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Applications of Topological Indices to Structure-Activity Relationship Modelling and Selection of Mineral Collectors

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Applications of Topological Indices to Structure-Activity Relationship Modelling and Selection of Mineral Collectors Indianloumal of Chemistry Vol. 42A, June 2003, pp. 1330-1 346 Applications of topological indices to structure-activity relationship modelling and selection of mineral collectors Ramanathan Natarajan*, Palanichamy Kamalakanan & Inderjit Nirdosh Department of Chemical Engineering, Lakehead University, Thunder Bay, Ontario, Canada P7B 5EI Received 8 January 2003 Topological indices (TI) are extensively used as molecular descriptors in building Quantitative Structure-Activity Relationships (QSAR), Quantitative Structure-Property Relationships (QSPR) and Quantitative Structure-Toxicity Relationships (QSTR). We have appli ed the QSAR approach for the first time to froth flotation and :nodelled the separation efficiencies (Es) of four seri es of coll ectors namely, cupferrons, o-aminothiophenols, mercaptobenzothiozoles and ary lhydroxamic acids used for the beneficiation of uranium, lead, zinc and copper ores, respectively. Principal components extracted from topological indices are found to form linear regression equations th at can predict the separati on efficiencies of the first three classes of coll ectors. Inclusion of substituent constant or quantum mechanical parameters did not improve th e fit and th is may be due to the absence of large variation in electronic effects among the molecules in each class. A quadratic fit has been obtained instead of linear regression in the case of arylhydroxamic acids. The separation efficiencies -of the members have been predicted within experimental error (±5%) by the best regression equations in each series. From the statistical models built, it may be generalized that Es = f(TI). To extend the applications of TI in the field of mineral processing, a similarity space of 587 arylhydroxamic acids has been constructed usi ng principal components extracted from Tis. Ten compounds have been selected for synthesis and testing. The approach appears to provide an efficient scientific tool for the selection of collectors from a vi rtual database and may lead to an inexpensive and quick method for the identification of new collectors. Introduction (QSTR). These models are used in predicting toxicity of chemicals. Well established QSTR models can be QSAR modelling 1o Quantitative Structure-Activity Relationship used to predice· the toxicity of not only the known (QSAR) and Quantitative Structure-Property but also the hypothetical compounds. Relationship (QSPR) studies are mathematical QSARs/QSPRs/QSTRs have become powerful tools in contemporary chemical and medicinal research, as quantification, which are extensively used 111 pharmaceutical and agricultural chemistry for they have made it possible to predict the biological screening compounds to be tested for specific activity, specific chemical activity, toxicity and the 3 environmental fate of a chemical even before its activit/- . Regression models have been developed to correlate an experimentally determined property or synthesis. 4 5 biological activity to the molecular structure • . The descriptors used in QSAR models are empirical, Topological indices as molecular descriptors theoretical, physicochemical properties6 and quantum To develop QSAR models with good predictive mechanically calculated parameters.7 Once a ability appropriate molecular descriptors have to be correlation between structure and biological activity chosen. A molecular descriptor aims at mathematical or a physicochemical property is established, it is characterization of a molecular structure or a specific characteristic of the structure as completely as possible to predict the activity/property of any number of structurally related compounds including those that possible. Molecular Connectivity Indices (MCI) are 2 8 9 the most widely used molecular descriptors. These are yet to be synthesized and tested • • . molecular meters, MCI, are known as graph invariants The regression models where toxicity of a chemical due to their formulations from the concepts of graph replaces the biological activity are sometimes referred theory and are more commonly referred to as to as Quantitative Structure-Toxicity Relations Topological Indices (TI) as they describe the topology of a molecule. The term topological indices (TIs) is *Perrnanent address: Campion Higher Secondary School, Tiruchirappalli, Tamil Nadu, India 620 001. used hereafter to refer to MCls in this article. The 8 10 email: [email protected] large number of models developed • with TIs prove NAT ARAJAN e/ al.: APPLICATIONS OF TOPOLOGICAL INDICES 1331 that several properties can be expressed as a function CheLating agents as mineraL collectors of topological indices. TIs are fundamental in nature Chelating agents attach themselves to a mineral and easily computable using simple mathematical surface by chelate formation. The chelating tendency tools owing to their conceptual simplicity. There is a of the compounds is higher for transition metals large number of TIs in use from simple connectivity which are rendered hydrophobic in preference to indices to 3D descriptors to orthogonal descriptors. A alkali and alkaline earth metals. The valuable recent review by Pogliani II explains the trend in the minerals are normally compounds of transition and graph theoretic descriptors. inner transition metals while the gangue and clay minerals are that of silica, calcium and aluminum. This makes chelating agents to perform better than Background on froth flotation conventional collectors and has therefore attracted 12·22 Mineral processing industry is facing a tougher attention as mineral collectors in flotation research. situation due to the exhaustion of high-grade ores and Table 1 lists the types of chelating agents tested to a steady decrease in the grade of existing low-grade float different types of minerals. Chelating collectors ores. Flotation is widely used to recover minerals suffer from two main defects: (i) absence of long from low-grade ores. The low selectivity of mineral­ hydrocarbon chain in their molecules and (ii) collectors currently in use and their limitations in prohibitively high cost effectively floating non-sulphidic minerals, increase Marabini and coworkers23 and Nirdosh and the complexity of the situation. This research focuses coworkers24 had demonstrated that the first defect on using concepts of QSAR approach in developing could be overcome by new synthesis methodologies. mineral collectors that are more selective for their Once it is established that a particular chelating agent application in froth flotation. enjoys good selectivity and has promise to be used, its Pre-concentration is an inevitable step in the production in bulk would be potentially economic. economic recovery of a metal from a low-grade ore. Froth flotation is the most widely used process in this SeLection of cheLating agents beneficiation step. Though it was initially developed The molecule of a chelating collector has two parts to concentrate sulphides of base metals, it has now viz., the chelating group (hydrophilic part) and the been expanded to float oxides and oxidized minerals hydrocarbon backbone (hydrophobic part). Though and non-metallic minerals such as phosphates, the chelating group can be decided from literature and fluorites and fine coal. Organic compounds called experiments done in solvent extraction (liquid-liquid collectors are added to a slurry of a finely ground ore extraction) of metals from process and waste to impart hydrophobicity to the minerals. When air is solutions, and also from solution chemistry of metal passed through such a slurry, the hydrophobic mineral ions and their interaction with various chelating particles adhere to the air bubbles. The mineralized air agents, one has to bear in mind that the metal ion bubbles rise to the surface of the slurry. To prevent under consideration in a mineral being floated is not the mineral falling back into the slurry, a frother is present as a completely free metal ion. Rather, it is added to the dispersion. The hydrophobized mineral present on the surface of the mineral as a unionized collects in the froth as the concentrate and is entity with only some of its valencies liberated during periodically removed. In addition to collectors and . grinding. Therefore, a chelating agent, which is a frothers, other auxiliary chemicals are also added to selective extractant for afree metal ion, may not be a modify the pH or the surface properties of the mineral selective collector for the mineral of the same metal. to effect the selective separation. For example thenoyltrifluoroacetone, a good Among the various types of chemicals used, the extractant for uranium ion, was not found to function collectors play the most significant role and the as a good collector for uranium minerals?5 It is true efficiency of mineral separation and recovery depends also for tributylphosphate (TBP).25 Marabini26, 27 had on the selectivity of the collector. Petroleum laid down a guideline to choose the chelating group sulphonates and carboxylates were used as collectors based on conditional constants. Conditional constants in the early days of flotation. These collectors lack in are nothing but modified form of thermodynamic selectivity because they act by physisorption. The stability constants where concentrations of limited selectivity shown in remote cases is obtained hydroxylated metal ion and protonated-ligand are only by varying pH because the point of zero charge used instead of the concentrations of free metal ion (pzq varies from mineral to mineral. and ligand: 1332 INDIAN J CHEM,
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