Mercury colloidal forms

Stordal, M.C., Gill, G.A., Wen, L.S., and Santschi, P.H. (1996) Mercury phase speciation in the surface waters of three Texas estuaries importance of colloidal forms. Limnol. 

Methyl and methylene groups adjacent to carbonyl groups are easily oxidized to carbonyls to yield a-keto aldehydes or a-diketones. The reagent of choice is selenium dioxide or selenious acid. The reaction is catalyzed by acids and by acetate ion and proceeds through transition states involving enols of the carbonyl compounds [518]. The oxidation is carried out by refluxing the ketone with about 1.1 mol of selenium dioxide in water, dilute acetic acid, dioxane, or aqueous dioxane [517]. The byproduct, black selenium, is filtered off, but small amounts of red selenium sometimes remain in a colloidal form and cannot be removed even by distillation of the product. Shaking the product with mercury [523] or Raney nickel [524] takes care of the residual selenium. The a-dicarbonyl compounds are yellow oils that avidly react with water to form white crystalline hydrates (equations 407 and 408). 

For the determination of particulate mercury, add-cleaned Teflon and quartz fibre filters, the latter combusted at 500 °C (Coquery and Cossa, 1995), are recommended. A significant fraction of the mercury in seawater is present in colloidal forms and separated with the aid of add-cleaned ultrafiltration cartridges (Stordal et oL, 19%). 

Discussion. J. Nessler in 1856 first proposed an alkaline solution of mercury(II) iodide in potassium iodide as a reagent for the colorimetric determination of ammonia. Various modifications of the reagent have since been made. When Nessler s reagent is added to a dilute ammonium salt solution, the liberated ammonia reacts with the reagent fairly rapidly but not instantaneously to form an orange-brown product, which remains in colloidal solution, but flocculates on long standing. The colorimetric comparison must be made before flocculation occurs. 

Using a glassy carbon electrode modified with a mercury film, Weber et al. [66] measured the association and dissociation rate constants for the complex formed between Pb + and the 18-crown-6 ether. It was found that Pb + forms a complex with 18-crown-6 with a stoichiometiy of 1 1 in both nitrate and perchlorate media. The formation constant, for the nitrate and perchlorate systems are (3.82 0.89) X 10 and (5.92 1.97) x lO mol Ls , respectively. The dissociation rate constants, are (2.83 0.66) x 10 with nitrate and (2.64 0.88) x 10 s with perchlorate as counter ion. In addition, the binding of Pb + with benzo-18-crown-6 embedded in a polymerized ciystalline colloidal array hydrogel has been also analyzed [67]. 

Babiarz et al. (2001) examined total mercury (Hg) and methyhnercury (Me-Hg) concentrations in the colloidal phase of 15 freshwaters from the upper Midwest and Southern United States. On average, Hg and Me-Hg forms were distributed evenly between the particulate (0.4 jm), colloidal, and dissolved (lOkDa) phases. The amount of Hg in the colloidal phase decreased with increasing specific electric conductance. Furthermore, experiments on freshwater with artificially elevated electric conductance suggest that Hg and Me-Hg may partition to different subfractions of colloidal material. The two colloidal Hg phases act differently with the same type of adsorbent. For example, the colloidal phase Hg correlates poorly with organic carbon (OC) but a strong correlation between Me-Hg and OC was observed. 

In the oxidation of hydroxylamine by silver salts and mercurous salts, the nature of the reaction product apparently depends upon the extent to which catalysis participates in the total reaction. This is illustrated by some results obtained with mercurous nitrate as oxidizing agent. The reaction is strongly catalyzed by colloidal silver, and is likewise catalyzed by mercury. The reaction of 0.005 M mercurous nitrate with 0.04 M hydroxylamine at pH 4.85 proceeds rapidly without induction period. The mercury formed collects at the bottom of the vessel in the form of globules when no protective colloid is present, so the surface available for catalysis is small. Under these conditions the yield is largely nitrous oxide. Addition of colloidal silver accelerates the reaction and increases the yield of nitrogen. Some data are given in Table III. 

Traces of sulfides were determined by CSV at pH 10 in the presence of cobalt(II) ions. Cobalt sulfide was accumulated at —0.5 V (versus SCE), probably in the form of colloidal particles occluded into the mercury sulfide layer [73]. In the cathodic scan, CoS catalyzed evolution of hydrogen, which was reflected in the current peak at about —1.6 V. 

At the end of this section focused on analytical problems, it should be mentioned that Thoming et al. [199] have evidenced that electrodialysis allows one to remove heavy metals from soils. During this process, the metals, including mercury, are transferred under the applied electric field to the pore water in either dissolved form or attached to colloids. This method is especially appropriate for the purification of fine-grained soils. 

Colloids The Thickness of the Double Layer and the Bulk Dimensions Are of the Same Order. The sizes of the phases forming the electrified interface have not quantitatively entered the picture so far. There has been a certain extravagance with dimensions. If, for instance, the metal in contact with the electrolyte was a sphere (e.g., a mercury drop), its radius was assumed to be infinitely large compared with any dimensions characteristic of the double layer, e.g., the thickness K-1 of the Gouy region. Such large metal spheres, dropped into a solution, sink to the bottom of the vessel and lie there stable and immobile. 

Colloidal arsenic is also formed by electrolytic reduction of a cold alkaline solution of arsenious oxide using a platinum cathode and a mercury anode,8 a small current density being employed a trace of... 

HgS Hgl2, Takei observed microscopic black spots which he attributed to colloidal mercury. Heating facilitates reversion of the crystal to the yellow form which is explained as a vaporization of the Hg deposits. If this mechanism proves to be correct, this process is merely a permanent photochemical decomposition of the complex and not a true photochromic phenomenon. 

Colloidal palladium converts mercury and mercuric oxide into colloidal solution, and thereby loses its own catalytic activity. It is suggested that possibly a hydrosol of palladium amalgam is formed.4... 

Mercury fulminate is prepared by dissolving mercury in nitric acid, after which the solution is poured into 95 % ethanol. After a short time, vigorous gas evolution takes place and crystals are formed. When the reaction is complete, the crystals are filtered by suction and washed until neutral. The mercury fulminate product is obtained as small, brown to grey pyramid-shaped crystals the color is caused by the presence of colloidal mercury. 

Plates of copper or zinc precipitate colloidal silver from solution.10 The solid forms are brittle, and amalgamate with mercury. Acids convert them into grey silver, without evolution of gas. 

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