Polymer Clay Composite Beads As Green Biosorbents For Copper & Chromium Removal From Industrial Waste Water
Introduction of Research Proposal
In the modern era of industrialization and urbanization the issue of heavy metals is becoming a growing concern. Industrial effluents always contain a lot of heavy metals which if not treated effectively may enter into the water bodies and cause serious environmental and health related issues. Among the heavy metals Cu (II) and Cr (VI) are the primary pollutants present in wastes released from paint, electroplating and pigment industries. Excessive concentrations of these metals in water may pose serious effects in human beings and animals. There are several conventional methods available for the removal of these two metals. Chemical precipitation, membrane based separations, ion exchange complexation and electrochemical treatment are some of the methods commonly employed. However most of these methods are not economical due to high cost and less sensitivity. Adsorption is one of the promising and less expensive techniques available for metal removal. There is a wide choice available for the selection of adsorbents for heavy metals and polymers find a promising position among all of them. However the use of synthetic polymers as adsorbents is again a threat to the environment. Thus today there is a growing need of developing natural, biodegradable and low cost alternatives to synthetic polymers. These materials are very economical as they are abundantly available in nature and are environmentally friendly. In the present work the use of three environmental friendly polymers, chitosan, polyvinyl alcohol and alginate is intended.
A brief description of these polymers is as follows.
- Chitosan is a derivative from N-deacylation of chitin, which is obtained as a major component from the shells of crustaceans. Chitin is the second most abundantly occurring biopolymer next to cellulose. Chitin and chitosan have biological and chemical properties such as non-toxicity, biocompatibility, high chemical reactivity, chirality, chelation and adsorption properties. The presence of amine groups makes chitosan unique among biopolymers, for example, its cationic behavior in acidic solutions and its affinity for heavy metal ions. Ion exchangers or adsorbents can be made on large scale and low cost from chitosan. These chitosan exchangers or adsorbents have potential applications in enzyme immobilization, base catalysis, protein separation and purification, sorption of precious metal ions for recovery or as catalysts after reduction, wastewater treatment to remove heavy metal ions and acidic dyes.
- Alginate: is another polysaccharide biopolymer composed of anionic blocks of 1-4 linked (L gluconic acid and (-D mannuronic acid [6]. Alginate also shows high affinity to metal ions but it has a tendency to swell in water. It lacks mechanical strength due to which it cannot be used as such for waste water treatment. To avoid this problem it can be used be combination with other polymers.
- Poly(vinyl alcohol): is a synthetic biodegradable polymer. It is a type of vinyl polymer derived from vinyl monomers containing carbon double bonds. Though most of the vinyl polymers are not environment friendly due to long degradation time, Poly (vinly alcohol) is one of the few vinyl polymers to have high bio-degradation rates due to the presence of hydroxyl groups that make it hydrophilic in nature. Just like chitosan, PVA and alginate clays have an inherent capability to remove heavy metals. Various clays that can be employed for heavy metal removal are kaolinite, alginate, bentonite, montmorillonite and fullers earth. The use of chitosan or clay as individual materials for removal of metals have several limitations such as chitosan is soluble in acidic solutions, lacks mechanical strength, shows deformation after drying, clay lacks flexibility, it is difficult to cast clay in the form of beads or films etc. These limitations can be overcome by the synergistic use in the form of composite beads of both organic and inorganic hybrid materials provided with properties that are inherent to both the components. In the present work it is proposed to prepare clay-bio polymer composites in the form of beads for the removal of copper and chromium from industrial waste water. The composite will be based on the intercalation of polymers in the layered silicates of clay giving composites which will be employed as robust and stable sensors as well as adsorbents for metal detection and removal in aqueous media.
Origin of Research problem
In and around Pune city there are several industries both small scale as well as large scale that are located near water bodies [10]. Most of the paint industries, dyes industries, electroplating industries, metal industries and chemical industries release their industrial wastes into the water bodies. These industrial waste waters contain considerable amount of heavy metal ions and other organic pollutants. As industrialization is fast progressing the contamination of the existing water resources is increasing day by day. It is also revealed that the presence of heavy metals in water increases particularly during Ganesh Festival due to the immersion of idols painted with synthetic paints. The presence of heavy metals leads to several deleterious effects on human health, animal life and aquatic life. The treatment of waste water containing heavy metals is always a challenging task. The removal of heavy metals from industrial waste water may not be the only solution to the issue but the degradation of these metal ions to less toxic forms and recovery of the metals in the pure form to make them usable for constructive purpose may be the ideal route of remediation. As mentioned in the introduction there are several methods of remediation that can be applied, however adsorption of heavy metals from aqueous samples on green biosorbents is the most promising and economical method.Thus to summarize the origin of this problem lies in the presence of heavy metal in waste waters and their serious impact on the environment.
Interdisciplinary relevance
The primary purpose of the green biosorbent beads proposed in the present work is removal of heavy metals and their degradation to less toxic form. Though the work serves as a means for environmental remediation it involves more than one disciplines in it. The selection of the polymers involves polymer science. The addition of clay component into the biosorbents and the intercalation of polymers into it involves Chemistry. The polymers and the clay samples proposed to be used in the bead preparation have been reported to possess excellent biocompatibility due to which they can be used as antimicrobial agents, used for enzyme immobilization, and for drug delivery systems. Thus the work happens to find relevance in Life science studies. The beads can be used for the removal of pharmaceutical and personal care products. Clay based composite materials have been reported in literature for preparation of energy based materials having applications in various disciplines like Electronics for generation of dielectric materials in electronic devices, in electrochemistry for batteries, and in Physics for fabrication of dye sensitized solar cell materials. Clay-Polymer composites can also find applications in gas sensors and gas storage devices having numerable applications in space studies. Thus the proposed work finds variety of applications in various fields of research.
Review of Research and Development in the subject
Water is indispensible for life and clean and potable water is the most essential basic need of mankind. Researchers all over the world are actively involved in developing newer technologies for removal of toxic pollutants like heavy metals from water. In recent years, polymer composites have attracted the attention of scientists and technologists in water purification due to improved processability, surface area, stability, tunable properties, and cost effectiveness. On similar lines clays as adsorbents have several advantages upon many other commercially available adsorbents in terms of low-cost, an abundant availability, high specific surface area, excellent adsorption properties, non-toxic nature, and large potential for ion exchange. Clays also contain exchangeable cations and anions on their surface making them easily employable for water treatment.Recently combining the advantages of both clay and polymers composites have been developed for water purification.
Biopolymer-clay nanocomposites based on chitosan intercalated in montmorillonite has been used in potentiometric detection of anions. Crosslinked chitosan/polyvinyl alcohol blend beads have been employed for removal and recovery of cadmium from waste water. Polyvinyl alcohol hydrogel beads crosslinked with sodium sulphate have been used for micro-organism immobilization and disinfection of water. Novel complex gel beads composed of hydrolyzed polyacrylamide and chitosan beads have been used to remove lead, copper and mercury ions from waste water.The kinetics and equilibrium modeling of heavy metal uptake from aqueous solutions and industrial waste waters has been studied using humic acid-immobilized polymer-bentonite clay composites. The biosorption of uranium has been reported using calcium alginate beads. Crosslinked chitosan/ Poly vinyl alcohol blend beads with high mechanical strength have been developed with good mechanical strength.
Significance of the study in the context of current status:In view of the work done so far as reported in literature in most of the cases a single polymer is employed and the study is limited to lab scale batch studies on synthetic samples. Unlike laboratory solutions, industrial effluents contain various metal ions. Hence it is necessary to investigate the selective removal of metals like Cu 2+ and Cr6+ in presence of co-existing metal ions from aqueous samples. There is also a need to develop a removal process which will assist not only in removal but in degradation these heavy metals to a form which is less toxic. With this purpose we intend to use following strategies which will bring innovation to present body of knowledge:
- Fabrication of the beads with different clay-polymer combinations.
- Cross linking of the composite beads (prepared using different combinations of chitosan, PVA and Alginate and clays) with crosslinkers so as to generate porosity and hydrophilic nature within beads
- Enhancement in the removal capacity and imparting selectivity towards metals ions by incorporating selective reagents in the beads
- Using these beads in generating a reusable continuous reactor bed for treatment of industrial waste water containing Cr (VI) and Cu (II) in presence of each other and other metal cations.
Objectives:With the background mentioned above the objectives behind the present work are as follows:-1. Development of an optimized procedure for preparation of green biosorbent polymer-clay beads for adsorption of copper and chromium2. Development of a continuous reusable reactor bed containing the optimized beads for environmental remediation of industrial waste water containing copper and chromium.
Methodology: The following points give the methodology of the work
a.Optimization of the preparation of beads
Different combinations of the selected polymers will be taken and the bead making process will be optimized. In brief the following procedure will be followedSelected polymers and clay samples will be weighed, dissolved in appropriate solvent (dilute acid / water), solution will be homogenized by ultrasonication and will be pipetted by means of syringe into sodium hydroxide or calcium chloride solution. After continuous stirring of beads in presence of mother liquour they will be filtered and dried. The formed beads will be subjected to further modifications like crosslinking, introduction of selective reagents into the beads, reduction of moisture in the beads by suspending them in organic solvent mixtures.
b.Characterization of the beads prepared
The beads prepared will be characterized by different techniques like Infrared Spectroscopy, Scanning Electron Microscopy, XRD studies, X-Ray Photoelectron specroscopy, Thermogravimetry, contact angle measurement for detecting the hydrophilic, hydrophobic character etc.The mechanical strength of the beads will also be detected. The surface area, density, pore volume, pore diameter and porosity of the beads will also be evaluated.
c. Batch extraction studies of Cr (VI) and Cu (II) by beads
The extraction of the selected metals into the beads will be evaluated based on various parameters like pH of extraction, adsorbent dose, contact time of extraction, adsorption kinetics, surface area of beads and the adsorption capacity. The concentration of metals in the solutions used before and after equilibration with the beads will be measured spectrophotometrically and/or by Atomic absorption spectrometer.
d.Adsorption Isotherms
The adsorption of metals on the beads will be studied using different adsorption models like Freundlich and Langmuir. In order to understand the kinetics of adsorption process Weber Morris and Boyd Plots will be constructed. The adsorption efficiency of the beads will also be evaluated at different temperatures from which the energy of activation and other thermodynamic parameters will be evaluated. Using this information the optimum temperature of adsorption will be evaluated.
e Interference studies
The adsorption of meatsl on the beads will also be studied in presence of other competing metal cations like Cd (II), Hg (II) Pb (II), Ni (II), Zn (II) etc.
f.Reusability studies
The reusability of the beads will be studied by desorption studies of Cr (VI) and Cu (II). This will be optimized depending on parameters like pH, contact time, temperature etc. The limiting number of cycles required for which the beads can be reused will be determined. After the limiting number of cycles the time taken for complete biodegradation of the beads (after complete extraction of metals) will also be monitored.
g. Construction of the reactor bed
A reactor bed will be constructed which will consist of an inlet and an outlet. The bed will be made up of the optimized and tested beads. Metal solution will be introduced into the bed through the inlet and the solution passing out of the reactor will be analyzed for residual metal concentration. Other parameters like the flow rate, packing procedure, size of the beads, dimensions of the reactor, reusability cycles, average lifetime and its disposal will be optimized.h.Application of the reactor bed for use in industrial waste water samples: After testing the reactor bed for laboratory metal samples, it will be tested for contaminated industrial waste water. Samples of industrial waste water released from electroplating industries, paint industries around Pune city will be collected and tested for removal of Cr (VI) and Cu (II).
