Quantum-chemical substantiation of the properties of the bioreagent oxidizing non-ferrous metal sulfides

Abstract

The paper determines the structural formula and quantum chemical characteristics of the most energetically probable, stable conformation of the bioreagent molecule formed during the oxidation of iron (II) ions by the autotrophic mesophilic iron-oxidizing bacteria Acidithiobacillus ferrooxidans in a solution of sulfuric acid consisting of iron (III) ion and three acid residues of glucuronic acid. The bioreagent oxidant is widely used in the industry for leaching metals from non-ferrous sulfide ores and enrichment concentrates. The quantum chemical characteristics of the bioreagent molecule are analyzed in comparison with the characteristics of anhydrous iron (III) sulphate, also used in hydrometallurgy as an oxidizer. The structure and quantum-chemical characteristics are studied using the method of molecular computer simulation, the theory of boundary molecular orbitals, and the Pearson principle. It has been established that the most energetically probable, stable conformation of the bioreagent molecule contains the acid residues of glucuronic acid of a non-cyclic structure. According to the research results, the bioreagent refers to the more rigid Lewis acid – electron acceptor – than iron (III) sulphate. The bioreagent molecule is less polarized, characterized by lower absolute electronegativity and 2 times larger volume. A theoretical substantiation of the greater persistence of primary sulphides – pyrite, pentlandite, chalcopyrite, relative to the secondary minerals – pyrrhotine, chalcocite and covellite is proposed based on the calculated values of the boundary molecular orbitals, absolute stiffness and electronegativity of iron, copper and nickel sulfides. The bioreagent characteristics that determine the interaction efficiency – volume, heat of formation, steric energy and its components, total energy, etc. are many times greater than for Fe2(SO4)3. The high oxidative activity of the bioreagent relative to Fe2(SO4)3 can be justified by the higher partial charge of the iron atom, the greater length of bonds between atoms, the lower energy of the lower free molecular orbitals and the greater degree of charge transfer during the interaction of the bioreagent with the sulfide minerals.