|Title of Invention||
A PROCESS FOR THE EXTRACTION OF ZINC FROM ZINC WASTE EFFLUENT
|Abstract||The present invention relates to a process for the extraction of zinc from zinc waste effluent. This invention particularly relates to the extraction and recycling of zinc from rayon waste effluent by solvent extraction with bis(2,4,4-trimethylpentyl) monothiophosphinic extractant (Cyanex 302), stripping of zinc-loaded organic with sulphuric acid and producing pure zinc sulphate, which can be used in the spinning bath of the rayon plant. The novelty of the present invention is the production of pure zinc sulphate solution from rayon waste effluent using Cyanex 302 leaving all the calcium in the raffinate as compared to available other processes. The purified zinc sulphate could be recycled to the spinning bath of the rayon plant or zinc metal/salt could be produced. The raffinate solution could be discharged in the sewerage without affecting the environment. The process not conserves the natural resources but also meet the strict environmental regulations.|
|Full Text||The present invention relates to a process for the extraction of zinc from zinc waste effluent
This invention particularly relates the extraction of zinc from rayon waste effluent by solvent extraction process using Cyanex 302 under controlled pH and 0/A ratio, stripping the zinc-loaded organic with sulphuric acid and producing pure zinc sulphate, which can be used in the spinning bath of the rayon plant. Alternatively, zinc sulphate sah or metal could be produced from the purified solution by crystallisation or electrolysis. Background of the invention.
In view of the increasing concern of environmental regulations, the discharge of industrial effluents in the sewerage or disposal of solid sludge as landfil is restricted due to presence of toxic metallic and other constituents. An effluent containing zinc and calcium is generated in the rayon plants. The acidic and alkaline effluents are usually mixed together and neutralised with lime or alkali to precipitate zinc as sludge which is disposed as landfill. In order to conserve the natural resources and meet the environmental regulations, an attempt has been made to develop a cost effective process following solvent extraction technique using organic extractant to recover zinc from rayon effluent.
Limited informations are available in the literature for the extraction and recycling of zinc fix>m the rayon' effluents [L.B. Bowen, J.H. Mallinson and J.H. Cosgrove, Chem. Eng. Progress, 1977, 73(5), pp.50-54; Roy and Sardesai, Chemical Concepts, 1977, Oct. 23; Trivedi and Giurdeep, Encyclopedia of Environmental Sciences, 1992, 21, ppvl425-1449, hidian Standard, 1980, IS: 9509-1980]. Usually, such effluents
containing zinc and calcium are neutralised with lime to precipitate zinc as sludge which is disposed as landfil [Indian Standard, 1980, IS: 9509-1980]. Bowen et al [L.B. Bowen, J.H. Mallinson and J.H. Cosgrove, Chem. Eng. Progress, 1977,73(5), pp.50-54] given an account of various processes used and problem faced dutring the processing of the sludge for the recovery of zinc. Roy and Sardesai  treated the sludge in sulphuric acid and produced solution containing 120 g/L of zinc. The solution contains iron and manganese as the major impurities, which are to be ronoved in order to get zinc sulphate solution suitable for spin bath containing less than 15 ppm iron and 5 ppm manganese as impurities. Iron was oxidised and precipitated following KMn04 process and electrochemical process. The required purity of solution was achieved by both the process routes. Manganese from the above iron free solution was removed by adding stoichiometric quantity of K2S2O3 at 800C and precipitating Mn as hydrated Mn02. These processes could not be adopted due to the problem in its purity of product and commercial feasibility.
Upadhyay and Pandey [J. Indl. Polln . Contl, 8(1), 1992, pp. 1-9] selected chemical precipitation method for the recovery of zinc from rayon effluent at 9.2 pH and the process is only applicable for the effluent having less than 3800 mg/L acid concentration. The drawback of the process is that it has limitation for high acidity of the effluent, high requirement of alkali to adjust high pH i.e. 9.2 and no information about the removal of calcium.
Rickelton and Boyle [W.A. Rickelton and R.J. Boyle, Solvent Extraction & Ion Exchange, 1990, 8(6), pp.783-797] tested the bis(2,4,4-trimethylpentyl) ghosphinic acid [Cyanex 27S], bis(2,4,4-trimethylpentyl) dithiophosphinic acid [Cyanex 301] and
bis(2,4,4-trimethylpentyl) monotbiophosphinic acid [Cyanex 302] for the recovery of zinc from rayon effiluent and found Cyanex 301 extract zinc effectively from high acidic solution in comparison to two other extractants as it forms strong complex with zinc. The drawback of this process is the requirement of high acid concentration for metal stripping from loaded solvent, which is not economical. Another solvent Cyanex 302 is also tested to extract zinc from more acidic solution as compared to Cyanex 272. But these are not complete process for the extraction of pure zinc from rayon effluent for recycling in the spinning bath.
Another important process route for extraction of zinc from rayon plant effluent using di-2ethylhexyl phosphoric acid [DEHPA] (10%) and Solvesso 150 (90%) is tested in Netherland [Envir. Sense. Case Study CS535]. Reinhard et. al. [H. Reinhard, H. Ottertun and T. Troeng, Proceedings of Symposium Chem. Engg. 1975, series 41] have also thed DEHPA for the extraction of zinc from efQuent of rayon plant. The major drawback of the process is that no work has been reported on the extraction and separation of zinc/calcium. Zinc can be recycled to the spinning-bath of the rayon manufacturing plant, but the zinc sulphate solution must be free from calcium, which is deleterious to the process as gypsum precipitates in the spinning bath.
As mentioned above suttempts have mostly been made for the extraction of zinc but no work has been reported on the extraction and separation of zinc/calcium. The solution contains calcium as m^br impurities which is required to be removed before recychng in the spinning bath of rayon industry because it will precipitate as gypsum and forms scale in the bath with the increase in concentration. No process has been developed
to remove calcium from rayon effluent, so that the pure zinc sulphate solution could be recycled to the spinning bath of rayon plant
The main objective of the present investigation is to provide a process for the extraction and recycling of zinc from rayon waste effluent, which obviates the drawback as detailed above.
Another object of the present investigation is to provide a process for extraction and recycling of pure zinc sulphate solution from rayon waste effluent by using monothiophosphinic extractant, stripping of zinc-loaded organic with sulphuric acid and producing pure zinc sulphate solution of required concentration. The purified solution can be used in the spinning bath of rayon plant.
The process of the present invention can be described as a reaction for selective extraction between the zinc ion present in the rayon effluent and the thiophosphinic extractant Cyanex 302 leaving all calcium in the raffinate. Zinc from the zinc-loaded Cyanex 302 is stripped with sulphuric acid to get pure zinc sulphate solution. The complex formation during the extraction is determined by plotting log D against the equilibriun pH of the solution and simultaneously slope analysis of the plot. The zinc exists predominantly as Zn2+ and extracted species are expected in the form of The reaction during extraction is as follows:
It selectively extracted zinc in the form of complex [R2Zn.3RH]org and retained all the calcium in the aqueous raffinate The extracted zinc was stripped with 10% sulphuric acid without affecting the stripping efficiency. The solvent is found suitable for the extraction and enrichment of zinc from the rayon effluent and the stripped solution thus obtained could be recycle in the spinning bath of the rayon plant. Alternatively, the metal or salt could be produced from the purified solution by electrolysis or crystallisation respectively for other applications. The raffinate obtained after the recovery of zinc could be disposed safely without affecting environment.
Accordingly, the present invention provides a process for extraction of zinc from zinc waste effluent which comprises
(i) preparing organic extractant from 5-10% monothiophosphinic acid and 1-
2% isodecanol diluted in kerosene oil, (ii) taking rayon waste effluent in a mixer and adding organic extractant at a
liquid to liquid ratio in the range between 5:1 to 30:1 (vol/vol), (iii) adjusting the equilibrium pH in the range of 2.2 to 4.5 by known method, (iv) separating the zinc-loaded organic by known method and washing thereof, (v) mixing said zinc-loaded organic and sulphuric acid of concentration 5-15% (vol/vol) at a liquid to liquid ratio in the range of 2:1 to 10:1 to get zinc sulphate solution, (vi) recovering zinc from the zinc sulphate solution by known method. In an embodiment of the present invention, the rayon waste effluent used may be selected from composition in range. Zn : 20-600 ppm
Ca :10-200 ppm
pH : 0.5 to 4.5
Medium : Sulphate
hi still another embodiment of present invention, the used sulphuric acid may be of commercial grade and may have concentration in range 90-270 g/L. The bis (2,4,4-trimethyl pentyl) monoMo-phosphinic acid extiactants may also be used without further purification.
In yet another embodiment of the preset invention the used cyanex 302 and sulphuric acid may be of commercial grade.
In the process of present invention the solvent extraction is carried out in one stage or two-stages to extract zinc leaving all the calcium in the raffinate The loaded zinc is stripped with sulphuric acid to get pure zinc sulphate solution.
Novelty of the present invention is the production of pure zinc sulphate solution from rayon waste effluent using Cyanex 302 leaving all the calcium in the raffinate as compared to available other processes. The produced zinc sulphate solution can be used in the spinning bath of the rayon manufacturing industry.
The following examples are given by way of illustration and should not be construed to limit the scope of invention.
The bis(2,4,4-trimethylpentyl) phosphinic extractants viz. Cyanex 272 was initially studied for the extraction and separation of zinc and calcium. 100 ml of 5% Cyanex 272 and 1% isodecanol in kerosene was mixed with 100 ml aqueous feed solution containing 2.13 g/L Zn and 0.118 g/L Ca for 5 minutes in a mixer at room temperature varying the pH from 2.16 to 4.21. The extraction of zinc in the organic phase increased from 17.84% to 99.71% whereas calcium extraction increased 11.86% to 23.72% with increase in the pH of the aqueous feed solution from 2.16 to 4.21 (TabIe-1). The solvent, Cyanex 272 is not selective for zinc as it also extracts calcium.
100 ml of the aqueous feed containing zinc was mixed with 100 ml of 5% Cyanex 302 (v/v) and 1% isodecanol diluted in kerosene to recover zinc from aqueous feed. The ratio of aqueous and organic was maintained to 1:1. The studies was made initially with different concentration of zinc in the aqueous feed at pH 3.00 as given in Table-2. The extraction of zinc decreased slightly from 99.98% to 98.25% with increase in zinc concentration from 0.31 g/L to 0.87 g/L. The distribution co-efScient also decreased from 9977 to 56.23 with increase in metal content The higher pH is required for the effective extraction of zinc from the concentrated aqueous solution.
300 ml of the rayon waste effluent containing 0.085 g/L zinc and 0.025 g/L calcium was mixed 100 ml 5% Cyanex 302 (v/v) modified with 1% isodecanol diluted in
kerosene with a magnetic stirrer for 5 minutes at room temperature (25-30 C). The equilibrium pH was adjusted by adding H2SO4 and NaOH. The results presented in Table-3 indicate increase in extraction of zinc fix)m 75.7% to 97.7% with rise m pH of the solution from 2.18 to 3.32 and no calcium was extracted from aqueous feed solution. The distribution ratio also increased with rise in the pH of the solution A plot made for logD against pH showed a slope of 1.08 indicating the formation of the complex [R2Zn.3RH]o,g.
Rayon waste effluent containing 0.085 g/L zinc and 0.025 g/L calcium was mixed with 7% Cyanex 302 (v/v) modified with 1.5% isodecanol diluted in kerosene at equilibrim pH 3.40 at different 0/A ratio 1:5 to 1:30. The results given in TabIe-4 indicate complete extractiion of zinc even at high 0/A ratio 1:30. Thus, the Cyanex 302 is more effective reagent for the extraction and enrichment of zinc and separation of calcium from the effluent solution of rayon industry.
In order to strip the loaded zinc containing 2.55 g/L from the organic extractant, 5% Cyanex 302 (v/v) modified with 1% isodecanol diluted in kerosene 50 ml of 10% sulphuric acid (v/v) was used. The stripping was carried out at different 0/A ratio 1:1 to 10:1 with a magnetic stirrer at room temperature. The results given in Table-5 indicate a complete stripping of zinc in one stage under the different stripping conditions. The stripped solution obtained at 0/A ratio 10:1 contains 25.48 g/L Zn which is quite suitable for the use in the spinning bath of the rayon plant. It requires minor adjustment of composition with respect to zinc and acid before recycling.
The major advantages of the present investigation are given below:
1. The Cyanex 302 is selective for the extraction and separation of zinc/calcium as compared to Cyanex 272.
2. Kinetics of the process is fast and it requires only S minutes for complete extraction of zinc. So very less energy is required.
3. The complete zinc is recovered leaving all calcium in the raffinate in only one stage of extraction. So, only one mixCT-setteller unit is required in comparision to other extractant.
4. No need of high temperature and copital intensive equipment as the extraction and stripping could be done at room temperature.
5. No consumption of additive or chemicals with solvent extraction process in comparison with cementation or precipitation process. The extractant, Cyanex 302 is recycled after extraction and stripping of zinc.
6. The process is suitable for exploitation on small scale and medium scale for recovery/ recycling of zinc firom the rayon effluent.
7. The purified zinc sulphate solution could recycled in the spinning bath of the rayon plant or alternatively zinc metal or salt could be produced by electrolysis or crystallisation respectively.
1. A process for the extraction of zinc from zinc waste effluent which comprises
(i) preparing organic extractant from 5-10% monothiophosphinic acid and 1-
2% isodecanol diluted in kerosene oil,
(ii) taking rayon waste effluent in a mixer and adding organic extractant at a
liquid to liquid ratio in the range between 5:1 to 30:1 (vol/vol),
(iii) adjusting the equilibrium pH in the range of 2.2 to 4.5 by known method, (iv) separating the zinc-loaded organic by known method and washing thereof, (v) mixing said zinc-loaded organic and sulphuric acid of concentration 5-
15% (vol/vol) at a liquid to liquid ratio in the range of 2:1 to 10:1 to get
zinc sulphate solution,
(vi) recovering zinc from the zinc sulphate solution by known method.
2. A process as claimed in claim 1, wherein rayon effluent y have the composition 0.05 -
0.60 g/L zinc and 0.01-0.05 g/L calcium and have pH range in the range of 0.5 to 4.5
in sulphuric acid.
3. A process as claimed in claims 1 to 2, wherein the used extractant monothiophosphinic acid and sulphuric acid is of commercial grade.
|Indian Patent Application Number||1869/DEL/2004|
|PG Journal Number||19/2012|
|Date of Filing||29-Sep-2004|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001,INDIA|
|PCT International Classification Number||C22B 19/00|
|PCT International Application Number||N/A|
|PCT International Filing date|