Removal of heavy metals from industrial waste water using polymer nano-composites based on agricultural wastes

Abstract

Environmental pollution by toxic metals comes from industrial, agricultural effluents and waste disposal from various sources. Many industries such as mining, metal plating and tanneries discharge waste containing heavy metal ions. As pollutants, heavy metals were studied from the point of view of persistence and toxicity.These toxic metals can occur brain damage, accumulative poisoning and cancer when existed above the tolerance levels.The effective and rapid removal of heavy metals (Pb, Cd, Hg and Cu,) are very important for the environmental remediation. Many processes were used to get rid of heavy metals from waste water, such as coagulation, chemical precipitation, membrane separation, solvent extraction, adsorption and ion exchange. As an alternative to chemical precipitation, membrane filtration, or sorption processes, ion exchange, with a wide variety sorbents have been examined. The sorbents used should have some properties, such as, long lifetime and high adsorption capacity, a high ability to reduce the concentration of heavy metals below the acceptable limits. Thus, it is a continuing need to develop and identify high efficient sorbents and low-cost for facile and the highest removal technique. The present work focused on preparing magnetic polymer composite composed of iron based nano-cores covered with two types of polymeric materials for removing Copper ions and lead from aqueous solution and industrial waste water. The first type is carboxymethyl-cyclodextrin (CM-CD) and poly ethylene glycol cyclodextrin polymer (PEG-CD).The second type is Hydrogel, based on 2-acrylamido-2-methyl-1-propansulfonic acid. This gel was synthesized via photo polymerization technique and used for the preparation of magnetic responsive composite hydrogels. The structure of the prepared materials was confirmed and thoroughly studied and correlated to their composition. Some modern techniques were used such as GPC , XRD, FTIR, TEM, and Flame Atomic Absorption Spectrometer. The thermal properties were studied via TGA in order to confirm the metallic content of these sorbents and investigate their durability at high temperatures. Comparing between the efficiency of nano sorbents under the same test conditions has been studied. The effect of several factors on the removal efficiency of these sorbents was studied. These factors involve effect of pH, temperature, contact time, gel structure, and presence of other cations to examine the selectivity of the prepared sorbents for the Copper ions if other cations were presented in the medium. It was showed that the removal process is the net result of two mechanisms: adsorption and absorption. The data proved that there is an optimum temperature for the magnetic nanocompsites at which they achieve maximum Copper removal as the removal efficiency of the micro-gels is temperature dependent. The effect of pH on the performance of both types of sorbents was investigated and showed limited efficiency at acidic pH and their removal performance was enhanced by increasing the pH of the medium until 5.5 after that value the solution precipitated. It was also found that the increase in the contact time between the sorbents and the ions improve the removal efficiency of the prepared sorbents. The data also showed that the increased crosslinker concentration reduces the probability of side reactions, which affect the crosslinking activity. The increase in maximum water sorption is related to the increase in the amount crosslinking agent MBA, EGDMA concentrations from 2 % to 7 % in all samples and thus improves the removal efficiency. The optimum temperature of the solution for reaching maximum adsorption was 45 0C. Maximum adsorption of metal ion was observed after 45 min. It was clear that the CD modified with PEG is more efficient than those modified with carboxy methyl because the metal affinity of PEG chain was greater than the metal affinity of carboxy methyl group. Furthermore, the adsorption process is spontaneous and exothermic in nature. The data showed that the tendency of the modified β-CD towards Pb2+ is more pronounced than Cu2+.