Chemicals neutralizing with

Determination of small concentrations of anions in samples containing 1 M sodium hydroxide and determination of trace cations in strong mineral acids are two examples where sample neutralization is needed. However, chemical neutralization with HCl or NaOH would introduce a high concentration of unwanted ions. A better way is to introduce the or OH needed for neutralization through an ion-exchange membrane. This process is called electrodialysis. 

Lewisite Destruction Process Rather than incinerate lewisite and its byproducts as originally proposed, the modified plan called for lewisite to be chemically neutralized with the collected arsenate salts and neutralizing solution inunediately stabilized in concrete without any incineration. This approach removed concerns regarding the potential for arsenic emissions during incineration. 

Most of the ions produced by either thermospray or plasmaspray (with or without the repeller electrode) tend to be very similar to those formed by straightforward chemical ionization with lots of protonated or cationated positive ions or negative ions lacking a hydrogen (see Chapter l).This is because, in the first part of the inlet, the ions continually collide with neutral molecules in the early part of their transit. During these collisions, the ions lose excess internal energy. 

In the United States, Hquid HLW from the reprocessing of defense program fuels was concentrated, neutralized with NaOH, and stored in underground, mild steel tanks pending soHdification and geologic disposal (see Tanks AND PRESSURE VESSELS). These wastes are a complex and chemically active slurry. Suspended in the supernatant Hquid are dissolver soHds which never went into solution, insoluble reaction products which formed in the tank, and salts which have exceeded their solubiHty limit. The kinetics of many of the reactions taking place are slow (years) so that the results of characterization... 

Chemical precipitation and solvent extraction are the main methods of purifying wet-process acid, although other techniques such as crystallisa tion (8) and ion exchange (qv) have also been used. In the production of sodium phosphates, almost all wet-process acid impurities can be induced to precipitate as the acid is neutralized with sodium carbonate or sodium hydroxide. The main exception, sulfate, can be precipitated as calcium or barium sulfate. Most fluorine and siUca can be removed with the sulfate filter cake as sodium fluorosiUcate, Na2SiFg, by the addition of sodium ion and control of the Si/F ratio in the process. 

North American Chemical Co. produces borax pentahydrate and decahydrate from Seades Lake brines in both Trona and West End, California (see Chemicals frombrines). The 88 km dry lake consists of two brine layers, the analyses of which are given in Table 11. Two distinct procedures are used for the processing of upper and lower lake brines. Borax is produced in Trona from upper lake brines by an evaporative procedure involving the crystallization of potash and several other salts prior to borax crystallization as the pentahydrate (104). A carbonation process is used in West End, California to derive borate values from lower lake brines (105). Raw lower stmcture brine is carbonated to produce sodium bicarbonate, which is calcined and recrystallized as sodium carbonate monohydrate. The borate-rich filtrate is neutralized with lake brine and refrigerated to crystallize borax. 

Fiber-Reactive Dyes. These dyes can enter iato chemical reaction with the fiber and form a covalent bond to become an iategral part of the fiber polymer. They therefore have exceptional wetfastness. Thein main use is on ceUulosic fibers where they are appHed neutral and then chemical reaction is initiated by the addition of alkaH. Reaction with the ceUulose can be by either nucleophilic substitution, using, for example, dyes containing activated halogen substituents, or by addition to the double bond in, for example, vinyl sulfone, —S02CH=CH2, groups. 

Neutralization Acidic or basic wastewaters must be neutrahzed prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equahzation basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a hquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutr zation. Limestone is used when reaction rates are slow and considerable time is available for reaction. Siilfuric acid is the primary acid used to neutralize high-pH wastewaters unless calcium smfate might be precipitated as a resmt of the neutralization reaction. Hydrochloric acid can be used for neutrahzation of basic wastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization. 

Chemical Reactivity - Reactivity with Water No rettpiion Reactivity with Common Materials No reaction Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water, neutralize with dilute acetic acid Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water Reacts to form flammable hydrogen gas Reactivity with Common Materials Reacts with acids to form toxic, flammable diborane gas. Slowly attacks and destroys glass Stability During Transport Stable unless contaminated with acids or is overheated, thereby forming flammable hydrogen gas Neutralizing Agents for Acids and Caustics Caustic formed by the reaction with water can be diluted with water and then neutralized with acetic acid Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

Aprotic solvents include those substances which may be considered to be chemically neutral and virtually unreactive under the conditions employed. Carbon tetrachloride and benzene come in this group, they possess low dielectric constants, do not cause ionisation in solutes and do not undergo reactions with acids and bases. Aprotic solvents are frequently used to dilute reaction mixtures while taking no part in the overall process. 

Figure 20-20 shows in schematic fashion some of the alternative paths leading from ores to pure metals. These paths include four general processes of which the essential chemical process is reduction to yield the neutral metal. First is separation. Generally, a metal ore obtained from a mine contains a particular compound of some desired metal mixed with various other materials. The mineral must be separated from these other contaminants. Separation often is followed by conversion, in which the mineral is treated chemically to convert it into a form that can be easily reduced. The third step is reduction. After a suitable compound has been obtained, it is reduced to free metal by chemical reaction with a reducing agent or by electrolysis. The metal obtained by reduction often contains small amounts of impurities, so the final step is refining to purify the metal. 

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