Kinetics of dehydration of sodium hydroxide melt upon evacuation was studied in relation to the temperature. The kinetic parameters of thermal decomposition of NaOH were evaluated. Methods for dehydration of the hydroxide melt were suggested.

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Complexation of lead(II) ions with hydroxide ions in nitrate-chloride solutions at 298 K was studied using potentiometric titration.The search for the optimal composition of the alkaline electrolyte is an important technological task in processing of scrap lead accumulators with an active paste containing lead(II) oxide [1].The high solubility of PbO in alkaline solutions is known to be due to formation of strong lead(II) hydroxide complexes [2,3]. The presence of both organic and inorganic admixtures and, in particular, chlorides in alkaline solutions strongly affects the complexation of lead(II) ions [135]. For example, it was found in [4] that mixed lead(II) hydroxidechloride complexes are formed at low alkali concentrations (<0.4 M) in a solution containing a mixture of sodium chloride and hydroxide.Proceeding with the studies [4, 5], we examined the complexation of Pb(II) in mixed nitrate-chloride solutions containing sodium hydroxide as an additive in order to analyze the effect of the concentration of chloride ions on the formation of lead hydroxide complexes and, if possible, to determine the composition of mixed chloride-hydroxide complexes. EXPERIMENTALThe complexation of lead(II) ions was studied by potentiometric titration at 298 K. The experimental technique and the electrochemical cell have been described earlier [4,5].We used as a supporting electrolyte aqueous solutions containing a mixture of sodium nitrate (0.3 3 1.0 M) and sodium chloride (0 3 0.7 M) with concentrations that allowed us to obtain a solution with an ionic strength equal to unity (in the limiting case, no sodium chloride was present, and the nitrate concentration was 1.0 M).The potentiometric titration was carried out with a sodium hydroxide solution containing sodium chloride, the concentrations of NaOH and NaCl being equal to the concentrations of NaNO 3 and NaCl, respectively, in the supporting electrolyte. This allowed us to maintain a constant ionic strength in a solution under study during all the experiments.The half-cell of the electrochemical cell under study can be represented as:ÄPb(Hg)³Pb(NO 3 ) 2 , NaNO 3 , NaOH, NaCl, (1) where Pb(Hg) is a lead amalgam electrode.A typical dependence of the potential of the amalgam electrode on the logarithm of the alkali concentration in solutions containing sodium chloride is shown in Fig. 1. It can be seen that the E3ln c OH ! Fig. 1. Potential of the indicator electrode, E, vs. the logarithm of the total concentration of hydroxide ions ln c OH ! in solution. Supporting electrolyte (M): 0.7 NaNO 3 + 0.3NaC1 + 1 10 !3 Pb(NO 3 ) 2 . (c OH !) Total concentration of hydroxide ions.

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