Oscillatory concentration pulses of some divalent metal ions induced by a redox oscillator

Abstract

Oscillations in the concentration of divalent ions Cd²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Ni²⁺ are induced by adding these species to the BrO₃⁻–SO₃²⁻ chemical oscillator in a flow reactor. Producing periodic pulses in the concentrations of these non-redox ions extends our earlier approach to generating forced periodic behavior. Instead of driving pH-dependent equilibrium reactions of the target ion by a pH oscillator backward and forward, we now couple a redox core oscillating reaction to two consecutive reactions taking place between the components of the oscillator and the target element. In the systems examined here, the oscillatory reductant SO₃²⁻ binds the free metal ion in a MSO₃ precipitate, reducing its level to a minimal value when [SO₃²⁻] is high, followed by release of the metal ion when the sulfite is oxidized by BrO₃⁻.