WO2012077033A2

WO2012077033A2 - Organic-inorganic composite material for removal of anionic pollutants from water and process for the preparation thereof

Info

Publication number: WO2012077033A2
Application number: PCT/IB2011/055454
Authority: WO
Inventors: Sadhana Suresh Rayalu; Nitin Kumar Labhasetwar; Amit Kumar Bansiwal; Dilip Kashinath Thakre; Sneha Manohar Jagtap
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2010-12-06
Filing date: 2011-12-05
Publication date: 2012-06-14
Also published as: AU2011340169A1; AU2017202855A1; CN103402624A; WO2012077033A3; CN103402624B; AU2019201715A1; AU2019201715B2

Abstract

Organic-inorganic composite material based on metal oxide and carbon, nitrogen and other elements/functional groups for removal of anionic pollutants like arsenic, fluoride etc., from water, and methods for making the same are disclosed. The modified composition may comprise different phases of metal oxides, supported or promoted by incorporation of nitrogen, carbon and other elements/groups. The organic-inorganic composite may be produced from at least one biogenic material such as chitin, chitosan, leaf, bio-membrane and a salt of metal like iron, aluminium etc. The organic-inorganic composite based adsorbent shows arsenic uptake capacity in the range of 0.2 to 1.3 mg/g and fluoride uptake capacity in the range of 5-50 mg/g under different conditions, which is substantially high from the other adsorbents known so far. A breakthrough regeneration of 98-99% has been achieved by using new regeneration protocol.

Description

ORGANIC-INORGANIC COMPOSITE MATERIAL FOR REMOVAL OF ANIONIC POLLUTANTS FROM WATER AND PROCESS FOR THE PREPARATION THEREOF " FIELD OF THE INVENTION

The present invention relates to organic-inorganic composite material useful for removal of anionic pollutants from water.

The present invention further relates to a process for synthesis of organic-inorganic composite materials which shows high removal efficiency for arsenic and fluoride, comprising of different phases of metal oxides, supported or promoted by incorporation of nitrogen, carbon and other elements/functional group, showing enhanced affinity and selectivity for arsenic and fluoride from water .

This invention further relates to process for synthesis of organic-inorganic composite materials using carbon sources such as biopolymers like chitin, chitosan and various low cost carbon sources like dried leaves, onions, banana peals, citrus and crab shells etc. for arsenic and fluoride removal from surface water, wastewater and drinking water.

BACKGROUND OF THE INVENTION

Arsenic and fluoride are two most widely occurring anionic pollutants present in groundwater, surface water and other water sources. Pollution due to arsenic and fluoride in the environment occurs worldwide and creates a major problem in safe drinking water supply. These pollutants are also found in the waste discharges from process streams in a number of industries like glass, electronics, steel, aluminium, pesticide, electroplating, ores and mineral processing and fertilizer manufactures. Due to the environmental and health impacts, these effluents have to be carefully treated before discharge to avoid the groundwater contamination.

Widespread occurrence of arsenic and fluoride above the prescribed limit in groundwater meant for human consumption has caused multidimensional health problems. Considering the health hazards associated with arsenic and fluoride World Health Organisation has prescribed a limit of 0.01 mg/1 and 1.0 mg/1 for arsenic and fluoride respectively for drinking water. Similarly the permissible limits as per Indian standard specification for drinking water (IS 10500) are 0.05 mg/1 and 1.5 mg/1 for arsenic and fluoride respectively. The problem of excess of these elements in drinking waters is aggravating day by day, as more surveys to assess the ground water quality have been undertaken. Millions of people round the globe are affected due to intake of excess arsenic and fluoride. Adverse health effects of arsenic include dermatological effects such as melanosis (pigmentation) and keratosis (rough, dry, popular skin lesions). Chronic exposure to arsenic may also cause reproductive, neurological, cardiovascular, respiratory, hepatic, haematological, and diabetic effects in humans. It is also an established fact that long term ingestion of arsenic can cause skin, bladder, and lung cancer. On the other hand the excess fluoride intake through contaminated drinking water can cause dental fluorosis which is an irreversible toxic effect on the tooth forming cells and in long term also lead to 'Skeletal fluorosis' which is a condition associated with prolonged accumulation of fluoride resulting in fragile bones having low tensile strength. Apart from teeth and bones, the interaction and involvement of soft tissues, organs and other systems of the body with fluoride also leads to non-skeletal fluorosis. The skeletal muscles, erythrocytes, gastro-intestinal mucosa, ligaments, spermatozoa and thyroid glands of human are also likely to be affected by increase fluoride levels in body. Fluoride toxicity may also lead to loss of appetite, gas formation and nagging pain in stomach, chronic diarrhea, chronic constipation and persistent headache. Unusual fatigue, loss of muscle power and weakness, excessive thirst and frequent urination, depression, tingling sensation in fingers and toes, allergic manifestations are also reported manifestations of excess fluoride intake.

The problem of excess fluoride in drinking ground water is widespread. In India alone, around 1 million people in 17 states are affected by this disease especially in Rajasthan, Madhya Pradesh, Andhra Pradesh, Tamil Nadu, Gujarat and Uttar Pradesh [Yadav et al., 2005] .

Reference may also be made to Chakrabati et al (2003) and Mondal et al. (1996), wherein it was reported that in India millions of persons in seven districts of West Bengal are drinking ground water with arsenic concentrations far above acceptable levels of O.Olmg/1 (Chakraborti, D., Mukherjee, S.C., Pati, S., Sengupta, M.K., Ramman, M.M., Chowdhury, H.K., Lodh, FL, Chanda, C.R., Chakraborti, A.K., Basu, G.K., 2003. Arsenic ground water contamination in middle Ganges plain, Bihar, India: a future danger? Environmental Health Perspective, 111(9), 1194-1201 and Mandal, B.K., Chowdhury, T.R., Samanta, G., Basu, G.K., Chowdhury, P.P., 1996. Arsenic in groundwater in seven districts of West Bengal, India - the biggest arsenic calamity in the world. Current Science, 70(11), 976-987).

The most important remedial action is prevention of further exposure by providing safe drinking water. However in most of the areas source substitution may be impossible due to non-availability of alternate sources and therefore removal of excess arsenic and fluoride is the only remedy. There are several techniques which can be categorised into four main categories namely precipitation, membrane processes and ion-exchange/adsorption onto various adsorbents. This invention relates to development of process based on adsorption using novel adsorbent based on the concept of enhanced incorporation of electropositive metal for improved affinity and selectivity for arsenic and fluoride. Extensive efforts are being made worldwide to develop materials for selective adsorption of arsenic and fluoride from numerous categories namely biological materials, mineral oxides, activated carbons, polymer resins, industrial byproducts/wastes, soils and sands, etc.

Reference may be made to Journal "Arsenic removal from water/wastewater using adsorbents— A critical review, Journal of Hazardous Materials 142 (2007) 1-53) by Dinesh Mohan, Charles U. Pittman Jr", wherein a detailed review of various materials for arsenic removal and their advantages and limitations are given. In-spite of extensive efforts, still there are many limitations of existing adsorbents that are restricting the success of adsorption based arsenic and fluoride removal plants in actual field conditions, particularly the lower affinity for these pollutants.

Reference may be made to U.S. Patent 4,717,554, wherein a method was developed for treating fluorine or fluorine compounds dissolved at low concentrations in drinking or industrial water. The adsorbent comprises of hydrated rare earth oxides or insoluble hydrated rare earth salts of at least one metal selected from the group of rare earth elements. The adsorbent works efficiently at lower pH and high temperatures. However, the main drawback of this process is that, it is highly pH and temperature dependent and therefore, cannot be applied for drinking water treatment. The present material does not show these drawbacks.

Reference may be made to U.S. Patent 5,043,072, wherein a method has been disclosed for treating fluoride containing water, which comprises a reaction step where a calcium compound like calcium hydroxide (slaked lime), calcium oxide and /or an aluminium compound like aluminium sulfate, polyaluminium chloride etc. are added to fluoride containing water while the pH value of the resulting suspended solution is adjusted to fall within the range of 6 to 8 wherein at least a part of the concentrated suspension to be formed in the membrane- separation step of the following stage is added to the suspended liquid. However, the drawbacks associated with this method are possibility of aluminium release, expensive and tedious process. This drawback has been overcome in this invention by appropriately improving the alumina which minimises the leaching of aluminium. Reference may also be made to Journal "A study on removal of fluorides from drinking water by adsorption onto low-cost materials, Environment Pollution Volume 99, 1998, page numbers 285 to 289 by M. Srimurali, A. Pragathi and J. Karfhikeyan, wherein various low cost materials like kaolinite, bentonite, charfines, lignite and nirmali seeds were investigated to assess their capacity for the removal of fluoride from water by batch adsorption studies. Studies were also conducted to determine optimum operating system parameters such as contact time, pH, dose and size of the adsorbent. It indicates that materials like nirmali seeds and lignite are not effective (removal 6 to 8%), whereas removal by kaolinite clay was slightly higher (18.2%), charfines and bentonite exhibited highest removal capacity of 38% and 46% respectively. However, this method faces difficulty in its practical application because the overall fluoride removal by these materials is not effective which has implications on reactor design and in turn on the cost of treatment.

Reference may also be made to journal "Experimental sorption of fluoride by kaolinite and Bentonite, Geoderma Volume 84, 1998, page numbers 89 to 108 by P.M.H. Kau, D.W. Smith, P. Binning" , wherein a method for fluoride removal has been developed using low cost materials like kaolinite and bentonite. Bentonite was found to be far superior fluoride sorbent than kaolinite quantitatively. However, these methods also require large dosage and longer contact time, which has implications on reactor design and in turn on the cost of treatment. The present material does not show these limitations.

Reference may be made to U.S. Patent 5,876,685, wherein a process has been disclosed for the removal and purification of substantially all of the fluoride ions contained in a waste process stream containing greater than 10 ppm of fluoride ions by using an anion exchange resin, followed by distillation, to recover the fluoride ion as an ultrapure hydrofluoric acid. Though, anion exchange resins are effective, but they are expensive, require frequent regeneration and have reduced capacity following repeated regeneration. This drawback has been overcome by appropriately designing the material to enhance its adsorption capacity by functionalising and then supporting metal oxides .This shall make the process more economical by virtue of high adsorption capacity of the material.

Reference may be made to U.S. Patent 6,210,589 Bl, wherein a process for removing fluoride from wastewater has been disclosed. A fluidised bed crystalliser containing calcium or magnesium, sodium and aluminium reagents to remove fluoride in wastewater has been developed. This method is useful for reducing high fluoride concentrations of industrial wastewaters. However, it cannot be applied for domestic purposes i.e., for drinking water because it involves a tedious process and generate hazardous or toxic sludge. This problem has been overcome by developing an improved material by modifying alumina. These adsorbents do not leach the toxic metals.

Reference may also be made to journal "Adsorption of fluoride onto mixed rare earth oxides, Separation and Purification Technology volume 24, 2001 page numbers 121 to 127 A. M. Raichur and M. J. Basu" wherein a process have been developed for fluoride removal using mixed rare earth oxides from synthetic solutions. The adsorbent, which is a mixture of rare earth oxides, was found to adsorb fluoride rapidly and effectively. The effects of various parameters such as contact time, initial concentration, pH and adsorbent dose on adsorption efficiency were investigated. However, the drawbacks associated with this method are low adsorption capacity, high dosage and cost of the materials. The present material does not show these limitations.

Reference may be made to U.S. Patent 6,331,256 Bl, wherein a process was developed for treating fluoride containing industrial waste water by using calcium carbonate and fixing it as calcium fluoride. The process comprises of adding calcium carbonate particles to fluoride containing water and circulating that mixture through the separating membrane apparatus. However, the drawbacks associated with this method are tedious and expensive process. This drawback has been overcome by appropriately designing the material to enhance its adsorption capacity by improving the alumina composition.

Reference may also be made to journal "Removal of fluoride from aqueous solution by using red mud, Separation and Purification Technology, volume 28, 2002, page numbers 81 to 86 Y. Cengeloglu, E. Kir and M. Ersoz", wherein a method for fluoride removal has been developed using Red mud from aqueous solutions. Red mud (bauxite wastes of alumina manufacture, mixed adsorbent with different metal oxides) emerges as an unwanted byproduct during the alkaline leaching of bauxite in the Baeyer process. It reveals that the removal of fluoride using red mud is based on the chemical nature and specific interactions with metal oxides surfaces. The fluoride adsorption capacity of activated form was found to be higher than that of the original form. However, the drawbacks associated with this method are high dosage and possibility of Al release. These drawbacks have been overcome by modifying the alumina compositions.

Reference may also be made to journal "Deflouridation of water using amended clay, Journal of Cleaner Production, volume 11, 2003, page numbers 439 to 444 M. Agarwal, K. Rai, R. Shrivastav, S. Dass", wherein a method has been developed for fluoride removal using amended clay. It investigates the role of vessels made from locally derived sample of silty clay for water defluoridation. Besides, fluoride sorption by clay and its chemically amended forms were also studied to investigate improvement opportunities of clay vessels with regard to their application for water defluoridation. The study revealed clay to be potent fluoride binder and amending it with Al (activated AI₂O₃), Fe (FeCi₃) and or Ca (CaCC^) significantly improved its fluoride sorption capacity. Fluoride sorption by amended Al, Fe, Ca, decreased in the same order. However, this method also requires large dosage and longer contacts time, which has implications on reactor design and in turn on the cost of treatment. Also the problem of release of aluminium or other metals is associated with it. This invention overcomes the drawback of this method by improving the alumina compositions.

Reference may also be made to journal "Physicochemical characterization and adsorption behaviour of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution, Journal of Colloid and Interface Science, volume 261, 2003, page numbers 213 to 220 P. D. Das, J. Das and K. Parida" wherein Zn / Al oxide obtained by the thermal decomposition of the corresponding Hydrotalcite like compounds (HTLs) which are also known as layered double hydroxides can be used as an effective adsorbent for the removal of fluoride. It shows that the fluoride adsorption increases with increased pH, reaching a maximum at pH 6.0. However, the drawbacks associated with this method are longer contact time and cost. The present material does not show these limitations. Reference may be made to journal "Use of oxide minerals to abate fluoride from water, Journal of Colloid and Interface Science, volume 275, 2004, page numbers 355 to 359 D. Mohapatra, D. Mishra, S. P. Mishra, G. Roy Chaudhury and R. P. Das", wherein a method was developed for fluoride removal using various oxide ores such as refractory grade bauxite (RGB), feed bauxite, manganese ore and hydrated oxides of manganese ores (WAD) from aqueous solutions. Fluoride adsorption studies were carried out at initial pH and adsorbent concentration of 10 g/1 at different time intervals using various oxide ores. RGB showed high fluoride removal efficiency compared to other adsorbents. However, the drawbacks associated with this method are its selectivity with respect to concentration and aluminium leaching into the water.

Reference may also be made to journal "Defluoridation of groundwater using brick powder as an adsorbent, Journal of Hazardous Materials, volume 128, 2006, page numbers 289-293 A. K. Yadav, C. P. Kaushik, A. K. Haritash, A. Kansal and Neetu Rani", wherein brick powder was studied for the removal of fluoride from synthetic as well as from two groundwater samples of different fluoride concentrations (i.e. 3.14 and 1.21 mg/1). Presence of other ions in ground water did not significantly affect the defluoridation process thereby indicating that brick powder is selective adsorbent for fluoride. Comparative studies of brick powder and commercially activated carbon revealed that brick powder is economical adsorbent for the removal of fluoride due to greater and easy abundance. However, this method suffers from drawback of having low fluoride removal capacity and therefore requires large dosage and longer contact time, which has implications on reactor design and in turn on the cost of treatment. The present adsorbent, however, shall make the process more economical by virtue of high fluoride uptake capacity of the material.

Reference may be made to journal "Defluoridation of drinking water using activated titanium rich bauxite, Journal of Colloid and Interface Science, volume 292, 2005, page numbers 1 to 10, N. Das, P. Pattanaik and R. Das", wherein an adsorptive method was developed for fluoride removal using thermally activated titanium rich bauxite (TRB). Bauxite ore from several parts of central India (especially in states like Jharkhand and Chattisgarh) mainly consists of oxide/oxyhydroxides of Ti and Al along with small amounts of Fe and Si. Adsorption with respect to variation of pH, adsorbent dose, initial fluoride concentration, presence of interfering ions and heat treatment were investigated by batch equilibrium experiments. Thermal activation at temperatures (300-450°C) greatly increased the adsorption capacity of TRB. However, bauxite ore mainly consists of aluminium, which may be leached into the water. The present material does not show this limitation.

Reference may also be made to US Patent application No. 20040005363A1, wherein a biodegradable biopolymer material consisting of silk fibroin and chitin, chitosan, chitosan derivates has been disclosed. This material can be used as metal ion adsorbing material, slow release medium etc. The drawbacks of this material are fouling of the adsorbent media leading to significant changes in treated water quality.

Reference may also be made to US Patent application No. 20040238449A1, wherein material based on organic/inorganic resin and chitosan for fixing metal ions from effluents has been disclosed. However, fluoride removal using chitosan derivatives prepared through complexation of metal ions like lanthanum, titanium etc. has not been disclosed.

Reference may be made to US Patent application No. 20060151396A1, wherein heavy metal chelate composition containing chitosan derivatives has been disclosed. The invention involves chelator compound containing chitosan derivatives and dithio carbamates. This compound can be used for treatment of wastewater, waste mud and garbage burned ash that contains heavy metals. The present adsorbent replaces biodegradable matrix like chitosan with non-biodegradable matrix and therefore, can be used for longer cycles of treatment. Reference may also be made to N. Sankararamakrishnan, A. Dixit, L. Iyengar and R. Sanghi (Removal of hexavalent chromium using a novel cross linked xanthated chitosan, Bioresource Technology, volume 97, 2006, page numbers 2377 to 2382), wherein cross liked chemically modified chitosan has been reported for removal of chromium. The adsorbent developed in this invention differs considerably by virtue of incorporation of amines and subsequent metal incorporation by chelation.

Reference may also be made to U.S. Patent No. 6,827,874 B2, wherein compositions, methods and kits based on chitosan for purifying, clarifying, nutrifying drinking water has been disclosed. The inventors have used chitosan as coagulant.

Reference may also be made to K. Jaafari, T. Ruiz, S. Elmaleh, J. Coma and K. Benkhouja (Simulation of a fixed bed adsorber packed with protonated cross-linked chitosan gel beads to remove nitrate from contaminated water, Chemical Engineering Journal, volume 99, 2004, page numbers 153 to 160) wherein removal of nitrate from water using protonated cross linked chitosan gel beads has been reported wherein a composition based on chitosan for removal of nitrate has been disclosed. Chitosan in the form of spheres or capsules have also been prepared for various applications.

Reference may be made to U.S. Patent No. 4,285,819, wherein functional magnetic particles comprising of chitosan and ferrous and ferric chloride has been disclosed. The particles in the form of macrosphere having hydroxyl and amine functionality of the chitosan forms chelate binding heavy metal cations like lead, copper and mercury and the chelates in turn bind anions such as nitrate, fluoride, phosphate and borate when added to waste aqueous streams contain dissolved ions. The metal cations like lead, copper and mercury are having low affinity for fluoride, which restricts the use of these reported materials for fluoride removal.

Reference may also be made to U.S. Patent No. 6,752,938 B2, wherein macrosphere composite of collagen and bioceramic powder coated with chitosan has been disclosed. This macrosphere has similar composition components of bone tissue and the collagen has a network of reconstituted fibres. This macrosphere has been used to carry cells, coat and fix bone growth factors and is applied in bone repair. However, this material has not been tested for fluoride removal.

Reference may also be made to U.S. Patent Application No. US 20050226938A1, wherein core shell nanoparticles based on chitosan has been disclosed. These nanoparticles can be used as detergents, as additives for pharmaceutical composition and for drug delivery. Reference may also be made to US Patent application No. 20060115511A1, wherein porous structures comprising chitosan alginate and divalent metal cations have been disclosed. Reference may be made to US Patent application No. 20030150802A1, wherein a biosorbent composition comprising of chitosan coated substrate has been disclosed. The inventors have claimed that this composition can be used for treating aqueous systems including wastewater for removal of heavy metals. The adsorbent developed in this invention differs completely.

Reference may be made to L. Dambies, T. Vincent and E. Guibal (Treatment of arsenic- containing solutions using chitosan derivatives: uptake mechanism and sorption performances, Water Research, 2002, volume 36, 15, page numbers 3699-3710) wherein chitosan gel beads, modified with molybdate were tested for removal of arsenic in both As(III) and As(V) forms. The sorbent show high removal efficiency for removal of As(V) from acid solutions, whereas the adsorption capacities are lower for As(III). However, the process is not suitable for removal of arsenic from drinking water at neutral pH since the efficiency is more in acidic solutions and also there is release of molybdate at lower pH. Moreover the residual arsenic concentrations are far above the regulations for drinking water.

Reference may also be made to Mohammad Outokesha, Hitoshi Mimura, Yuichi Niibori, Kouichi Tanaka (Preparation of stable alginate microcapsules coated with chitosan or polyethyleneimine for extraction of heavy metal ions, Journal of Microencapsulation, 23, 3, 2006, 291 - 301) wherein alginate macrocapsules coated with chitosan or polyethyleneimine for extraction of heavy metals has been reported. The adsorbent and process developed in this invention differs completely with this invention.

Reference may be made to Feng Yi, Zhao-Xia Guo, L.-X.Li-Xia Zhang, Jian Yu and Qiang Li (Soluble eggshell membrane protein: preparation, characterization and biocompatibility, Biomaterials, Volume 25, 2004, Pages 4591 to 4599) wherein the preparation, characterization and biocompatibility of soluble eggshell membrane (SEP) are reported. The dissolution process, which is the key step of the preparation of SEP, has been followed by scanning electron microscopy (SEM) to observe the changes of the surfaces and thickness of the eggshell membrane (ESM). The composition of SEP has been investigated by amino acid analysis and elemental analysis. The adsorbent and process developed in this invention differs completely with this invention.

Reference may be made to W.T. Tsai et al. W.T. Tsai, J.M. Yang, C.W. Lai, Y.H. Cheng, C.C. Lin, C.W. Yeh (Characterization and adsorption properties of eggshells and eggshell membrane, Bioresource Technology, Volume 97, 2006, Pages 488 to 493) wherein the chemical and physical characterization of eggshell and eggshell membrane particles prepared from the hen eggshell waste is reported. Under the characterization measurements investigated, it was found that the pore structures of the two biomaterials belong to a typical Type II, indicating that they should be basically characteristic of nonporous materials or materials with macropores or open voids. Further, the chemical composition of the resulting eggshell particle was strongly associated with the presence of carbonate minerals from the Fourier transform infrared (FTIR) spectra. In contrast to the resulting eggshell membrane particle, the presence of functional groups of amines and amides was observable because of its chemical composition of fibrous proteins. Though the report deals with characterisation of ES and ESM, no efforts have made to use ES and ESM for developing adsorbent for defluoridation and removal of other pollutants.

Reference may be made to Qun Dong, Huilan Su, Di Zhang, Zhaoting Liu, Yijian Lai (Synthesis of hierarchical mesoporous titania with interwoven networks by eggshell membrane directed sol-gel technique, Microporous and Mesoporous Materials, volume 98, 2007, pages 344 to 351) wherein Hierarchical mesoporous titania with interwoven networks was successfully prepared through a surface sol-gel process followed by a calcination treatment and using eggshell membrane (ESM) as the biotemplate. The biotemplating synthesis was systematically investigated by controlling calcination temperature (550-800 °C), heating rate (1-35 °C/min), impregnant pH value (1-3), and so on. The adsorbent and process developed in this invention differs completely with this invention.

Reference may be made to U.S. Patent 20030132155 Al, wherein a process for removal of arsenic using chemically treated zeolites has been disclosed. The zeolites used were chemically modified using metals salts of iron, copper, aluminium etc. The organic component prepared from dried leaves has not been utilized in the said patent. Moreover, the zeolite used in the said patent is a very costly as compared to leaf powder which is a waste material and is abundantly available.

Reference may also be made to U.S. Patent 6,849,187, wherein Shaniuk disclosed a porous ferric hydroxide prepared by simultaneously combining an iron salt and hydroxide compound and then recovering the ferric hydroxide. The resulted porous ferric hydroxide can be used for removal of arsenic. However the said invention is not an orgnic- inorganic nanocomposite prepared using an organic component obtained from dried leaves and metal component obtained from various metal salt precursors. Furthermore, the organic-inorganic nanocomposite disclosed in present invention is low cost and more efficient as compared to reported one.

Reference may also be made to U.S. Patent NO. 7314569, wherein Cadena et al. disclosed a method and composition using akaganite and iron oxide as an ion adsorption medium for removal of arsenic from water. However the said invention is not an organic-inorganic nanocomposite prepared using an organic component obtained from dried leaves and metal component obtained from various metal salt precursors. Furthermore, the organic-inorganic nanocomposite disclosed in present invention is low cost and more efficient as compared to reported one.

Reference may also be made to U.S. Patent 7,378,372, wherein Sylvester disclosed a metal oxide modified or impregnated activated carbon as a sorbent to remove arsenic and other contaminants. However the approach used in said invention is entirely different from the present invention. In the present invention dried leaf powder is used in combination with metal salts to prepare an organic-inorganic nanocomposite which is many more times cost effective than activated carbon based sorbents since the cost of activated carbon is exorbitant. Moreover the preparation of activated carbon is very tedious and hazardous whereas the dried leaf powder used in present invention is prepared by simple process of drying and crushing waste leaves.

Reference may also be made to U.S. Patent No. 7459086, wherein Gaid disclosed a method for removal of arsenic, iron and manganese from water by passing it through a bed of filter comprising of manganese dioxide grains and iron based material including hydroxide, oxide or metal silicate. However, the filter media disclosed in said invention does not include an organic portion which imparts synergistic effect for removal of arsenic by providing support to metal oxide and providing better surface area and diffusibility.

Reference may be made to U.S. Patent 6,896,813, wherein a matrix based on cellulose substrate and iron (ferric) oxyhydroxide for removal of toxic metal ions has been disclosed. However the present invention differs with this reported invention in respect of different substrate used for incorporation of various forms of iron and is also based on waste organic materials like dried leaves which makes it very inexpensive as compared to utilisation of cellulose pulp as substrate. Also the materials developed in present invention is having improved affinity for both inorganic arsenite (As(III)) and arsenate (As(V)).

Reference may also be made to U.S. Patent 6,914,034, wherein Vo developed adsorbents for removing anions of heavy metals in which oxygen containing compounds of iron copper and/or aluminium is incorporated in porous carbon by impregnation or dispersion of a suitable precursor of such compounds. However in present invention the porous carbon support has been replaced with organic matter produced from dried leave powder which is a waste materials and is abundantly available. This makes the present material very low cost as compared to porous carbon. Moreover, the present materials is having equal affinity for both As(III) and As(V) which is note possible with reported materials.

The material developed in the present invention overcomes the following drawbacks of the conventional materials and process in prior art:

• Problem of limited adsorption capacity /efficiency of anion removal with conventional adsorbents.

· Lack of cost effectiveness of other adsorbents by offering low cost materials for anionic pollutants removal from drinking water .

• Provide cost effective process by using natural and low cost raw materials.

• Overcomes problem of sludge generation associated with conventional chemical methods.

· Overcomes problem of leaching of toxic metals like aluminium etc.

• Lack of selectivity of conventional adsorbents for anionic pollutants at low concentrations.

• Lack of selectivity of conventional adsorbents for anionic pollutants in presence of other anions like sulphate, carbonate, bicarbonate.

· Problem of hazardous sludge generation by virtue of restriction of reaction to active sites on the adsorbent material.

• Problem of hazardous chemical handling etc. by providing technically non-tedious and clean process.

• Provides non-toxic materials for anionic pollutants removal, which does not alter total dissolved solids, taste and odor of water.

• Problem of leaching of anionic pollutants by their immobilization into the adsorbent matrix through bio composite formation.

• Problem of slow kinetics of anionic pollutants removal by offering a rapid adsorption process.

· Problem of requirement of electricity and /or special reactors/ apparatus for removal of anionic pollutants from drinking water. OBJECTIVE OF THE INVENTION

The main object of the present invention is to provide organic-inorganic composite material useful for removal of anionic pollutants from water and process for the preparation thereof, which obviates the drawbacks of the hitherto known prior art as detailed above.

Another objective of the present invention is to develop a process for synthesis of organic- inorganic composite composed of metal oxide and other elements namely carbon, nitrogen, oxygen etc. which shows high arsenic and fluoride removal efficiency, comprising chitin or by replacing chitin with different low cost carbon sources namely chitosan, leaf, onion, banana peals, citrus fruits waste, etc. and metal ions namely aluminium, iron, titanium, lanthanum, magnesium, calcium etc. individually or in all possible combinations, having the ability to sequester anions, in specific arsenic and/or fluoride.

Yet another objective of the present invention is to use chitin, leaf, onion, banana peels, citrus fruit waste, crab shell etc as a template as well as carbon source for preparation of organic- inorganic composite for its application for removal of arsenic and/or fluoride from water .

Yet another objective of the present invention is to use organic-inorganic composite material for the removal of arsenic and fluoride in the presence of other anions like sulphate, carbonate and bicarbonate and cations from drinking water.

Yet another objective of the present invention is to regenerate arsenic or fluoride sorbed material by chemical treatment and other methods.

Yet another objective of the present invention is to study the reuse and to regenerate arsenic or fluoride sorbed material using alum and other reagents with and without heat. SUMMARY OF THE INVENTION

Accordingly, present invention provides an organic inorganic composite material comprising 55 to 75% metal salt, 4 to 15% biogenic template and the remaining being oxygen.

In an embodiment of the present invention, said composite material useful for the removal of anionic pollutants from water.

In yet another embodiment of the present invention, anionic pollutants are selected from fluoride and arsenic and are selectively removed from drinking water in batch and continuous mode. In yet another embodiment of the present invention, metal salts are selected from alumina or iron oxide.

In yet another embodiment of the present invention, biogenic templates are selected from the group consisting of chitin, chitosan, leaf, sodium alginate, banana peels, citrus peels or crab shell waste.

In yet another embodiment of the present invention, A process for the synthesis of organic- inorganic composite material as claimed in claim 1 and the said process comprising the steps of:

a) dissolving metal salt in water to obtain 10-80% metal solution;

b) mixing 10-60% amount biogenic template to metal solution as obtained in step (a) followed by stirring for period in the range of 1 to 24 h to obtain suspension;

c) drying of suspension as obtained from step (b) at temperature in the range of 50-110°C for a period in the range of l-6hrs to obtain dried mass;

d) calcining of dried mass as obtained in step (c) at temperature in the range of 450-500°C with heating rate of 5-7°C/min for 5-6h in presence of oxygen to obtain calcined dried mass;

e) washing the calcined dried mass as obtained in step (d) with water in the ratio ranging between 1:20 to 1:50 by shaking for a period in the range of 1-3 h followed by drying at temperature in the range of 100-250°C for period in the range of 3-24 h to obtain organic-inorganic composite material.

In yet another embodiment of the present invention, alumina and iron based organic- inorganic composite material has the following characteristics:

Alumina based organic-inorganic composite material

a) Surface area: 50-350 m²/g;

b) d5o average particle size of 23 micron;

c) Elemental analysis: Alumina = 55-75wt%; Carbon= 4-15 wt%; d) XRD phases: crystalline as well as amorphous alumina phases;

Iron based organic-inorganic composite material Surface area: 50-150 m²/g;

a) Pore volume 0.01 to 0.02 cmVg;

b) Pore size: 80-150 A;

c) Surface Elemental Composition (obtained using EDX (mass %)): Iron 77.25 %, Oxygen: = 17.66 % Carbon= 5.09 %;

d) XRD phases: Amorphous iron oxide phases. In yet another embodiment of the present invention, said composite material loaded with anionic pollutant is reusable by refluxing with using regeneration media without heating or by heating directly in sunlight at temperature in the range of 90-110°C.

In yet another embodiment of the present invention, regeneration media is selected from 2- 10% alum and 0.5 to 1% sodium hydroxide.

In yet another embodiment of the present invention, arsenic and fluoride removal efficiency is in the range of 70 to 99.73%.

In yet another embodiment of the present invention, organic-inorganic composite adsorbent has been characterized using XRD, SEM, FTIR etc.

In yet another embodiment of the present invention, fluoride is selectively adsorbed at different pH ranging between 5 to 9.

In yet another embodiment of the present invention, arsenic is selectively adsorbed at different pH ranging between 4 to 9. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is graph showing optimization of alumina loading in chitin based organic- inorganic composite (Conditions: Initial fluoride cone: 50.0 mg/L; adsorbent dose: 3g/L; contact time: 24 h)

Figure 2 shows different steps of process for preparation of organic inorganic composite. Figure 3 represents XRD spectrum of alumina based composite adsorbent.

Figure 4 represents SEM spectrum of alumina based composite adsorbent.

Figure 5 represents FTIR spectrum of alumina based composite adsorbent.

Figure 6 represents EDX spectrum of iron based composite adsorbent.

Figure 7 represents XRD spectrum of iron based composite adsorbent.

Figure 8 represents SEM spectrum of iron based composite adsorbent.

Figure 9 represents FTIR spectrum of iron based composite adsorbent.

DETAILED DESCRIPTION OF THE INVENTION SYNTHESIS OF ALUMINA BASED ORGANIC-INORGANIC COMPOSITE ADSORBENT

A new improved organic-inorganic composite based material has been developed using biogenic template as carbon and nitrogen source for supporting/doping metal oxide as well as formation of different metal oxide phases. The details of the process are as follows: Step 1: Dissolve 4.63g of alum (commercial grade) in 25ml of double distilled water. 3g of chitin (other templates including leaf, citrus peels, banana peels etc) was added to alum solution and agitated for 4h on horizontal rotary shaker to make homogeneous slurry. During agitation, the amide and the carboxyl groups in chitin bind with aluminium ions in solution. The alumina loading was varied and 25% alumina loading was found to be optimal as shown in Figure 1.

Step 2: After the completion of shaking, the slurry from step 1 was dried in oven at 110 °C for 3 h to evaporate water.

Step 3: Calcination of the dried mass from step 2 at 450°C with heating rate of 5 °C/min for 6h in presence of oxygen results in carbonized alumina supported composite.

Step 4: The calcined mass from step 3 is washed thoroughly to remove the unreacted aluminium ion and then subjected to drying.

Step 5: The washed product of step 4 is subjected to drying at 70°C. The bio template based adsorbent is here after referred to as organic-inorganic composite adsorbent.

Characterization of composite adsorbent

This adsorbent was characterized with respect to its chemical composition.

Chemical composition

The material was analyzed by using ICP-AES technique as well as CHN analyzer. Perkin Elmer ICP-OES 4100 BV instrument was used for the analysis of acid digested samples, while CHN analysis was carried out using Vario Elementar instrument. Approximate chemical analysis results for composite adsorbent are as follows: C: 11.4, AI2O₃: 72, H₂0: 13, Ca: 1.3, Na: 2.1 (all values are in weight %).

Structural investigations

The structural details and phase identification have been carried out by XRD analysis of the adsorbent. Power X-ray diffraction studies were carried out on Phillips analytical diffractometer with monochromated CuK radiation (λ-1. 4 A). The scanning range of 2Θ was set between 3° and 60°. The basic refinement of XRD data has been done and efforts were made for phase identification. The XRD analysis shows the presence of multiple phases with prominent presence of crystalline as well as amorphous phases of alumina. However, presence of crystalline calcium sulfate and calcium carbonate was also observed in the material. This in away suggest a composite material with complex mixture of amorphous and crystalline phases, dominated by alumina and calcium based compounds. Morphology of composite adsorbent

The Scanning electron microscopic studies suggests the presence of both coarse and fine particles with irregularly shaped particles of alumina with agglomerates of small particles adhered on eggshell particles. Fine particles were observed with size range of 10-20 micron and coarse particles in the range of 30-60 microns. Some long flat needle shaped particles were also observed in the size range of 70-100 microns.

FTIR Analysis

The IR absorption has been investigated on Brucker spectrometer by making pallets of material in KBr. FTIR spectrum of composite adsorbent is shown in Figure 5. The IR peak at 3624 cm^"1 can be assigned to the -NH stretching vibration which is overlapped by broad adsorption peak of -OH group. The peak at 1660 cm^"1 represents stretching vibration of C=0 group. The peak observed at 1424 and 1364 cm^"1 can be assigned to the vibration of - OH group of primary alcoholic group and CO-NH group of amide respectively. The intense peak appears at 1124 cm^"1 and corresponds to the vibration of -SO₄ groups. The peaks at 742 and 673 cm^"1 can be attributed to Al-O stretching mode and appears as a broad band and O-Al-0 bending mode respectively.

SYNTHESIS OF IRON OXIDE BASED ORGANIC-INORGANIC COMPOSITE ADSORBENT

Iron oxide based organic-inorganic composite based material has also been developed using biogenic template as carbon and nitrogen source for supporting/doping metal oxide as well as formation of different metal oxide phases. The details of the process are as follows: Step 1: Dissolve 69 g of ferrous sulphate in 250 ml of double distilled water. 4 g of biotemplate was added to iron solution and agitated for 16 h on horizontal rotary shaker to make homogeneous slurry. During agitation, various functional groups present on biotemplate bind with ferrous ions in solution.

Step 2: After the completion of shaking, the solution was filtered and dried in oven at 110°C for 2 h to evaporate water.

Step 3: Calcination of the dried mass from step 2 at 500°C under controlled conditions results in iron based organic inorganic composite.

Step 4: The calcined mass from step 3 is washed thoroughly to remove the unreacted metal ion and then subjected to drying.

Step 5: The washed product of step 4 is subjected to drying at 70°C. The biotemplate based adsorbent is here after referred to as organic-inorganic composite adsorbent. Regeneration of composite adsorbent

Composite adsorbent loaded with fluoride was subjected to regeneration using different concentrations of NaOH, Alum and combinations of regenerant. The regenerated adsorbent was again tested for fluoride adsorption capacity.

Structural investigations and morphology of composite adsorbent

The SEM and EDX analysis was carried out using JEOL-JSM-6380A using 15Kv accelerating voltage with different magnifications. SEM results were taken in electronic forms on 35mmB/W film and the adsorbent were pre-coated with gold before scanning for 30 min. The surface morphology of FeL (leaf based iron oxide) obtained from SEM is given in fig.2.The scanning electron micrographs show agglomeration of amorphous particles of different sizes and no crystalline phases were observed. The EDX spectrum as given in fig.3 also confirms the presence of iron, carbon and oxygen. BET-SA analysis was calculated using Micromeritics ASAP-2000 at the boiling temperature of nitrogen.BET Surface area of FeL was found to be 116.47m²/g.

The powder XRD patterns of FeL were recorded on Rigaku Miniflex-II Diffractometer. The powdered sample was scanned between 2Θ ranges from 20 to 80°.The above spectrum pattern shows no sharp peaks which clearly indicates highly amorphous nature of the material.

FTIR Analysis

The FTIR spectrum of the material was carried out using KBr pellets and the spectra was recorded on BRUKER, Model vertex 70 spectrometer. The FTIR spectra of FeL presented in Fig .1 shows the peak at 1060.77 cm^"1 which is attributed to Fe-OH structural vibration and 2343.96 cm ^"1 is due to -CH stretching vibration.

Disposal of Arsenic and fluoride saturated composite adsorbent

Composite adsorbent loaded with fluoride and arsenic was coated with gel mixture of cellulosic material like chitosan to encapsulate the laden composite adsorbent. Encapsulated adsorbent was calcined and then tested for leaching of pollutants for a long time period. Encapsulated material can be then disposed of safely.

The organic inorganic composite material developed by formation of different metal oxide phases supported on nitrogen enriched carbon is new and not reported in literature so far. The process for synthesis of improved adsorbent has been optimized by varying conditions in feasible parametric changes. Low temperature operations, readily available raw materials, highly reproducible simple process and unused reactant & process water recycling are special features of the process. The structural investigations infer the crystalline as well as metal oxide phases. The organic-inorganic composite incorporated with metal oxides, carbon, nitrogen, etc. and synergy of these elements seems to be responsible for high arsenic and fluoride adsorption capacity in the presence of sulphate, carbonate and chloride. The material in the present invention thus is an improved composition and the process for its synthesis is also novel and not reported in literature.

The improved adsorbent material developed has been used for adsorption of arsenic and/or fluoride from simulated water of composition related to drinking water. The need for this kind of versatile material for arsenic and/or fluoride removal is being realized, to overcome problems of conventional materials and processes which are energy intensive, expensive and non-selective. Novel arsenic and fluoride specific adsorbent, with the characteristic to adsorb arsenic and/or fluoride in presence of other anions is desired for low arsenic and fluoride adsorption process, which overcomes the drawback of conventional materials and processes.

In specific, the organic-inorganic composite based adsorbent shows high adsorption capacity for arsenic and fluoride even in presence of higher concentration of accompanying ions. The adsorbent also shows fast kinetics, which will be of immense importance from practical point of view. The adsorbent does not show considerable effect of pH in the normal operating range. The arsenic and fluoride adsorption capacity is much better than the commercial adsorbents (benchmark material) with respect to most of the parameters studied. The probable reasons for improved adsorption capacity and selectivity of the materials can be attributed to the following:

• The template is expected to facilitate formation of nano-crystallites of metal oxides phases with improved physical properties.

• The metal oxide phases supported on N-enriched nonporous and macroporous carbon seems to impact property of selectivity and stabilization to metal oxide phases.

• Synergistic effect of different metal oxide phases could also be responsible for the improved arsenic and fluoride uptake properties.

• The property of enhanced adsorption could also be due to surface acidity in composite adsorbent. Examples

The following examples are given by way of illustration therefore should not be construed to limit the scope of the present invention.

Example 1

4.63 g of alum (commercial grade) was dissolved in 25 ml of distilled water. 3g of chitin was added into alum solution and the mixture was shaken on horizontal rotary shaker for 4 hours. This mixture was transferred to a china dish and dried at 110°C in oven for 3 hours and calcination was carried out at 450°C for 6 hours in muffle furnace. Calcined material was then ground in a mortar pestle and washed with distilled water in 1:20 (material: distilled water) ratio by shaking on horizontal rotary shaker for 1 hour. Finally material was dried at 70°C in oven for 4 hours.

This c-supported alumina was evaluated for fluoride removal from water by mixing the desired quantity of adsorbent in 250 ml PVC conical flasks with 100 ml test solution at room temperature (25+3°C). These flasks, along with test solution and adsorbent, were shaken on horizontal rotary shaker to study the various control parameters. The adsorbent dose was varied from 0.01 to 0.3 g/50 ml. At the end of the desired contact time, the conical flasks were removed from shaker and allowed to stand for 2 min for settling the adsorbent. Then, samples were filtered using whatmann Filter Paper No. 42 and filtrate was analyzed for residual fluoride concentration by using fluoride ion selective electrode (Orion number 9409). The results are presented in Table 1. The fluoride adsorption capacity of c-supported alumina was also compared with chitin based media and activated alumina and the results are given in Table 2.

Table 1: Defluoridation of water using C-supported alumina

(Condition: Initial fluoride cone. = 9.8 mg/L; Contact time: 24h; Temp: 27 °C) Dose (g/50ml) Final concentration of Fluoride removal (%)

fluoride (mg/1)

0.01 7.84 14.78

0.03 5.1 44.56

0.06 2.22 75.86

0.08 1.28 86.08

0.1 1.14 87.60

0.2 0.13 98.55

0.3 0.068 99.26

Table 2: Comparison of fluoride adsorption capacities of c-supported alumina and activated alumina in drinking water.

(Condition: Initial fluoride cone .= 9.8 mg/L; Contact time: 24h; Temp: 28 °C)

Example 2

The same synthesis protocol was repeated as mentioned in example 1 for the synthesis of adsorbent based on Crab shell waste. The composite adsorbent was synthesized by using crab shell as a substitute of chitin. The as synthesized composite adsorbent was evaluated for fluoride removal from drinking water and the results are shown in Table 3.

Example 3

The same synthesis protocol was repeated as mentioned in example 1 for the synthesis of adsorbent based on leaves. The composite adsorbent was synthesized by using leaves as a substitute of chitin. The optimal alumina loading in case of leaves based adsorbent is 50 wt %. The as synthesized leaves based adsorbent was evaluated for fluoride removal from drinking water and the results are shown in Table 3. Example 4

The same synthesis protocol was repeated as mentioned in example 1 for the synthesis of adsorbent based on citrus peels. The composite adsorbent was synthesized by using citrus fruit peals/waste as a substitute for chitin. The as synthesised composite adsorbent was evaluated for fluoride removal from drinking water and the results are shown in Table 3.

Example 5

The same synthesis protocol was repeated as mentioned in example 1 for the synthesis of adsorbent based on sodium alginate. The composite adsorbent was synthesized by using sodium alginate as a substitute for chitin. The as synthesized sodium alginate based adsorbent was evaluated for fluoride removal from drinking water and the results are shown in Table 3.

Example 6

The same synthesis protocol was repeated as mentioned in example 1 for the synthesis of adsorbent based on banana peals. The composite adsorbent was synthesized using banana peals as a substitute of chitin. The as synthesized composite adsorbent was evaluated for fluoride removal from drinking water and the results are shown in Table 3.

Table 3: Evaluation of different composite adsorbent for fluoride removal in drinking water.

Conditions: Initial concentration= 8.84(mg/L); Dose=0.3g/100 ml; Contact time =24 h; Temp: 27 °C

Adsorbents Equilibrium % Removal

fluoride

concentration

(mg/L)

Chitin based adsorbent 0.068 99.26

Leaf based adsorbent 0.44 95.02

Sodium alginate based adsorbent 1.16 86.88

Banana peel based adsorbent 1.36 84.62

Citrus peel based adsorbent 1.12 87.33

Crab shell waste based 1.98 77.60

adsorbent Example 7

Solution of FeS0₄ of different concentrations was prepared by dissolving appropriate quantities of FeS0₄ in 250 ml of deionised water. 4 g of dried leaf powder was added to FeS0₄ solution and the mixture was kept for shaking for 16 hours. After shaking the solid mass was separated by filtration using filter paper and dried at 50°C for 5 hours. After drying the mass was calcined at 500°C for 4 hours. The calcined material was washed thoroughly and air dried. The concentration of the FeS0₄ was varied from 0.01 to 1 M. The powdered organic-inorganic iron based composite was used for adsorption of arsenite and arsenate. The efficiency of sample is illustrated in Table 4.

Table 4: Removal of arsenite and arsenate using composite material prepared with different concentrations of FeS0₄

Conditions: Initial conc.:= Arsenite 0.595, Arsenate: 0.546 mg/1; Contact time: 24h,

Adsorbent dose: 2 g/1; Temp: 26 °C

Example 8

The same procedure was repeated as described in example 7 for preparation of organic- inorganic iron based composite with 1M of FeS0₄ solution. Different doses of composite varied between 0.2 to 6 g/1 were used for removal of arsenite and arsenate. The efficiency of sample is illustrated in Table 5.

Table 5: Removal of arsenite and arsenate using different doses of composite material Conditions: Initial conc.:= Arsenite 0.468, Arsenate: 0.510 mg/1; Contact time: 24h; Temp: 27 °C

Adsorbent dose Arsenite removal Arsenate removal

(g/i) Final arsenite % Arsenite Final arsenate % Arsenate concentration removal concentration removal (mg/1) (mg/1)

0.2 0.388 17.09 0.387 24.12 0.6 0.261 44.23 0.313 38.63

1.0 0.245 47.65 0.220 56.86

2.0 0.168 64.10 0.170 66.67

6.0 0.077 83.55 0.061 88.04

Example 9

The same procedure was repeated as described in example 7 for preparation of organic- inorganic iron based composite with 1 M of FeSC solution. The kinetic study was conducted to using organic-inorganic iron based composite by mixing fixed dose of adsorbent and withdrawing samples at different time intervals to study the effect of contact time. The contact time was varied between 5 to 360 minutes. The results are illustrated in Table 6.

Table 6: Removal of arsenite and arsenate using different doses of composite material Conditions: Initial conc.:= Arsenite 1.0 mg/1, Arsenate: 2.90 mg/1; Adsorbent dose (g/l):3g/l; Temp: 28 °C

Contact time Arsenite removal Arsenate removal (minutes) Final arsenite % Arsenite Final arsenate % Arsenate concentration removal concentration removal (mg/1) (mg/1)

5 0.535 46.82 2.038 32.00

10 0.516 48.71 0.235 92.16

20 0.512 49.11 0.117 96.10

40 0.500 50.30 0.084 97.20

60 0.495 50.80 0.068 97.73

80 0.421 58.15 0.058 98.06

110 0.403 59.94 0.058 98.06

120 0.390 61.23 0.036 98.80

140 0.376 62.62 0.034 98.87

180 0.349 65.31 0.036 98.80

210 0.341 66.10 0.023 99.23

240 0.338 66.40 0.026 99.13

270 0.334 66.80 0.034 98.87

300 0.332 67.00 0.030 99.00 330 0.33 67.20 0.023 99.23

360 0.292 70.97 0.008 99.73

Example 10

The saturated composite adsorbent from example 1-6 was regenerated by refluxing with 5% alum for 1-6 hours at temperature of 100-110°C. The sample was regenerated with 100% efficiency.

Example 11

The saturated composite adsorbent from example 1-6 was regenerated by refluxing with 5% alum for 1 hour directly in sunlight. The sample was regenerated with 100% efficiency. Example 12

The saturated composite adsorbent was regenerated using different concentrations of regenerating media. The results are illustrated in Table 7.

Table 7: Regeneration of composite adsorbent

Conditions: Initial fluoride conc.:47.0 ppm, Dose: 0.3g/100 ml, shaking time: 24 h; Temp: 27 °C

Regeneration media F^" cone, (ppm)

2% Alum 13.5

5% Alum 14.0

10% Alum 15.6

10% Alum calcination at 450°C 17.1

0.5% NaOH 37.4

1% NaOH 44.3

ADVANTAGES OF THE INVENTION

• Improved selectivity of organic-inorganic composite adsorbent for arsenic at low concentrations and in presence of competing anions

• Improved selectivity of organic-inorganic composite adsorbents for fluoride at low concentrations and in presence of competing anions

• Enhanced adsorption efficiency of organic-inorganic composite adsorbents for arsenic and fluoride at wide range of concentration and in presence of competing anions

• Cost effective adsorbent for arsenic and fluoride removal

• Avoidance of sludge generation associated with conventional chemical method namely alum treatment, chemical precipitation etc.

• Avoidance of hazardous chemical handling etc. by providing technically non-tedious and clean process.

Claims

1 We claim:

1. Organic inorganic composite material comprising 55 to 75% metal salt, 4 to 15% biogenic template and the remaining being oxygen.

2. Organic inorganic composite material as claimed in claim 1, wherein said composite material useful for the removal of anionic pollutants from water.

3. Organic inorganic composite material as claimed in claim 2, wherein anionic pollutants are selected from fluoride and arsenic and are selectively removed from drinking water in batch and continuous mode.

4. Organic inorganic composite material as claimed in claim 1, wherein metal salts are selected from alumina or iron oxide.

5. Organic inorganic composite material as claimed in claim 1, wherein biogenic templates are selected from the group consisting of chitin, chitosan, leaf, sodium alginate, banana peels, citrus peels or crab shell waste.

6. A process for the synthesis of organic-inorganic composite material as claimed in claim 1 and the said process comprising the steps of:

a) dissolving metal salt in water to obtain 10-80% metal solution;

c) drying of suspension as obtained from step (b) at temperature in the range of 50-110°C for a period in the range of l-6hrs to obtain dried mass; d) calcining of dried mass as obtained in step (c) at temperature in the range of 450-500°C with heating rate of 5-7°C/min for 5-6h in presence of oxygen to obtain calcined dried mass;

7. Organic-inorganic composites material as claimed in claim 1, wherein alumina and iron based organic-inorganic composite material has the following characteristics:

Alumina based organic-inorganic composite material

a) Surface area: 50-350 m²/g; 2 b) CI50 average particle size of 23 micron;

c) Elemental analysis: Alumina = 55-75wt%; Carbon= 4-15 wt%;

d) XRD phases: crystalline as well as amorphous alumina phases;

Iron based organic-inorganic composite material Surface area: 50-150 m²/g; a) Pore volume 0.01 to 0.02 cm³/g;

b) Pore size: 80-150 A;

d) XRD phases: Amorphous iron oxide phases.

8. Organic inorganic composite material as claimed in claim 1, wherein said composite material loaded with anionic pollutant is reusable by refluxing with using regeneration media without heating or by heating at temperature in the range of 90-110°C OR directly in sunlight.

9. Organic inorganic composite material as claimed in claim 6, wherein regeneration media is selected from 2-10% alum and 0.5 to 1% sodium hydroxide.

10. Organic inorganic composite material as claimed in claim 1, wherein arsenic and fluoride removal efficiency is in the range of 70 to 99.73%.

11. Organic-inorganic composite material useful for removal of anionic pollutants from water and process for the preparation thereof substantially as herein described with references of examples and drawing accompanying the specification.