FIELD OF INVENTION:
This invention relates to the method of utilization of lime dust for neutralization of
acidic wastes.
BACKGROUND OF THE INVENTION:
Chemicals such as NaOH or Na2CO3 is generally used for the neutralization of
acidic wastes from the steel plants.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a method for utilization of lime dust for
neutralization of acidic wastes;
Another object of this invention is to propose a method which can be employed in
all other areas of integrated steel plants where HCL is used in bulk quantities;
Further object of this invention is to propose a method utilizing lime dust waste
generated during the calcinations process;
SUMMARY OF THE INVENTION:
According to this invention there is a method of utilization of time dust of
neutralization of acidic wastes comprising dissolving lime dust in water to
produce separately the supernatant having pH about 10 by decantation; adding
the said supernatant to the acidic waste having pH about 2 till the color of the
indicator changes, and the pH is about 8.

DETAILED DESCRIPTION OF THE INVENTION:
Lime is required in huge quantities for iron and steel making process. Lime
required for neutralization is produced in Maerz Kilns by the calcinations process
wherein Limestone is burnt to produce lime, the process also generates huge
amount of lime dust which is considered as a process waste.
CaCO3 = CaO + CO2
The composition of lime dust is as follows:
%CaO: 95-98%
%SiO2: 05-1.0%
%MgO: 0.5-1.0%
%A12O3: 0.2-0.5%
This lime dust on dissolution in water gave a basic solution of pH around 10.
Owing to the above basic properties of lime, it was felt that this process waste
generated in the Maerz Kiln can be used for neutralization of acidic wastes.
The lime dust was reacted with the 15% HC1 solution waste generated in the
laboratory. The resultant solution was found to have a pH of 8 and hence from
environmental point of view safe for disposal. The reaction mechanism of the
neutralization is given below:
CaO + 2HC1 = CaC12 + H2O.

Detailed Process flow:
• Lime dust is collected from the plant
• It is dissolved in water
• The supernatant liquid (A) is separated by decantation.
• Acidic waste (B) is stored in a jar to which is added phenolphthalein
indicator.
• Solution A is added to B till the color changes to pink.
• This indicates the end of the neutralization process.
• The resultant neutralized solution is then safely disposed off.
Process Parameters
• PH of the acidic waste is about 2
• PH of lime solution is about 10.
• PH of neutralized solution is about 8
EXAMPLE:
In Chemical Laboratory various types of samples of ores, fluxes, iron and steel
etc are analysed for its chemical composition by first dissolving the sample in an
inorganic acid like HCI, HNO3, etc and then subsequently measuring by ICP
spectrometer. After the measurement process, the left over sample is a waste
and its pH is 2. This left over solution is collected in a jar to which
phenolphthalein indicator is added. The lime solution is prepared and kept
separately. The lime solution is then to the container containing the acidic waste
till the colour changes to pink indicating the end of the neutralization reaction.
The neutralized solution is then disposed off.

WE CLAIM:
1. A method of utilization of lime dust of neutralization of acidic wastes
comprising:
dissolving lime dust in water to produce separately the supernatant having
pH about 10 by decantation;
adding the said supernatant to the acidic waste having pH about 2 till the
color of the indicator changes, and
the pH is about 8.
2. The method as claimed in claim 1, wherein the said indicator used is
phenolphthalein.
3. The method as claimed in claim 1, wherein the said supernatant is added
till the color of the indicator changes into pink.
4. The method as claimed in claim 1, wherein said lime dust comprises on
%CaO: 95-98%
%SiO2: 0.5-1.0%
%MgO: 0.5-1.0%
%A12O3: 0.2-0.5%

A method of utilization of lime dust of neutralization of acidic wastes comprising:
dissolving lime dust in water to produce separately the supernatant having pH
about 10 by decantation; adding the said supernatant to the acidic waste having
pH about 2 till the color of the indicator changes, and the pH is about 8.