Hydroxide coprecipitation, magnesium

Wu and Boyle [837] have developed a method using magnesium hydroxide coprecipitation and isotopic dilution mass spectrometry to determine lead, copper, and cadmium in 1 ml seawater samples, with detection limits of 1,40, and 5 pM, respectively. 

Tuzen, M., Saygi, K.O., Soylak, M. Separation and speciation of selenium in food and water samples by the combination of magnesium hydroxide coprecipitation-graphite furnace atomic absorption spectrometric determination. Talanta 71, 424-429 (2007)... 

Several other hydroxides have been used both for general coprecipitation and for specific separations. Lanthanum hydroxide has been used (47, 48) as a convenient collector and subsequent release agent for atomic absorption spectroscopy. Titanium hydroxide coprecipitates copper and zinc from seawater (49), and chromium(III) hydroxide precipitates cadmium(II) (50) and zinc (57). Other authors have used magnesium hydroxide (52, 53), manganese dioxide (54, 55), and zirconium hydroxide (56, 57) to collect trace metals from natural waters. Thallium(III) was coprecipitated with zirconium hydroxide at pH 4.3-6.7 and thallium(I) at pH 7.0-13.0 (57). Beryllium (58) and antimony (59) can be quantitatively coprecipitated with a variety of hydroxides including titanium and zirconium, depending on the pH used. 

The magnesia and alumina suspension is prepared by treatment of an aqueous solution, containing aluminum and magnesium salt in the desired proportion, with sodium hydroxide. The coprecipitated aluminum and magnesium hydroxides are collected by filtration, washed free of soluble salts, and stabilized by the addition of a suitable hexatol. 

The presence of normal concentrations of sodium, magnesium, and strontium have no net effect on the determination of calcium above the approximate level of accuracy of about 0.1% so that no correction factor seems necessary. A sufficient amount of titrant must be added to complex at least 98% of dissolved calcium before the buffer is added this apparently reduces the loss of calcium by coprecipitation with magnesium hydroxide. 

Petit [563] has described a method for the determination of tellurium in seawater at picomolar concentrations. Tellurium (VI) was reduced to tellurium (IV) by boiling in 3 M hydrochloric acid. After preconcentration by coprecipitation with magnesium hydroxide, tellurium was reduced to the hydride by sodium borohydrate at 300 °C for 120 seconds, then 257 °C for 12 seconds. The hydride was then measured by atomic absorption spectroscopy. Recovery was 90 - 95% and the detection limit was 0.5 pmol/1. 

Andreae [564] coprecipitated tellurium (V) and tellurium (VI) from seawater and other natural waters with magnesium hydroxide. After dissolution of the precipitate with hydrochloric acid, the tellurium (IV) was reduced to tellurium hydride in 3 M hydrochloric acid. The hydride was trapped inside the graphite tube of a graphite furnace atomic absorption spectrometer, heated to 300 °C, and tellurium (IV) determined. Tellurium (VI) was reduced to tellurium (IV) by boiling with hydrochloric acid and total tellurium determined. Tellurium (VI) was then calculated. The limit of detection was 0.5 pmol per litre and precision 10-20%. 

Coprecipitation upon partial precipitation of the natural calcium and magnesium with sodium hydroxide. 

In support of that explanation, X-ray analysis of the catalyst after use indicated the presence of MgO. Hence, the catalytically active phase was finely divided copper in intimate contact with magnesia, quasi as carrier. The same phenomenon was observed with the Zintl-phase alloys of silver and magnesium. Such catalysts were then deliberately prepared by coprecipitation of copper and silver oxides with magnesium hydroxide, followed by dehydration and reduction. Table I shows that these supported catalysts had the same activation energies as those formed by in situ decomposition of copper and silver alloys with magnesium. 

Several workers have observed the inhibition of autoxidative degradation of cellulose or its model compounds in the presence of magnesium compounds (8-14, 18). However, the mechanism for the observed inhibition process has been a matter of some controversy. Some workers have attributed their observation to the stabilization of peroxides by magnesium compounds (8, 9, 11). Robert has suggested that the metallic catalysts are adsorbed on or coprecipitated with magnesium hydroxide (13). Other workers are convinced that the... 

In many non-phosphate samples, uranium can be coprecipitated with magnesium hydroxide or otherwise concentrated and extracted from a sulfate system into an extractive scintillator containing a high-molecular-weight tertiary amine sulfate. 

Palladium black was prepared from palladium nitrate and formaldehyde solution by dropwise addition of potassium hydroxide solution (50 wt. %) at about 10°. The solution and precipitate were warmed at about 60° and the precipitate washed several times by decantation. It was then placed in a Soxhlet extractor and washed for 48 hr. (about 100 times). The precipitate was then dryed at 110°. The palladium-silver system is known to be one of complete miscibility (3). Alloys of silver-palladium were prepared following a procedure discussed elsewhere 4). Their preparation involved a low-temperature coprecipitation of both metals from a solution containing proper amounts of their nitrates. Alloy formation was checked by means of x-ray diffraction patterns which were obtained with Cu-Ka radiation. The computed lattice constants are shown in Fig. 1 to be a linear function of the alloy composition. Hydrogen, used for pretreatment of all samples, was obtained from a commercial tank and purified by passage through a Deoxo unit, magnesium perchlorate, and a charcoal trap immersed in liquid nitrogen. 

Kopito and Shwachman (K7) have described a method for the analysis of lead in either freshly voided or partially decomposed urine. The lead in 25 or 50 ml of urine is coprecipitated on bismuth hydroxide by adding bismuth nitrate and ammonia. After centrifuging, the precipitate is dissolved in acid to a final volume of 5 ml, and this solution is aspirated. With a 25-ml sample, 0.05-0.2 ppm of lead can be determined. The bismuth does not interfere with the lead absorption, and it suppresses interferences from sodium, potassium, calcium, magnesium, and phosphates. This procedure appears to offer sufficient sensitivity and the advantages of freedom from interference and simplicity in operation. Control of pH is not critical. Kopito and Shwachman claim that in... 

The literature contains numerous examples of the use of hydroxides as coprecipitants of trace metals because the hydroxides are easily produced, very flocculant, and capable of removing both ionic and nonionic species from solution due to their large surface area. Sodium, calcium, and magnesium are not generally recovered to any extent which makes the method useful for seawater samples. One difficulty with any precipitation method is the extensive time required for a careful precipitation and filtration. 

Amounts smaller than 0.15 y manganese per drop may be detected 100 - 150 ml water is treated with a few drops of sodium hydroxide solution, boiled, and filtered. The calcium and magnesium carbonates thus precipitated by the carbonate in the alkali coprecipitate any manganese dioxide formed. The mixture is filtered through a quantitative paper and tested on the paper with benzidine solution. A blue color indicates manganese. As little as 1.2 y manganese (dilution 1 25,000,000) may be detected. 

It should be noted that magnesium aluminum layered double hydroxides (MgAl-LDHs) have also been widely used as flame retardants for polymer materials. Similarly, MgAl-LDHs can be synthesized by reaction of aluminum and magnesium salts as precursor and sodium hydroxide as precipitator via the coprecipitation method and other preparation routes. ... 

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