Precipitation Ion-exchange

Kilogram quantities of americium as Am can be obtained by the processing of reactor-produced plutonium. Much of this material contains an appreciable proportion of Pu, which is the parent of Am. Separation of the americium is effected by precipitation, ion exchange, or solvent extraction. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Am from its parent 241Pu and the other isotopes present can be effected by precipitation, ion exchange, or solvent extraction. 

Wastewater treatment in the copper sulfate industry can further be improved, particularly the removal of the toxic metals, through sulfide precipitation, ion exchange, and xanthate processes. Addition of ferric chloride alongside alkaline precipitation can improve the removal of arsenic in the wastewater. 

Steam stripping Air stripping Biological nitrification Chemical oxidation Ion exchange Solvent extraction Biological oxidation (aerobic) Wet oxidation Activated carbon Chemical oxidation Chemical precipitation Ion exchange Adsorption Nano-filtration Reverse osmosis Electrodialysis... 

The main techniques that have been used to dispose of industrial effluents include chemical precipitation, ion exchange, electrochemical processes, and adsorption onto various adsorbents and/or membrane filtration. Although all of these techniques are capable of removing heavy metals to some extent, adsorption by solid substrates is preferred because of its high efficiency, easy handling and cost as well as the availability of adsorbent. 

For practical (real) catalyst systems, precipitation, ion exchange, impregnation and sol-gel processing procedures are used. In precipitation methods, a hydroxide or a carbonate of a metal may be precipitated from a solution of a metal salt onto the support material held in the solution. Thus, a copper-silica catalyst may be prepared using a Cu-nitrate solution in which silica is suspended. Additives of any alkali cause the precipitation of copper hydroxide onto the silica support. This is then dried and normally reduced in hydrogen at moderate temperatures ( 400-500 °C) to form the catalyst. In co-precipitation techniques , the support is precipitated simultaneously with the active catalyst. In the ion-exchange method, for example, highly dispersed Pt on... 

Procedures for the determination of 11 elements in coal—Sb, As, Br, Cd, Cs, Ga, Hg, Rb, Se, U, and Zn—by neutron activation analysis with radiochemical separation are summarized. Separation techniques include direct combustion, distillation, precipitation, ion exchange, and solvent extraction. The evaluation of the radiochemical neutron activation analysis for the determination of mercury in coal used by the Bureau of Mines in its mercury round-robin program is discussed. Neutron activation analysis has played an important role in recent programs to evaluate and test analysis methods and to develop standards for trace elements in coal carried out by the National Bureau of Standards and the Environmental Protection Agency. 

In certain cases, the primary process objective is to keep solid particles in suspension. Areas of application involve catalytic reactions, crystallization, precipitation, ion exchange, and adsorption. Axial flow and pitched-blade turbines are best suited in providing the essential flow patterns in a tank to keep the solids in suspension. The suspended solid is characterized by two parameters ... 

Describe the chemical and physical processes that take place from the addition of the initial alginate drop to a divalent metal ion solution to the final, equilibrium bead. (Hint Think in terms of precipitation, ion exchange, and diffusion.)... 

Part III covers the various unit processes employed in water and wastewater treatment including water softening water stabilization coagulation removal of iron and manganese by chemical precipitation removal of nitrogen by nitrihcation-denitrihcation removal of phosphorus by chemical precipitation ion exchange and disinfection. 

In general, water is softened in three ways chemical precipitation, ion exchange, and reverse osmosis. Only the chemical precipitation method is discussed in this chapter. 

Solute recovery. So far we have discussed the waste management of a solute in a solvent. Now we are going to discuss solute recovery for reuse. There are different methods of solute recovery, for example, precipitation, ion exchange, ultrafiltration, and reverse osmosis. 

Concentration of dilute electrolytes An ion-exchange column is effective for collecting ionic substances from large volumes of dilute solutions. By elution employing a small volume of solution, a considerable concentration effect can be achieved. As examples may be cited the concentration of cations and anions in natural waters, beryUium from bones, copper from milk, and silver in atmospheric precipitation. Ion-exchange beads have been proposed as chemical microstandards since they can retain small measurable quantities (10 g) of ions such as sodium, potassium, calcium, and uranium. It is highly desirable that the beads be uniform in size and homogeneous in the trace constituent. 

For the treatment of low and intermediate level wastes, three processes are generally adopted, namely, chemical precipitation, ion exchange, and evaporation. The efficiency of the treatment scheme is judged by the values of decontamination factor (DF) and volume reduction factors (VRFs), which are defined as follows ... 

The applications of membrane technology have grown significantly in the last decade. Some advantages of membrane technologies are continuous performance, low energy consumption, modular stmcmre, and easy installation or automation. Due to this, nowadays membrane processes have become an ideal complement or even a suitable replacement of conventional separation processes (evaporation, chemical precipitation, ion exchange, etc.). 

Figure k illustrates in schematic form the precipitation-ion exchange process devised and developed for reducing the actinide concentration of the PRF salt waste, when solidified, to or below 10 nCi/g. This process involves (a) Addition of... 

Figure 4. Precipitation-ion exchange scheme for removal of actinides from Hanford PRF salt waste...

Evaporation of the leach water from 1000 g of phosphogypsum and X-ray diffraction of the resulting crystals did not identify any compounds of trace elements. Trace elements may exist as sulfates, such as mercuric sulfate, or as calcium salts, such as calcium selenate, in equilibrium with a saturated solution of calcium and sulfate ions from gypsum. Further isolation of trace elements by extraction, precipitation, ion exchange, or other means would so alter this equilibrium that the original amounts and types of compounds present would not be determined. Literature studies of phase equilibria in saturated gypsum solutions were used to identify possible trace element compounds. 

A variety of distinct but interrelated phenomena may be involved in the adsorption process of metal ions onto activated carbons adsorption (physical adsorption or chemisorption), surface precipitation, ion exchange, and surface complexation. The metal sorption is often not the result of one mechanism but of several reactions. The mechanisms involved and their degree of importance seem to depend on the materials and the operating conditions used. 

The environmental technology section includes reviews of waste water treatment and air and waste minimization/pollution prevention. Waste water treatment procedures discussed include biological treatment, activated carbon adsorption, air and steam stripping, chemical precipitation, ion exchange, and membrane separation. 

Because the sea has remained constant in its composition for the recent geologic past, it has been described plausibly in terms of a steady state model. For a steady state ocean, for each element, E, the equation (d[E]/dt) input = (d[E]/dt) sedimentation can be written. Because the rate of sedimentation is controlled largely by the rate at which an element is converted (precipitation, ion exchange, biological activity) into an insoluble and settleable form, the residence time is affected by the readiness of the elements to react. Hence, elements that are highly oversaturated (e.g., Al, Fe) have detention times that correspond to the time necessary for ocean mixing ( 103 years). On the other hand, elements with low reactivity such as Na or Li have very long residence times ( 108 years)... 

Chemical. Precipitation, co-precipitation, ion-exchange, and surface adsorption can transfer contaminants from groundwater to the immobile solid phases and reduce the contaminant concentrations. 

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