Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PREPARING DETERGENT BUILDER ZEOLITE -A FROM
KIlVIBERLITE TAILINGS
Field of the invention
The present invention relates to a process for the preparation of detergent
builder
Zeolite-A from Kimberlite tailings. More particularly, the present invention
relates to the use
of active silica content of Kimberlite tailings to prepare detergent builder
Zeolite-A in a
manner that allows the preparation of sodium silicate and further interacting
with soluble
aluminate species in aqueous form to obtain the Zeolite-A.
Background of the invention
Zeolites are crystalline aluminosilicates with a regular three-dimensional
porous
lattice structure built up from Si04 and A104 tetrahedra in which the negative
charges are
compensated by mono or multivalent cations. These cations are exchangeable
without the
lattice structure being destroyed. Their use as water softener is mainly
attributed to this
property. Hard water contains calcium and/or magnesium salts, which greatly
reduce the
surfactant effect of soaps and detergents. The exchange of sodium ions present
in the zeolite
for the calcium and magnesium ions present in the water softens the hard
water. Generally,
phosphates are used as builder in household detergents. Due to the increasing
awareness
about the polluting effect and non-biodegradable property of phosphates, many
countries
have banned or curtailed the use of phosphates in household detergents.
Zeolite-A is
established as the most suitable substitute for phosphate builder in
detergents. Under the
circumstances, use of Zeolite-A is increasing as detergent builder.
Zeolites are inorganic materials having high thermal and hydrothermal
stability.
These materials are also chemically stable at ambient temperatures towards
many organic
compounds. Zeolites owing to the presence of molecular dimensional pores are
also used as
molecular sieves and as adsorbents for drying, purification and separation of
compounds.
They have significant adsorption capacity of water even at very low partial
pressures and
hence are effective desiccants, with a capacity of up to more than 25% of
their weight. They
are also used to remove volatile organic chemicals from air streams, separate
isomers and
mixtures of gases.
Zeolites can act as shape-selective catalysts either by transition state
selectivity or by
exclusion of competing reactants on the basis of molecular diameter. Zeolites
have also
emerged as solid acid catalysts and have substituted conventional acids like
sulphuric acid in
many applications. A variety of organic transformations, namely, alkylation,
acylation,
isomerisations, oxidation is being carried out employing zeolite based
catalysts where zeolite
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acts as a catalyst or catalyst support. The industrial sectors where zeolites
have made
substantial impact as catalysts and adsorbents include: petroleum refining,
synfuels
production, and petrochemical production.
The largest volume wise application of zeolite is in detergent industry with
Zeolite-A
being used as detergent builder. The specific properties which make Zeolite-A
suitable as
phosphate substitute detergent builder include:
= The high cation exchange capacity even at higher temperature makes Zeolite-A
effective
in removal of water hardness ions, particularly calcium.
= It gives alkaline reaction in aqueous medium with pH less than 12.
= It does not cause encrustation on the fabric.
= Detergent grade Zeolite-A crystals are cubic in shape with rounded corners
and edges and
can pass through the mesh of the fabrics allowing easy removal during rinsing.
= The surfactant adsorption capacity of the Zeolite-A is several times higher
than the
polyphosphates.
= Zeolite-A absorbs unwanted water-soluble molecules from the dirt.
= It coagulates the colloidal dirt particles and pigments causing easy removal
from the
aqueous phase.
= It does not clog the sewerage.
= It does not exert any negative influence upon biological sewerage
purification.
= It does not remobilize heavy metals.
= Zeolite-A is toxicologically innocuous.
Conventionally, Zeolite-A is synthesized using aluminum and silicon rich
material as
the starting materials in the presence of an alkali. Aluminum trihydrate,
Aluminum alkoxide,
and Sodium aluminate are used as aluminum source and fume silica, sodium
silicate and
colloidal silica are employed as silica source. Mixing solutions of silicate
and aluminate
produce aluminosilicate gel that precipitates. The gel thus formed is then
crystallized to
Zeolite-A by aging in the mother liquor at higher temperature. Such processes
are described;
for example, in US Patents 2,841,471 and 2,847,280 (1958), and in French
Patent 1,404,467.
The cost of production of Zeolite-A depends largely on the starting materials
used,
especially, for the detergent builder Zeolite-A, where the volumes employed
are very large.
Since conventional detergent builders like sodium tripolyphosphate (STPP) are
economically
attractive compared to Zeolite-A, in many countries there is a resistance to
substitute STPP
by Zeolite-A in spite of eco-friendly nature of the latter. Therefore,
research efforts are
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directed towards developing a process for Zeolite-A synthesis wherein the
Zeolite-A
developed can be economically competitive to STPP.
Kimberlite tailings are produced as a huge solid waste during diamond mining.
For
example, in a country like India from its Panna diamond mines, typically
around 100 tones of
Kimberlite is generated per 10 carat of diamond mined. Around 3-4 million
toines of
Kimberlite is already accumulated during previous diamond mining in India.
With an
estimated life of 20 years for the Panna diamond mines, huge quantity of
Kimberlite tailing is
likely to be available in the country. Considering this problem on the global
scale, as
countries like South Africa and Canada are also involved in diamond mining,
the quantity of
Kimberlite tailings to be generated is of a serious concern. Therefore, it is
pertinent to look
for technical solutions to gainfully utilize Kimberlite tailings accumulated
during diamond
mining. The Kimberlite being rich in magnesia and silica, there is an
opportunity to develop
magnesium and silica based products from this materials. Therefore, efforts
were made to
prepare value-added product like Zeolite-A. The value-addition *of Kimberlite
will not only
make diamond mining process more economical but will also make it an eco-
friendly.
Kimberlite with a typical chemical composition given below is rich source of
silica and
therefore considered as a potential starting material for the preparation of
Zeolite-A.
The typical chemical composition of Kimberlite is given below:
Si02 30 - 32%, A1203 2- 5%, Ti02 5- 8%, CaO 8. - 10%, MgO 20 - 24%, Fe203 5-
11%,
LOI 13 - 15%.
US Patent 3,101,251 (1963) discloses a process for producing Zeolite-A wherein
a
non-kaolinitic aluminosilicate in admixture with an alkali metal hydroxide is
fused at a.
temperature from 330 to 370 C. An aqueous reaction mixture is formed with this
fused
admixture. This reaction mixture has water to sodium oxide molar ratio of from
35:1 to
200:1, a sodium oxide to silica molar ratio of from 1.3:1 to 2.5:1, and silica
to alumina molar
ratio of from 0.8:1 to 3: 1. This reaction mixture is reacted at a temperature
from 20 to 120 C
until Zeolite-A is formed. The process has limitations of high temperature
alkali fusion of
aluminum and silica containing solids prior to crystallization.
US Patent 5,965,105 (1999) disclosed a process for the synthesis of Zeolite-A
using
fly ash. In this process, fusion mixture was obtained by mixing fly ash and
caustic soda in a
ratio of 1:1.2 and optionally adding sodium aluminate or aluminium hydroxide.
This fusion
mixture was heated at 500-600 C for about 1-2 hours, to obtain a fused mass.
This fused
mass was treated with distilled water for 8-10 hours with simultaneous
optional addition of
sodium aluminate or alum solution, in the presence or absence of NaC1,
followed by optional
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addition of Zeolite-A seeds to obtain amorphous aluminosilicate slurry;
subjecting the said
slurry to hydrothermal crystallization at about 90-110 C for 2 to 4 hours to
obtain Zeolite-A
crystals. However, this process requires .very high reaction temperature and
high processing
time in cooling, milling and mixing, moreover, seeding of Zeolite-A crystal is
also necessary.
The process has limitation of fusion of fly ash and caustic soda at a high
temperature of 500-
600 C making the process energy intensive.
Production of high purity fine size Zeolite-A by adding organic acid to silica
and /or
alumina-silica, sodium aluminate and sodium hydroxide is described in Japanese
Patent
54,081,200, (1997). The limitation of this patent is that the addition of
organic acid to silica
and alumina source is required.
US Patent 4,089,929 describes use of mineral aluminosilicate raw materials to
produce low-iron zeolitic-aluminosilicates. Methods for preparation and use of
zeolite
containing cation exchanger using expanded clays/ceramics are described in US
Patent
5,976,490. These processes include calcination of raw materials which is an
energy intensive
process. Calcined material is treated further with alkali solution to produce
desired product.
US Patent 4,405,484 (1983), describes a process for preparing zeolite powder
having
high flow ability i.e. general flow index (expressed as the sum of indexes of
the repose angle,
spatula angle, compressibility and degree of cohesiveness) of from 30 to about
50 and at least
99 weight % of particles are having a particle size of 1-5 microns. The
zeolite powder is
prepared by adding an alkali metal aluminate to an aqueous zeolite slurry
containing 30-52
wt. % of zeolite (as anhydride) and having pH of not higher than 12.8;
adjusting the pH of 'the
slurry to a value not higher than 11; and then, drying the slurry. The zeolite
powder is useful
as a builder for detergent. The process requires pH adjustment and zeolite
slurry.
Indian Patents 182635 and 182636 describe improved processes for preparing
aluminosilicate gel and manufacture of detergent grade zeolite from it under
milder
conditions of temperature and time. However, the use of commercially available
sodium
aluminate powder as a source of alumina is contributing much to the production
cost.
Wantae Kim et al. (Journal of Chemical. Engineering of Japan, Vol. 33, No. 2,
pp.
217-222, 2000) investigated a novel process for synthesizing Zeolite-A and X
from kaolinite
activated by dry grinding. The process consists of grinding of kaolinite and
subsequent
reaction with NaOH solution at 60 C. Zeolite-A and X can be synthesized from
the process
under normal pressure. Crystallization of Zeolite-A and X is influenced by the
activated state
of kaolinite. The drawback associated with this is the requirement of grinding
which is an
energy intensive process.
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US Patent 6,641,796 describes a method for making zeolites and zeolite
mixtures
having enhanced cation exchange properties i.e. >200 mg CaCO3/gram anhydrous
zeolite.
This method include mixing a sodium silicate solution, a sodium aluminate
solution, and an
amorphous aluminosilicate initiator gel in a mixing vessel to create an
aluminosilicate
synthesis gel, and crystallizing the aluminosilicate synthesis gel to form
zeolite crystals. The
drawback of this method is the requirement of initiator gel to produce
aluminosilicate
synthesis gel.
US Patent 6,773,693 describes preparation of fine A-type zeolite particle
having an
average primary particle size of 0.1 m m or less. The process for preparing
the fine A-type
zeolite particle comprise reacting a silica source with an aluminum source in
presence of an
organic compound having an oxygen-containing functional group and a molecular
weight of
100 or more. Requirement of adding organic compound is a limitation of this
process.
Objects of the invention
The main object of the invention is to provide a process for preparing
detergent
builder Zeolite-A from Kimberlite tailing which obviates the drawbacks
detailed above.
Another object of the invention is to make use of silica content present in
Kimberlite
tailings for the preparation of detergent builder Zeolite-A.
Still another object of the invention is to prepare detergent builder Zeolite-
A at
atmospheric pressure and high temperature in the range 70 to 100 C.
Yet another object of the invention is to prepare detergent builder Zeolite-A
having
molar ratio of Si02/A1203 = 2.0 0.1, Na20/ A1203 = 1.0 0. land H20/ Na20= 4
to 5.
Yet another object of the invention is to prepare Zeolite-A having calcium
binding
capacity 160-170 mg CaO per gram of absolute dry zeolite which makes it
suitable as a
detergent builder.
Yet another object of the invention is to provide a process for preparing
Zeolite-A
with crystalinity>98% as measured by X-Ray diffraction and average particle
size<5.O m, as
measured by Laser diffraction with whiteness index of >97% measured by Digital
reflectance
meter.
The objects and other objects of the invention were achieved by the methods
provided
in the following detailed description.
Summary of the invention
The present invention discloses - a process for the preparation of detergent
builder
Zeolite-A from Kimberlite tailings by preparing sodium silicate from acid
treated Kimberlite
which is rich in silica content (-70 -75 %).
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The present invention provides a process for the preparation of Zeolite-A from
Kimberlite tailings, the process comprising:
i. treating sieved Kimberlite tailings fraction with a mineral acid to remove
acid soluble
impurities as filtrate and obtain a residue;
ii. washing the residue with demineralized water till the residue is free from
acid;
iii. digesting the acid treated Kimberlite tailing residue with an alkali to
obtain sodium
silicate;
iv. adding desired quantity of caustic soda solution to sodium silicate;
v. preparing sodium aluminate solution by dissolving required quantity of
alumina
trihydrate in sodium hydroxide solution;
vi. removing insoluble impurities present in sodium aluminate solution;
vii. dosing the sodium aluminate solution to the sodium silicate solution to
form amorphous
aluminosilicate gel;
viii. heating the aluminosilicate gel to convert amorphous aluminosilicate gel
to crystalline
Zeolite-A in a product slurry;
ix. cooling the product slurry and separating the Zeolite-A as a wet cake from
a filtrate.
x. washing the wet cake with demineralized water;
xi. drying the washed wet cake of the product;
xii. pulverizing the dried wet cake.
In another embodiment of the invention, the Zeolite-A is obtained as a fine
powder
with a whiteness index greater than 98%, calcium binding capacity 160-170mg
CaO/g of
absolute dry zeolite, crystalinity greater than 98% and average particle size
less than 5.0
microns.
In another embodiment of the invention, the Kimberlite tailing is first sieved
by
passing through 60 Mesh and has chemical constituents in the range Si02 30-
32%, A1203 2-
5%, Ti02 5-8%, CaO 8-10%, MgO 20-24%, Fe203 5-11% and loss on ignition 13-15%.
In another embodiment of invention, the mineral acid is selected from the
group
consisting of HCI and HNO3 in a concentration in the range of 1 to 10 N.
. In yet another embodiment of the invention the acid treatment is carried out
at a
temperature in the range of 75 to 100 C for a period in the range of I to 6
hours.
In another embodiment of the invention the acid treated Kimberlite tailing has
a
chemical composition in the range of Si02 73-77%, R203 3-4%, Ti02 10-13%, CaO
+ MgO
0.5-1.0% and loss on ignition 5-6%.
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In another embodiment of the invention, the acid treated Kimberlite tailings
are
treated with sodium hydroxide solution in a concentration in the range of 6 to
10%.
In a further embodiment of the invention, the alkali treatment is carried out
at either
boiling temperature in an open vessel or at a temperature in the range of 95
to 200 C in a
closed vessel and for a period in the range of 1 to 6 hours.
In another embodiment of the inventibn, the Na2O/SiOZ mole ratio in step (iv)
is
varied in the range of 0.6 to 1Ø
In another embodiment of the invention, in step (iv) the Na2O/SiO2 mole ratio
is in the
range of 0.5 to 1.0 and H20/Na2O mole ratio is in the range of 30 to 40.
In another embodiment of the invention, aluminum trihydrate powder having
A1203
content in the range of 63 to 65% is added to the caustic soda solution and
the mass heated to
temperature in the range of 70 to 100 C till complete dissolution takes place.
In another embodiment of the invention, the Na20/Al203 mole ratio is in the
solution
obtained in step (v) is varied in the range of 1.8 to 2.2 and H20/Na2O mole
ratio is in the
range of 25 to 30.
In another embodiment of present invention, in step (vi) the insoluble
impurities in
step (vi) are removed from the sodium aluminate solution by filtration or
flocculated and
settled using a flocculating agent.
In another embodiment of the invention, in step (vii) the sodium aluminate
solution of
step (vi) is added to the sodium silicate solution of step (iv) under
continuous stirring at
ambient temperature in the range of 25 to 40 C and for a period 30 to 120
minutes.
In another embodiment of the invention, the aluminosilicate gel has a
composition
3.2 0.1 Na20: 2.0 0.2 Si02: A1203: 105 10 H20 and is agitated at room
temperature for 10
to 15 minutes.
In another embodiment of the invention, the gel containing amorphous
aluminosilicate is crystallized by heating at a temperature in the range of 70
to 100 C for a
period in the range of 1 to 5 hours to convert the amorphous solid to
crystalline Zeolite-A.
In another embodiment of the invention, the product slurry obtained t the end
of step
(viii) is cooled in step (ix) in a stainless steel jacketed reactor and the
product Zeolite-A
separated by filtration.
In one embodiment of the invention, the filtrate obtained in step (ix)
contains NaOH
and minor quantities of Si02 and A1203 and is recycled in the process.
In another embodiment of the invention, the wet cake of the product is washed
with
demineralized water till pH of the wash water is between 10.5 and 11.
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In another embodiment of the invention, the washed wet cake of product
contains 40
to 50% moisture and is dried in a dryer at 110 C for 5 to 7 hours.
In another embodiment of the invention, the dried lumps of the product are
pulverized
in micro or impact type pulverizer.
The present invention also provides a process for the preparation of detergent
builder
Zeolite-A from Kimberlite tailing generated as solid waste during diamond
mining having
chemical constituents in the range Si02 30-32%, A1203 2-5%, Ti02 5-8%, CaO 8-
10%, MgO
20-24%, Fe203 5-11% and loss on ignition 13-15% which comprises passing the
Kimberlite
tailing through 60 mesh screen and treating the sieved fraction with 1 to 10 N
hydrochloric or
nitric acid at temperature in the range of 75 to 100 C for a specified period
in the range of 1
to 6 hours to remove acid soluble impurities, recovering the acid treated
Kimberlite tailing
after washing with demineralized water till free from acid and digesting the
acid treated
Kimberlite tailing having chemical composition in the range of Si02 73-77%,
R203 3-4%,
Ti02 10-13%, CaO + MgO 0.5-1.0% and loss on ignition 5-6% with an alkali such
as sodium
hydroxide solution having concentration in the range 6 to 10 percent at 95-200
C for a period
of 1 to 6 hours either in an open vessel or in a closed system to prepare
sodium silicate
having 13-21% Si02 and 4-7% Na2O with molar ratio of Si02:Na20 = 2.8-3.3,
adjusting the
Na20 /SiO2 mole ratio in the range of 0.5 to 0.8 and H20/Na2O mole ratio in
the range of 30
to 40 by adding sodium hydroxide solution, dosing the sodium aluminate
solution prepared
separately by dissolving required quantity of aluminum trihydrate in sodium
hydroxide
solution at 70 to 100 C so as to obtain Na20 / A1203 mole ratio in the range
of 1.8 to 2.2 and
H20/Na20 mole ratio in the range 25 to 30, to the sodium silicate solution
under continuous
stirring at ambient temperature in the range of 25 to 40 C and in a specified
period in the
range of 30 to 120 minutes to form aluminosilicate gel, heating the gel having
composition
3.2 0.1 Na20: 2.0 0.2 Si02: A1203: 105 10 H20 in the temperature range
of 70 to 100 C
for a time in the range of 1 to 5 hours there by converting the amorphous
aluminosilicate gel
to crystalline Zeolite-A, cooling the product slurry to <50 C and separating
the product by
conventional filtration technique, storing the filtrate mainly containing
sodium hydroxide and
minor quantities of SiOZ & A1203 in a storage tank which may be recycled in
the process,
washing the wet cake of the product with demineralized water till the pH of
the wash water is
between 11 and 10.5, drying the washed wet cake of the product containing 40
to 50%
moisture in a dryer at 110 C for 5 to 7 hours followed by pulverizing the
dried lumps of the
product using micro or impact type pulverizer and the powder product is stored
in appropriate
container or silos.
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Brief description of the accompanying drawings
In the drawings accompanying this specifications figure 1 represents XRD
patterns of
SASIL (Degussa-Henkel product) and CSMCRI 4A (produced as per Example 10 of
the
present invention). Figure 2 represents SEM of the product detergent builder
Zeolite-A
prepared as in Example 10.
Detailed description of the invention
In the process of the present invention detergent builder Zeolite-A is
prepared from
Kimberlite tailings generated as solid waste during diamond mining. Kimberlite
tailings are
treated first with mineral acid to remove acid soluble impurities, followed by
treatment of
alkali solution with silica rich acid treated Kimberlite to obtain sodium
silicate which is
further treated with sodium aluminate to obtain aluminosilicate gel and
subsequently heated
to produce crystalline Zeolite-A. The product Zeolite-A is suitable as
detergent builder.
The present invention relates to a process for the preparation of detergent
builder
Zeolite-A from Kimberlite tailings which comprises
i. passing Kimberlite tailings generated during diamond mining through 60 Mesh
screen.
ii. treating the sieved (-60 mesh) fraction having chemical constituents in
the range Si02
30-32%, A1203 2-5%, Ti02 5-8%, CaO 8-10%, MgO 20-24%, Fe203 5-11% and loss
on ignition 13-15%, with mineral acid such as hydrochloric or nitric acid
having
concentration in the range of 1 to 10 N at a temperature in the range of 75 to
100 C for
a specified period in the range of 1 to 6 hours to remove acid soluble
impurities as
filtrate. The residue is washed with demineralized water till free from acid.
iii. digesting the acid treated Kimberlite tailing having chemical composition
in the range
of Si02 73-77%, R203 3-4%, Ti02 10-13%, CaO + MgO 0.5-1.0% and loss on
ignition 5-6%, with an alkali such as sodium hydroxide solution having
concentration
in the range of 6 to 10 percent at a temperature in the range of 95-200 C for
a period
of 1 to 6 hours either in an open vessel or in a closed system to prepare
sodium
silicate having 13-21% SiO2 and 4-7% Na20 with molar ratio of Si02:Na20 in the
range of 2.8-3.3.
iv. adding calculated quantity of caustic soda solution to sodium silicate to
adjust the
Na20 /SiO2 mole ratio in the range of 0.5 to 0.8 and H2O/Na2O mole ratio in
the range
of 30 to 40.
v. preparing sodium aluminate solution by dissolving required quantity of
alumina
trihydrate in sodium hydroxide solution at 70 to 100 C. The Na20 / A1203 mole
ratio
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in the solution is in the range of 1.8 to 2.2 and the H20/Na20 mole ratio is
in the
range 25 to 30.
vi. removing the insoluble impurities present in sodium aluminate solution
either by
conventional filtration technique or by flocculating and settling it using
commercially
available flocculating agents.
vii. dosing the sodium aluminate solution to the sodium silicate solution
under continuous
stirring at ambient temperature in the range of 25 to 40 C and in a specified
period in
the range of 30 to 120 minutes to form aluminosilicate gel.
viii. heating the gel having composition 3.2 0..1 NazO: 2.0 0.2 Si02:
A1203: 105 10
H20 in the temperature range of 70 to 100 C for a time in the range of 1 to 5
hours
thereby converting the amorphous aluminosilicate gel to crystalline Zeolite-A.
ix. cooling the product slurry to < 50 C and separating the product by
conventional
filtration technique. The filtrate mainly containing NaOH and minor quantities
of
Si02 & A1203 is stored in a storage tank and may be recycled in the process.
x. washing the wet cake of the product with demineralized water till the pH of
the wash
water is between 11 and 10.5.
xi. drying the washed wet cake of the product containing 40 to 50% moisture in
a dryer at
110 C for 5 to 7 hours.
xii. pulverizing the dried lumps of the product using micro or impact type
pulverizer and
the powder product is stored in appropriate container or silos. This product
is
industrially useful as detergent builder.
This Zeolite -A is obtained as a fine powder having whiteness index more than
98%,
calcium binding capacity 160-170mg CaO/g of absolute dry zeolite, crystalinity
greater than
98% and average particle size less than 5.0 microns.
Kimberlite tailing passing through 60 Mesh and having chemical constituents in
range
Si02 30-32%, A1203 2-5%, Ti02 5-8%, CaO 8-10%, MgO 20-24%, Fe203 5-11% and
loss on
ignition 13-15% is used as starting material for preparing detergent grade
Zeolite-A.
Kimberlite tailings are treated with mineral acid like HCl and HNO3 in a
concentration range
of 1 to 10 N and at elevated temperature in the range of 75 to 100 C for a
specified period in
the range of 1 to 6 hours to remove acid soluble impurities. Acid treated
Kimberlite tailing
with chemical composition in range of Si02 73-77%, R203 3-4%, Ti02 10-13%, CaO
+ MgO
0.5-1.0% and loss on ignition 5-6% is then treated with sodium hydroxide
solution in the
concentration range of 6 to 10% at either boiling temperature in an open
vessel or at higher
temperature in range of 95 to 200 C in a closed vessel and allowed to react
for a period in the
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range of 1 to 6 hours. A calculated quantity of caustic soda solution is added
to sodium
silicate solution and the Na20 /Si02 mole ratio is be varied in the range of
0.6 to 1Ø The
sodium silicate solution may have H2O/Na2O mole ratio in the range of 30 to
40.
Aluminum trihydrate powder having A1203 content in the range 63 to 65% is
added to
a requisite quantity of caustic soda solution and the mass heated in the
temperature range of
70 to 100 C till complete dissolution takes place. The Na20 / A1203 mole ratio
in the solution
is varied in the range of 1.8 to 2.2 and H2O/Na2O mole ratio in the range of
25 to 30.
The sodium aluminate solution is either filtered by conventional technique or
insoluble matters are flocculated and settled using commercially available
flocculating
agents. The sodium aluminate solution is then added to the sodium silicate
solution under
continuous stirring at ambient temperature in the range of 25 to 40 C and in a
specified
period in the range of 30 to 120 minutes to form an aluminosilicate gel
containing amorphous
aluminosilicate. The aluminosilicate gel has a composition 3.2 0.1 Na20: 2.0
0.2 Si02:
A1203: 105 10 H20 is agitated at room temperature for 10 to 15 minutes. The
gel containing
amorphous aluminosilicate is then crystallized in the temperature range of 70
to 100 C for a
time in the range of 1 to 5 hours to convert the amorphous solid to
crystalline Zeolite-A.
After completion of Zeolite-A formation the product slurry is cooled down in a
stainless steel jacketed reactor and the product separated by conventional
filtration technique.
The filtrate mainly containing NaOH and minor quantities of Si02 and A1203 is
stored in the
proper storage tank and can be recycled in the process. The wet cake of the
product Zeolite-A
is washed with demineralized water till the pH of the wash water is between
10.5 and 11. The
washed wet cake of product contains 40 to 50% moisture and is dried in dryer
at 110 C for 5
to 7 hours. The dried lumps of the product are subjected to pulverization in
micro or impact
type Pulverizer and the powder product is stored in appropriate container or
silos.
Kimberlite tailing generated as solid waste during diamond mining contains
silica as
Si02 30-32%, Aluminum as A1203 2-5%, Titanium as Ti02 5-8%, calcium as CaO 8-
10%,
Magnesium as MgO 20-24%, Iron as Fe203 5-11% and loss on ignition 13-15%.
Moreover,
the X-Ray diffraction analysis indicated that Kimberlite contains Serpentine
as a major
mineral constituent. Serpentine is a layered material. It is possible to
destroy the layered
structure of Serpentine by chemical treatment. This produces silica in active
form and can be
used to prepare other siliceous materials.
Considering the above points, it was thought to enrich the silica content of
Kimberlite
tailing either physically or chemically. Physical methods such as sieving,
froth-floatation,
sedimentation and hydro cyclone separation were considered, but were not tried
since such
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separation is based on either difference in particle size or density of the
material. Chemical
and mineralogical analysis led us to believe that the constituents present in
Kimberlite are
integral part of the material and are therefore not easy to separate by
physical methods.
Therefore, only chemical treatment was tried. Treatment of Kimberlite tailing
with
alkali solution resulted in leaching of aluminum in form of sodium aluminate
and of titanium
in form of sodium titanate along with leaching of silica as sodium silicate.
During storage of
such leachate hydrolysis takes place due to which some solids separate out.
Thus, the leachate
was not stable on storage. Therefore, alkali treatment of tailings was not
considered feasible.
It was decided to subject the Kimberlite tailing to, acid treatment. When
Kimberlite
tailing is treated with mineral acid like HCl and HNO3 in the concentration
range of 1 to 10 N
and at elevated temperature in the range of 75 to 100 C for a specified period
in the range of
1 to 6 hours the acid soluble impurities could be removed effectively as
evidenced by the
chemical composition of the acid treated Kimberlite tailing i.e. Si02 73-77%,
R203 3-4%,
Ti02 10-13%, CaO + MgO 0.5-1.0% and loss on ignition 5-6%. For preparing
sodium
silicate, the acid treated Kimberlite tailing was digested under controlled
conditions with
NaOH solution keeping solid to liquid ratio as 1:4. This has produced sodium
silicate
havingl3-21% Si02 and 4-7% Na20 with molar ratio of SiO2:Na2O = 2.8-3.3. This
sodium
silicate was stable on storage.
According to batch size, gel composition and contents of sodium silicate,
sodium
aluminate solution is prepared. This is added at a controlled rate and at
ambient temperature
to sodium silicate solution taken previously in a stainless steel reactor.
Slurry of reaction
mixture is allowed to crystallize at temperature 70-100 C for 1 to 5 hours
until Zeolite-A
formation takes place. Zeolite-A slurry is filtered and washed till filtrate
pH was -11 to 10.5.
Wet cake thus obtained is dried in a dryer and dry powder was pulverized and
subjected to
analysis. The comparison of the properties of detergent builder Zeolite-A
produced according
to present invention (Example 10) and SASIL (Degussa - Henkel) is given in
Table 1.
The whiteness index of the product was determined using a Digital Reflectance
Meter
(Photo Electric Instruments (P) Ltd., Jodhpur, India). Calcium binding
capacity is determined
by measuring the uptake of calcium by one gram of Zeolite-A from one liter of
water having
30 degree hardness. Average particle size is measured as dry powder using
Laser diffraction
method (Mastersizer 2000, particle size analyzer, Malvern, UK). The morphology
of the
Zeolite-A crystals was examined by Scanning Electron Microscope (LEO). Powder
X-Ray
diffraction analysis was performed to determine percent crystalinity using
Philips MP3 X-
Ray diffractometer and CuKa as a source of X-rays. Values of d-spacing
reported in the
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WO 2006/070399 PCT/IN2004/000436
literature for Zeolite-A-(12.20 0.20, 8.60 0.20, 7.05 0.15, 4.07 0.08,
3.68 0.07, 3.38
~ 0.06, 3.26 0.05, 2.96 0.05, 2.73 0.05, 2.60 0.05 k) are used as the
basis for the
identification and quantification of crystalline phase. Chemical composition
is determined by
conventional wet chemical analysis methods and the pH was measured using pH
meter.
The process for the production of detergent builder Zeolite-A according to the
present
invention uses a new kind of raw material which is a solid waste generated
during diamond
mining, hitherto not used for the purpose. Considering the scientific
knowledge about the
type of impurities present in Kimberlite tailing it was possible to remove it
by acid treatment.
The inventive steps involved in the process include
~ Use of new kind of silica source which is a solid waste generated during
diamond mining.
~ Using raw material (Kimberlite tailing) without pre-drying or crushing
~ Enrichment of silica content by removing acid soluble matters by treatment
with
commercially available acid.
~ Preparing storage stable sodium silicate by alkali treatment of silica rich-
acid treated
Kimberlite tailing.
~ Preparing detergent builder Zeolite-A using the sodium silicate prepared as
above.
The following examples are given by way of illustration and therefore should
not be
construed to limit the scope of the present invention.
Example 1
500 g of Kimberlite tailing was digested in a round bottom flask with 100 g
NaOH
and 1280 g of tap water at boiling temperature with continuous stirring for 5
hours under
reflux. conditions. After completion of the digestion, sodium silicate was
separated by
filtration. For the preparation of sodium aluminate solution 7.9g of NaOH and
6.3g of
aluminum trihydrate were dissolved in 17.4g of water under continuous stirring
and heating.
62g of sodium silicate (having 2.93 % Na20 and 7.75 % Si02) was taken in a
stainless steel
vessel and to this sodium aluminate solution was added at the controlled rate
and at ambient
temperature under continuous stirring for the gel formation. It was then
transferred in a
closed reactor and crystallized at 95 C for 2.5 hours. After crystallization,
the product slurry
was filtered and washed with deionized water till the pH of the filtrate was -
10.5. Wet cake
was dried in oven at 110 C for 6 hours. X-Ray diffraction analysis of this
product showed a
pattern that matches with reported values for Zeolite-A.
Example 2
500 g of Kimberlite tailing was digested in a round bottom flask with 100 g
NaOH
and 1280 g of tap water at boiling temperature with continuous stirring for 5
hours under
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reflux conditions. After completion of the digestion, sodium silicate was
separated by
filtration. For the preparation of sodium aluminate solution 7.9g of NaOH and
6.3g of
aluminum trihydrate were dissolved in 17.4g of water under continuous stirring
and heating.
62g of sodium silicate (having 2.93 % Na20 and 7.75 % SiO2) was taken in a
stainless steel
vessel and to this sodium aluminate solution was added at the controlled rate
and at ambient
temperature under continuous stirring for the gel formation. It was then
transferred in a
closed reactor and crystallized at 95 C for 1.0 hours. After crystallization,
the product slurry
was filtered and washed with deionized water till the pH of the filtrate was -
10.5. Wet cake
was dried in oven at 110 C for 6 hours. X-Ray diffraction analysis indicated
that the product
obtained is amorphous phase which may be due to insufficient crystallizations
time.
Example 3
72g of Kimberlite tailing was digested in a round bottom flask with 20g NaOH
and
200g of tap water at boiling temperature with continuous stirring for 5 hours
under reflux
conditions. After completion of digestion, sodium silicate was separated by
filtration. For
preparing sodium aluminate solution 7.44g of NaOH and 6.28g of aluminum
trihydrate were
dissolved in 54.46g of water under continuous stirring and heating. 25.20g of
sodium silicate
(having 8.62% Na20 and 19.05% Si02) was taken in a stainless steel vessel and
to this
sodium aluminate solution was added at a controlled rate and at ambient
temperature under
continuous stirring for gel formation. After preparation of gel, 100mg of
Zeolite-A crystals
were added as seeds. It was then transferred in a closed reactor and
crystallized at 95 C for
1.0 hour. After crystallization, product slurry was filtered and washed with
deionized water
till pH of filtrate was -10.5. Wet cake was dried in oven at 110 C for 6
hours. X-Ray
diffraction analysis indicated that the product obtained is amorphous phase
which may be due
to insufficient crystallizations time. This also inferred that seeding was not
beneficial.
Example 4
500 g of Kimberlite tailing was digested in a round bottom flask with 400 g
NaOH
and 1300 g of tap water at boiling temperature with continuous stirring for 5
hours under
reflux conditions. After completion of the digestion, sodium silicate was
separated by
filtration. For the preparation of sodium aluminate solution 2.7g of NaOH and
6.27g of
aluminum trihydrate were dissolved in 40.74g of water under continuous
stirring and heating.
42g of sodium silicate (having 13.64 % Na20 and 11.31 % Si02) was taken in a
stainless
steel vessel and to this sodium aluminate solution was added at the controlled
rate and at
ambient temperature under continuous stirring for the gel formation. It was
then transferred in
a closed reactor and crystallized at 95 C for 1.0 hours. After
crystallization, the product
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WO 2006/070399 PCT/IN2004/000436
slurry was filtered and washed with deionized water till the pH of the
filtrate was -10.5. Wet
cake was dried in oven at 110 C for 6 hours. The product was found to be X-Ray
amorphous.
Example 5
200 g of Kimberlite tailing was digested in a round bottom flask with 2 lit of
6:4 HCl
at boiling temperature with continuous stirring for 6 hours under reflux
conditions. After
completion of reaction the slurry was filtered using vacuum filter and wet
cake washed
thoroughly till free from acid with tap water. Then the wet cake was dried in
oven at 110 C.
3.0 g Acid treated Kimberlite powder (having 80.87% Si02, 3.38% R203, 0.47%
CaO+MgO);
5.12g of alkali, 3.13 8g of aluminum trihydrate were taken into 3 6.40g of
water. After mixing
thoroughly, the reaction mixture was crystallized at 95 C for 2.5, 5.5, 8.5,
21.5 and 23.5
hours. After completion of crystallization at different time, the product
slurry was filtered and
washed with deionized water till the pH of the filtrate was 11. Wet cake was
dried in oven at
110 C. X-Ray diffraction showed that Zeolite-A formation has not taken place.
Example 6
200g of Kimberlite tailing was digested in a round bottom flask with 2 lit of
6:4 HCl
at boiling temperature with continuous stirring for 6 hours under reflux
conditions. After
completion of reaction slurry was filtered using vacuum filter and wet cake
washed with tap
water thoroughly till free from acid. Wet cake was dried in oven at 110 C.
3.Og Acid treated
Kimberlite powder (having 85.65% Si02, 1.27% R203, 0.48% CaO+MgO); 5.12g of
alkali,
3.138g of aluminum trihydrate were taken in 36.40g water. After mixing
thoroughly, reaction
mixture was crystallized at 110 C for 2.5, 5.5, 8.5, 21.5 and 23.5 hours.
After completion of
crystallization at different times, product slurry was filtered and washed
with deionized water
till pH of the filtrate was 11. Wet cake was dried in oven at 110 C. X-Ray
diffraction pattern
showed presence of different phases of crystalline alumino silicates such as
Zeolite-A,
Zeolite-X, hydroxysodalite and phillipsite along with gibbsite and Anatase
phases.
Example 7
70 g of Kimberlite tailing was treated with 1:1 HCl at 95-100 C under
continuous
stirring keeping solid to liquid ratio 1:10 for 5 hrs, then the slurry was
filtered and washed
thoroughly till free from acid with tap water and dried at 110 C. For the
preparation of
sodium silicate 16 g of NaOH was dissolved in 200 ml of water and taken in to
stainless steel
autoclave. To this, 50 g of acid treated Kimberlite was added under continuous
stirring. Then
the reactor was closed and heated for 5 hours at 150 C under autogenous
pressure conditions.
After completion. of reaction sodium silicate was separated by filtration. For
the preparation
of sodium aluminate solution 5.91g of NaOH, 4.48g of aluminum trihydrate and
26.25 g of
CA 02592499 2007-06-26
WO 2006/070399 PCT/IN2004/000436
water were mixed under continuous stirring and heating till a clear solution
is obtained.
25.54 g of sodium silicate (having 4.25 % NazO and 13.4 % Si02) was taken in a
stainless
steel reactor and to this sodium aluminate solution was added at the
controlled rate under
continuous stirring for the gel formation. It was then transferred in the
Teflon bombs for
hydrothermal treatments for 0.5, 1.5, 2.5, 3.5 and 4.5 hours of
crystallization at 95 C. After
crystallization slurry was filtered and washed with deionized water till the
pH of the filtrate
was 11. Wet cake was dried in oven at 110 C. X-Ray diffraction results showed
the presence
of highly crystalline phase of Zeolite-A for all crystallization time except
for 0.5 hr.
Example 8
2.7 kg of Kimberlite tailing was treated with 1:1 HCI at 95-100 C under
continuous
stirring keeping solid to liquid ratio 1:4 for 3 hours. The slurry was then
filtered and washed
thoroughly with tap water till free from acid and dried in oven at 110 C. For
the preparation
of sodium silicate 0.64 kg of NaOH was dissolved in 8 lit of water and taken
in a stainless
steel reactor. To this 2 kg of acid treated Kimberlite was added under
continuous stirring.
Then the reacting mass was heated at boiling temperature for 3.5 hours. After
completion of
reaction time sodium silicate was separated by filtration. For the preparation
of sodium
aluminate solution 250 g of NaOH, 190 g of aluminum trihydrate and 1390 g of
water were
mixed and dissolved under continuous stirring and. heating. Sodium aluminate
solution was
filtered to remove insoluble impurity. 1000 g of sodium silicate (having 4.7 %
Na20 and 14.5
% Si02) was taken in stainless steel reactor and to this sodium aluminate
solution was added
at the controlled rate and at ambient temperature under continuous stirring
for the gel
formation. Temperature of the gel was raised to 95 C and maintained for 1
hour for the
crystallization of Zeolite-A. After completion of crystallization, the product
slurry was
filtered and washed with deionized water till the pH of the filtrate was 11.
Wet cake was
dried in oven at 110 C. X-Ray diffraction showed that the product obtained is
Zeolite-A.
XRD pattern of this sample matches with the reported XRD pattern of Zeolite-A.
Example 9
2.7kg of Kimberlite tailing was treated with 1:1 HCl at 95-100 C under
continuous
stirring keeping solid to liquid ratio 1:4 for 3 hours. The slurry was then
filtered and washed
with tap water till wet cake becomes acid= free. Then it was dried in oven at
110 C and the
dried solid was used for the preparation of sodium silicate. For the
preparation of sodium
silicate 0.64 kg of NaOH was dissolved in 8 lit of water and taken in to
stainless steel
autoclave. To this 2 kg of acid treated Kimberlite was added under continuous
stirring. Then
the reactor was heated at boiling temperature under reflux conditions for 3.5
hours. After
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completion of reaction, sodium silicate was separated by filtration. 288 g of
sodium silicate
(having 4.78 % Na20 and 13.9 % Si02) was taken in stainless steel reactor. For
the
preparation of sodium aluminate solution 68 g of NaOH, 53 g of aluminum
trihydrate and
370 g of water were mixed under continuous stirring and heated till the
solution becomes
clear. Then it.was filtered to remove insoluble impurity. Sodium aluminate
solution was then
added in to sodium silicate previously taken in stainless steel reactor at
controlled rate and at
ambient temperature under continuous stirring within 1 hour. Then the reaction
mixture was
crystallized at 93-95 C for 1 hr. After crystallization, the slurry was
filtered and washed with
deionized water till the pH of the filtrate was 11. Wet cake was dried in oven
at 110 C. X-
Ray diffraction showed that product obtained was Zeolite-A. XRD of this sample
matches
with the reported pattern of XRD of Zeolite-A.
Example 10
23 Kg of Kimberlite tailing was treated with 1:1HC1 at 95-100 C under
continuous
stirring keeping solid to liquid ratio 1:4 for 3 hours. The slurry was then
filtered and washed
with tap water till wet solid cake becomes acid free. Then it was dried in
oven at 110 C. For
the preparation of sodium silicate 5.44 kg of NaOH was dissolved in 68 liter
of water and
taken in a stainless steel reactor. To this 17 kg of acid treated Kimberlite
was added under
continuous stirring. Then the reactor was heated for 3.5 hours at boiling
temperature under
reflux conditions. After completion of reaction the slurry was filtered and
sodium silicate was
collected as filtrate. 22.47 kg of sodium silicate (having 4.77 % Na20 and
14.63 % Si02) was
taken in stainless steel reactor. For preparation of sodium aluminate solution
5.68 kg of
NaOH, 4.3 kg of aluminum trihydrate and 32.30 kg of water were mixed and
dissolution
completed by heating under continuous stirring. Insoluble impurities of sodium
aluminate
were separated by filtration. After filtration, sodium aluminate solution was
added in to
sodium silicate previously taken in stainless steel reactor at controlled rate
and at ambient
temperature under continuous stirring within 1 hour. Then the reaction mixture
was
crystallized at 95 C for 1 hour. After crystallization, the slurry was
filtered and washed with
deionized water till the pH of the filtrate was 11. Wet cake was dried in oven
at 110 C. X-
Ray diffraction pattern showed that product obtained is Zeolite-A.
X-Ray diffraction patterns of the product (Example 10) and SASIL are shown in
Fig.
1. SEM of the product showed Cubic crystal structure of Zeolite-A with rounded
corners and
edges having average particle size of less than 4 microns (Fig 2). The present
invention
provides a flexible process leading to a product of international quality.
Furthermore, the
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WO 2006/070399 PCT/IN2004/000436
process is cost-effective because of the utilization of Kimberlite a solid
waste generated from
diamond mining.
Table 1. Comparison of properties of detergent builder Zeolite-A produced as
per the
present invention (Example 10) and SASIL (Degussa -Henkel).
Property Example 10 SASIL
A earance: Fine powder Fine powder
Whiteness index,%, >98 >95
Calcium Binding Capacity, mg CaO/g of 160-170 >155
absolute dry zeolite
Loss on ignition, (lhour at 800 C),% 20-22 21.5 - 22.5
pH of 5% aqueous slurry 11.0 -11
Average Particle Size, m, -4.0 <5.0
Chemical Analysis
Si02, % 33 - 36 32.5 -33.5
A1203 ,% 27 - 29 27. 5-28. 5
Na20,% 14-16 7.5
C stallinit , %, >98 > 98
Bulk Density, g/ml 0.45 - 0.55 -0.40
The main advantages of the present invention are:
1. Kimberlite tailings generated as a solid waste during diamond mining is
converted to
a detergent builder Zeolite-A via production of sodium silicate, and'the
product is
value added material suitable for applications in detergent industry.
2. Alternative source of silica for producing detergent builder Zeolite-A for
commercial
application has been found.
3. Acid treatment of Kimberlite tailing provided special advantage of removing
all the
major acid soluble impurities and converting it in to active silica source.
4. Filtrate collected after acid treatment of Kimberlite tailing can be used
to recover
magnesium and iron salts.
5. The treatment of alkali with acid treated Kimberlite provided special
advantage'of
producing sodium silicate suitable for wide commercial applications.
6. The process according to the present invention involves simple unit
operations.
7. The process does not involve high temperature fusion and is not energy
intensive.
8. The present process contributes towards solid waste utilization thereby
improving the
environmental quality of diamond mining and makes diamond mining economical
and
eco-friendly.
18
