FORM 2
THE PATENTS ACT, 1970
(Act 39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
Title "A METHOD FOR TREATING CALCIUM
CHLORIDE CONTAINING ACIDIC EFFLUENT GENERATED FROM PHOSPHORIC ACID MANUFACTURING PROCESS"
Name: Gujarat Alkalies and Chemicals Limited
Address: P.O. Petrochemicals - 391 346,
Dist.: Vadodara, Gujarat, India.
Nationality: Indian

Field of the Present Invention:
This invention relates to treatments of effluent wastes from acid manufacturing processes. More particularly, this invention relates to treatment of Calcium Chloride rich effluent generated during Phosphoric Acid manufacturing process.
Background of the Present Invention:
In Phosphoric Acid manufacturing process, Rock Phosphate is dissolved/reacted in Hydrochloric Acid. Phosphoric Acid is separated from leach liquor, which is also known as Dissolution Liquor by Solvent Extraction. The Solvents used are C4 and C5 Alcohols. The Organic Phase is stripped by water to obtain dilute Phosphoric Acid solution also known as Weak Acid. The Weak Acid is concentrated stage-wise with heavy metal removal. The Concentrated Acid is bleached as well steam-stripped to remove Fluoride. The product so produced is "Technical Grade Phosphoric Acid." The stripped Solvent is reused in the process. The process generates a Brine Solution, which is a liquid waste containing Calcium Chloride, Fluoride and other impurities of highly acidic nature. This manufacturing process has an advantage of producing high purity Phosphoric Acid, but one of its environmental problems is related to disposal of acidic liquid waste with high Calcium Chloride content, approximately, 18- 20%; Fluoride content, approximately, 0.3- 0.5%; P2O5 content, approximately, 0.05 -0.1%; and heavy metal impurities. The acidic liquid waste is required to be treated for safe disposal in the effluent channels, but neutralization of acidic liquid waste with Calcium Hydroxide (lime) generates solid waste, which in turn requires large land-fill area and increases process operations.
US 1816285 has reported production of Calcium Nitrate and mixed fertilizer along with Phosphoric Acid by using Nitric Acid as leaching agent in the process.
US 2819955 has reported treatment of impure Calcium Nitrate by Ammonia to lower the acidity and converting Phosphoric impurities into fertilizer.
General manufacturing processes for Calcium Nitrate are reported in several Patents like US 1966395, US3518071, EP3 434647A1, EP1 807351 B1 & EP1 280736 B1.

General method to produce Calcium Nitrate is by treating Limestone (Calcium Carbonate) with Nitric Acid, followed by neutralization with Ammonia. Calcium Nitrate is also a by-product of the Phosphoric Acid production by Nitric Acid. Calcium Nitrate can also be prepared from an aqueous solution of Ammonium Nitrate and Calcium Hydroxide.
The present invention provides environment friendly solution for treating Calcium Chloride rich acidic effluent generated from Phosphoric Acid manufacturing process based on Rock Phosphate and Hydrochloric Acid. The process gives a value-added product in the form of high purity Calcium Nitrate Tetrahydrate >99.50% while avoiding generation of solid waste that otherwise would have to be disposed in a land¬fill. Thus, precious land can be used for better purposes than using it as land-fill.
The process is easy to operate on commercial scale with unit operation like concentration, liquid phase reaction, distillation, neutralization, filtration, crystallization under the moderate temperature conditions.
The present invention is a novel approach that achieves dual objective of both, treating the acidic waste effectively and simultaneously manufacturing a value-added high purity product i.e. >99.50% Calcium Nitrate Tetrahydrate, which is suitable for industrial application/use.
Summary of the Present Invention:
The present invention discloses a method for treating Calcium Chloride containing acidic effluent generated from Phosphoric Acid manufacturing process. The acidic effluent may include 18-20% Calcium Chloride, 0.05 - 0.1% P2O5, and 0.3-0.5% Fluoride.
In the first step, Calcium Chloride concentration in the acidic effluent is increased up to 35-40% by distilling out excess water. Then Calcium Chloride is converted into Calcium Nitrate Tetrahydrate by reacting at 120°C - 135°C with dropwise addition of 60 - 70% Nitric Acid and simultaneously distilling out at 105 - 110°C any Hydrochloric Acid formed during the reaction. Concentration of the recovered Hydrochloric Acid is 18 - 20%. Crude reaction mass having Calcium Nitrate

Tetrahydrate and impurities comprising Calcium Phosphate and Calcium Fluoride is then diluted and the impurities are removed by neutralization with Calcium Carbonate and Ammonia Solutions. Neutralization brings the pH of the Calcium Nitrate Solution up to 5.50 - 6.00. The precipitated impurities are removed by filtration. The filtrate obtained after filtration has a dilute Solution of pure Calcium Nitrate Tetrahydrate, which is further concentrated up to 50%. The concentrated Calcium Nitrate Solution is subjected to crystallization at 14 - 18°C for 24-48 hrs at humidity 30 ± 5 to yield high purity Calcium Nitrate Tetrahydrate. Calcium Nitrate Tetrahydrate with >99.50% purity can be yielded.
Detailed Description of the Present Invention:
The present invention is a novel approach to treat Calcium Chloride containing acidic effluent generated from Phosphoric Acid manufacturing process by effectively converting it into high purity Calcium Nitrate Tetrahydrate that is suitable as Fertilizer and has other Industrial applications.
The process has following steps:
Step -1:
Acidic liquid waste having 18 - 20% Calcium Chloride is concentrated up to of 35 -40% by distillation at 105 - 110°C temperature with removal of excess water.
Step - II:
Acidic liquid waste having a 35 - 40% Calcium Chloride is treated with known amount of Nitric Acid (Conc 60 - 70%) by dropwise addition in the reaction pot, maintaining the temperature 120 - 135°C, throughout the addition of Nitric Acid. During the reaction, Hydrochloric Acid formed is simultaneously distilled out. This reaction is continued till Calcium Chloride is completely converted into crude Calcium Nitrate.
Step - III:
The crude Calcium Nitrate Solution is further diluted and purified by neutralization process. In the neutralization process, the crude Calcium Nitrate Solution is

neutralised by Calcium Carbonate and Ammonia Solutions up to pH: 5.5. to 6.0. At this pH, impurities get precipitated and separated by filtration. The filtrate contains pure Calcium Nitrate, while the solids separated by filtration are a mixture of Calcium Phosphate, Calcium Fluoride, only a small amount of Calcium Nitrate, and less than 1% metallic impurities.
Step - IV
Pure Calcium Nitrate Tetrahydrate having purity > 99.5% is obtained by concentrating the filtrate followed by crystallization at 14 - 18°C for 24 - 48 hrs. at humidity 30+/- 5.
Example:1
500 gms. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stopped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid waste. This is followed by dropwise addition of 189 gms Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1 followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30± 5. The crystallized Calcium Nitrate tetrahydrate obtained was 141 gms. with purity > 99.50% and percentage yield around 95.5%. The residue generated in the process was 34.40 gm, which is found to be a mixture Calcium Phosphate,

Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.
Example:2
5.0 kg. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stopped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid waste. This is followed by dropwise addition of 1.89 kgs Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1 followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30+ 5. The crystallized Calcium Nitrate tetrahydrate obtained was 1.41 kgs. with purity > 99.50% and percentage yield around 96,8%. The residue generated in the process was 320 gm, which is found to be a mixture Calcium Phosphate, Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.
Example:3
5.0 kg. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stooped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid

waste. This is followed by dropwise addition of 2.08 kgs Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1 followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30± 5. The crystallized Calcium Nitrate tetrahydrate obtained was 1.432 kgs. with purity > 99.50% and percentage yield around 96.95%. The residue generated in the process was 332 gm, which is found to be a mixture Calcium Phosphate, Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.
Example:4
5.0 kg. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stopped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid waste. This-is followed by dropwise addition of 1.70 kgs Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1

followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding-pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30+ 5. The crystallized Calcium Nitrate tetrahydrate obtained was 1.35 kgs. with purity > 99.50% and percentage yield around 91.94%. The residue generated in the process was 340 gm, which is found to be a mixture Calcium Phosphate, Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.
Example:5
10.0 kg. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stopped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid waste. This is followed by dropwise addition of 3.78 kgs Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1 followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30± 5. The crystallized Calcium Nitrate tetrahydrate obtained was 2.845 kgs. with purity > 99.50% and percentage yield around 96.44%. The residue

generated in the process was 685 gm, which is found to be a mixture Calcium Phosphate, Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.
Example:6
15.0 kg. Acidic liquid waste of Phosphoric Acid plant (containing 20% Calcium Chloride, 0.1% P2O5, 0.5% Fluoride and other metal impurities) was charged in a reaction flask attached with distillation assembly. The reaction mass was heated up to 105 - 110°C temp, to remove excess of water by distillation. The distillation was stopped after attaining the concentration of Calcium Chloride 35 - 40% in the liquid waste. This is followed by dropwise addition of 5.67 kgs Nitric Acid (Concentration 60 - 70%) maintaining the reaction temperature in between 120 - 135°C with simultaneously distilling out the Hydrochloric Acid, which is generated during the reaction.
After completion of reaction, the Crude mass left behind is the mixture of Calcium Nitrate, Calcium Phosphate, Calcium Fluoride and metallic impurities. Purification of crude Calcium Nitrate was carried out by dilution using the distillate of step-1 followed by neutralizing the mass with Calcium Carbonate & Ammonia solution up to pH 5.5 - 6.0. In the neutralization process, the impurities get precipitated and removed by simple filtration. The filtrate containing pure Calcium Nitrate in dilute form, is further concentrated up to 50% by removing excess of water by distillation.
Finally, the concentrated Calcium Nitrate solution was subjected to crystallization by seeding pure Calcium Nitrate and keeping the mass for 24 - 48 hrs. at 14 - 18°C & humidity 30± 5. The crystallized Calcium Nitrate tetrahydrate obtained was 4.295 kgs. with purity > 99.50% and percentage yield around 96.9%. The residue generated in the process was 990 gm, which is found to be a mixture Calcium Phosphate, Calcium Fluoride, small amount of Calcium Nitrate and less than 1% metallic impurities.

We Claim:
1. A method for treating Calcium Chloride containing acidic effluent generated
from Phosphoric Acid manufacturing process comprising the following steps:
the step of concentrating Calcium Chloride containing acidic effluent up to
35-40% Calcium Chloride by distilling out excess water;
the step of converting the Calcium Chloride in the acidic effluent into
Calcium Nitrate Tetrahydrate by reacting the concentrated acidic effluent
with Nitric Acid and simultaneously distilling out any Hydrochloric Acid
formed during the reaction;
the step of diluting the crude reaction mass having Calcium Nitrate
Tetrahydrate and removing any impurities by neutralization with Calcium
Carbonate and Ammonia Solutions; and
the steps of concentrating and crystallizing the remaining mass to yield
Calcium Nitrate Tetrahydrate.
2. The process as claimed in Claim 1, wherein Calcium Nitrate Tetrahydrate has >99.50% purity.
3. The process as claimed in Claim 1, wherein the acidic effluent comprises: 18-20% Calcium Chloride, 0.05 - 0.1% P2O5, and 0.3-0.5% Fluoride.
4. The process as claimed in Claim 1, wherein the acidic effluent is concentrated to 35 - 40% Calcium Chloride by distillation at 105 - 110°C.
5. The process as claimed in Claim 1, wherein reaction of the concentrated acidic effluent is carried out with Nitric Acid at 120°C - 135°C with dropwise addition of Nitric Acid.
6. The process as claimed in Claim 5, wherein the Nitric Acid concentration is 60 -70%.
7. The process as claimed in Claim 5, wherein Hydrochloric Acid generated during the reaction is simultaneously distilled out.
8. The process as claimed in Claim 7, wherein concentration of the recovered Hydrochloric Acid is 18 - 20%.
9. The process as claimed in Claim 1, wherein the crude reaction mass of Calcium Nitrate having impurities comprising Calcium Phosphate and Calcium Fluoride is diluted.

10. The process as claimed in Claim 9, wherein the crude Calcium Nitrate Solution is purified by neutralization to precipitate impurities.
11. The process as claimed in Claim 10, wherein the neuralization is carried out using Calcium Carbonate and Ammonia Solutions.
12. The process as claimed in Claim 10, wherein neutralization is carried to bring the pH of the Calcium Nitrate Solution up to 5.50 - 6.00.
13. The process as claimed in Claim 10, wherein the precipitated impurities are removed by filtration.
14. The process as claimed in Claim 13, wherein the filtrate obtained after filtration has a dilute Solution of pure Calcium Nitrate Tetrahydrate, which is further concentrated up to 50%,
15. The process as claimed in Claim 14, wherein the concentrated Calcium Nitrate Solution is subjected to crystallization at 14 - 18°C for 24-48 hours at humidity 30 ± 5 to crystallize the Calcium Nitrate Tetrahydrate.
16. The process as claimed in Claim 1, wherein the percentage yield of Calcium Nitrate Tetrahydrate is more than 95%.