Recrystallization lead sulfate

Plate curing. Pallets with plates are placed in a high humidity chamber and left to cure at 35 °C for 48—72 h. During the curing process, lead in the paste is oxidized, the basic lead sulfates recrystallize and the plates are then dried to moisture content <0.5%. 

When the paste is ready, it is poured into an intermediate paste feeder (hopper) from where it is charged periodically (in batches) into the pasting machine mounted under the hopper. The paste is stirred in the hopper to maintain its homogeneity and to allow recrystallization of basic lead sulfates to reach an advanced stage. 

The principal impurities ia technical-grade bode acid are the by-product sulfates, <0.1 wt %, and vadous minor metallic impurities present in the borate ores. A bode acid titer is not an effective measure of purity because overdrying may result in partial conversion to metabotic acid and lead to B(0H)2 assays above 100%. High putity bode acid is prepared by recrystallization of technical-grade matedal. 

Lead tetraacetate is added in small quantities, with stirring, to an ice-cold suspension of 11 g. of ethyl 3-(D-arabino-tetrahydroxybutyl)-5-methyl 4-furoate in 100 ml. of benzene plus 40 ml. of glacial acetic acid. Addition is stopped when there is a positive reaction with potassium iodide-starch paper. The mixture is stirred for a further ten minutes, filtered, and the benzene solution washed twice with water. The benzene layer is then dried with anhydrous sodium sulfate, filtered, and the filtrate evaporated to dryness. The residue (6 g.) is mixed with a solution of 7.5 g. of sodium hydroxide plus 20 g. of silver nitrate in 40 ml. of water, and heated for 40 minutes on a steam bath. The aqueous solution is filtered, acidified to Congo Red while being cooled with ice, and the crystals formed are removed by filtration, washed with ice-cold water, and dried over phosphorus pentoxide in the vacuum desiccator yield, 2.2 g. After recrystallization from water, the product has m. p. 234r-235°. 

Boron trifluoride etherate (37.9 ml) was added to a stirred solution of 3a-hydroxy-5a-pregnane-ll,20-dione (6.64 g, 20 mmol) and lead tetraacetate (10.1 g, 22 mmol) in dry benzene (280 ml) and methanol (15.1 ml) at room temperature. After 2 h the mixture was poured into water (2 L) and extracted with ether (1 L). The combined ether extracts were washed successively with sodium bicarbonate solution and water, dried over magnesium sulfate, and concentrated in vacuo to give a white crystalline mass. Four recrystallizations from acetone-petroleum (b.p. 40°-60°C) gave 21-acetoxy-3a-hydroxy-5a-pregnane-ll,20-dione as fine needles (4.22 g, 54%), melting point 172°-173°C. 

Heterogeneous exchange of radionuclides on carbonates has already been mentioned. Exchange on other sparingly soluble minerals (e.g. halides, sulfates, phosphates) may lead to rather selective separation of radionuclides. Following the exchange at the surface, ions may be incorporated into the solids in the course of recrystallization, which is a very slow but continuous process. Anomalous solid solutions with radioactive ions of different charges may also be formed. 

The rate of aging is strongly influenced by other solutes in solution and thus can be increased or decreased by the presence of excess lattice ions in solution. Barium sulfate ages more slowly in barium ion solution than in sulfate and more slowly in sulfate than in water. The aging of silver chloride is impeded by silver ion, but speeded by chloride ion a similar effect exists for silver bromide. For lead chromate no particular lattice ion effect was noticed. Apparently the rate of aging does not parallel solubility, which is decreased by the common ion effect. Kolthoff and others postulated that the solubility in the adsorbed water layer may be different from that in the bulk of the solution. For example, in the case of silver chloride in the presence of adsorbed chloride ion, the solubility may be increased owing to the formation (Section 7-7) of AgCl2 in the immediate vicinity of the surface. It appears likely that the adsorbed lattice ion also has a pronounced effect on the rate of recrystallization, which is not necessarily parallel with solubility even in the adsorbed water layer. 

In the case of a diffusion-limited reaction, hydrodynamic factors, such as turbulent flow, may influence the dissolution process. Humidity fluctuations also may alter the solute concentrations in the moisture film at the rock surface, and they may result in the dissolution and recrystallization, not only of the carbonates, but also of the secondary minerals, such as calcium sulfate. Wetting and drying cycles may lead to measureable changes in fluid composition at the stone surface. 

Freshly distilled aniline (93 g) and sulfur (32 g) are stirred in an oil-bath at 135-145° while lead oxide (160 g) is added during 5.5 h. Stirring is continued for a further 0.5 h, after which the dark oily product is cooled, treated with 20% sodium hydroxide solution (30 ml), and extracted three times with boiling alcohol. The alcohol is distilled off and the excess of aniline is removed in steam. Treatment with dilute hydrochloric acid affords the hydrochloride, which is dissolved in water, treated with charcoal, and reconverted into the base by alkali. The base can be further purified by way of the sulfate and after final recrystallization from 35 % alcohol has m.p. 107-108°. 

Careful optimization of the process leads to efimination of the minor explosions and improved yield. The method itself has however been superseded by the diamine complex route. These complexes are synthesized by the reaction of acidic copper salt of 5-nitrotetrazole with the relevant diamine (mostly 1,2-ethylenediamine or less frequently 1,3-diaminopropane) in the presence of copper sulfate [4,40,41,46, 56,66]. These coordination compounds could be readily purified by recrystallization from water and they are safer and easier to handle in the dry state than the sodium salt (1,2-ethylenediamine complex only bums when impacted by 2.5 kg hammer from 50 cm) [42, 46]. 

To improve the performance of lead-acid batteries, some soluble sulfate such as SnS04, Na2S04, and Li2S04 can be added to the electrolyte to help the battery recover from deep discharge according to the common ion effect. As a general rule, the total quantity of the additive should not be more than 15 g/L. This kind of additive mainly improves sulfation and recrystallization. Furthermore, such additives... 

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