Metal hydroxide scavenging

An interesting example is the controlled decomposition of polytetrafluoroethene for the generation of tetrafluoroethene which is used as a hydroxide scavenger in the processing and growth of metal fluoride single crystals. 

The destiny of most biological material produced in lakes is the permanent sediment. The question is how often its components can be re-used in new biomass formation before it becomes eventually buried in the deep sediments. Interestingly, much of the flux of phosphorus is held in iron(lll) hydroxide matrices and its re-use depends upon reduction of the metal to the iron(ll) form. The released phosphate is indeed biologically available to the organisms which make contact with it, so the significance attributed to solution events is understandable. It is not clear, however, just how well this phosphorus is used, for it generally remains isolated from the production sites in surface waters. Moreover, subsequent oxidation of the iron causes re-precipitation of the iron(lll) hydroxide floes, simultaneously scavenging much of the free phosphate. Curiously, deep lakes show almost no tendency to recycle phosphorus, whereas shallow... 

By precipitation of its hydroxide, with ammonia, or with an acetate buffer at pH 4.5-5.0, Al can be separated from metals having hydroxides precipitated at higher pH values. Traces of aluminium are separated by using Ti, La, Zr, or Fe(III) as scavenger. It is possible to precipitate Al(OH)3 with ammonia at pH 5 in the presence of Fe masked by reduction to Fe(II). In order to separate aluminium from chromium, Cr(III) can be masked by oxidation to Cr(VI). The precipitation of Al(OH)3 in the presence of H2O2 enables one to separate Al from Ti and V. 

In the absence of large quantities of other metals, mercury can be separated by precipitation as the sulphide, by saturating an acidic aqueous solution with hydrogen sulphide. Cadmium, As, and Cu are used as scavengers. Traces of Hg are also precipitated quantitatively as the sulphide from a neutral or weakly alkaline medium. A suitable metal sulphide or hydroxide may be used as the collector [10]. 

Sulfur-containing nucleophiles react with cyanuric chloride to form sulfanyl-substituted 1,3,5-triazines.42,96,97 In the presence of sodium hydroxide, sodium sulfide and cyanuric chloride give the trisodium salt of 1,3,5-triazine-2,4,6-trithiol (13), which is used as a scavenger of heavy metals.98,99... 

Iron is the most biologically important trace metal nutrient, and its chemical behavior is perhaps the most complex. Its stable oxidation state in oxygen-containing waters is Fe(m), which forms sparingly soluble iron hydroxide and oxide precipitates. This oxide formation and the tendency of ferric ions to adsorb onto particle surfaces results in the scavenging of iron from seawater via particulate aggregation and settling processes. This removal results in... 

Various physical-chemical treatment processes effectively remove heavy metals from waste-waters. One such treatment is lime precipitation followed by activated-carbon filtration. Activated-carbon filtration may also be preceded by treatment with iron(III) chloride to form an iron(III) hydroxide floe, which is an effective heavy metals scavenger. Similarly, alum, which forms aluminum hydroxide, may be added before activated-carbon filtration. 

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