Sulfate control precipitation

An alternative process for opening bastnasite is used ia Chiaa high temperature roastiag with sulfuric acid followed by an aqueous leach produces a solution containing the Ln elements. Ln is then precipitated by addition of sodium chloride as a mixed sulfate. Controlled precipitation of hydroxide can remove impurities and the Ln content is eventually taken up ia HCl. The initial cerium-containing product, oace the heavy metals Sm and beyond have been removed, is a light lanthanide (La, Ce, Pr, and Nd) rare-earth chloride. 

The gels precipitated as described above are not useful in ion-exchange systems because their fine size impedes fluid flow and allows particulate entrainment. Controlled larger-sized particles of zirconium phosphate are obtained by first producing the desired particle size zirconium hydrous oxide by sol—gel techniques or by controlled precipitation of zirconium basic sulfate. These active, very slightly soluble compounds are then slurried in phosphoric acid to produce zirconium bis (monohydrogen phosphate) and subsequently sodium zirconium hydrogen phosphate pentahydrate with the desired hydrauhc characteristics (213,214). 

A standard stock solution of sirolimus was prepared in methanol. Controls and standard working solutions were prepared by spiking blank whole blood with the stock solution. Standards, controls, and patient whole blood (10 fi. ) were transferred to 1.5 mL polypropylene tubes, mixed with 40 fiL of 0.1M zinc sulfate solution, precipitated with 100 fiL of methanol containing the IS (2 fig/L), vor-texed vigorously for 5 sec, and centrifuged at 10,500 g for 5 min. Supernatants were collected and assayed. The injection volume was 20 fiL. The retention times of sirolimus and ascomycin were 0.93 and 0.89 min, respectively. The total run time was 2.5 min. Representative MRM chromatograms of a patient sample are shown in Figure 11.6. 

Cathodic precipitates increase cathodic site passivity with precipitation of insoluble compounds. Frequendy used cathodic precipitation inhibitors are CaCOs, MgCOs, or zinc sulfates that precipitate as Zn(OH)2. The efficiency of these inhibitors is only controlled by pH adjustment. Calcium carbonate (limestone) dissolves in water as calcium bicarbonate Ca(HC03)2- Carefid pH control forms smooth and hard calcium carbonate barrier films. Once the precipitate is formed, pH must be carefully controlled to avoid film dissolution at lower pH values ... 

This section is included here to make the discussion of precipitation more nearly complete. There are many other techniques for the control of sulfate in brine, especially in membrane-cell plants. Because not all these come under the heading brine treatment and because of its importance, sulfate control is the topic of a separate section (Section 7.5.7). There, the chemistry of calcium sulfate is explored in more detail. 

Concentrated Purge. New methods of sulfate control have been developed in response to the membrane-cell brine problem. These include a novel application of the familiar ion-exchange technique and a process based on the relatively new technique of nanofiltration. The processes use physical or chemical means to make a partial separation between chloride and sulfate the problem of disposal of the sulfate remains. By concentrating the sulfate and removing most of the chloride, they may allow safe, legal, and economic disposal of the sulfate by a simple purge. In other cases, their value lies in providing a much smaller stream to be treated for the ultimate disposal of the sulfate (e.g., by precipitation). 

Benzidine methods make use of the very low solubility of benzidine sulfate which can be isolated and titrated as an add as in the method of Rosenheim and Drummond (79), or determined by means of a color reaction such as that with hydrt en peroxide and ferric chloride (91), or sodium fi-naphthoquinone-4-sulfonate(59),orbydiazotizationandcoupling(33,55,72). The colorimetric methods are claimed to be very sensitive. The benzidine method provides a rapid method for estimating ethereal sulfate but since, like the Folin (43) method, it is a difference method it becomes less reliable as the inorganic. ethereal sulfate ratio increases. The precipitation of benzidine sulfate by the original method, especially from hydrolyzed urines, may occasionally be capricious, even to the extent that less benzidine sulfate is precipitated from hydrolyzed urine than from unhydrolyzed urine. This difficulty can be largely overcome by preliminary removal of phosphates and precipitation under conditions recommended by Fiske (42). Under experimental conditions dietary control may serve to ensure that the excretion of phosphate is so low as not to interfere with precipitation of benzidine sulfate (e. g.. Maw (63)). 

Electrochemical polymerization is less frequently employed for bulk P(ANi) production and more frequently for production of thin films for spectroelectro-chemical or similar characterization. In a typical procedure, ANi monomer is dissolved in an aqueous sulfuric acid solution (white ANi-sulfate first precipitated is shaken in solution until it redissolves). A potential of less than +0.9 V (vs. Pt quasireference) is then applied to a suitable electrode (e.g. Pt) on which the P(ANi) film is desired. Polymerization is rapid, and film thickness is controlled coulometrically. The polymer film is washed before further characterization. The cyclic voltammo-grams of such P(ANi) films display the dual-redox-peaks characteristic of poly-(aromatic amines) P(ANi) has also been electropolymerized in acetonitrile medium, but the overall properties of the polymer so obtained are considerably inferior to that obtained in aqueous medium. 

Aqueous solutions of the metal salts, usually nitrates or sulfates, are precipitated with an alkali such as sodium carbonate. Ammonium carbonate ean be used to avoid residual sodium impurity, but it is relatively expensive. Occasionally precipitation conditions are controlled to form complex catalyst precursors and higher-activity products. If necessary, any support material can be added as a powder before the alkali is added. 

The lignitic coals of the northern United States tend to have low sulfur contents, making them attractive for boilet fuels to meet sulfur-emission standards. However, low sulfur content coals have impaired the performance of electrostatic precipitators. The ash of these coals tends to be high in alkaline earths (Ca, Mg) and alkaUes (Na, K). As a result, the ash can trap sulfur as sulfites and sulfates (see Airpollution control methods). 

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. 

The pulp and paper industry and potable and wastewater treatment industry are the principal markets for aluminum sulfate. Over half of the U.S. aluminum sulfate produced is employed by the pulp and paper industry. About 37% is used to precipitate and fix rosin size on paper fibers, set dyes, and control slurry pH. Another 16% is utilized to clarify process waters. The alum sold for these purposes is usually Hquid alum. It is frequendy acidic as a result of a slight excess of H2SO4. Aluminum sulfate consumption by the pulp and paper industry is projected to remain constant or decline slightly in the near term because of more efficient use of the alum and an increased use of alkaline sizing processes (13). 

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

As the most significant point sources of phosphorus are those from sewage treatment works (STW), control of phosphorus loading is most readily achieved either by precipitation of phosphorus with iron salts (iron(lll) sulfate or iron(lll) chloride) or by biological removal. The latter can only effectively be achieved in STWs using activated sludge and there have been many descriptions of this technique. ... 

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