Unexpected Phenomena in the Mercury(II)−Chlorite Ion System:  Formation and Kinetic Role of the HgClO₂⁺Complex

Abstract

On the basis of time-resolved spectrophotometric measurements, the formation of a novel chlorito complex, HgClO2 +, was confirmed under acidic condition in the mercury(II)−chlorite ion system. The complex formation occurs within the dead time of the stopped-flow instrument applied (τd ∼ 1 ms). The stability constant of HgClO2 + was determined from the initial part of the kinetic traces recorded at the characteristic 325 nm absorbance maximum of the complex: K = 41.7 ± 1.9 M-1, ε325 = 727 ± 24 M-1 cm-1 (I = 1.0 M (NaClO4), 25.0 °C). An intense formation of chlorine dioxide was observed which is due to mercury(II)-catalyzed decomposition of chlorite ion. At longer reaction times, when most of the chlorite ion is consumed, the concentration of chlorine dioxide abruptly drops to its final value. This unique feature of the reaction is attributed to an autocatalytic redox cycle which is initiated by an electron transfer step between the coordinated chlorite ion and chlorine dioxide. The proposed mechanism postulates the formation of a Cl(II) intermediate which rapidly oxidizes both ClO2 - and ClO2.

Simultaneous Removal of SO2 and Hg0 by Composite Oxidant NaClO/NaClO2 in a Packed Tower

“…When factors such as pH and temperature in the absorbing liquid changed, a series of decomposition reactions occurred. Based on the experimental results from Zhao et al’s and Fábián et al’s studies, 40 , 41 the ionic components in the NaClO/NaClO 2 solution were mainly ClO 3 – , ClO 2 – , ClO – , and Cl – . Under acidic conditions, the redox potentials of ClO – /Cl – , ClO 2 – /Cl – , and ClO 3 – /Cl – were 1.48, 1.57, and 1.45 V, respectively.…”

Removal of Hg0 with sodium chlorite solution and mass transfer reaction kinetics

“…This conclusion was confirmed in Figure 3. Fábián et al [15] reported that a novel chlorite complex HgClO 2 + played also an important role during the oxidation of Hg 0 . In order to further reveal the reaction mechanism, two parallel samples were taken from the bubble reactor, and the concentration of Hg 2+ in the spent absorption solution was determined.…”

“…By combining the discussions mentioned above and results of removal product analysis, and by referring to previous research results [15], the reaction mechanism for removing Hg 0 by acidic NaClO 2 solution was proposed as follows: 2 2 ClO H HClO …”

Experiments on and mechanism of simultaneous removal of Hg0, SO2 and NO from flus gas using NaClO2 solution

“…When the concentration of hydrogen ion (H + ) increased, the transient amount of ClO 2 decreased and the reactions become faster. Fábián et al [13] reported the formation of a novel chlorite complex, HgClO 2 + , and showed that this species played a significant role in the consumption of ClO 2 .…”