Hypochlorite metal removal

Precipitate formation can occur upon contact of iajection water ions and counterions ia formation fluids. Soflds initially preseat ia the iajectioa fluid, bacterial corrosioa products, and corrosion products from metal surfaces ia the iajectioa system can all reduce near-weUbore permeability. Injectivity may also be reduced by bacterial slime that can grow on polymer deposits left ia the wellbore and adjacent rock. Strong oxidising agents such as hydrogen peroxide, sodium perborate, and occasionally sodium hypochlorite can be used to remove these bacterial deposits (16—18). 

Trisodium phosphate is strongly alkaline many of its appHcations depend on this property. For example, many heavy-duty cleaning compositions contain trisodium phosphate as a primary alkalinity source. The crystalline dodecahydrate itself is marketed as a cleaning compound and paint remover. Traditionally, trisodium phosphate has been used in water softening to remove polyvalent metal ions by precipitation as insoluble phosphates. Because the hypochlorite complex of trisodium phosphate provides solutions that are strongly alkaline and contain active chlorine, it is used in disinfectant cleaners, scouring powders, and automatic dishwashing formulations. 

Anhydrous zinc chloride can be made from the reaction of the metal with chlorine or hydrogen chloride. It is usually made commercially by the reaction of aqueous hydrochloric acid with scrap zinc materials or roasted ore, ie, cmde zinc oxide. The solution is purified in various ways depending upon the impurities present. For example, iron and manganese precipitate after partial neutralization with zinc oxide or other alkah and oxidation with chlorine or sodium hypochlorite. Heavy metals are removed with zinc powder. The solution is concentrated by boiling, and hydrochloric acid is added to prevent the formation of basic chlorides. Zinc chloride is usually sold as a 47.4 wt % (sp gr 1.53) solution, but is also produced in soHd form by further evaporation until, upon cooling, an almost anhydrous salt crystallizes. The soHd is sometimes sold in fused form. 

Other Important Considerations with Membranes Oxidizers such as sodium hypochlorite (i.e., CIO2), bromine, iodine, and ozone, which are typically used in the disinfection of wastewater, are not well tolerated by thin-hlm membranes. Such disinfectants can thus influence the efficacy of membranes in removing contaminants such as PPCPs. Furthermore, membranes can become fouled by microorganisms that can metabolize the membrane material. Thus, microbial counts of >100 cells/mL can be problematic. Likewise, dead-cell debris can also cause fouling. Membranes can also be fouled by heavy metals such as chromium. Thus, if heavy metals are deemed a problem, they should be precipitated from the wastewater prior to the filtration with membranes. 

Caution. Chalcogenophenols have an unpleasant odor and are toxic. H2S, H2Se, or H2Te may be liberated on treatment with acid or exposure to the open air. These compounds should therefore be handled under inert gas in a well-ventilated hood. Contaminated glassware should be treated with sodium hypochlorite (bleach) solution for several hours and rinsed thoroughly with water and acetone before removal from the fume hood. Mercury and mercury salts are highly toxic, and skin and eye contact must be avoided. Mercury residues should be disposed of as toxic heavy metal waste. 

Chlorites do not explode on impact if the metal surfaces are carefull y cleaned and org matter is not present the film of oxide normally occurringona hammer is sometimes sufficient to cause d eton. In other respects chlorites should be handled with the same precautions reqd for hypochlorites or chlorates(qv). A chlorite soln should be removed from any surface at once by thorough washing and should not be allowed to dry on a fabric as this combination is very flammable. Also strong acids should not come in contact with chlorites as the chlorine dioxide(qv) evolved is very expl. In addn, strong chlorite solns react violently with sulfur so that a rubber stopper should not be used in a bottle contg chlorite solns(Ref 7)... 

When granular metallic iron smaller than 0.5 mm was used, an optimum reaction rate was obtained. The ratio of metallic iron to hypochlorite concentration was approximately 1.1-fold in terms of the stoichiometric ratio. The contact time of granular metallic iron with chlorinated water was approximately 25 min thus, at pH less than 7, the chlorine residues were totally removed within 25 min from the beginning of the reaction. 

The detoxification of catalysts poisoned by Group V or VI compounds can be accomplished by reactions in which these inhibitors are converted to substances that do not have unshared electron pairs. For instance, bivalent sulfur compounds can be oxidized to sulfones or sulfonic acids by treatment with hypochlorite or hydroperoxides. "2,108 Thiophene, dimethyl sulfide and other sulfur and metal ion poisons as well as phosphorous"" and arsenic compounds " can be removed from platinum by washing the catalyst with acetic acid. This method for the reactivation of the catalyst is simpler than the oxidation techniques. Acidic or basic inhibitors are removed by the addition of an appropriate amount of base or acid, respectively. The effect of a small amount of inhibitor can frequently be overcome by the use of a larger amount of catalyst. 

A common application of redox chemistry is to remove tarnish from metal objects. Other oxidizing agents and reducing agents are useful in everyday life. For example, when you add chlorine bleach to your laundry to whiten clothes, you are using an aqueous solution of sodium hypochlorite (NaClO), an oxidizing agent. It oxidizes dyes, stains, and other materials that discolor clothes. Table 19.1 summarizes the different ways to describe oxidation-reduction reactions. 

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