FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
&
THE PATENT RULES, 2005
(As Amended by Patents Amendment Rules – 2006)
COMPLETE SPECIFICATION (See Section 10 and Rule 13)
TITLE OF INVENTION:
A process to recover zinc from process effluent generated during rayon manufacturing process.
APPLICANT:
Aditya Birla Science and Technology Company Private Limited, Aditya Birla Center, 2nd Floor, ‘C’ wing, S.K. Ahire Marg, Worli, Mumbai- 400025, 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 process to recover zinc from process effluent generated during rayon manufacturing process. More particularly, the present invention relates to a process to recover zinc up to 93% to 99% from said process effluent.
BACKGROUND OF THE INVENTION
[002] During manufacture of viscose rayon fibre, the viscose solution is passed through a spinneret into a spin bath containing a mixture of coagulants such as sulphuric acid, sodium sulphate and zinc sulphate. The spin bath contains about 1% zinc sulphate that particularly helps in maintaining strength and properties of the fibre. Usually for preparing zinc sulphate, zinc metal sheets are dissolved in sulphuric acid. However, the cost of these zinc metal sheets is quite high and they are also toxic in nature. Therefore, there is need to decrease the use of zinc metal sheets for preparing zinc sulphate.
[003] Moreover, post spinning, during washing of the viscose fibre, there is generation of process effluent that contains all the impurities including zinc. A pre-determined quantity of process effluent is recycled however the excessive process effluent is sent to a clarifier wherein it is chemically precipitated with lime. A sludge containing zinc and calcium sulphate is formed that is discarded off to the cement industry. This increases the consumption of zinc in the process per day (approx. 888 kg / day).
[004] Earlier attempts have been made to mix the process effluent with caustic (NaOH) as it an easier method however as the cost of caustic is on a higher side, clarification of entire quantity of process effluent becomes difficult. This increases the cost of the process and generation of more toxic waste per day.
[005] Hence, there is a need for an efficient process to recover zinc from process effluent that

would solve some of the problems present in the prior art.
SUMMARY OF THE INVENTION
[006] According to an embodiment of the present invention, there is provided a process to recover zinc from process effluent generated during rayon manufacturing process, comprising the steps of a) mixing said process effluent having pH in the range of 2.5 to 3 into a solvent mixture comprising 3% - 15% of Di-(2-ethylhexyl) phosphoric acid solvent in kerosene, to form an effluent mixture, to allow extraction of zinc into an organic layer, wherein the process effluent and solvent mixture are mixed in the ratio of 1:1; b) separating out the zinc rich organic layer from the effluent mixture and reacting it with 10% sulphuric acid to allow zinc to be stripped of the organic layer, wherein the ratio of the sulphuric acid to the organic layer is 1:1 to 1:5; and c) separating zinc sulphate obtained in the reaction of step b) from remaining organic layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[007] Figure 1 depicts a schematic diagram showing the overall process for recovery of zinc from the process effluent, according to the embodiments of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[008] As set out in the claims, the present invention eliminates or reduces the aforementioned problems of the prior art by providing a process for recovering zinc from process effluent generated during rayon manufacturing process such that the recovery efficiency of zinc from the effluent stream is around 93% to 99%.
[009] In an embodiment, liquid-liquid extraction is carried out in the present invention by using a solvent mixed in kerosene. Preferably, the solvent is Di-(2-ethylhexyl) phosphoric acid (DEHPA).

[010] The present invention provides a process for recovering zinc from process effluent, as more clearly depicted in Figure 1, wherein DEHPA solvent is mixed in kerosene to prepare a solvent mixture. Preferably, the volume of DEHPA solvent mixed in deodorized kerosene is 3%-15%. Thereafter, this solvent mixture is mixed with the process effluent in a ratio of 1:1 to form an effluent mixture. In the effluent mixture, zinc gets extracted from the process effluent into the solvent mixture to form a zinc rich organic layer and a raffinate of aqueous layer. In a next step, this zinc rich organic layer is separated from the effluent mixture and treated with 10% sulphuric acid (H2SO4) to allow zinc to be stripped of the organic layer and form zinc sulphate. In the last process step, zinc sulphate is separated from the remaining organic layer and directly fed into various streams or spin bath in the rayon manufacturing process.
[011] In an embodiment, the ratio of sulphuric acid to the organic layer is 1:1 to 1:5. In another embodiment, the organic layer is recycled back to the solvent mixture. The raffinate of aqueous layer is further removed and treated to extract any impurities from it. In a preferred embodiment, extraction and stripper takes place inside a mixer settler.
[012] In an embodiment, the pH of the process effluent is maintained between 2.5-3 and preferably at 2.8 as the extraction of zinc from the process effluent is maximum at this pH.
[013] In an embodiment, during the mixing of solvent mixture and process effluent, a continuous stream with small flow rate of sodium hydroxide (NaOH) is added to maintain the pH of the process effluent. The amount of NaOH needed is very low as pH change during extraction process is not significant.
[014] In a preferred embodiment, the process is carried out at room temperature and atmospheric pressure.

[015] In all embodiments, the efficiency of extraction of zinc into the organic layer is 95%-97% and the efficiency of stripping of zinc from the organic layer into the sulphuric acid is 90%-97%.
[016] Advantages and benefits of composite clinker, according to the embodiments of the present invention, would become more apparent from the below experimental details to a person skilled in the art.
Example 1:
[017] First Stage:
a) 50 ml of 5% DEHPA and kerosene mixture was mixed with 50 ml of effluent;
b) In the mixture of step a), zinc got extracted into solvent layer from the effluent stream;
c) This mixture was then phase separated into solvent and aqueous layer. The pH of aqueous layer was maintained at pH of 2.8 to 3. This is because the solvent DEHPA is acidic in nature and to improve zinc extraction from effluent, pH is needed to be maintained in that range.
Table 1: Following table indicate the efficiency of extraction with different volume % of DEHPA in kerosene.

Sr. No.
1
2
3
4
5 Vol % of Solvent in kerosene Zinc in effluent, mg Zinc in aqueous layer, mg Zn in Solvent, mg % Extraction

1% DEPHA 88.80 46.06 42.74 48%

3% DEPHA 44.40 2.22 42.18 95%

5% DEPHA 44.40 0.09 44.31 100%

10% DEPHA 44.40 1.88 42.52 96%

15% DEPHA 44.40 0.08 44.32 100%
Observations:
• It was observed from above table that the optimum volume % of DEHPA for optimum extraction is 3-10%.
• Maximum extraction was observed at 5% volume of DEHPA in kerosene.
• The O: A (organic: aqueous) ratio of mixing used was 1:1.

[018] In order to evaluate the mixing ratio of 1:1. Few experiments were conducted, in which different O: A ratio was tried. The results are captured in the table below:

Sr. No. Vol% in kerosene Organic : Aqueous ratio % Extraction
1 5% DEHPA 1 100%
2 5% DEHPA 0.9 99%
3 5% DEHPA 0.7 94%
4 5% DEHPA 0.5 83%
Observations:
• The above results also show that 1:1 ratio of O: A is ratio required for maximum extraction of zinc from effluent into the solvent.
Example 3:
[019] Second Stage:
a) The ratio of the solvent with extracted zinc to 10% H2SO4 is maintained at 2:1.
b) It was observed that the extraction efficiency changes with the ratio of H2SO4 and solvent with extracted zinc used in the process.
Table 3: The table below gives the overall extraction of zinc from effluent used.

Sr. No Zinc in feed , mg Zinc in
aqueous layer,
mg Zn in
Solvent,
mg Zn in H2SO4, mg %
Recovery
of Zn in
H2SO4
from solvent Overall Extraction
1 1% DEPHA 88.80 46.06 42.74 41.4 96.86 % 47%
2 5% DEPHA 44.40 0.09 44.31 39.3 88.69% 89%
3 10% DEPHA 44.40 1.88 42.52 40.0 94.07% 90%
4 15% DEPHA 44.40 0.08 44.32 40.1 90.47% 90%
[020] The procedure for the above experiments is as follows:

1. O : A was maintained as 1:1 for extraction of zinc from effluent to the solvent.
2. Extracted organic layer : 10% H2SO4 used in second stage of mixing was 5:1.
The following table shows that same solvent can be used in 3-4 cycles without extra addition of the solvent.
Table 4: The following process represents recycling of the solvent:

Sr. No Zinc in
Effluent,
mg Organic:
Aqueous
Ratio for
extraction of
zinc in solvent
from effluent Zinc
extracted
in
solvent,
mg Zinc in
aqueous
layer,
mg Total
Zinc
recovered
in
H2SO4
in two
steps, mg %
Extraction
of Zinc
from
effluent
into solvent %
Recovery
of Zinc
from Solvent
in H2SO4 Overall %
recovery
of zinc
Cycle 1 395.16 1.00 392.65 2.51 392.00 99.36% 99.83% 99.20%
Cycle 2 364.08 1.00 358.02 6.06 354.03 98.33% 98.89% 97.24%
Cycle 3 337.44 1.00 332.3 4.22 312.03 97.57% 92.47% 90.22%
Cycle 4 319.68 1.00 316.83 2.84 293.07 92.48% 91.68% 84.79%
Cycle 5 301.92 1.00 399.23 2.68 252.69 91.24% 83.69% 76.36%
[021] To study the loss of solvent during each cycle, the solvent after use of each cycle is titrated by potentiometric titration to find out phosphoric acid quantity in the solvent.
Table 5: Following table indicates loss of solvent with cycles:

Sr. No Cycles DEHPA
in solvent,
gpl % Loss
with original
1 Original solvent mixture 45.42
2 Cycle 1 44.84 1.27%
3 Cycle 2 44.16 2.77%
4 Cycle 3 42.93 5.48%
5 Cycle 4 42.90 5.55%

[022] As the treated aqueous stream will need to be sent to the effluent treatment and Recovered zinc in H2SO4 is needed to be sent to the viscose process, total organic content increase in both the streams is needed to know. Hence, following table shows the total organic content in aqueous streams and recovered H2SO4 stream. It can be seen that TOC in H2SO4 is significantly lower and hence this stream can be utilized in the process.

Sr. No TOC in aqueous layer, ppm TOC in H2SO4, ppm
1 Original Solvent 825 0
2 Cycle 1 1066 4.58
3 Cycle 2 874 0
4 Cycle 3 845 0
5 Cycle 4 767 6
Conclusion:
• Higher efficiency of zinc recovery from highly zinc concentrated (800-1000 ppm) process effluent of viscose stream (85-99%) was observed.
• Preferable volume % of DEHPA in kerosene needed for high extraction efficiency: 3- 15% volume.
• Solvent can be used up to 4 cycles without addition of fresh solvent.
• % Loss of solvent in 4 cycles is around 5.5%.
[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.

WE CLAIM:
1. A process to recover zinc from process effluent generated during rayon manufacturing
process, comprising the steps of:
a) mixing said process effluent having pH in the range of 2.5 to 2.8 into a solvent mixture comprising 3% - 15% of Di-(2-ethylhexyl) phosphoric acid solvent in kerosene, to form an effluent mixture, to allow extraction of zinc into an organic layer, wherein the process effluent and solvent mixture are mixed in the ratio of 1:1;
b) separating out the zinc rich organic layer from the effluent mixture and reacting it with 10% sulphuric acid to allow zinc to be stripped of the organic layer, wherein the ratio of the sulphuric acid to the organic layer is 1:1 to 1:5; and
c) separating zinc sulphate obtained in the reaction of step b) from remaining organic layer.

2. The process as claimed in claim 1, wherein a continuous stream of NaOH is added in step a) to maintain the pH of the process effluent.
3. The process as claimed in claim 1, wherein the organic layer of step c) is recycled back to the solvent mixture of step a).
4. The process as claimed in claim 1, wherein the efficiency of extraction of zinc into the organic layer in step a) is 95-97%.
5. The process as claimed in claim 1, wherein the efficiency of stripping of zinc from the organic layer in step c) is 90-97%.