Amalgam decomposition

Other Phenomena Interaction of metallic Pb in the mercury phase [38] and amalgam decomposition in alkaline medium [39] have also been discussed. Formation of anodic monolayer PbCOs or Pb3(C03)2(0H)2 on Pb(Hg), depending on pH, in carbonate or bicarbonate solutions, has been detected using electrochemical methods (chronoamper-ometry and linear sweep voltammetry) and powder X-ray diffractometry [40]. 

Amalgam Decomposition Reaction (4), representing the production of alkali and hydrogen from amalgam and water in the decomposer, corresponds... 

Other products of an alkali amalgam decomposition process are sodium sulfide from polysulfide solutions, sodium dithionide from hydrogen sulfide, hydra-zobenzene or aniline from nitrobenzene, and adiponitrile from acrylonitrile. Last but not least alkali metals can be prepared directly from the amalgam [33]. 

Sodium amalgam containing about 0.2 wt % Na is decomposed with water in the amalgam decomposition tower (see Section 5.1.2 for details related to the design of the amalgam decomposer) of... 

The design of the amalgam decomposition tower is thus achieved by combining the electrochemical principles with the chemical engineering concepts involved in describing packed columns. 

The three major steps in the amalgam chlor-aUcali process, shown in Fig. 4.9.1, are brine treatment, electrolysis, and amalgam decomposition. Purilied brine is sent to the electrolyzer to produce chlorine and sodium amalgam at the anode and cathode, respectively. The sodium amalgam is then sent to the amalgam decomposer to produce caustic soda of 50% concentration. Mercury, after decomposition, is recycled to the top of the cell. The overall process of amalgam decomposition can be described as ... 

This reaction is facilitated by contacting the sodium amalgam with gr hite, ds illustrated in Fig. 4.9.2. The amalgam decomposition reaction is an electrochemical process... 

FIGURE 4.9.6. NTU of the amalgam decomposition tower as a function of the amalgam concentration and of the operation factor under the condition of yj = 0 [1]. 

Table 4.9.1 shows that the exothermic heat of reaction is slightly more than 7,000 kcalhr This supplies the heat of formation of the caustic solution and then contributes about 5,(XX) kcal hr to the sensible heat of the flowing mercury. Therefore, the operating temperature, t, of the amalgam decomposition tower depends on the flow rate and the incoming temperature of mercury or amalgam, tNa-ng- A typical temperature increase is about 20°C. 

Vertical decomposers are towers packed with graphite spheres or particles 8-20 mm in diameter. A typical cross section is 0.35 m per l(X)kA of cell load. The amalgam flows from the top and water is fed into the bottom of the tower. Since the volume of the decomposer is small, it is necessary to cool the hydrogen generated during the course of the amalgam decomposition reaction. The mercury inventory is small with the vertical decomposer. However, the caustic contains more mercury. 

The amalgam leaves the cells, which are sloped to permit gravity flow. Each mercury cell has a companion denuder or decomposer. This is a short-circuited cell, usually packed with graphite, in which amalgam decomposition in the presence of added water regenerates the mercury and forms caustic soda or potash ... 

Mercury cell caustic soda liquor is a high-grade product, low in chloride and chlorate impurities and, because of its traditional associations, known as Rayon grade. It is produced directly by amalgam decomposition at the strength at which it is sold. This usually contains 46.8% NaOH (i.e. 100Tw caustic liquor). 

Chlorine and Caustic Technology, Overview and Traditional Processes, Fig. 3 Amalgam decomposition at a graphite surface... 

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