Spontaneous Decomposition of Industrially Manufactured Sodium Hypochlorite Solutions

Abstract

Spontaneous decomposition of industrially manufactured aqueous solutions of sodium hypochlorite was studied. The rate constants of the decomposition reactions were calculated for different pH values.In view of the exceedingly high toxicity and volatility of metallic mercury (MPC for habitats 0.0003 mg m !3 ) [1] and its wide use, the problem of efficient salvation in tackling with possible mercury spillage events remains a matter of current interest. For this purpose, new demercurization methods are being developed and the already existing techniques are being improved. At present, the most widely used methods are those in which mercury is oxidized with strong oxidizing agents [2,3]. In developing a demercurizer, with industrially manufactured sodium hypochlorite (HC) solutions as an oxidizing agent, it became necessary to assess the stability of solutions of this kind in storage and to study the oxidizing activity of these industrial solutions at various pH values.HC solutions are nonequilibrium systems that undergo spontaneous decomposition. The problem of spontaneous decomposition of HC solutions has been extensively studied. The influence exerted by the concentration, temperature, and acidity on decomposition processes has been analyzed and the possible mechanisms and kinetic characteristics of decomposition have been reported [4 38]. In the known studies, solutions of both calcium and sodium HC were examined. Model solutions have been mostly studied, with the HC solutions having low concentrations: 0.013 0.20 M in terms of active chlorine.The aim of this study was to assess the stability of industrially manufactured concentrated HC solutions in order to determine the maximum shelf life of solutions of this kind. Another goal was to determine the kinetic characteristics of real solutions used to prepare the demercurizing agent.The choice in developing the demercurizer was made in favor of sodium HC, taking into account its availability as a solution, high content of active chlorine, and high stability against decomposition in an alkaline medium (compared with calcium HC) [9]. The behavior of the solutions was analyzed at two temperatures, 25 and 35oC, in view of the regional climatic conditions (the maximum summer temperature is not, as a rule, higher than 35oC). EXPERIMENTAL As object of study served industrially manufactured (Berezniki Soda Plant Open Joint-Stock Company) sodium HC solution with a concentration of 180 3 200 g l !1 in terms of active chlorine. Model solutions were prepared by passing at (0 35oC) Cl 2 obtained by reacting chemically pure hydrochloric acid with KMnO 4 through a NaOH solution containing no carbonates. The excess amount of the alkali was about 20 g l !1 . The reaction vessel was cooled with a mixture of NaCl and ice. The pH values of the solutions were measured with an EV-74 ionometer with glass and silver chloride electrodes.In stability studies, the alkaline (pH 13.5) HC solutions under study were thermostated in hermetically sealed polyethylene jars for 3 months. The pH value...

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“…Hypochlorites, both in the form of solutions and in the crystalline state, are more stable compared to hypochlorous acid [22][23][24][25]. Highly concentrated solutions of sodium hypochlorite are one of the main commercial products of this class, which are widely used as bleaching agents and disinfectants.…”

“…Hydrates are more stable, but still under normal conditions spontaneously decompose. Hypochlorites of alkali and alkaline earth metals are well soluble in water (g/100 g H2O at 20 °C): LiOCl -72; NaOCl -54.3; Ca (OCl)2 -33.3 [22].…”

“…As noted above, the possibility of dissociation of HClO or H2OCl + by the main type (HClO → OH -+ Cl + and H2OCl + → H2O + Cl + ) has not been found experimentally. However, in acidic solutions and especially in the presence of excess chloride ions, the formation of protonated H2OCl + particles can be considered as an intermediate in the intermolecular oxidationreduction reaction: (22) According to this scheme, the reaction of combined oxidation and reduction of chlorine atoms is essentially the result of the movement of the chlorine atom in the activated complex from hypochlorite to chlorine anion. Therefore, the addition of a hydrogen ion can be considered as a process that initiates the processes of breaking the O-Cl bond and the simultaneous formation of the Cl-Cl bond.…”

Potentiometric Determination of Chlorate Impurities in Hypochlorite Solutions

“…However, in the process of synthesis, as well as during long-term storage, chlorites and chlorates accumulate in solutions. They form due to disproportionation and interaction with impurities in the solution, especially with iron-group metal ions which act as catalysts for the decomposition of hypochlorite [4, 5]. The rate of accumulation of chlorites and chlorates during storage depends on many factors: a solution composition, pH, temperature, the action of light, and a container material.…”

Generation of Pure Oxygen from Briny Water by Binary Catalysis

“…Nonetheless, anion rejection alone cannot explain the OER selectivity of FeO x ∧CoP i , which produces pure O 2 . No current is observed for ClO − at the ring (Figure 4), nor is any ClO − detected by chemical analysis, suggesting the decomposition of ClO − by the FeO x overlayer, consistent with Fe(III) oxy(hydroxide) to accelerate hypochlorite decomposition 36 and the iron ion to be especially effective at promoting ClO − disproportionation to Cl − and O 2 under oxidizing conditions. 37 To assess if the FeO x overlayer, in addition to halide anion rejection, promoted ClO − decomposition, RRDE experiments were performed on 1 mM NaClO solutions (Figure S14) with a glassy carbon disk electrode overlaid with MO x .…”