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...
Dissolution of mercury in aqueous solutions of sodium hypochlorite at pH 5.9 38.5, the corresponding reaction order, and the mechanism of this process were studied. The ratio of the rates of mercury oxidation and sodium hypochlorite decomposition was analyzed.Salts of hypochlorous acid, hypochlorites, find wide application as strong oxidizing agents, their oxidizing power being largely determined by the acidity of the medium.The aim of this study was to assess the possibility of using a sodium hypochlorite (NaClO) solution at pH 5.9 3 8.5 for oxidation of mercury and to determine the rate constants of mercury dissolution via its oxidation to Hg 2+ ions in the above-mentioned acidity range. EXPERIMENTALMercury was oxidized with an aqueous solution of NaClO at pH 5.9, 6.5, 6.9, and 8.5 and temperatures of 25 and 50oC; the concentration in terms of active chlorine was 0.3 3 0.8 M. The required acidity was created with a buffer phosphate solution obtained by adding orthophosphoric acid, potassium dihydrophosphate, and sodium hydrophosphate to the NaClO solution. The pH value was monitored with an EV-74 ionometer with glass and silver chloride electrodes.The NaClO solution was produced by passing chlorine through a carbonate-free solution of sodium hydroxide at a temperature of 35_0oC. The reaction vessel was cooled with a mixture of sodium chloride and ice. Chlorine was obtained by reacting chemically pure hydrochloric acid with potassium permanganate. The concentration of the hypochlorite was determined iodometricaly.A mercury drop of mass 0.053 0.15 g was placed in a hermetically sealable glass jars thermostated at 25 and 50oC, and 50 ml of a sodium hypochlorite solution with certain acidity was added. The Hg 2+ concentration was determined at regular intervals of time by a selective spectrophotometric technique with dithizone [1]. The optical density of the solutions was determined with a KFK-2 photoelectric colorimeter.Mercury is a metal that is liquid at room temperature. The high surface tension allows even comparatively large mercury drops to take the shape of a sphere, the body with the smallest relative surface area. Dissolution of mercury is a heterogeneous process that occurs at the interface and depends on the area and state of the surface. Kinetic characteristics of the process of mercury dissolution in sodium hypochlorite solutions were determined using the formula established experimentally by A.N. Shchukarev for the rate of dissolution of a solid body in a liquid [2,3]. This formula made it possible to calculate the rate constant k of mercury dissolution:where w is the dissolution rate; S, area of contact between the solid and liquid; c, concentration of the substance being dissolved in the bulk of the liquid; c s , concentration of a saturated solution; and k, constant for the given experimental conditions.As the concentration of a saturated solution was taken the maximum possible concentration of Hg 2+ ions. The latter was determined from the mass of the mercury drop and the volume of the hypochlori...
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