed have increased, but that this can be 
such that it will become impossible to obtain an ordered structure that is 
present throughout the whole final product due to the formation of 
impermeable films on the various reagents. 
Furthermore, an activator is employed preferably for the formation of clay 
in order to accelerate the conversion process for the formation of a 
material with a stable ordered structure. Transition metal compounds such 
as magnesium sulphate, ferrous sulphate and manganese oxide have proven to 
be very suitable for employment as an activator. 
A clay modifier is further added to the mixture of starting substances to 
be converted. Preferably a calcium compound is employed as a clay 
modifier. 
An embodiment of the process according to the invention that particularly 
deserves preference includes the employment of a hearth ash containing a 
glass fraction, obtained through the incineration of household or 
industrial waste, for the formation of a clay-like material with a stable 
ordered structure. 
It should be noted that the composition of such a hearth ash depends on the 
waste material supplied and the process conditions implemented, and 
consequently is inconstant. At present this hearth ash is mainly employed 
in fills, in road foundations and as an aggregate in concrete. There is no 
application for the remainder (approximately 150,000 tons a year) as a 
result of which it has to be dumped. The problem with hearth ash is that 
it contains heavy metals, which upon leaching pollute the environment in 
an extremely undesirable way. 
Surprisingly, it has now been found that hearth ash can be employed as a 
raw material for the formation of a layered, clay-like material by 
utilizing the glass fraction present in hearth ash. The metallic elements 
of hearth ash prove to be incorporated or absorbed into the clay matrix. 
Thus a fixation of the hazardous metallic elements is obtained. By 
subsequently incorporating the formed, layered, clay-like material into a 
cement matrix, a building material is obtained in which the various 
metallic elements are no longer perceptible in the leaching tests carried 
out. 
Furthermore, the invention relates to a layered, clay-like material 
obtained by having waste, which is polluted with inorganic compounds and 
subjected to incineration, in a pulverized state at a mainly neutral pH, a 
temperature of 30.degree.-45.degree. C. and in the presence of water is 
reacted with a pulverized, mainly amorphous, silicon oxide source. 
The amorphous silicon oxide source present in this may be a glass fraction 
that is already present in the material, which has been subjected to 
incineration. In that case, a very valuable product is obtained from waste 
material. 
If, however, the waste material which has been subjected to incineration 
has an insufficient quantity of a silicon oxide source, boron glass or 
cullet, for example, may be added so that the formation of the clay matrix 
can still take place. 
Finally, the invention relates to a process for immobilizing waste material 
polluted with inorganic material, whether subjected to incineration or 
not, by incorporating the inorganic material into a layered, clay-like 
material obtained by applying the process according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLE I 
So-called AVI (waste processing industry) silicate slags that were finely 
ground to a particle size of mainly about 100 .mu.m were used as a 
starting material. AVI silicate slags are generated by burning household 
waste and sewage sludge and contain heavy metals as pollutants. 
Furthermore, these slags contain glass beads in which a part of the heavy 
metals has already been fixed. 
A quantity of aluminum sulphate was added to the finely ground slag 
material and the pH of the mixture was brought up to a value of 
approximately 7. Furthermore, as an activator for the formation of clay, 
magnesium sulphate was added. The mixture thus obtained was brought up to 
a temperature of approximately 40.degree. C. and brought into contact with 
water, in the course of which the mixture was continuously turned over. 
After approximately 1 month the starting material had converted into a 
layered, clay-like material. 
EXAMPLE II 
In this example, cullet that had been finely ground to a particle size of 
approximately 80 .mu.m was used as a starting material. Analysis of the 
cullet employed showed that the material contained approximately 3% 
Al.sub.2 O.sub.3. 
An equivalent quantity of manganese oxide was added to the finely ground 
cullet as well as just enough water so that the particles almost began to 
adhere to each other. The pH of the mixture formed was brought up to 
approximately 6. 
By continuously turning the mixture over at a temperature of approximately 
32.degree. C. a layered, clay-like material was formed, in which the 
conversion was complete after approximately 5 weeks. 
Adding ferrous sulphate to the mixture to be turned over resulted in 
completion of the conversion in approximately 3 weeks. 
The clay-like material obtained had the capacity to absorb various metal 
salts present in an aqueous solution. 
EXAMPLE III 
The procedure described in Example I was repeated. The clay-like material 
formed was incorporated into a cement matrix of blast furnace slag cement 
according to the manner known per se. From the product obtained after 28 
days of hardening, not a single heavy metallic element could be detected 
in leaching tests.