Ion Exchange Properties of Metal (III) Phosphates

Abstract

The presence of metals in portables waters, domestic wastewater and industrial effluents is a subject of serious concern to communities and municipalities. The heavy metals discharge in waste – waters above certain limits have a toxic effect on both human and aquatic life. The tremendous increase in industrial activity, ubiquitous nature of heavy metals, their extreme toxicity even in trace quantities, their tendency for bio-accumulation in food chain and their growing population have become a matter of great public concern throughout the world. The environmental protection agencies (EPA) and the other regulatory agencies have set limits on the concentration of all the metals commonly encountered in industrial wastewater streams. This demands the industries to treat their effluents in order to reduce the level of metals in the discharge streams within the stipulated limits and fulfil the requirements to obtain discharge permit. A number of processes for the separation of these metals from water are practised and many more are being in progress. Good amount of efforts are also being made to improve and apply already existing and well established technologies to solve specific problems. However, several problems still exist, both economic and technical, concerning the removal of metal ions from the wastewater. The ion exchange is by far the most rapid, effective and versatile technique, which demand the less skills then those of others. Today, a wide array of improved organic and inorganic ion exchangers with a great variety of properties are used in industries. About 90% of all ion exchangers produced are used in water treatment. The ion exchange process is the only way to prepare highly pure water essentials for electrical power generation and electronics components manufacture. The ions exchangers have also found special utility in hydrometallurgy, medical research, food technology and agriculture. Sugar juices and syrups are being softened, decolorized and deionized by means of ion exchange. In nuclear power plants the ion exchangers are used to purify the water entering and leaving the reactors. Moreover, an extensive literature is available about the exchange of metal ions on inorganic/organic ion exchange materials including phosphates of zirconium and titanium. The zirconium and titanium phosphate exhibit ion exchange properties and are regarded as the best exchangers for the removal of corrosion products from reactor cooling water, separation of radioisotopes, actinides, and divalent ions and are also used as sorbents in biological systems. However, very little is known about the separation properties of other metal phosphates like iron, chromium, aluminium and titanium phosphates. The metal (III) phosphate are highly insoluble solid materials and are of great significance in water purification and also play an important role in corrosions of metals and alloys. The phosphorus of the present study was therefore to investigate the sorption properties of the metal (III) phosphates toward the metal ions under different experimental conditions of temperature, concentration and PH of the system etc., etc. It was concluded during the present investigation that all the three metal (III) phosphates have appreciable exchange capacities toward the metal cations like Cr^3,Pb^2,Cu^2,Zn^2,Ni^2,Co^2,Fe^2,Cd^2,Mg^2,K^1,Na^1,and Li^1 ions and can be used as scavengers for these metal cations in both the acidic and alkaline solutions. Further, the present studies revealed that all the three metal phosphate are highly selective toward the Pb^2 ions being one of the well-known pollutants specially in the roadside soil of our country. The present studies thus confirmed the ion exchange behaviour of the metal and as such they may find their use in water softening and deionization, in the separation and isolation of actinides, radioisotopes, divalent and monovalent ions, in industries specially in reducing the corrosion of metal alloy and also in biological system etc. The following work was done during the course of the present investigations The samples AIPO4, CrPo4 and FePO4 were synthesized in the laboratory. All these three samples of metal (III) phosphate were then characterized by using different physico-chemical techniques, such as FTIR, ERD, Electron probe Microanalysis, Atomic absorption spectrometer, Spectronic 20D and Surface area. The potentiometric titration studies of AIPO4, CrPO4 and FePO4 in the presence of alkali, alkaline earth, divalent transition metals and trivalent metal ions were carried out. The sorption studies of AIPO4,CrPo4 and FePO4 in the presence of Cr^3,Pb^2,Cu^2,Zn^2,Ni^2,Co^2,Fe^2,Cd^2,K^1 ions were also undertaken as a function of pHs, concentration and temperature of the system. The desorption of Zn^2 from the Zn enriched sample was studied as a function of pH. The spectroscopic studies such as FTIR, EPM, and SEM were also performed before and after sorption of metal ions on the metal (III) phosphates. Data Evaluation: The data was evaluated using Henderson-Hasselbalch and Kurbatov equations. Applying the Langmuir formalism, a modified form of the isotherm was developed and was applied successfully to the data. Publications: Based upon the data presented here, two papers have published in the foreign International journals. The references of which are as under: J. Colloid and interface Science (U.S.A), 220, 63-70 (1999) Adsorption science and Technology (U.K), 17, 715-727 (1999) The reprints of these two papers are also included with this report. In addition, currently two more papers from the data of this project are under the preparation, which would be submitted soon for publications.