PbS concentration, increase

There is an optimal concentration of HCIO4 which allows formation of the honeycomb-like stmctures with the maximal surface area [39]. The decrease of number of holes and the increase of their diameter observed after the optimal concentration of this acid are due to coalescence of neighboring hydrogen bubbles. The effect of the different parameters of electrolysis was comparable with those observed in the case of Cu. The mean diameter of the pores increased as the Pb concentration increased. As the current density increased, the porous Pb films became uniform while, at the same time, the pore size, wall thickness, and wire diameter became smaller. The pore size of the deposited porous film was closely related to the size of the hydrogen bubbles that departed from the electrode. A high current density facilitates the departure of the H2 bubbles with a smaller bubble size. 

In a separate study, Igwe and Abia46 determined the equilibrium adsorption isotherms of Cd(II), Pb(II), and Zn(II) ions and detoxification of wastewater using unmodified and ethylenediamine tetraacetic acid (EDTA)-modified maize husks as a biosorbent. This study established that maize husks are excellent adsorbents for the removal of these metal ions, with the amount of metal ions adsorbed increasing as the initial concentrations increased. The study further established that EDTA modification of maize husks enhances the adsorption capacity of maize husks, which is attributed to the chelating ability of EDTA. Therefore, this study demonstrates that maize husks, which are generally considered as biomass waste, may be used as adsorbents for heavy metal removal from wastewater streams from various industries and would therefore find application in various parts of the world where development is closely tied to affordable cost as well as environmental cleanliness.46... 

Increases in Pb concentrations of 30 times have been measured in Lake Washington caused mainly through the burning of leaded fuel in internal combusion engines. Significant increases in the concentrations of Zn (6 times), Pb (13 times), and Cu (8 times) have been introduced by man s activity near Sinclair Inlet, probably as a result of shipyard s activities. 

The other metals exhibit different vertical profiles. The dissolved concentrations of Pb and Cu do not exhibit subsurface concentration maxima and, hence, do not appear to undergo any redox reactions. Their dissolved concentrations decline with increasing depth and are likely controlled by precipitation into sulfide minerals as the particulate concentrations increase rapidly with depth in the anoxic zone. In the anoxic waters, sulfide is supplied by in situ sulfate reduction. 

Properties of thin layers of lead electrodeposited on vitreous carbon have been found identical with that of metallic lead [304]. Therefore Pb and Pb02 coated reticulated vitreous carbon (RVC) electrodes [185] can be applied as electrodes in lead-acid batteries, as reviewed in [305]. The deposition of lead on carbon is through the diffusion-controlled process with instantaneous or progressive nucleation, for high and low Pb + concentration, respectively, and three-dimensional growth mechanism. The number of nucleation sites increases with deposition overpotential, as shown for vitreous [306] and glassy carbon [307] electrodes. The concentration dependence of the nucleation... 

Increase in pH (= increase in [OH ]) shifts the equilibrium to the left, resulting in a lower concentration of free Pb ions and thus a slower reaction to give PbSe. This means that, in contrast to the deposition from a selenourea bath described earlier, the rate is dependent on Pb concentration and possibly independent of hydroxide concentration at a constant free-Pb concentration. This would then suggest that the opposite mechanism, i.e., a complex decomposition, is effective for the selenosnlphate bath. It is stressed that these conclusions on selenide formation... 

The thickness of the fdms using the carboxylate complex was not dependent on the Pb concentration (at least from 10 mM up). It was, however, very dependent on the pH value, with a sharp maximum, the position of which was dependent on the anion of the lead salt and, more so, on the hydroxide used (Na, K, NH4). The thickness varied from <50 nm to 300 nm. The film thickness was also moderately dependent on deposition temperature, increasing with increase in temperature (in contrast to the more usual decrease in terminal thickness with increasing temperature). It is not certain, however, whether these thicknesses (and others measured in this study) were actually terminal thicknesses or only the thickness measured after a certain time. 

Thermodynamic analysis can be useful also in predicting the effect of gas-phase composition on defect concentrations in the solid and, implicitly, on the electrical properties of the deposited film (I, 95, 96). This technique has been used to predict the concentration and change in electrical carriers from electrons to holes in PbS with increasing sulfur pressure over the PbS crystal (96). 

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