Thallium deposition

When burned in suitable pits, pyrite yields, among other products, sulfur dioxide, arseniouS and selenious adds, and the oxide of thallium, which are carried over into the first lead chamber, with the ferruginous dust. In this first chamber, espedally if it has no other communication with the following ones than the gas pipe, the oxide of thallium deposits and accumulates, and finally thallium sulfate, with sulfates of lead, iron, and other foreign substances coming fiom the pyrite. 

Thallium deposition proceeds in a more complex manner but leads to some very interesting SH results [122]. The CV for the system is shown in Fig. 5.14 with the corresponding SH response during the various stages of deposition shown in Fig. 5.15a-e. The first three deposition peaks in the CV (A, -A3) are assumed by previous studies to correspond to the sequential formation of two intertwined... 

Although both SH transients in Fig. 5.21 fall to a minimum at about the same time, their form is quite different and qualitative comparisons are useful. The isotropic contribution, /pp(/), decays as a single exponential, in agreement with previous measurements of submonolayer thallium deposition on polycrystalline electrodes [54]. The solid line in Fig. 5.21 a is an exponential fit with r = 10.7 msec. The exponential form suggests that the deposition occurs by an absorption, rather than a nucleation, mechanism [154]. The transient anisotropic response is not as simple. In fact, the initial fall in /ps( ) in Fig. 5.21 b is not a simple decaying exponential. The differing time dependencies for the isotropic and anisotropic responses suggests that f, the bulk anisotropic susceptibility element which is the only common element, is not the main source of the nonlinear response in either case. 

AE = 0. In the overpotential region, where the final coverage should be independent of E, the overlayer is formed faster as the overpotential increases. The result suggests that activation energy is supplied by the overpotential. Similar results were reported in related SHG measurements of the UPD kinetics of thallium deposition on polycrystalline electrodes within the overpotential region [54]. 

J. M. Robinson, G. L. Richmond, Time Resolved SH Rotational Anisotropy Measurements of Thallium Deposition on Cu(lll), in preparation. 

The anodic process is oxygen evolution, whereas the cathodic process changes from thallium deposition to include cadmium deposition and eventually also hydrogen evolution, as the potential is gradually increased. 

In experiments with thallium deposition [143], the calculated and measured slopes became parallel after a charge corresponding to 1.5 atomic layers of thallium covered the gold surface has been passed. In this case the difference between the calculated and measured frequency, <5/, is... 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Stripping voltammetry procedure has been developed for determination of thallium(I) traces in aqueous medium on a mercury film electrode with application of thallium preconcentration by coprecipitation with manganese (IV) hydroxide. More than 90% of thallium present in water sample is uptaken by a deposit depending on conditions of prepai ation of precipitant. Direct determination of thallium was carried out by stripping voltammetry in AC mode with anodic polarization of potential in 0,06 M ascorbic acid in presence of 5T0 M of mercury(II) on PU-1 polarograph. 

Thus excess of Mn(IV) hydroxide represents itself as a collector of thallium which practically completely passes into a deposit, and interfering metal ions (Cu, Cd, Pb, Ni, etc.) remain in a solution and are separated providing high selectivity of thallium determination. Effect of some factors on the value of analytical signal of thallium has been investigated at the stages of water pretreatment. Based on of these data the unified technique for thallium determination has been developed and tested on natural waters. The method proposed allows to determine content of thallium in waters which is 10 times lower than it is required by maximum allowable concentration limits. 

Due to the experimental difficulties involved, there have been only three reports of XSW measurements at electrochemical interfaces. Materlik and co-workers have studied the underpotential deposition of thallium on single-crystal copper electrodes under both ex situU9 and in situ120 conditions. In addition, they report results from studies in the absence and presence of small amounts of oxygen. 

Just a few years after the discovery of the deposition and electroactivity of Prussian blue, other metal hexacyanoferrates were deposited on various electrode surfaces. However, except for ruthenium and osmium, the electroplating of the metal or its anodizing was required for the deposition of nickel [14], copper [15,16], and silver [9] hexacyanoferrates. Later studies have shown the possibilities of the synthesis of nickel, cobalt, indium hexacyanoferrates similar to the deposition of Prussian blue [17-19], as well as palladium [20-22], zinc [23, 24], lanthanum [25-27], vanadium [28], silver [29], and thallium [30] hexacyanoferrates. 

As an example [13] we consider the underpotential deposition of thallium on silver (Fig. 15.13). At potentials above the onset of the upd of thallium the SHG signal decreases, at first slowly, then more rapidly. The adsorption of thallium causes a strong rise in a(o ), because the region in which the electronic density decays to zero becomes more extended with an angle of incidence of 45° this shows up as a drastic increase in the signal. A similar behavior is seen in other systems, and often even fractions of a monolayer can be detected. 

Figure 15.13 Cyclic voltammogram (top) and SHG signal for the underpotential deposition of thallium on silver The letters in the voltammogram denote various adsorption (A) and desorption (D) peaks. Reprinted with permission from Ref. 13.

Rehk per M, Frank M, Hein JR, Porcelli D, Halliday A, Ingri J, Liebeh au V (2002) Thallium isotope variations in seawater and hydrogenetic, diagenetic, and hydrodiermal ferromanganese deposits. Earth Planet Sci Lett 197 65-81... 

Waszczuk et al. [329] have carried out radiometric studies of UPD of thallium on single-crystal Ag electrode from perchloric acid solutions. Deposition of Tl on Ag(lOO) to obtain monolayer, bilayer, and bulk crystallites has been studied by Wang et al. [330]. These studies have shown that apart from the substrate geometry, the nature of the substrate-adatom interactions also influence the structure of the UPD metal adlayers. This is because of the fact that, contrary to Au and Pt electrodes, Tl forms a well-ordered bilayer phase before bulk deposition on Ag(lOO) surface occurs. 

In the case of Bi and T1 phases only very short reaction times (of the order of minutes) are possible because of the evaporation of Bi and Tl. This may be compensated by using excess Bi and T1 in the solution or by modification of the solvent (mixture of water and glycerol) that enhances the solubility of Bi and allows the use of less nitric acid in the solution. A more homogeneous deposition results in a better product after heat treatment. Figure 9 shows a typical resistivity measurement for a thallium film that has, however, a very weak critical current (50 A/cm2 at 77K). 

TlSe was first deposited from a solution of thallium(l) acetate and selenosulphate with added NaOH and hydrazine at room temperature [97]. The initial films were... 

---