Precipitation 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. 

Precipitation and Purification. During the hydrolysis, control tests are made by turbidimetric titration of samples taken intermittently. When the desired degree of hydrolysis is reached, the ester is precipitated from the reaction solution into water. It is important for the precipitate to have the proper texture for subsequent washing to remove acid and salts for thermal stabilization. Before precipitation, the reaction solution is usually diluted with additional aqueous acetic acid to reduce the viscosity. If a flake texture is desired, the solution is poured into a vigorously stirred, 10—15% aqueous acetic acid. To precipitate the acetate in powder form, dilute acetic acid is added to the stirred reaction solution. In both cases, the precipitated ester is suspended in 25—30% aqueous acid solutions and finally washed with deionized water. The dilution, precipitation temperature, agitation, and strength of the acid media must be controlled to ensure uniform texture. 

A compound whose solubility increases with temperature can be purified by recrystallization. The impure solid is dissolved in a minimum volume of hot water. The hot solution is filtered to remove insoluble impurities, and then the solution is cooled in an ice bath. The solubility of the compound decreases as the temperature drops, causing the substance to precipitate from solution. Soluble impurities usually remain in solution. Purification by recrystallization is not restricted to aqueous solutions. An organic solid can be purified by recrystallization from an appropriate organic solvent. 

If a diluted solution of dithiole 182 and sulfur monochloride in ether were mixed at low temperature, tetrathiane 183 was formed in low yield (1995JOC8056). The precipitation and purification of the final product were achieved by cooling the mixture to —78 °C (Scheme 92). 

Other methods currently in use for Ca determination in concretes are based entirely on precipitations for purification of the Ca. Suarez et al (2000) utilise a chromate precipitation for removal of Ba and Ra from the solution. This is a pH dependant precipitation, and the chromate solution resulting from this requires a separate waste stream. The method has a total of 9 steps after sample dissolution, and has decontamination factors of >10" for Ba and Co, >10 for Sr and >10 for Eu. The minimum detectable activity by liquid scintillation counting is 0.29 Bq/g for Ca (0.034 Bq/g Ca). 

An extra purification step is needed when long DNA fragments are used after step 4, add 1 volume of alkaline precipitation solution and 2.5 volumes of cold 100% ethanol (mix gently) and incubate for at least 20 min at -20°C (see Note 7). 

After solution purification, cobalt can be deposited as Co(II) or Co(III) hydroxide. The cobalt solutions are often too low in cobalt for direct electrowinning. In this case, cobalt hydroxide is precipitated, thickened, and redissolved to cobalt tankhouse electrolyte and then electrowon [77]. The cobalt hydroxide has been reduced in electric furnaces to an alloy with 80% Co, 18% Fe, and 0.8% Ni, cast to anodes, and electrorefined. The process was done in Flybinette cells, and the solution contained 60-120 g L 1 Co, pH was 3.3-48, and the temperature was 60 °C. The current density was 160-240 A m-2, cell voltage was 1.2-1.8 V, and the current efficiency was 95%. This process is not used anymore because of the lack of... 

Good descriptions of the production of aluminum can be found in the literature (Grjotheim etal. [7], Grjotheim and Welch [8], Grjotheim and Kvande [9], Burkin [10], and Peterson and Miller [11]). Referring to Fig. 2 [12], the first step in the production of aluminum from its ore ( bauxite ) is the selective leaching of the aluminum content (present as oxides/hy dr oxides of aluminum) into hot concentrated NaOH solution to form sodium aluminate in solution. After solution purification, very pure aluminum hydroxide is precipitated from the cooled, diluted solution by addition of seed particles to nucleate the precipitation. After solid-liquid separation the alumina is dried and calcined. These operations are the heart of the Bayer process and the alumina produced is shipped to a smelter where the alumina, dissolved in a molten salt electrolyte, is electrolyt-ically reduced to liquid aluminum in Hall- Heroult cells. This liquid aluminum,... 

Bulk (batch) Simpler equipment No diluent impurities May require solution and subsequent precipitation for purification and/or fabrication May require reduction to usable particle size Broad molecular weight distribution Inefficient heat and mass transport at higher conversion... 

The above strategies (iron distribution, acid leaching and the modified neutral leaching) have collectively improved arsenic removal from the circuit, and hence improved the quality of the preconcentrate feed to the indium-germanium plant. With increasing experience in the operation of the new lead smelter, the fiime quality has also improved. This ftirther facilitates solution purification through iron precipitation as well as the production of indium and germanium. 

Louis P., Cobalt Solution Purification By Solvent Extraction or by Selective Precipitation , Hydrometallurgy of Nickel and Cobalt 2009, 39 Annual Hydrometallurgical Meeting, Sudbury, Canada, 2009, 255-270... 

May require solution and subsequent precipitation for purification and/or fabrication... 

Purification of the Methylamine HCI is in order now, so transfer all of the crude product to a 500mL flask and add either 250mL of absolute Ethanol (see end of FAQ for preparing this) or, ideally, n-Butyl Alcohol (see Footnote 4). Heat at reflux with a Calcium Chloride guard tube for 30 minutes. Allow the undissolved solids to settle (Ammonium Chloride) then decant the clear solution and cool quickly to precipitate out Methylamine HCI. Filter rapidly on the vacuum Buchner funnel and transfer crystals to a dessicator (see Footnote 3). Repeat the reflux-settle-cool-filter process four... 

MetaUic ions are precipitated as their hydroxides from aqueous caustic solutions. The reactions of importance in chlor—alkali operations are removal of magnesium as Mg(OH)2 during primary purification and of other impurities for pollution control. Organic acids react with NaOH to form soluble salts. Saponification of esters to form the organic acid salt and an alcohol and internal coupling reactions involve NaOH, as exemplified by reaction with triglycerides to form soap and glycerol,... 

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