Claims:We Claim:
1. A hydrogel composition for absorption of heavy metals comprising:
(a) 4-15 wt.% of a carboxymethyl cellulose (Na) salt;
(b) 5-15 wt.% of ammonium chloride;
(c) 5-15 wt.% of an alkali salt; and
(d) a solvent.

2. The hydrogel composition as claimed in claim 1, wherein the carboxymethyl cellulose (Na) salt is present in a range of 5-10%, the ammonium chloride is present in a range of 6-10% and the alkali salt is present in a range of 6-10% by weight of the total composition.

3. The hydrogel composition as claimed in claim 1, wherein the alkali salt is selected from a group consisting of sodium hydroxide, sodium bicarbonate, sodium sulfide, sodium acetate, sodium carbonate, and potassium cyanide.

4. The hydrogel composition as claimed in claim 1, wherein the solvent comprises deionized water, distilled water, or regular tap water.

5. The hydrogel composition as claimed in claim 1, wherein the hydrogel is cast on a supporting and absorbing agent.

6. The hydrogel composition as claimed in claim 1, wherein the supporting and absorbing agent comprises activated charcoal, cotton fiber or cotton mesh.

7. The hydrogel composition as claimed in claim 1, wherein the activated charcoal is present in a range of 0.01-2% or the cotton fiber or the cotton mesh is present in a range of 10-80% by weight of the total composition.

8. The hydrogel composition as claimed in claim 7, wherein the activated charcoal is present in a range of 0.1-0.5% or the cotton fiber or the cotton mesh is present in a range of 30-50% by weight of the total composition.

9. The hydrogel composition as claimed in claim 1, wherein the heavy metals are selected from a group consisting of copper, cadmium, lead, chromium, silver, mercury, arsenic, manganese, and mixtures thereof.

10. The hydrogel composition as claimed in claim 1, wherein the hydrogel is rejuvenated by using 1N HCl solution.

11. A process for preparing a hydrogel for absorption of heavy metals comprising the steps of:
(a) mixing a carboxymethyl cellulose sodium salt, ammonium chloride and an alkali salt in distilled water boiled at 40°C to form a solution;
(b) continuously stirring the solution for 30 minutes and boiling till the temperature of the solution reaches up to 80-100°C;
(c) cooling the solution to a temperature in a range of 60-70°C and placing it on a flat mold made of glass, mica, or plastic;
(d) drying the hydrogel at room temperature or oven drying at 60? to completely dry out the hydrogel; and
(e) washing the hydrogel with water to remove unreacted monomer.

12. The process as claimed in claim 11, wherein the solution in step (c) is placed in a mold pre-aligned with cotton fiber or cotton mesh at a temperature of 60-70°C.

13. The process as claimed in claim 11, wherein the solution in step (c) is mixed with charcoal and then cast on the flat mold at a temperature of 60-70°C.

14. The process as claimed in claim 11, wherein the carboxymethyl cellulose (Na) salt is present in a range of 4-15%, the ammonium chloride is present in a range of 5-15%, the alkali salt is present in a range of 5-15%, the activated charcoal is present in a range of 0.01-2% or the cotton fiber or the cotton mesh is present in a range of 10-80% by weight of the total composition.

15. The process as claimed in claim 11, wherein the carboxymethyl cellulose (Na) salt is present in a range of 5-10%, the ammonium chloride is present in a range of 6-10%, the alkali salt is present in a range of 6-10% and the activated charcoal is present in a range of 0.1-0.5% or the cotton fiber or the cotton mesh is present in a range of 30-50% by weight of the total composition.

16. A process for absorption of heavy metals from contaminated wastewater comprising the steps of:
(a) taking a sample of a wastewater contaminated with heavy metals and recording an initial concentration of heavy metals in the sample, by using UV-VIS spectrophotometer at 660 nm;
(b) adding a carboxymethyl cellulose hydrogel as claimed in claim 1 to the sample;
(b) incubating the sample with the carboxymethyl cellulose hydrogel for 24 hours; and
(c) recording a final concentration of heavy metals in the sample by using UV-VIS spectrophotometer at 660 nm.
, Description:FIELD OF THE INVENTION:

[0001] The present invention relates to a carboxy methyl cellulose hydrogel and a process for its production thereof. More particularly, the present invention relates to the use of natural polymers to prepare the hydrogel, using activated charcoal, cotton fibers or cotton mesh as a base, useful as a heavy metal absorbent. The polymer material belongs to natural macromolecular material application, e.g., used with salt solution as a cross-linker for the treatment of wastewater contaminated with heavy metals, e.g., rich sewage with high concentration of heavy metals.

BACKGROUND OF THE INVENTION:

[0002] Hydrogels are polymeric materials with three-dimensional network structure having hydrophilic polymer chains as well as their ability to absorb and retain a large volume of water in their interstitial structures. Upon contact with water, hydrogels continue to absorb and swell to form three-dimensional structure due to the presence of hydrophilic groups in their polymer networks and osmotic pressure. With the growing environmental concerns and an emergent demand, researchers throughout the globe are concentrating particularly on naturally derived hydrogels due to their biocompatibility, biodegradability, and abundance. Cellulose-based hydrogels are therefore, considered as useful biocompatible materials.

[0003] Water contains many heavy ions such as Cd2+, Pb2+, Cr6+, Hg2+, Ag+ and Cu2+, making the water highly toxic due to their presence. These heavy metals are also called as health concern metals, as they cause negative effect in humans, animals, and plants, and simply remain non-biodegradable. The concentration of these heavy metals is increasing in water due to various natural and human activities. With increasing industrialization, the use of heavy metals in various products has also increased. As a result, during and after the use of such products enriched in heavy metals, the heavy metals are bound to reach the water bodies eventually, causing environmental pollution.

[0004] As a remedy to this problem, reduction of the amount of heavy metals present in contaminated wastewater is carried out by absorbing these heavy metals. This is a common approach practiced in several countries. In regular practice of reducing the number of heavy metals, multiple ion-exchangers are used which are capable of absorbing heavy metals present in the contaminated wastewater. These ion-exchangers remain as synthetic polymers in nature and many times fail to convert 100% cross linking of monomers. These monomers, when released in water, make the water toxic to humans and to the environment.

[0005] Till date heavy metal absorption from contaminated wastewater has been carried out by techniques like ion-exchange, adsorption, complexation, precipitation, and sedimentation. All these methods involve the addition of some chemicals in contaminated wastewater, resulting in removal of metals from the contaminated wastewater. The inventors of the present invention have utilized a unique biologically produced hydrogel which showcases increased surface area and better absorption ability of heavy metals from contaminated wastewater in a safe mode without addition of any dissolved synthetic chemical in the contaminated wastewater. This makes the process eco-friendly and a low-cost method for contaminated wastewater treatment.

[0006] US publication 5962005A discloses a transparent cellulose hydrogel having a transmittance of visible light of not less than 70%/mm and a tensile strength of not less than 10 kg/cm2, wherein the hydroxyl groups of cellulose constituting the hydrogel are not chemically crosslinked. It also discloses a process for producing a transparent cellulose hydrogel, comprising coagulation and regeneration of cellulose from a cellulose solution using an aqueous solution containing an organic solvent in a proportion of 20-95 wt.%.

[0007] CN patent 102941069B discloses a hydrogel capable of being used as a heavy metal absorbent and a preparation method of the hydrogel. The hydrogel comprises agar (~1-20%), sodium carboxymethylcellulose (~3-50%), polyvinylpyrrolidone (~1-20%), and other natural macromolecular materials such as alginate or gelatin (~0-5%).

[0008] CN patent application 110270317A discloses a preparation method of cellulose base hydrogel adsorbent for treatment of wastewater contaminated with heavy metals, which includes the following steps: (1) cotton yarn after drying is placed in cellulose dissolution liquid, is refrigerated to cellulose after being dispersed with stirring and is completely dissolved, obtains fiber plain solution; (2) sodium hydroxide is added in the mixed solution of dimethyl sulfoxide, epoxy chloropropane and triethylene tetramine, after mixing evenly obtain modified solution; (3) poly-vinyl alcohol solution is added into cellulose solution, sequentially adds ammonium persulfate, acrylic monomers after mixing and N, N- methylene-bisacrylamide, stirring polymerization obtain gelatinous polymer; and (4) gelatinous polymer is put into modified solution, impregnates and heats reaction, product alcohol after reaction with water obtains cellulose base hydrogel adsorbent after cleaning repeatedly.

[0009] CN patent application 107082894A discloses preparation of a double-network hydrogel adsorbent based on waste cotton cloth material, it is characterized in that: sodium hydroxide/urea dicyandiamide solution is dissolved in waste cotton cloth material, cellulose solution is obtained; the cellulose solution containing acrylamide, crosslinking agent I and the solution of initiator is well mixed, and adds crosslinking agent II, after being further well mixed, is crosslinked and polymerization, to produce the hydrogel.

[0010] Jiayin Hu et al. discloses a facilely prepared, recyclable sodium carboxymethyl cellulose–ammonium phosphomolybdate composite (CMC–AMP) synthesized by chemical cross-linking and used for Cs+ removal. Furthermore, CMC–AMP can be reused five times using ammonium chloride as the eluent without an obvious decrease in absorption activity. The results reveal that CMC–AMP can be used as a low cost and recyclable Cs+ adsorbent.

[0011] US patent 6960617B2 discloses a method of forming a hydrogel material having enhanced mechanical strength properties comprising at least one ethylenically-unsaturated monomer and a multi-olefinic crosslinking agent.

[0012] CN patent 102941069B discloses a hydrogel capable of being used as a heavy metal absorbent and a preparation method of the hydrogel. Good-biocompatibility natural polymer materials of agar, sodium carboxymethylcellulose, derivations of the sodium carboxymethylcellulose, synthesized high polymer polyvinylpyrrolidone and the like are used as hydrogel raw materials.

[0013] Amal El Halah et al. discloses application of hydrogels as adsorbent materials of metallic ions. The hydrogels are crosslinked polymeric materials containing functional groups (carboxylic acids, amines, hydroxyls, and sulfonic acids, etc.) can be used as complexing agents for the removal of metal ions from aqueous solutions, sometimes selectively and with the possibility of recovering them, presenting advantages over other techniques for eliminating them.

[0014] From the referred prior arts, it can be seen that preparation of hydrogel using non-toxic harmless natural macromolecular material is not available till date for bio-absorption of heavy metals from contaminated wastewater. Heavy metals like Cd2+, Pb2+, Cr6+, Hg2+, Ag+ and Cu2+, being toxic metals are not removed efficiently in a quick way once they get dissolved in wastewater. Use of synthetic polymer gel further adds up its monomer contamination making the wastewater more polluted.

[0015] To address these problems, uses of natural cross-linking agents are recommended to produce eco-friendly hydrogel with better stability. In terms of the available materials of natural origin, many materials showcase good biocompatibility, wide range of material sets, and availability in abundance as well as good biodegradability. However, hydrogel application in contaminated wastewater treatment finds a major challenge due to the fragile nature of the hydrogel. Thus, the inventors of the present invention have added supporting material to the hydrogel (i.e., cotton and charcoal) making them capable to work in tough conditions. Therefore, the present invention utilizes biologically origin monomers which can be used to absorb heavy metals from contaminated wastewater, on the hydrogel which is formed for better stability and reusability. The present invention utilizes an eco-friendly, biodegradable, abundantly available raw material for producing hydrogel without imparting any contamination or negative effect to the wastewater.

SUMMARY OF THE INVENTION:

[0016] The present invention discloses novel hydrogels formed by combining naturally available materials like carboxymethyl cellulose (CMC) (Na) salt, ammonium chloride (NH4Cl) and alkali, and cast on charcoal, cotton fibers and/or cotton mesh acting as supporting and absorbing agents, to absorb heavy metal from contaminated wastewater. More particularly, the present invention discloses a method for production of the carboxymethyl cellulose hydrogel.

TECHNICAL ADVANTAGES OF THE INVENTION:

[0017] The present invention has the following advantages over the cited prior arts:
non-toxic and harmless natural raw materials to produce eco-friendly hydrogels,
hydrogels providing better biocompatibility, biodegradability, stability, and reusability,
hydrogels showcasing increased surface area and better absorption ability of heavy metals in a safe mode without addition of any dissolved synthetic chemical in contaminated wastewater,
charcoal, cotton fibers and cotton mesh acting as supporting and well as absorbing agents making the hydrogels capable of handling tough environmental conditions,
low-cost hydrogel for contaminated wastewater treatment,
ability of the hydrogels to be reused by the process of rejuvenation of hydrogel in HCl.

OBJECTIVES OF THE INVENTION:

[0018] It is a primary objective of the present invention to provide an improved hydrogel having ability to absorb heavy metals present in contaminated wastewater.

[0019] It is another objective of the present invention that the hydrogel comprises carboxymethyl cellulose (Na) salt, ammonium chloride and alkali prepared in an aqueous solution and cast on activated charcoal, cotton fibers or on cotton mesh.

[0020] It is a further objective of the present invention to provide a method for production of carboxymethyl cellulose hydrogel that can be used for heavy metal absorption.

[0021] It is another objective of the present invention to provide a hydrogel-based process for absorption of heavy metals present in contaminated wastewater. A stepwise description of the hydrogel-based process for heavy metal absorption comprises:
taking a sample of wastewater contaminated with heavy metals and recording the initial concentration of heavy metals in the sample, by using UV-VIS spectrophotometer at 660 nm;
adding a carboxymethyl cellulose hydrogel to the sample of wastewater contaminated with heavy metals;
incubating the sample with the carboxymethyl cellulose hydrogel for 24 hours; and
recording the final concentration of the heavy metals in the sample of contaminated wastewater, by using UV-VIS spectrophotometer at 660 nm.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0022] Figure 1 illustrates hydrogel cast on mica sheet comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl+alkali dried at room temperature; and (d) CMC+NH4Cl+alkali oven drying.
Figure 2 illustrates hydrogel cast on glass comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl dried at 4°C; (d) CMC+NH4Cl+Alkali dried at room temperature; (e) CMC+NH4Cl+Alkali oven drying; and (f) CMC+NH4Cl+Alkali dried at 4°C.
Figure 3 illustrates hydrogel cast on plastic comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl dried at 4°C; (d) CMC+NH4Cl+Alkali dried at room temperature; (e) CMC+NH4Cl+Alkali oven drying; and (f) CMC+NH4Cl+Alkali dried at 4°C.
Figure 4 illustrates hydrogel cast on cotton mesh and cotton fibers comprising (a) CMC+NH4Cl and (b) CMC+NH4Cl+Alkali.
Figure 5 illustrates charcoal mixed hydrogel.
Figure 6 illustrates dry hydrogels.
Figure 7 illustrates absorption of heavy metals.
Figure 8 illustrates reusable hydrogels treated with hydrochloric acid (HCl).
Figure 9 illustrates cotton mesh hydrogel soaked in heavy metal solution for 24 hrs.
Figure 10 illustrates dried cotton mesh hydrogel after absorption.
Figure 11 illustrates reusable cotton mesh hydrogel after treatment with hydrochloric acid (HCl).
Figure 12 illustrates remaining heavy metals after absorption with carboxymethyl cellulose hydrogel as well as cotton mesh hydrogel respectively.

ABBREVIATIONS:
CMC: carboxymethyl cellulose
AMP: ammonium phosphomolybdate
NH4Cl: ammonium chloride
Na: sodium
HCl: hydrochloric acid
Au: Absorbance units
Cu: Copper
Cd: Cadmium
Pb: Lead
Cr: Chromium
Ag: Silver
Hg: Mercury

DETAILED DESCRIPTION OF THE INVENTION:

[0023] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps of the process, features of the system, referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features.

Definitions
[0024] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are collected here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have their meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0025] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0026] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0027] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

[0028] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0029] The term “sample” is used to mean wastewater contaminated with heavy metals from sewage, industrial processes, mineral extraction processes, household processes, etc. It is not limited to a certain quantity as it could be a small quantity for quality check or a large quantity for absorption of heavy metals from contaminated wastewater at an industrial level.

[0030] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0031] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products and methods are clearly within the scope of the disclosure, as described herein.

[0032] The present invention relates to an improved hydrogel comprising carboxymethyl cellulose (Na) salt, ammonium chloride and alkali salt prepared in an aqueous solution and cast on activated charcoal, cotton fibers or on cotton mesh. The use of activated charcoal will act as both supporting material for hydrogel and as well as absorbing agent for the heavy metals in the contaminated wastewater. The use of cotton as fibers or as a mesh gives required strength to the hydrogel and assures its easy recovery after reaction. The biological-origin hydrogel assures precipitation along with absorption on the hydrogel.

[0033] In an embodiment of the invention, the hydrogel composition for heavy metal absorption from contaminated wastewater comprises carboxymethyl cellulose (Na) salt present in a range of 4-15%, ammonium chloride present in a range of 5-15%, and alkali salt present in a range of 5-15%, by weight of the total composition of the hydrogel and a solvent to form an aqueous solution. This hydrogel is cast on activated charcoal present in a range of 0.01-2% or on cotton fibers or on cotton mesh present in a range of 10-80% by weight of the total composition. Further, the solvent comprises deionized water, distilled water, or regular tap water.

[0034] In a preferred embodiment of the invention, the hydrogel composition for heavy metal absorption from contaminated wastewater comprises carboxymethyl cellulose (Na) salt present in a range of 5-10%, ammonium chloride present in a range of 6-10%, and alkali salt present in a range of 6-10% by weight of the total composition of the hydrogel and a solvent to form an aqueous solution. This hydrogel is cast on activated charcoal present in a range of 0.1-0.5% or on cotton fibers or on cotton mesh present in a range of 30-50% by weight of the total composition. Further, the solvent comprises deionized water, distilled water, or regular tap water.

[0035] In an embodiment of the invention, the hydrogel composition reduces the concentration of heavy metals from contaminated wastewater by 50-90% as compared to the initial concentration of heavy metals of the contaminated wastewater as disclosed in Table 1 and Figures 9-12. This reduction in concentration of heavy metals depends upon the type of hydrogel used and is recorded by the UV-VIS spectrophotometer at 660 nm.

[0036] In an embodiment of the invention, the present invention provides rejuvenation of the hydrogel by treatment with 1N HCl after the absorption of the heavy metals from contaminated wastewater, so that the hydrogel can be reutilized. The heavy metals are released in concentrated form in the 1N HCl solution.

[0037] In one embodiment, the heavy metals comprise copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr), silver (Ag), mercury (Hg)arsenic, manganese, and/or mixtures thereof.

[0038] In another embodiment, the alkali salt is selected from a group consisting of sodium hydroxide, sodium bicarbonate, sodium sulfide, sodium acetate, sodium carbonate and potassium cyanide.

[0039] In one embodiment, the present invention discloses four types of hydrogels - (a) carboxymethyl cellulose (Na) salt, ammonium chloride implemented without cotton fiber or cotton mesh or activated charcoal; (b) carboxymethyl cellulose (Na) salt, ammonium chloride implemented with cotton fibers; (c) carboxymethyl cellulose (Na) salt, ammonium chloride implemented with cotton mesh; and (d) carboxymethyl cellulose (Na) salt, ammonium chloride implemented with activated charcoal.

[0040] In detailed embodiment, the hydrogel composition comprises the following components.
Carboxymethyl cellulose (Na) salt: Carboxymethyl cellulose (Na) salt is generally used as viscosity modifier or as thickener to stabilize an emulsion. The salt used to form the hydrogel is of biological origin and is biodegradable in nature with a swelling and microporous feature. The salt is soluble in water.

[0041] Ammonium chloride: It is an inorganic compound soluble in water. It showcases cross linking ability with carboxymethyl cellulose (Na) salt as well as with the added alkali salt in water as a solvent.

[0042] Alkali salt: Addition of the alkali salt along with carboxymethyl cellulose (Na) salt and ammonium chloride enhances the hydrogel formation and reduces bubble formation in hydrogel.
[0043] Activated charcoal: Activated charcoal is selected from the black powder of wood charcoal and represents its high material absorbing properties. Activated charcoal may also be selected from other alternative sources including black powder of bone char, coconut shells, peat, etc. In the present invention, activated charcoal is involved in structural binding of hydrogel with charcoal and provides added heavy metal absorption ability.

[0044] Cotton fibers or cotton mesh: These are used as a surface for polymerization of monomer and as a smooth binder for the hydrogel. Cotton material act as a strong supporting surface to the hydrogel for easy recovery post absorption of heavy metals from contaminated wastewater. They may be available in the form of cotton fibers or cotton mesh. Cotton mesh refers to net-like structure made of cotton similar to that used in medicinal purposes like wound dressing.

[0045] In an embodiment of the invention, the present invention provides a process for producing the hydrogel that can be used as a heavy metal absorbent. The process comprises the steps of:
(a) mixing a carboxymethyl cellulose sodium salt, ammonium chloride and an alkali salt in 100 ml of distilled water boiled at 40°C to form a solution;
(b) continuously stirring the solution for 30 mins and boiling till the temperature of the solution reaches up to 80-100°C;
(c) cooling the solution to a temperature in a range of 60-70°C and placing it on a flat mold made of glass, mica, or plastic;
(d) drying the hydrogel at room temperature or oven drying at 60? to completely dry out the hydrogel; and
(e) washing the hydrogel with water to remove unreacted monomer.

[0046] In yet another embodiment, the solution in step (c) is placed in a mold pre-aligned with cotton fiber or cotton mesh at a temperature of 60-70°C.
In another embodiment, the solution in step (c) is mixed with charcoal and then cast on mold at a temperature of 60-70°C.

[0047] Furthermore, different types of hydrogels formed have been disclosed in Figures 1-12. Figure 1 illustrates hydrogel cast on mica sheet comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl+alkali dried at room temperature; and (d) CMC+NH4Cl+alkali oven drying. Figure 2 illustrates hydrogel cast on glass comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl dried at 4°C; (d) CMC+NH4Cl+Alkali dried at room temperature; (e) CMC+NH4Cl+Alkali oven drying; and (f) CMC+NH4Cl+Alkali dried at 4°C. Figure 3 illustrates hydrogel cast on plastic comprising (a) CMC+NH4Cl dried at room temperature; (b) CMC+NH4Cl oven drying; (c) CMC+NH4Cl dried at 4°C; (d) CMC+NH4Cl+Alkali dried at room temperature; (e) CMC+NH4Cl+Alkali oven drying; and (f) CMC+NH4Cl+Alkali dried at 4°C. Figure 4 illustrates hydrogel cast on cotton mesh and cotton fibers comprising (a) CMC+NH4Cl and (b) CMC+NH4Cl+Alkali. Figures 5-8 illustrates charcoal mixed hydrogel, dry hydrogels, absorption of heavy metals, and reusable hydrogels treated with hydrochloric acid (HCl). Figures 9-12 illustrate cotton mesh hydrogel incubated in wastewater contaminated with heavy metals for 24 hrs, dried cotton mesh hydrogel after absorption of heavy metals, reusable cotton mesh hydrogel after absorption of heavy metals, and the remaining wastewater after absorption of heavy metals with carboxymethyl cellulose hydrogel as well as cotton mesh hydrogel, respectively.

[0048] Additionally, in Figure 12, the first tube contains a sample of contaminated wastewater with heavy metals; and the second tube contains a cotton mesh hydrogel incubated in the sample of contaminated wastewater. It is observed that the second tube indicates a change in color as compared to the first tube, which denotes that heavy metal (copper sulphate) from the sample of contaminated wastewater has been absorbed by the cotton mesh hydrogel. The alkali present in the cotton mesh hydrogel undergoes a chemical reaction that results in the color change of the sample of contaminated wastewater in the second tube. The light blue color of the first tube is changed to a yellowish green color in the second tube as shown in Figure 12. Further, the third tube contains the sample of wastewater after absorption of heavy metals by the cotton mesh hydrogel and precipitation of dissolved solids. Therefore, the results show a significant absorption of heavy metals from the sample of contaminated wastewater. The precipitation of dissolved solids in the third tube results in the formation of a clear solution which denotes the absorption of heavy metals from the sample of contaminated wastewater into the cotton mesh hydrogel. Therefore, from Figure 12, it can be concluded that the use of cotton mesh hydrogel substantially reduces the concentration of heavy metals from the sample of contaminated wastewater.
[0049] In another embodiment, the formed dried hydrogel can be stored at room temperature. The dried hydrogel can be directly put in the contaminated water for a period of 2 hours to remove the heavy metal contaminants.

[0050] In another embodiment, the carboxymethyl cellulose sodium salt, activated charcoal, cotton fibers or cotton mesh are all available as macromolecular materials.

[0051] In another embodiment of the invention, the dried hydrogel when placed in a wastewater contaminated with heavy metals, absorbs the heavy metals as well as precipitates dissolved solids in a period of 2 to 24 hours depending upon the concentration of the heavy metals in the wastewater. After absorption of heavy metals from the sample of contaminated wastewater, the hydrogel can be rejuvenated by using 1N HCl. The heavy metals absorbed by the hydrogel are precipitated in the form of dissolved solids in the 1N HCl.

[0052] In an embodiment of the invention, the present invention provides a process for hydrogel-based heavy metal absorption from contaminated wastewater. A stepwise description of the hydrogel-based process for heavy metal absorption comprises:
taking a sample of wastewater contaminated with heavy metals and recording the initial concentration of heavy metals in the sample, by using UV-VIS spectrophotometer at 660 nm;
adding a carboxymethyl cellulose hydrogel to the sample of wastewater contaminated with heavy metals;
incubating the sample with the carboxymethyl cellulose hydrogel for 24 hours; and
recording the final concentration of the heavy metals in the sample of contaminated wastewater, by using UV-VIS spectrophotometer at 660 nm.

[0053] The percentage of heavy metals absorbed by the hydrogel is calculated by recording the initial and final concentration of heavy metals in the sample of contaminated wastewater, to observe the difference in the values. The following formula is used to calculate the % absorption of heavy metals in the sample:
% Absorption = (Initial concentration-Final concentration)/(Initial concentration) x 100
EXAMPLES:
[0054] Having described the basic aspects of the present invention, the following non-limiting examples illustrate specific embodiments thereof. Those skilled in the art will appreciate that many modifications may be made in the invention without changing the essence of the invention. The composition of the improved hydrogels mentioned in the present invention is illustrated by the following examples.

Example-1
[0055] Carboxymethyl cellulose (Na) salt (CMC-Na) in a range of 4-15 wt.% was dissolved in distilled water containing a range of 5-15 wt.% of ammonium chloride and was boiled and cast on a mica sheet/glass/plastic mold with a thickness of 1 mm. Further, it was washed with running water to remove unreacted monomers resulting in a transparent as well as a strong cellulose hydrogel. It was further dried at 30-45? for 6-7 days or oven dried at 60? for 5 days which helped the hydrogel to completely dry out. The dried hydrogel was incubated in a sample of contaminated wastewater with heavy metals for 24 hrs. The hydrogel absorbed the heavy metals from the sample as well as precipitated dissolved solids in a period of 2 to 24 hours. The hydrogel with absorbed heavy metal was separated from the sample and then the hydrogel was rejuvenated by using 1N HCl. The heavy metals absorbed by the hydrogel were precipitated in the 1N HCl.

Example-2
[0056] Carboxymethyl cellulose (Na) salt (CMC-Na) in a range of 4-15 wt.% was dissolved in distilled water containing a range of 5-15 wt.% of ammonium chloride and a range of 5-15 wt.% of alkali salt. It was boiled and cast on a mica sheet/glass/plastic molds with a thickness of 1 mm. Further, it was washed with running water to remove unreacted monomers resulting in a transparent as well as a strong cellulose hydrogel. It was further dried at 30-45? for 6-7 days or oven dried at 60? for 5 days which helped the hydrogel to completely dry out. The dried hydrogel was incubated in a sample of contaminated wastewater with heavy metals for 24 hrs. The hydrogel absorbed the heavy metal as well as precipitated dissolved solids in a period of 2 to 24 hours. The hydrogel with absorbed heavy metal was separated from the sample and then the hydrogel was rejuvenated by using 1N HCl. The heavy metals absorbed by the hydrogel were precipitated in the 1N HCl.

Example 3
[0057] The hydrogel composition as prepared in Example 1 and Example 2 was cast along with cotton mesh and kept for drying for 2-3 weeks. The dried hydrogel was incubated in a sample of contaminated wastewater with heavy metals for 24 hrs. The hydrogel absorbed the heavy metals from the sample as well as precipitated dissolved solids in a period of 2 to 24 hours. The hydrogel with absorbed heavy metal was separated from the sample and then the hydrogel was rejuvenated by using 1N HCl. The heavy metals absorbed by the hydrogel were precipitated in the 1N HCl. This hydrogel had better recovery efficiency and displayed high strength due to the presence of cotton mesh which provided support as well as helped in absorbing the heavy metals in the sample of contaminated wastewater.

Example 4
[0058] The hydrogel composition as prepared in Example 1 and Example 2, was further mixed with cotton fibers. The dried hydrogel was incubated in a sample of contaminated wastewater with heavy metals for 24 hrs. The hydrogel absorbed the heavy metal as well as precipitated dissolved solids in a period of 2 to 24 hours. The hydrogel with absorbed heavy metal was separated from the sample and then the hydrogel was rejuvenated by using 1N HCl, in which the heavy metal was precipitated. This hydrogel with cotton fibers exhibited higher strength because of the addition of cotton fibers.

Example 5
[0059] To the composition as prepared in Example 1 and Example 2, activated charcoal powder in a range of 0.01-2 wt.% was added and kept for drying for 2-3 weeks. The dried hydrogel was incubated in a sample of contaminated wastewater with heavy metals for 24 hrs. The hydrogel absorbed the heavy metal as well as precipitated dissolved solids in a period of 2 to 24 hours. The hydrogel with absorbed heavy metal was separated from the sample and then the hydrogel was rejuvenated by using 1N HCl. The heavy metals absorbed by the hydrogel were precipitated in the 1N HCl. The charcoal acts as both absorbing material and supporting material to the hydrogel. The results showed that activated charcoal was substantially effective in absorption of heavy metals from the sample of contaminated wastewater.

Example 6: Process for absorption of heavy metals from contaminated wastewater
[0060] The hydrogel-based process for heavy metal absorption was performed on 100 ml sample of contaminated wastewater containing 0.5 gm of heavy metal contaminant. The heavy metal contaminant was selected from copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr), silver (Ag), mercury (Hg), arsenic, manganese and/or mixtures thereof. 5 gm carboxymethyl cellulose hydrogel (dimension: 5 cm x 5 cm) was added to the 100 ml sample of contaminated wastewater with heavy metals. The sample with the hydrogel was incubated for 24 hours. The results showcased the percentage absorption of heavy metals from the sample. The initial and final concentration of heavy metals present in the sample was recorded using a UV-VIS spectrophotometer at 660 nm and the value was obtained in Au (Absorbance units). The percentage of heavy metals absorbed by the hydrogel was calculated based on the initial and final concentration of heavy metals in the sample. The following formula was used to calculate the % absorption of heavy metals:
% Absorption = (Initial concentration-Final concentration)/(Initial concentration) x 100

[0061] The final concentration of the heavy metals in the sample of contaminated wastewater was calculated after absorption of heavy metals from the sample using the hydrogels of Example 1-5. The comparison of initial and final concentrations of heavy metals and the resultant percentage absorption of heavy metals from the sample of contaminated wastewater using hydrogels of Example 1-5 are disclosed in Table 1 to 6.

Table 1: % Absorption of Heavy Metals (Cu) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with copper (Cu) 0.028 - -
2 Example 1 0.028 0.020 29
3 Example 2 0.028 0.025 11
4 Example 3 0.028 0.010 64
5 Example 4 0.028 0.019 32
6 Example 5 0.028 0.024 14

Table 2: % Absorption of Heavy Metals (Cd) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with cadmium (Cd) 0.018
2 Example 1 0.018 0.016 11
3 Example 2 0.018 0.016 11
4 Example 3 0.018 0.010 44
5 Example 4 0.018 0.014 29
6 Example 5 0.018 0.012 33

Table 3: % Absorption of Heavy Metals (Pb) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with lead (Pb) 0.010
2 Example 1 0.010 0.008 20
3 Example 2 0.010 0.009 10
4 Example 3 0.010 0.005 50
5 Example 4 0.010 0.008 20
6 Example 5 0.010 0.008 20

Table 4: % Absorption of Heavy Metals (Cr) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with chromium (Cr) 0.026
2 Example 1 0.026 0.024 8
3 Example 2 0.026 0.022 15
4 Example 3 0.026 0.018 31
5 Example 4 0.026 0.025 4
6 Example 5 0.026 0.024 4

Table 5: % Absorption of Heavy Metals (Ag) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with silver (Ag) 0.008
2 Example 1 0.008 0.007 13
3 Example 2 0.008 0.007 13
4 Example 3 0.008 0.004 50
5 Example 4 0.008 0.006 25
6 Example 5 0.008 0.005 38

Table 6: % Absorption of Heavy Metals (Hg) in the Sample of contaminated wastewater using Hydrogel
Sr. No. Examples Initial Concentration (Au) Final Concentration (Au) % Absorption
1 Sample of wastewater contaminated with mercury (Hg) 0.020
2 Example 1 0.020 0.019 5
3 Example 2 0.020 0.018 10
4 Example 3 0.020 0.014 30
5 Example 4 0.020 0.016 20
6 Example 5 0.020 0.015 25

[0062] The experiments provided in the above Examples 1-6 have been conducted using small samples of wastewater contaminated with heavy metals. However, the hydrogel of the present invention can be used for absorption of heavy metals from contaminated wastewater at an industrial level.