The Removal of Inorganics

The use of electrolysis to remove heavy and transition metal ions from industrial effluents is now a mature technology. Provided that, within the environment of the effluent, hydrogen evolution does not overwhelm the cathodic deposition of a metal, the metal can be removed from the effluent and recycled metals including Au, Ag, Pt, Pd, Cu, Ni, Pb, Hg, Cd, Zn, Sn have been successfully removed using electrochemical technology. The challenge is to remove the metal ion, present in low concentration, at an acceptable rate (current density) and energy consumption (and hence current efficiency). 

One approach to achieve these goals employs three-dimensional electrodes [4, 116, 117] where the mass transfer-limiting current, for metal ion removal is given by 

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The technology is primarily applicable to the removal of inorganic fumes, vapors, and gases (e.g., chromic acid, hydrogen sulfide, ammonia, chlorides, fluorides, and SOj) volatile organic compounds (VOC) and particulate matter (PM), including PM less than or equal to 10 micrometers ( m) in aerodynamic diameter (PM,q), PM less than or equal to 2.5 m in aerodynamic diameter (PMj 5), and hazardous air pollutants (HAP) in particulate form (PM ap)-... 

The primary target of studies on photocatalytic semiconductor suspensions has been water cleavage by visible light. Suspension-based photocatalytic processes are also useful for the removal of inorganic (metal ions) and organic pollutants, the reduction of CO2, the photodestruction of bacteria and viruses, and various organic reactions an example is the use of Pt-loaded CdS for the photocatalytic racemization of L-lysine [210]. 

The removal of inorganic salts from reaction mixtures afforded by polymeric materials may be simply and effectively accomplished by dialysis,166 178 after decomposition of remaining periodate with ethylene glycol130 131 or butylene glycol. 161 170 Alternatively, the iodate and periodate ions may be removed as such, or after reduction to free iodine. The iodate and periodate ions have been effectively precipitated by means of sodium carbonate plus manganous sulfate,6 or by lead dithionate,191 barium chloride,24 192 193 strontium hydroxide194 202 or barium hydroxide,203 204 lead... 

The determination of dissolved organic carbon by oxidation methods in water comprises three analytical steps the removal of inorganic carbon from the sample, oxidation of the organic compounds to carbon dioxide, and the quantitative determination of the resulting carbon dioxide. The methods of oxidation can be classified into three major groups ... 

Hannaker and Buchanan [82] used a method based on wet oxidation with potassium persulfate [83] for the determination of dissolved organic content in concentrated brines following the removal of inorganic carbonates with phosphoric acid. The method involves wet oxidation with potassium persulfate at 130 °C followed by a hot copper oxidation and gravimetric measurement of the carbon dioxide produced. The technique overcomes difficulties of calibration curvature, catalytic clogging, and instrument fouling often encountered with instrumental methods. 

Gershey et al. [58] have pointed out that persulfate and photo-oxidation procedures will determine only that portion of the volatile organics not lost during the removal of inorganic carbonate [30,79,92,181]. Loss of the volatile fraction may be reduced by use of a modified decarbonation procedure such as one based on diffusion [98]. Dry combustion techniques that use freeze-drying or evaporation will result in the complete loss of the volatile fraction [72,79, 92,93],... 

Maeda, S., S. Nakashima, T. Takeshita, and S. Higashi. 1985. Bioaccumulation of arsenic by freshwater algae and the application to the removal of inorganic arsenic from an aqueous phase, n. By Chlorella vulgaris isolated from arsenic-polluted environment. Separation Sci. Technol. 20 153-161. 

Chemical addition for the removal of inorganic compounds is a well-established technology. There are three common types of chemical addition systems that depend upon the low solubility of inorganics at a specific pH. These include the carbonate system, the hydroxide system, and the sulfide system. 

Dousova et al. [142] found that calcined Mg/Al LDHs were effective in removal of As (V) compounds from aqueous solutions at 293 K and neutral pH utilizing the memory effect . More than 70 % of As (V) compoimds were removed from aqueous solution at low sorbent-solution ratios. Parida et al. also studied the affinity of Mg/Fe LDHs toward the removal of inorganic selenite (SeOs ) from aqueous media [143]. The results indicated that the efficacy of SeOs removal increases with a decrease in either pH or temperature. 

Offers potential applications in the removal of inorganic constituents, such as heavy metals, that conventional soil washing technology lacks. 

Nakajima, T., Xu, Y.-H., Mori, Y. et al. (2005) Combined use of photocatalyst and adsorbent for the removal of inorganic arsenic(III) and organoarsenic compounds from aqueous media. Journal of Hazardous Materials, 120(1-3), 75-80. 

X-ray crystallographic analysis of the orange single crystals, which were obtained after the removal of inorganic salts and naphthalene, has revealed that the structure of the orange crystal is that of the digermene ( )-Tbt(Mes)Ge=Ge(Mes)Tbt 10, the dimer of the germylene Tbt(Mes)Ge 2225. The details of the structural analysis of 10 will be discussed later. 

The chelator, 2,3-dimercapto-1 -propanesuifonic acid (DMPS) binds with metals via a sulfate and two sulhydryl groups. It is used for the removal of inorganic and methyl mercury and may reduce the toxicides of cQpper, nickel, and cadmium (Zuiderveen, 1994). 

Chapter 2 considers the removal of inorganic water contaminants using photocatalysis. Metal cations react via one-electron steps first leading to unstable chemical intermediates, and later to stable species. Three possible mechanisms are identified (a) direct reduction via photo-generated conduction band electrons, (b) indirect reduction by intermediates generated from electron donors, and (c) oxidative removal by electron holes or hydroxyl radicals. The provided examples show the significance of these mechanisms for the removal of water contaminants such as chromium, mercury, lead, uranium, and arsenic. 

Finally, Chapters 24—27 deal with the environmental apphcations of carbons as adsorbents for the removal of pollutants from aqueous solutions. These four chapters are highly complementary. Thus, Chapter 24, which addresses the problems associated with the removal of inorganic species, finds its alter ego in Chapter 25, which deals with the adsorption of organic solutes from dilute aqueous solutions. Both chapters provide insights into the fundamental reasons for the performance exhibited by a carbonaceous adsorbent. The global topic of water purification using carbons as adsorbents is addressed in Chapter 26, which... 

Many phosphoryl acceptors are activators by virtue of directing the reaction toward products by the removal of inorganic phosphate in the form of the phosphate-acceptor compound. 

Bailey, D. A. and Thomas, E. V. The removal of inorganic nitrogen from sewage effluents by biological denitrification. Wat. Poll. Cont. 74(5) 497 (1975). 

DESALINATION - The removal of inorganic dissolved solids from water. 

The use of nonpolar solvents such as hexane or toluene allows for the removal of inorganic or amine salts which may otherwise interfere with subsequent reactions. 

It has also been found that the selectivity of fluoridation and yields of products can be improved by changing the reaction conditions [87]. In particular, the use of low polarity aromatic solvents (benzene or toluene) and/or the removal of inorganic salts result in dramatically increased yields of fluorinated arenes... 

The removal of inorganic and organic sulfurfrom coal is benefidal because combustion of coal releases the sulfur into the atmosphere where it contributes to acid rain. Microorganisms having the capability to use thiophene as a food source are being exploited for the desulfurization of coal. 

This treatment involves the removal of inorganic and organic compounds by adsorption. It results in an extremely high-purity effluent, where the BOD can be reduced by over 99%, to 1 mg L. ... 

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