The Complex Dynamics And Mechanism Of The Oxidation Of Sulfide

In the thesis, we studied the complex dynamics of the oxidation of sulfide by the bromate and chlorite in aqueous solution in a batch reactor and a continuous - flow stirring tank reactor. The oxidation reactions of sulfide by the bromate and chlorite can exhibit autocatalytic production of pH clock, bistability, and sustained oscillations in pH and redox potential. Computer can simulate the complex dynamics behavior observed during the experiment. Their application of ore flotation has been studied.1. The oxidation of sulfide by the bromate Large-amplitude changes in pH (2.5 pH units) and potential (250 mV) of a platium electrode has been measured during the oxidation of sulfide by bromate ion in in a batch reactor. In basic medium, there is an initial rise in pH followed by a drop. The source of the oscillation in this simple chemical reaction is a two-way oxidation of HS^-/H₂S by the BrO₃^-: a hydrogen ion consumption by oxidation to sulfur (0), and a hydrogen ion production by oxidation of sulfur (0) to S₂O₃^2-, which is shown here by capillary electrophoresis to be an important final oxidizing product of oxidation of S ( 0 ) by BrO₃^-. A simple reaction scheme, consisting of the protonation equilibria of HS^-and S^2-, HS^- and H₂S, H⁺and OH- , the oxidation of HS^-/H₂S by the BrO₃^- to S (0), the oxidation of S (0) to S₂O₃^2-(â…¡) has successfully been used to simulate the observed dynamical behavior.In acidic medium, there is an initial drop in pH followed by an induction period and by an autocatalytic drop. The source of the oscillation in this simple chemical reaction is a two-way oxidation of HS^-/H₂S by the BrO₃^-: a hydrogen ion consumption by oxidation to sulfur(0), and a hydrogen ion production by oxidation of sulfur(0) to SO₃^2-, while oxidation of HSO₃^- to SO₄^2- produces H⁺ in an autocatalytic manner. A simple reaction scheme, consisting of the protonation equilibria of HS^-and S^2-, HS^- and H₂S, SO₃^2- and HSO₃^-, H⁺ and OH- , the oxidation of HS^-/H₂S by the BrO₃^- to S (0), the oxidation of S (0) to SO₃^2-(â…£) , and oxidation of HSO₃^- to SO₄^2- has successfully been used to simulate the observed clock behavior and bistability in acidic medium.2. The oxidation of sulfide by chlorite Sustained oscillations in pH and redox potential are obtained in the chlorite-sulfide system in a continuous-flow stirred tank reactor (CSTR). The source of the oscillation in this simple chemical reaction is a two-way oxidation of HS^-/H₂S by the ClO₂^-: a hydrogen ion consumption by oxidation to sulfur (0), and a hydrogen ion production by oxidation of sulfur (0) by OCl-/ClO₂^- to S₂O₃^2-, and oxidation of S₂O₃^2- by ClO₂^- to SO₃^2-(â…£), while oxidation of HSO₃^- to SO₄^2- produces H⁺ in an autocatalytic manner. A simple reaction scheme, consisting of the protonation equilibria of HS^-and S^2-, HS^- and H₂S, SO₃^2- and HSO₃^-, OCl- and HOCl, H⁺ and OH- , the oxidation of HS^-/H₂S by the ClO₂^- to S₈(0), the oxidation of S₈(0) to S₂O₃^2-(â…£) , and oxidation of S₂O₃^2-(â…£) by ClO₂^- to SO₃^2- , and oxidation of HSO₃^- to SO₄^2- has successfully been used to simulate the pH oscillatory behavior observed in a CSTR. Temperature is found to have a significant effect on the oscillatory behavior and shows Arrhhenius-like behavior. The value of Ea=87.3 kJ·mol^-1 was obtained for the apparent energy of the oscillations.Autocatalytic oxidation of HSO₃^- by ClO₂^- is the major source of positive feedback of hydrogen ions. The reaction between H₂S and ClO₂^- formation S8, which consumes H⁺, is an important source of negative feedback. A mechanistic model consisting of 5 protonation-deprotonation equilibria and 9 redox reactions is proposed for the oscillatory reaction between S^2- and ClO₂^-. The 11 species included are HS^-, H₂S, S8, S₂O₃^2-, SO₃^2-, HSO₃^-,OCl^-, HOCl, ClO₂^-, H⁺ and OH-. In contrast to the H₂O₂–S^2- oscillation reactions, S₂O₃^2- is shown here by capillary electrophoresis to be an important intermediate. Simulations give excellent qualitative agreement with the pH oscillatory behavior observed in a CSTR .3. pH– Control by Using marble The shape, the periodic time, the region of pH changes can be controlled by using different amounts and grade size of solid granular or lumpy marble. The shape, the periodic time, the region of pH changes can be controlled by using a magnetic stirrer bar with different rpm . The smaller of grade size of solid granular or lumpy marble , the larger of pH changes in region. The larger of the stirring rate, the larger of pH changes in region. Solid granular or lumpy marble used by removal of the H⁺ from the oxidation of sulfide by the bromate ion in the CSTR. A possibility of the new technology of the pH-control has been recognized in ore flotation.