La gestión con el INDA para lograr la adjudicación de las tierras

complex as to be virtually impossible to achieve. The results of any model study will therefore be somewhat limited. Modelling of this kind does however provide qualitative information concerning the process and may suggest alternative quantitative approaches to the actual steelmaking problem.

3.2 * Preliminary Experiments

3.2.1 The reaction between sodium amalgam and water

For the initial experiments, small quantities of amalgam were pro­ duced by dissolving sodium metal in mercury under a layer of liquid paiaffin to prevent oxidation. Prior to use, the excess paraffin was

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removed with a pipette and the amalgam surface washed with petroleum ether. This too was removed with a pipette.

The reaction between sodium amalgam and distilled water proved

to be very slow. 25 ml samples of amalgam, containing initially 0.6 wt.$Ha were allowed to react with approximately 50 ml. of distilled water in a 100 ml. beaker. Without agitation, the removal of sodium took several weeks to go to completion.

The hydrogen evolved by the reaction between sodium and water

appeared to accumulate on the surface of the amalgam as a raft of bubbles at the centre of the bath. These tended to leave the raft in a steady stream from one or two localised areas. It was interesting to note that hydrogen bubbles appeared to be capable of nucleating and growing at the interface between the amalgam and the beaker. Once a bubble reached some critical size it appeared to rise up the interface between the amalgam and the beaker, cross the amalgam meniscus and join the raft on the surface

This type of behaviour is probably further evidence in favour of Frumkin* s suggestion that a glass surface may catalyse the reaction between sodium amalgam and water. Since mercury does not wet glass, a thin film of water can probably exist between the surface of the beaker and the amalgam. The solubility of hydrogen in mercury is very low and hence bubbles can form at the interface, the reaction being catalysed by the glass surface.

Allowing a nitrogen jet to impinge onto the pool of amalgam produced considerable turbulence and splashing, but did not significantly increase the sodium removal rate. Figure 9 illustrates the extent of sodium removal achieved under these conditions. This was determined by allowing the jet to impinge onto the pool for a known period of time, after which a sample of the aqueous phase was removed and titrated against standardised hydro­ chloric acid solution to determine the amount of sodium hydroxide formed and hence the amount of sodium removed from the bath. It is interesting to note that the rate of sodium removal appears to be constant. In­ creasing the jet momentum increased the rate of sodium removal, presumably by creating a greater interfacial area for reaction. No attempt was made to determine the blowing rate in these early experiments.

The rate of reaction of sodium amalgam with water is clearly in­ adequate to sustain a dynamic foam and hence an alternative system was sought. By using an acidified aqueous phase, and hence increasing the hydroxonium ion concentration in solution, a marked increase in the rate of hydrogen evolution and. general violence of the reaction was achieved.

3.2.2 The reaction of sodium amalgam with acid solutions

The course of the reaction between a 25 ml sample of amalgam, initi­ ally containing about 0.6 wt.$ Na, and an acidified aqueous solution was followed by monitoring the volume of hydrogen evolved, using the simple apparatus shown in Figure 10 (a). Aqueous solution of known acid con­ centration and of just sufficient volume to neutralise all the sodium present was introduced into the reaction vessel and the volume of gas evolved measured using a gas burette.

Typical results are illustrated in Figures 11 and 12.

Figure 11 shows that by increasing the concentration of the acid in the aqueous phase, the rate of gas evolution also increases. Additions of glycerol to the aqueous phase appear to reduce the rate of gas evolution. The rates of reaction produced by strong and weak acids are compared in Figure 12. At similar concentrations, strong acids such as hydrochloric produce a faster rate of reaction than weaker acids such as ethanoic and phosphoric. Clearly these results suggest that the concentration of free hydroxonium ions plays an important role in determining the kinetics of the process.

The effect of jetting onto a pool of amalgam covered by a layer of acidified aqueous solution was qualitatively investigated using the simple apparatus shown in Figure 10 (b). 50 ml of amalgam, containing initially about 0.6 wt.^Na, were covered by a similar volume of water-glycerol solution in a 250 ml. beaker. A nitrogen jet was allowed to impinge onto the bath, causing considerable splashing from the amalgam pool. Concen­ trated acid was introduced into the aqueous phase, from a reservoir, at a uniform rate.

During the course of the reaction the "slag” layer was transformed into a foam, the volume of which could be up to five times that of the

original aqueous phase present. The foam volume attained depended upon the viscosity of the aqueous phase and the rate of introduction of acid. Considerable numbers of amalgam droplets were observed falling through the foam layer, generally leaving streamers of hydrogen bubbles behind them. These droplets could take several seconds to traverse the height of the foam layer and many were left adhering to the walls of the beaker and the lance after termination of the experiment. During the early stages of the blow, large numbers of amalgam droplets could be ejected directly into the gas phase above the bath, without unduly disturbing the slag layer. This behaviour was generally observed when the aqueous phase was very viscous, but ceased once a reactive foam had developed. This is somewhat similar to the phenomenon known as sparking which occurs during the early

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