Process solution purification

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Zinc. The electrowinning of zinc on a commercial scale started in 1915. Most newer faciUties are electrolytic plants. The success of the process results from the abiUty to handle complex ores and to produce, after purification of the electrolyte, high purity zinc cathodes at an acceptable cost. Over the years, there have been only minor changes in the chemistry of the process to improve zinc recovery and solution purification. Improvements have been made in the areas of process instmmentation and control, automation, and prevention of water pollution. 

Solvent Extraction Reagents. Solvent extraction is a solution purification process that is used extensively in the metallurgical and chemical industries. Both inorganic (34,35) and organic (36) solutes are recovered. The large commercial uses of phosphine derivatives in this area involve the separation of cobalt [7440-48-4] from nickel [7440-02-0] and the recovery of acetic acid [61-19-7] and uranium [7440-61-1]. 

Pharmaceuticals. Pharmaceuticals account for 6% of the Hquid-phase activated carbon consumption (74). Many antibiotics, vitarnins, and steroids are isolated from fermentation broths by adsorption onto carbon foUowed by solvent extraction and distillation (82). Other uses in pharmaceutical production include process water purification and removal of impurities from intravenous solutions prior to packaging (83). 

Cyclohexene The commercially available reagent was washed with aqueous solution of ferrous sulfate, dried with anhydrous sodium sulfate and distilled(bp.83.0°C). The distilled cyclohexene was passed through an alumina column. This process of purification was repeated three times. 

The small peak at 1.25 ppm is representative of an impurity(ies) that was not removed during the extraction process. Further purification from an ethanolic solution reduces the impurity(ies) to an insignificant level. These peak positions are in excellent agreement with literature values for natural rubber (Hevea). 

Earlier iterative solutions of the CSE for the 2-RDM often required that the 2-RDM be adjusted to satisfy important A-representabUity conditions in a process called purification [18, 24]. The solution of the ACSE automatically maintains the A-representability of the 2-RDM within the accuracy of the 3-RDM reconstruction. Necessary A-representability conditions require keeping the eigenvalues of three different forms of the 2-RDM, known as the D, Q, and... 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

First, any material added to a process solution other than pure water or replenishment chemistry must be considered at least a potential contaminant, requiring later removal through purification or solution disposal. Therefore, adding tap water to a process solution, when replacing evaporative losses with either "fresh" water or captured rinses containing diluted process chemistry, hastens the demise of that solution, thereby increasing waste generation. 

It may be possible to improve the operation of zinc cyanide process solutions and effect enormous reductions in waste generation.[12][13] After improving operations, it may be further possible to capture and return "escaped" process solution from the rinsing system. However, even if cyanide plating systems could be "close-looped" and the process solutions successfully maintained using standard purification techniques, the trend is definitely towards the substitutes. It may be necessary to operate... 

The most important problem is that of contamination of process solutions. Just to take one example, that of nickel, sodium and calcium concentrations have been shown to increase when dragout is returned to the process solution, likely sources being the water used for rinsing. These contaminants interfere with the plating process. Organics, chlorides, and heavy metals, from sources including the process solution itself and the work being processed, can also accumulate and pose problems. And finally, nickel metal can rise to undesirable concentrations because of the difference in anode and cathode efficiencies. While these problems may take years to manifest themselves in a low-volume operation, eventually treatment and purification is required.[20]... 

The investigated compounds were synthesized and characterized by various synthetic groups and are described elsewhere (see publication list). They were used without further processing or purification in solutions of various solvents as mentioned in the text. 

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