Precipitation purification

Dissolution and Characterization of Final Products. The washed product slurry was adjusted to 8M HNO3 and heated to about 40°C to dissolve the oxalate precipitate. A comparison of the major impurities before and after the oxalate precipitation purification step for the sodium nitrate solution is given in Table I, and for the aluminum nitrate solution in Table II. These two solutions have been combined and will be stored to await processing by high pressure ion exchange in the MPPF. 

In precipitation purification, heavy metal ions such as copper and arsenic are precipitated as their sulfides and sulfate is precipitated as barium sulfate. 

A mixture of 10 g (45 mmol) of dibenzoylmethane, 10.9 g (90 mmol) of benzylamine and a drop of cone, hydrochloric acid was refluxed for 8 h. After cooling to room temperature and addition of ether the mixture was washed with water. After evaporation of the ether and addition of petroleum ether (bp 60 - 70 °C) the crude product precipitated. Purification with petroleum ether and ether afforded 12.2 g (86%) colorless 1.2.5a, mp 101 °C. 

Gravimetric methods have seldom been used in routine clinical chemistry. This is mainly due to difficulties encountered in the preparation of the precipitate (purification) and in weighing. However, gravimetric methods are used in many other laboratories and, when searching for a special determination, it can be enlightening to take cognizance of this mode of working. 

Fig. 50a. stem for precipitation, purification and isolation in the absence of air-, ff) condensation trap of the vacuum system J) reaction flask K) condenser M) flask with PaOsJ 0) filter tube with extension 0 and glass frit 0" 1-7) ground joints e-7 stopcocks metal... 

Then we directly carried out click reaction between 40-fold excess of alkyne-PS and alkyne-(PlBA-N3)2 to result in PS-PfBA-PS triblock while 5-fold excess is not enough to suppress the self-polycondensation of alkyne-(PiBA-N3)2 chains (Fig. 4.16a). However, one problem to deal with is how to remove the excess of alkyne-PS chains from the mixtures of reaction products. Further TFA de-protection of tertiary butyl group into carboxyl group leads to the corresponding HB-(PAA) -g-(PS)n+i and PS-PAA-PS, which would facilitate the removal of excess alkyne-PS chains. In the precipitation-purification step, we repeated dissolution-precipitation cycle three times to remove excess alkyne-PS, where cyclohexane was used as precipitant, which is a good solvent for short PS, but a very poor solvent for HB-(PAA) -g-(PS) +i and PS-PAA-PS copolymers. Finally, purified white-powder of amphiphilic copolymer HB-(PAA)io-g-(PS)n = 6.30 x 10 g/mol), HB-(PAA)47- -(PS)48 (Afw = 2.60 X 10 g/mol) and their linear triblock analogues PS-PAA-PS (Afw = 7.50 X 10 g/mol) were obtained. 

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... 

The plutonium usually contains isotopes of higher mass number (Fig. 1). A variety of industrial-scale processes have been devised for the recovery and purification of plutonium. These can be divided, in general, into the categories of precipitation, solvent extraction, and ion exchange. 

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,... 

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

The resuspended and formulated Fraction II precipitate normally contains some aggregated IgG and trace substances that can cause hypotensive reactions in patients, such as the enzyme prekail ikrein activator (186). These features restrict this type of product to intramuscular adininistration. Further processing is required if products suitable for intravenous adininistration are required. Processes used for this purpose include treatment at pH 4 with the enzyme pepsin [9001-75-6] being added if necessary (131,184), or further purification by ion-exchange chromatography (44). These and other methods have been fiiUy reviewed (45,185,187,188). Intravenous immunoglobulin products are usually suppHed in the freeze-dried state but a product stable in the solution state is also available (189). 

The sweet water from continuous and batch autoclave processes for splitting fats contains tittle or no mineral acids and salts and requires very tittle in the way of purification, as compared to spent lye from kettle soapmaking (9). The sweet water should be processed promptly after splitting to avoid degradation and loss of glycerol by fermentation. Any fatty acids that rise to the top of the sweet water are skimmed. A small amount of alkali is added to precipitate the dissolved fatty acids and neutralize the liquor. The alkaline liquor is then filtered and evaporated to an 88% cmde glycerol. Sweet water from modem noncatalytic, continuous hydrolysis may be evaporated to ca 88% without chemical treatment. 

Potassium removal is required because the presence of potassium during electrolysis reportedly promotes the formation of the a-Mn02 phase which is nonbattery active. Neutralization is continued to a pH of approximately 4.5, which results in the precipitation of additional trace elements and, along with the ore gangue, can be removed by filtration. Pinal purification of the electrolyte Hquor by the addition of sulfide salts results in the precipitation of all nonmanganese transition metals. 

Merthiolate/T4- )4-< 7 (3), sodium ethyLmercurithiosahcylate, known also as thimersol, is prepared from a 1 1 ratio of ethyhnercuric chloride/7(97-27-. and disodium thiosahcylate ia ethanol. After removal of the sodium chloride by filtration, the free acid is precipitated by acidification with dilute sulfuric acid. Purification is achieved by recrystallization from 95% ethanol, and the product, merthiolate, is obtained by neutralization with a stoichiometric amount of sodium hydroxide. 

The removal of copper from the pregnant nickel solution in the Sherritt-Gordon process is an example of purification by precipitation of a fairly insoluble compound. First, in the copper boil step, ammonia is driven off by heating the solution, and some copper sulfide precipitates. The residual copper is removed by a dding hydrogen sulfide for the chemical precipitation of mote copper sulfide. 

The cementation of gold and the purification of the ziac electrolyte ate usually carried out ia cylindrical vessels usiag mechanical agitation. The cementation of copper is carried out ia long narrow tanks called launders, ia rotating dmms, or ia an iaverted cone precipitator (see Copper). 

Gas Reduction. The use of a gaseous reduciag agent is attractive because the metal is produced as a powder that can easily be separated from the solution. Carbon dioxide, sulfur dioxide, and hydrogen can be used to precipitate copper, nickel, and cobalt, but only hydrogen reduction is appHed on an iadustrial scale. In the Sherritt-Gordon process, the excess ammonia is removed duting the purification to achieve a 2 1 ratio of NH iNi ia solution. Nickel powder is then precipitated by... 

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. 

Metals less noble than copper, such as iron, nickel, and lead, dissolve from the anode. The lead precipitates as lead sulfate in the slimes. Other impurities such as arsenic, antimony, and bismuth remain partiy as insoluble compounds in the slimes and partiy as soluble complexes in the electrolyte. Precious metals, such as gold and silver, remain as metals in the anode slimes. The bulk of the slimes consist of particles of copper falling from the anode, and insoluble sulfides, selenides, or teUurides. These slimes are processed further for the recovery of the various constituents. Metals less noble than copper do not deposit but accumulate in solution. This requires periodic purification of the electrolyte to remove nickel sulfate, arsenic, and other impurities. 

The older methods have been replaced by methods which require less, if any, excess sulfuric acid. For example, sulfonation of naphthalene can be carried out in tetrachloroethane solution with the stoichiometric amount of sulfur trioxide at no greater than 30°C, followed by separation of the precipitated l-naphthalenesulfonic acid the filtrate can be reused as the solvent for the next batch (14). The purification of 1-naphthalenesulfonic acid by extraction or washing the cake with 2,6-dimethyl-4-heptanone (diisobutyl ketone) or a C-1—4 alcohol has been described (15,16). The selective insoluble salt formation of 1-naphthalenesulfonic acid in the sulfonation mixture with 2,3-dimethyl aniline has been patented (17). 

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