IONIC LIQUID (CYPHOS IL 102) FOR THE SEPARATION AND RECOVERY OF SOME TRANSITION METAL IONS

Abstract

Transition metals are necessary and valuable for rapid industrialization of emerging economies. Transition metals are extensively used in various alloys, electrical and electronic industries, petroleum refineries, electroplating industry and infrastructure construction owing to their unique properties, such as high melting and boiling temperatures, high density, good thermal and electrical conductivity and catalytic properties. Due to ever increasing demand, ceaseless exploitation of metal containing ore and mineral resources the primary mineral supplies are becoming more and more insufficient leading to increasing exploitation of secondary sources. In addition, the industries produce metal loaded effluents and improper disposal of these wastes becomes a key factor in metal contamination. The recovery or recycling of valuable metals from industrial waste will not only have an impact on the economy but partly help in environment protection. Liquid-liquid extraction also known as solvent extraction is an effective separation technique for the recovery of metal values. Solvent extraction permits very simple and clean separation of metals at both micro as well as macro concentrations, hence can be easily extended from bench level to plant scale. The technique is economically cheap as it does not require any sophisticated apparatus or instrumentation. Its applications extend to a wide range of industries such as chemical, metallurgical, nuclear, petrochemical, food, pharmaceutical as well as in waste management. It can be employed to concentrate and separate metal ions and to determine stoichiometry and stability of complexes extracted into an immiscible liquid phases. Over the years, a variety of commercial extractants such as carboxylic and sulphonic acids, chelating agents, organophosphorus compounds and high molecular weight amines have been employed for extraction, separation and recovery of different metal ions. Use of many of these extractants has been declined due to some of their drawbacks like water solubility, emulsion formation, poor selectivity, release of H+ ions into the aqueous phase and other hydrometallurgical considerations which adversely affect the extraction efficiency. Therefore, newer reagents are worth investigating to explore the possibility of obviating the aforementioned drawbacks. Lately, ionic liquids have emerged as a new class of extractants to overcome the above mentioned drawbacks. Ionic liquids have unique properties such as negligible vapour pressure, high thermal stability, non-flammability, good extraction power and strong hydrophobicity. In view of some inherent advantages and on the basis of literature survey the author has explored the iv potential of Cyphos IL 102 (trihexyl(tetradecyl)phosphonium bromide) for the extraction, separation and recovery of zinc, cadmium, molybdenum and vanadium. The effect of fundamental extraction parameters on the partition of metal ions has been studied. Based on the extraction trends optimum conditions for binary separations have been worked out. After generating the required extraction data the procedures have been developed to recover the metals from real matrices such as Zn-plating mud, spent Zn-C and Ni-Cd batteries, petroleum refinery spent catalyst and spent V2O5 catalyst. In addition, metal values have been recovered in the form of metal oxides from the loaded organic phase/strip solution in high purity. It may be important to point out here that the present efforts are focused to develop a suitable separation chemistry which can be conveniently scaled up at a plant scale. For the sake of clarity and convenience of presentation, the work included in the thesis is indexed in the following six chapters, I. General Introduction. II. Materials, Equipments and Methodology. III. Distribution Studies on Zn(II) and Cd(II) and recovery of Zn from zinc plating mud using Cyphos IL 102. IV. Recovery of Zn and Cd from spent Zn-C and Ni-Cd batteries using Cyphos IL 102. V. Distribution Studies on Mo using Cyphos IL 102 and recovery of molybdenum from petroleum refinery spent catalyst. VI. Distribution studies on V(V) and recovery of vanadium from spent V2O5 catalyst using Cyphos IL 102. Chapter I discusses about the increasing demand of metals and advantages of liquid-liquid extraction technique. A brief discussion on phosphonium based ILs and literature review on their use for the extraction, separation and recovery of various metals is presented. The aims and objectives of the present study are defined and a summary of the research work executed is given. v Chapter II includes details of chemicals, materials and equipments used during the course of present study. The distribution studies were carried out using Atomic Absorption Spectrometry (AAS)/Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The procedures adopted for distribution studies, dissolution of different matrices and the analysis of the data are explained. Chapter III embodies studies on Cyphos IL 102 for the extraction and recovery of cadmium(II) and zinc(II) from hydrochloric acid medium. The influence of phase variables such as concentration of H+, extractant and chloride ion, nature of acid (HCl, H2SO4 and HNO3), diluent and equilibration time and temperature on the extraction of Cd(II) and Zn(II) have been investigated. The stoichiometry of extracted metal species has been proposed. The saturation capacity, hydrolytic stability and recycling power of extractant have been evaluated. Various stripping agents have been tried for the stripping of Cd(II) and Zn(II) from the loaded organic phase. In addition to Cd(II) and Zn(II), the partition behavior of associated metal ions namely, Mn(II), Fe(II), Ni(II), Co(II) and Fe(III) from chloride medium at different acid molarities has been investigated. Binary separations of Cd(II) and Zn(II) from each other and other associated metal ions have been achieved. Based on the extraction data a separation scheme is designed and applied to a synthetic mixture. The developed separation scheme has been successfully applied to zinc plating mud for the recovery of Zn(II). Chapter IV includes separation and recovery of zinc and cadmium from spent batteries. The influence of extractant concentration for the leach liquor of Zn-C and Ni-Cd batteries has been investigated. Mc-Cabe Thiele extraction and stripping isotherms have been drawn for the quantitative extraction and recovery of Zn and Cd at different aqueous:organic (A:O) phase ratios. Simultaneously, counter current extraction and stripping simulation were carried out to confirm the data obtained from Mc-Cabe Thiele diagrams. Besides ZnO and CdO are synthesized using the loaded organic phase and characterized using XRD, FE-SEM and EDX techniques. Chapter V presents extraction, separation and recovery of Mo(VI) from hydrochloric acid medium. The influence of fundamental extraction variables on Mo(VI) extraction has been evaluated. Loading capacity, hydrolytic stability and recycling capacity of the extractant have also been evaluated. Binary separations of Mo(VI) from other associated metal ions have been achieved vi with high separation factors. Optimized conditions have been employed for the extraction and recovery of Mo(VI) from petroleum refinery spent catalyst leach liquor. Quantitative and selective extraction of Mo from spent petroleum refinery catalyst was achieved in two stages at aqueous:organic phase ratio of 3:2. Quantitative stripping of Mo was obtained with 1.0 mol/L (NH4)2CO3 in two stages at O:A=1:1. Molybdenum trioxide was prepared by thermal decomposition from stripped solution and characterized by XRD, FESEM and EDX techniques. Chapter VI includes distribution studies on V(V) from sulphate medium. The influence of different extraction variables on V(V) extraction has been evaluated. Different stripping agents have been examined for back extraction of vanadium. Hydrolytic stability, loading and recycling capacity of the extractant have been determined. Partition behavior of associated metal ions namely Mn(II), Fe(II/III), Al(III), Cr(III), Ti(IV), Mo(VI) and W(VI) is investigated. The extraction data offer conditions for the binary separation of V(V) from associated metal ions with high separation factors. Optimized parameters have been employed for the extraction and recovery of V(V) from spent V2O5 catalyst. To find out the number of stages required to achieve quantitative extraction/stripping of vanadium, McCabe-Thiele plots were drawn, which were further verified by counter current simulation studies. Vanadium oxide has been synthesized using thermal decomposition and characterized by XRD, FESEM and EDX techniques. The thesis concludes with a brief discussion on the findings of the present investigations. The work presented in the thesis has been able to suggest simple separation and recovery procedures for Zn(II), Cd(II), Mo(VI) and V(V), using a commercial extractant Cyphos IL 102. The bench level studies indicate that equilibration is fast, phase separation is quicker and no additional modifier is required. Moreover, the extractant has high loading capacity and can be recycled up to several cycles. These investigations suggest that Cyphos IL 102 has the potential to conveniently recover zinc, cadmium, molybdenum and vanadium from spent electronic/industrial waste. The proposed procedures can be easily scaled up at the plant scale with some additional inputs.