Unitized Mercury Cathode Apparatus for Electrolytic Removal of Metals

Abstract

A convenient dual unitized apparatus is described for rapid electrolytic removal of heavy metals from solutions of reactive elements, such as alkali metals, alkaline earth metals, and aluminum, using a mercury ca thode of new design. The apparatus consists of a self-contained immersion electrode assembly coupled to a high-capacity Tungar rectifier and a suitable control panel. It allows convenient, efficient use.with high current densities, permits easy washing of the electrode assembly without re-solu-THE removal of interfering metals prior to the determination of other elements offers numerous difficulties. If precipitation of the undesirable elements is to be employed, it is necessary to anticipate occlusion and to choose a suitable method or reagent that will not introduce interfering elements. It is often difficult to obtain reagents sufficiently free from the element to be determined; sometimes, subsequent removal of excess reagent offers additional difficulties. By contrast, electrolysis with the mercury cathode ( 7) eliminates virtually all these problems when applicable. With suitable apparatus it is generally possible to perform the electrolysis in a fraction of the time required for most chemical separations, leaving a dilute acid solution almost completely free of metallic elements.According to Lundell and Hoffman (8), the metals which-are quantitatively deposited in the mercury cathode are: chromium, iron, cobalt, nickel, copper, zinc, gallium, germanium, molybdenum, rhodium, palladium, silver, cadmium, iridium, tin, rhenium, indium, platinum, gold, mercury, thallium, bismuth, and polonium. Other elements which are completely removed from solution but not quantitatively deposited in the mercury are osmium, which is partially volatilized as the tetroxide at the anode, selenium and tellurium, which are reduced to the elemental state but remain unamalgamated, load, which may be partially deposited on the anode, and arsenic,

The Mercury Cathode and its Applications.

“…The low cost of such a unit permits its use in a series of cells. This trend towards compactness has been further developed by Johnson, Weaver, and Lykken (73), who devised a compact, sturdy, self-contained immersion electrode, very similar to the Moldenhauer and Tutundzic cells described earlier. They sought efficiency and speed in removal of the mercury amalgam, elimination of the need for decantation and filtration, reduction of the overheating that accompanies high current densities, and ease and strength in handing.…”

“…The acid most commonly used is undoubtedly sulfuric acid. Although concentrations of this acid up to 5 M have been used (121), it is generally agreed that the concentration should be as low as possible without permitting precipitation to occur (28,37,73,81,152). The inefficiency of the cells reported by early investigators may have been due to their use of too high a concentration of acid (112), although the recording of acid concentrations in terms of "drops" makes this point somewhat obscure.…”

“…Spoon-shaped cathodes, which were suspended in the electrolyte, were developed for determination (114,163) and the English workers Chirnside, Dauncey, and Proffitt, in an effort to obtain a simple inexpensive cell, devised the first unitized apparatus for the separation of metals (27,28). An extremely compact and convenient cell has been constructed in the Shell Development Laboratory (73,119,131,171).…”

The Polarographic Determination of Titanium in Steels and Nickel-Base Alloys

“…The rate a t which iron is deposited in a mercury-cathode cell is favorably affected by the use of fresh mercury, a low concentration of sulphuric acid, , agitation of the mercury, and by the proper choice of spacing for the anode relative to the cathode (1,5,14,15,17). The rate of iron removal increases with increasing current density, but care must be taken to prevent undue boiling of the solution.…”

Polarographic Theory, Instrumentation, and Methodology

“…Lingane and Meites (68) developed a method using this principle for the rapid and accurate determination of vanadium in steels and ferroalloys. Electrolytic separations with a mercury cathode have also been recommended by Johnson, Weaver, and Lykken (38), who developed a convenient immersion type of mercury cathode, and by Rabbitts (93), who described an improved form of the Melaven type cell. The optimum conditions for the removal of such metals as iron, copper, zinc, nickel, cobalt, chromium, lead, tin, and molybdenum by constant current electrolysis with a mercury cathode have been studied by Parks, Johnson, and Lykken (90).…”