Claims:We Claim:
1. A method of increasing the Hunter Whiteness of white cement by 1-10%, wherein at least one carboxylic acid is mixed with water to form a mixture which is sprayed on white cement clinker from which the white cement is to be obtained.
2. The method as claimed in claim 1, wherein the mixture is sprayed to cool the white cement clinker for time period between 10 seconds to 5 minutes, after burning the clinker in a kiln.
3. The method as claimed in claim 1, wherein the mixture changes the valency of the iron present in the white cement clinker from ferric to ferrous.
4. The method as claimed in claim 1, wherein the carboxylic acid is selected from a group consisting of oxalic acid, formic acid, acetic acid, citric acid and a combination thereof.
5. The method as claimed in claim 1, wherein 1 wt. % to 20 wt. % of carboxylic acid is mixed with 100 volume % of water.
Dated this 23rd day of January, 2020
, Description:FORM 2
TH PATENT ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION
A method of increasing the Hunter Whiteness of white cement.

APPLICANTS
Aditya Birla Science and Technology Company Pvt. Ltd., Aditya Birla Centre, 2nd Floor, ‘C’ wing, S. K. Ahire Marg, Worli, Mumbai 400030, Maharashtra, India.

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
[001] The present invention relates to a method of increasing the Hunter Whiteness of white cement. More particularly, the present method increases the Hunter Whiteness of the white cement by 1-10%.
BACKGROUND OF THE INVENTION
[002] The whiteness is understandably one of the most important properties of white cement. White cement is made from raw materials with a low content of coloring elements such as Fe, Mn, Cr and Ti. High-grade limestone or chalk containing less than 0.15 wt.% Fe2O3 and less than 0.015 wt.% MnO is used, and of white clay or kaolin and other materials which should not contain more than 1 wt.% FeO and 0.8 wt.% TiO2. Gypsum, active and inert mineral additives are introduced in grinding stage and must also exhibit whiteness corresponding to cement of the given class. The raw materials, the intermediate product and the final product must also be protected from contamination at all stages of the technology. The whiteness degree is determined according to the reflection coefficient in percent of the absolute scale.
[003] Currently, in order to increase the whiteness, the fired clinker is quenched with water. For this purpose, the clinker at 1450°C to 1500°C is withdrawn from the kiln through a special outlet into a water bath and passed into a drying chamber where it is dried at temperatures not exceeding 300°C.
[004] The content of Fe2O3 in white cement may vary over the range of 0.35 to 0.5 wt.%. If the limit is exceeded, the iron oxides are responsible for a greenish shade of the clinker which is undesirable in certain applications, for example, for architectural applications of white cement. The following reducing reactions of colouring ions take place during manufacture of white cement clinker in a reducing atmosphere:
Fe3O4 + CO =3FeO + CO2
Fe2O3 + CO = 2FeO + CO2
MnO2 + CO = MnO + CO2
2CrO3 + 2CO = Cr2O3 + 2CO2 + O2
[005] The colouring effect of Fe, Cr, and Mn cations depends on their valency in the crystalline phases in cement. Oxidized forms of free oxides of Fe3+, Mn3+ and Mn4+ absorb more light than reduced forms Fe2+ and Mn2+. The higher the temperature and/or the concentration of the reducing agent, the whiter the cement appears to human eye. This is important particularly in the cooling of white cement clinker. If it is cooled slowly from the initial temperature in the kiln (1200 - 1100 °C or lower) in the presence of oxygen, the colouring oxides of higher valent metals will be reformed. Contrarily, if the cooling is quick, the high-temperature reduced crystalline forms are “frozen-up” and the light absorption will be lower.
[006] Therefore, there is a need a method to increase the whiteness of white cement which solves the problem of the prior art.
SUMMARY OF THE INVENTION
[007] According to an embodiment of the present invention, there is provided a method of increasing the Hunter Whiteness of white cement by 1-10%, wherein at least one carboxylic acid is mixed with water to form a mixture which is sprayed on white cement clinker from which the white cement is to be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS
[008] Figure 1 illustrates a comparative graph of the IR spectra between control experiment and oxalic acid, in accordance with the embodiments of the present invention;
[009] Figures 2 depicts a comparative graph of the IR spectra between control experiment and formic acid, in accordance with the embodiments of the present invention; and
[010] Figure 3 illustrates a comparative graph of the IR spectra between control experiment and acetic acid, in accordance with the embodiments of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[011] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed process and system, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
[012] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
[013] Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
[014] As set out in the claims, the present invention aims to increase the whiteness index of white cement by 1% to 10%. In this method, at least one carboxylic acid is mixed with water to form a mixture which is sprayed on white cement clinker from which the white cement is to be obtained. The addition of carboxylic acid in the quenching water changes the ionic state of iron during the clinker quenching process. The present invention aims at freezing the iron in reduced form Fe2+ and convert the Fe3+. In other words, the mixture changes the valency of the iron present in the white cement clinker from ferric to ferrous.
[015] The ferrous salts of the carboxylic acid increase the whiteness of the clinker. Light absorption is lower in Fe2+ in the form of ferrous salts as compared to their respective ferric counterparts and it leads to increase the whiteness index of white cement. During rapid quenching with oxalic acid, formic acid and acetic acid in a water bath of low-ferric clinker the whiteness is promoted by reducing the valency of iron oxides, by changing the coordination of colouring oxides and as a result of adjusting the proportions of the aluminate and silicate phases.
[016] According to an embodiment of the present invention, the mixture is sprayed to cool the white cement clinker for time period between 10 seconds to 5 minutes, after burning the clinker in a kiln.
[017] In another embodiment, the carboxylic acid is selected from a group consisting of oxalic acid, formic acid, acetic acid, citric acid and a combination thereof. preferably, 1 wt. % to 20 wt. % of carboxylic acid is mixed with 100 volume % of water.
[018] Experimental Data:
Advantages and benefits of the embodiments of the present invention would become more apparent from the below experimental details to a person skilled in the art.
[019] The following process was followed for carrying out all experiments:
1. Raw mix (RM) was made into nodules of roughly 1gm each with distilled water;
2. These nodules were left to dry in an oven at 60°C for a few hours;
3. They were heated in platinum crucibles in the furnace with the following furnace program:
a. Ramping at 10°/min till 1200°C
b. Ramping at 5°/min till 1450°C
c. Dwelling for 45 mins at 1450°C
d. End
4. The clinkers thus formed were removed and quenched by dipping into the quenching liquid, removing immediately and keeping drying on filter paper. Quenching liquid was an acid solution of the above-mentioned acids;
5. The damp clinkers were then left to dry in the oven at 60°C for several hours;
6. The dried clinkers were ground in a cup mill for roughly 2 to 3 min to get required blain size; and
7. The powdered samples were thus submitted for spectrophotometer for determination of Hunter Whiteness. Hunter Whiteness was found to increase by 10% points as compared to the control (only water quenching).
Example 1
[020] Experiments were carried out using a carboxylic acid with quenching water to freeze iron present in the clinker in Fe++ form. In all cases, Hunter whiteness index of clinker was found to increase from 88 to 92. As can be seen in Table 1, different carboxylic acids were used while carrying out the experiments and consistent result was observed in all cases.

Table 1

Experiment Description WI (Hunter):
1 Clinker quenched in water (CONTROL) 88.63
2 Clinker quenched in 12.01% oxalic acid solution 92.14
3 Clinker quenched in 4.59% formic acid solution 92.35
4 Clinker quenched in 5.99% acetic acid solution 91.56

Example 2:
[021] XRD Rietveld Analysis has been carried out for control sample (water quenching) and experimental sample (acid quenching), it has been observed that the Alite phase (C3S) and Tri-calcium Aluminate (C3A) phases are comparatively high in experimental sample quenched with carboxylic acid (Table 2). The whiteness of cement increases with increasing content of tricalcium silicate (C3S) and aluminate. Fourier-transform infrared spectroscopy (FTIR) revealed the presence of ferrous oxalate, ferrous formate and ferrous acetate in experimental sample quenched with the carboxylic acid solutions (Fig 1, Fig 2 and Fig 3). In the figures -
a: Control Sample;
b: Sample with Oxalic Acid;
c: Ferrous Oxalate;
d: Calcium Oxalate;
e: Control Sample;
f: Sample with Formic Acid;
g: Ferrous Formate;
h: Calcium Formate;
i: Control Sample;
j: Sample with Acetic Acid;
k: Ferrous Acetate;
l: Calcium Acetate

Table 2
Experiments with white cement raw Meal) Mineral Phases (XRD Rietveld Analysis of White Cement Clinker)
Alite (C3S) Belite (C2S) Tricalcium Aluminate (C3A) Calcium Alumino Ferrite (C4AF) Free Lime(CaO) Periclase

Control 50.10 38.03 7.26 -- 1.58 3.03
Oxalic Acid 55.90 34.28 7.88 -- 0.05 1.89
(Conc: 12.01%)
Formic Acid (Conc: 4.59%) 52.12 36.78 7.62 -- 0.72 2.76
Acetic Acid (Conc: 5.99%) 52.31 37.17 7.56 -- 0.94 2.02

Example 3:
[022] To see the distribution of aluminoferrite same experiment has been carried out using grey cement composition (Table 3). A comparative phase analysis of control sample (water quenching) and experimental sample (Carboxylic acid quenching) revealed that the Alite phase (C3S) and Tri-calcium Aluminate (C3A) phases are comparatively high and aluminoferrite, dicalcium silicate (C2S) and free lime are comparatively low in experimental sample quenched with oxalic acid and a similar case in that of formic acid and acetic acid as well.
On oxalic acid quenching they are fixed to a smaller number of particles of type aluminoferrite while separating white calcium aluminates. The whiteness of cement increases with increasing content of tricalcium silicate (C3S) and aluminate and decreases with increasing content of calcium aluminoferrite and dicalcium silicate (C2S).

Table 3
Experiments with Grey cement raw Meal) Mineral Phases (XRD Rietveld Analysis of Grey Cement Clinker)
Alite (C3S) Belite (C2S) Tricalcium Aluminate (C3A) calcium aluminoferrite (C4AF) Free Lime (CaO) Periclase

Control 64.66 10.98 1.67 20.15 1.03 1.51
Oxalic Acid 66.81 9.96 3.49 18.00 0.48 1.26
(Conc: 12.01%)
Formic Acid (Conc: 4.59%) 67.51 9.85 3.58 16.75 0.78 1.53
Acetic Acid
(Conc: 5.99%) 67.03 8.48 3.72 18.57 0.76 1.44

[023] The foregoing description of specific embodiments of the present invention has been presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.