PRODUCTION OF COMMERCIALLY USEFUL MATERIALS FROM WASTE GYPSUM BOARDS

REVALORISATION COMMERCIALE DES PANNEAUX DE GYPSE RECUPERES

English Abstract

A commercially useful material is produced from
waste gyproc boards containing calcium sulfate dihydrate,
by a method comprising the steps of (a) grinding the waste
gyproc boards to obtain particles having a substantially
uniform size; (b) drying the particles obtained in step
(a) to obtain moisture-free particles; (c) heating the
moisture-free particles obtained in step (b) at a
temperature of 128 to 162°C to convert the calcium sulfate
dihydrate to calcium sulfate hemihydrate; (d) adding water
to the product obtained in step (c) to form a paste;
(e) forming the paste obtained in step (d) into a shaped
product of a predetermined size; and (f) drying the shaped
product obtained in step (e) at a temperature of 105 to
120°C to obtain a commercially useful material. The
materials produced by the method of the invention can be
used for a variety of industrial and household purposes.
Typical uses include the absorption of oil, grease and
chemicals on floors and elsewhere, in animal toilet
applications as a cat box absorbent, as carriers for
chemicals, such as pesticides and herbicides, in various
agricultural and horticultural applications. They can also
be used as fillers for agricultural and horticultural
applications. When admixed with an adhesive agent such as
Portland cement, epoxy or polyester adhesives, they can be
applied onto walls and/or floors to provide a decorative
coating.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A method of producing a commercially useful
material from waste gyproc boards containing calcium
sulfate dehydrate, comprising the steps of:
a) grinding the waste gyproc boards to obtain
particles having a substantially uniform size;
b) drying the particles obtained in step (a) to
obtain moisture-free particles;
c) heating the moisture-free particles obtained
in step (b) at a temperature of 128 to 162°C to convert
the calcium sulfate dehydrate to calcium sulfate
hemihydrate;
d) adding water to the product obtained in step
(c) to form a paste;
e) forming the paste obtained in step (d) into
a shaped product of a predetermined size; and
f) drying the shaped product obtained in step
(e) at a temperature of 105 to 120°C to obtain a
commercially useful material.
2. A method as claimed in claim 1, wherein step
(b) is carried out by heating the particles obtained in
step (a) at a temperature of 105 to 120°C.
3. A method as claimed in claim 1, wherein step
(c) is carried out at a temperature of about 145°C.
4. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with at least one
additive for increasing absorption characteristics of the
material obtained in step (f).
5. A method as claimed in claim 4, wherein said
additive is selected from the group consisting of wood
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cellulose fibers, textile fibers, paper pulp, peat fines,
mineral fines, charcoal, agricultural waste materials and
porous plastic materials.
6. A method as claimed in claim 5, wherein said
additive comprises wood cellulose fibers.
7. A method as claimed in claim 6, wherein the
cellulosic fibers are added in an amount of 0.5 to
30 wt.%.
8. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with an additive for
increasing density of the product obtained in step (f).
9. A method as claimed in claim 8, wherein said
additive comprises powdered slag.
10. A method as claimed in claim 9, wherein the
powdered slag is added in an amount of 5 to 80 wt.%.
11. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with an additive for
increasing hardness of the product obtained in step (f).
12. A method as claimed in claim 10, wherein said
additive is powdered slag.
13. A method as claimed in claim 11, wherein the
powdered slag is added in an amount of 1 to 80 wt.%.
14. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with an additive for
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increasing water-resistance of the product obtained in
step (f).
15. A method as claimed in claim 14, wherein said
additive comprises gypsum plaster.
16. A method as claimed in claim 14, wherein the
gypsum plaster is added in an amount of 10 to 80 wt.%.
17. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with an additive
selected from the group consisting of fungicidal agents
and coloring agents.
18. A method as claimed in claim 1, further
including the step of dry-mixing the product obtained in
step (c), prior to adding water, with powdered slag,
gypsum plaster and cellulosic fibers.
19. A method as claimed in claim 18, wherein the
powdered slag, gypsum plaster and cellulosic fibers are
added in amounts of about 25 wt.%, 20 wt.% and 5 wt.%,
respectively.
20. An absorbent material derived from waste gyproc
boards and produced by a method as defined in any of
claims 1, 4, 5, 6, 11, 12, 14, 15, 18 and 19.
21. A filler material derived from waste gyproc
boards and produced by a method as defined in claim 1, 8
or 9.
22. A decorative coating material derived from
waste gyproc boards and produced by a method as defined
in any of claims 1, 11, 12, 14, 15 and 17.
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Description

CA 02236486 1998-OS-O1
"Production of Commercially Useful
Materials from Waste Gyproc Boards"
The present invention pertains to improvements
in the field of waste recycling. More particularly, the
invention is directed to a method of producing
commercially useful materials from waste gyproc boards.
Waste gyproc boards coming from demolition and
:LO gyproc board factories represent a serious threat to t=he
environment as they accumulate by thousands to hundred
thousands of tons in many dumping sites. They retain
humidity and thus promote the formation of undesirable
mildew. Degradation of the calcium sulfate contained in
:L5 the waste gyproc boards under the influence of infra-red
and ultraviolet radiations causes the generation of H2S
and S02 which contaminate the environment.
Gyproc boards contain calcium sulfate dihydrat:e,
:?0 silicon dioxide, cellulosic fibers as well as various
metal oxides such as aluminum oxide, calcium oxide, ferric
oxide and magnesium oxide. Calcium sulfate dehydrate is
known to have liquid absorbing properties, as disclosed
for example in U.S. Patent Nos. 4,163,674 and 4,264,543.
a?5 However, waste gyproc boards are not suitable for use as
absorbents or any other useful products such as fillers
for agricultural and horticultural applications.
It is therefore an object of the present
~s0 invention to overcome the above drawbacks and to provide a
method of producing a commercially useful material fx-om
waste gyproc boards.
According to one aspect of the invention, there
.5 is thus provided a method of producing a commercially
useful material from waste gyproc boards containing
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CA 02236486 1998-OS-O1
calcium sulfate dehydrate. The method of the invention
comprises the steps oi=:
a) grinding the waste gyproc boards to obtain
particles having a substantially uniform size;
b) drying the particles obtained in step (a) to
obtain moisture-free particles;
c) heating the moisture-free particles obtained
in step (b) at a temperature of 128 to 162°C to convert
the calcium sulfate dehydrate to calcium sulfate
T_0 hemihydrate;
d) adding water to the product obtained in step
(c) to form a paste;
e) forming the paste obtained in step (d) into
a shaped product of a predetermined size; and
J_5 f) drying the shaped product obtained in step
(e) at a temperature of 105 to 120°C to obtain a
commercially useful material.
The present invention also provides, in another
~'.0 aspect thereof, a commercially useful material derived
from waste gyproc boards and produced by the above method.
Applicant has found quite unexpectedly that
commercially useful products, particularly liquid
25 absorbing materials, filler materials for agricultural and
horticultural applications and decorative coating
materials for walls and floors, can be produced at a low
cost from waste gyproc boards by converting the calcium
sulfate dehydrate contained in the waste gyproc boards to
~:0 calcium sulfate hemihydrate having binding properties and
serving to bind the other components of gyproc boards. The
waste gyproc boards must first be ground to obtain
particles having a substantially uniform size, which are
then dried to obtain moisture-free particles, for example,
a5 by heating the partic:Les at a temperature of 105 to 120°C
in a circulating air oven for a period of time sufficient
to evaporate all traces of water. The moisture-free
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CA 02236486 1998-OS-O1
particles are heated at a temperature of 128 to 162"C,
preferably about 145°C, to partially dehydrate the calcium
sulfate dihydrate and to thereby convert same to calcium
sulfate hemihydrate. Care should be taken to avoid heating
the moisture-free particles at a temperature above 162 "C,
since at a temperature of 163°C calcium sulfate
hemihydrate loses all its water of crystallization and is
converted to anhydrous calcium sulfate. Water is added to
the resulting product to form a paste. The paste is formed
7_0 into a shaped product of a predetermined size, for
example, granules, pellets or balls, and the shaped
product is then dried at a temperature of 105 to 120°C to
obtain the desired absorbent or filler material. If t:he
shaped product is dried at a temperature less than 105°C,
7_5 the evaporation of water is insufficient so that t:he
absorption characteristics of the final product are
adversely affected. At a temperature above 120°C, on t:he
other hand, there is a partial conversion of the hydrated
calcium sulfate to calcium sulfate to calcium sulfate
~'.0 hemihydrate, which weakens the final product and leads to
the formation of cracker therein.
Various additives can be dry-mixed with t:he
product obtained in step (c) with a view to increasing t:he
~~5 absorption characteristics, density, hardness and/or
water-resistance of t:he material obtained in step (f);
fungicidal agents and/or coloring agents can also be
added. For example, when it is desired to increase t:he
absorption characteristics of the final product, wood
DSO cellulose fibers, textile fibers, paper pulp, peat fines,
mineral fines, charcoal, agricultural waste materials such
as corn stalks and peanut shells, or porous plast=ic
materials can be added. Use is preferably made of
cellulosic fibers in an amount of 0.5 to 30 wt.$. When it
~S5 is desired to increase the density of the final produces,
powdered slag can be added it is preferably used in an
amount of 5 to 80 wt. g. Since powdered slag exhibits
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CA 02236486 1998-OS-O1
binding properties, it can also be used to increase the
hardness of the final product. In such a case, the
powdered slag is preferably added in an amount of 1 to 80
wt.~. When using powdered slag, acidified water is
preferably added in step (d) to reduce the pH so that t:he
final product has a pH of about 7. On the other hand, when
it is desired to increase the water-resistance of the
final product, gypsum plaster which is also called
"Plaster of Paris" can be added. The gypsum plaster is
7.0 preferably used in an amount of 10 to 80 wt.~. A clumping
agent such as sodium ~>icarbonate can also be added.
A particularly preferred absorbent material
produced in accordance with the invention is derived from
7.5 about 50 wt.~ waste gyproc boards and contains about
25 wt.$ powdered slag, about 20 wt.$ gypsum plaster and
about 5 wt.~ cellulosi.c fibers. Such an absorbent material
not only exhibits increased hardness and absorption
characteristics but is also highly resistant to
~!0 degradation by water.
A particularly preferred filler
material
produced by the methcrd of the invention is derived from
about 50 wt.~ waste gyproc contains about
boards
and
a!5 25 wt.~ gypsum plaster and about 25 wt.~ powdered slag.
Such a filler material. exhibits
not
only
increased
density
and :hardness but is alsoresistant to degradation by
water.
.0 The materials produced in accordance with the
invention can be used for a variety of industrial and
household purposes. Typical uses include the absorption of
oil, grease and chemicals on floors and elsewhere, in
animal toilet applications as a cat box absorbent, as
a5 carriers for chemical~~, such as pesticides and herbicides,
in various agricultural and horticultural applications.
They can also be used as fillers for agricultural and
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CA 02236486 1998-OS-O1
horticultural applications . When admixed with an adhesive
agent such as Portland cement, epoxy or polyester
adhesives, they can be applied onto walls and/or floors to
provide a decorative coating.
The following non-limiting examples illustrate
the invention.
EXAMPLE 1:
7.0 120 kg of the waste humid gyproc boards were
broken down into small particles and dried at 115°C in an
air dryer until the particles became moisture-free. The
temperature of the dryer was gradually increased to heat
the moisture-free part=icles at a temperature of 150°C for
J.5 a duration of 20 minutes. The particles thus obtained
which contained hemihydrated calcium sulfate are
hereinafter referred t:o "H.H.C.S. particles".
kg of the H.H.C.S. particles were mixed with
~!0 a suitable amount of water to form a paste suitable for
shaping into granules. The granules were dried at 115°C
then broken down into different mesh sizes from mesh 5 to
40. '.Che broken granules were then redried in the same
dryer at 115°C.
a! 5
EXAMPLE 2:
5 kg of the H.H.C.S. particles obtained in
Example 1 were well mixed with 2 kg of gypsum plaster.
Water was added to th.e resulting mixture to form a paste
a0 suitable for shaping into granules. The granules were
dried at 115°C and then broken down into different mesh
sizes from mesh 5 to 40. The broken granules were then
redried in the same dryer at 115°C.
.C 5 EXAMPLE 3
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 3 kg of gypsum plaster.
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CA 02236486 1998-OS-O1
EXAMPLE 4:
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 4 kg of gypsum plaster.
EXAMF?LE 5:
Example 2 w.as repeated, except that the H.H.C.S.
part_Lcles were mixed 'with 5 kg of gypsum plaster.
EXAMI?LE 6:
Example 4 was repeated, except that 0.5 kg of
defibrated waste hygienic paper was added to the mixture
containing the H.H.C.S. particles and gypsum plaster,
prior to adding the water.
EXAMPLE 7:
Example 2 was repeated, except that the H.H.C..S.
particles were mixed with 1 kg of powdered slag.
EXAMPLE 8:
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 2 kg of powdered slag.
EXAMPLE 9:
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 3 kg of powdered slag.
EXAMPLE 10:
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 4 kg of powdered slag.
EXANfPLE 11:
Example 2 was repeated, except that the H.H.C.S.
particles were mixed with 5 kg of powdered slag.
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CA 02236486 1998-OS-O1
EXAMPLE 12:
Example 8 was repeated, except that 1 kg of
gypsum plaster was added to the mixture containing the
H.H.C.S. particles and powdered slag, prior to adding the
water.
EXAMPLE 13:
Example 12 was repeated, except that the amount
of pc>wdered slag added was 2 kg.
EXAMPLE 14:
Example 12 was repeated, except that the amount
of powdered slag added was 3 kg.
EXAM~?LE 15:
Example 12 was repeated, except that the amount
of powdered slag added was 4 kg.
EXAMI?LE 16:
Example 12 was repeated, except that the amount
of powdered slag added was 5 kg.
The bulk density, hardness, water absorption and
resistance to water of the products obtained in Examples 1
through 16 were tested.
The bulk density was determined by filing a
graduated cylinder without tamping. The hardness was
determined according to the standard test ASTM # E728-91,
and compared with i~he hardness of granules made from
100 wt.o gypsum plaster. The water absorption was
determined according to the procedure described in US
Patent No. 4,183,763 (col. 11). The resistance to water
was determined by soaking' the granules (2 g) in water for
2-4 hours and compressing with a spatula.
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CA 02236486 1998-OS-O1
The results are reported in the following Table:
Ex. Bulk Water Resistance Suitable
No. density Hardness absorp- to water application
pound / tion
feet3
1 46 56$ 0.8 Week Animal litter
2 48 71$ 0.65 Moderate Animal litter
3 49 80$ 0.6 Moderate Animal litter
4 51 86$ 0.55 Moderate Animal litter
5 50.5 99.5$ 0.5 Good Animal litter
6 45.2 83~ 0.75 Moderate Animal litter
7 50 80$ 0.6 Good Animal litter
8 55 92~ 0.5 Good Animal litter
9 58 99$ 0.6 Good Animal litter
10 62 102 0.5 Very good Animal litter
&
absorbent
11 69 106$ 0.4 Very good Absorbent
12 56 1259s 0.38 Very good Absorbent
13 58 142$ 0.3 Very good Absorbent
14 63 167$ 0.3 Very good Absorbent
15 68 189$ 0.31 Excellent Absorbent
16 72 207$ 0.29 Excellent Absorbent
_ g