Sulfate control

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. 

For calcium carbonate or calcium sulfate control under high-stress conditions, use PMA. It is suitable for use at up to 1,300 psig. 

Question 3.4 How Is the Toxicity of Barium Sulfate Controlled for X-Rays ... 

The support of colleagues Arthur Wilson in polyimide processing and helpful discussions, and Qiarles Baker in preparation and application of the sodium lauryl sulfate controlled contamination solutions is gratefully acknowledged. Mary Mayfield and James Field assisted in the processing of the samples, and Ronald Huff made some of the electrical measurements. Their careful work is much appreciated. 

Total activity used for protamine sulfate control 32 units... 

Reaction (18-6) is considered to be the rate-limiting step. This is analogous to the oxidation of oxalate by permanganate (Section 17-2), where a critical intermediate is a complex between oxalate and Mn(III). The rate-limiting step is reversible in that the 204" radical can reoxidize the Ce(III) to Ce(IV). The concentration of sulfate controls the amount of the Ce(IV)-oxalate reactive intermediate formed, but not its specific rate of decomposition. Thus the error in the Fe(II)-Ce(IV) titration in the presence of oxalate can be decreased by the addition of sulfate. Phosphate also inhibits the Ce(IV)-oxalate reaction. 

Caraco, N., Cole, J. J., Likens, G. N. (1989). Evidence for sulfate-controlled phosphorus release from sediments of aquatic systems. Nature, 341, 316-318. 

The system allows easy sulfate control, good cr retal growth, and low nucleation rates. 

Selection of salt, chemical treatment ion exchange selection of barium salt or alternative process for sulfate control... 

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. 

The major anionic impurity in most brine systems is sulfate. Control of its concentration is an issue mostly in membrane cells. In the diaphragm-cell process, sulfate passes with the rest of the anolyte into the cathode side of the cells. It can be separated from caustic soda in the evaporators and purged from the system as Glauber s salt This is covered in Section 9.4.2.1. Mercury cells are least sensitive to sulfate. Its concentration is frequently allowed to build to the point where dissolution of calcium sulfate from the salt is inhibited. The greatest problem then caused by the sulfate is a reduction in the solubility of NaCl or KCl. 

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). 

D.A. Santos, Sulfate Control in Brine from Poor-Quality Raw Salt, SecondNafion Global Users Forum, Fayetteville, NC (1993). 

A.2.2. Membrane Cells. The bulk of the sulfate in the electrolysis circuit moves into the catholyte only in diaphragm cells. In membrane cells, it remains in the anolyte. Even when a salt contains only a modest amount of sulfate, then, it can accumulate by recycle and exceed the allowable concentration in the cells. For this reason, the many techniques of sulfate control described in Section 7.5.7 have been developed. 

Generic Names morphine sulfate controlled-release tablet morphine sulfate extended-release... 

Ruhr JW, Bankova L, Funchs S, et al. Fruit acids and sodium hydroxide in the food industry and their combined effect with sodium lauryl sulfate controlled in vivo tandem irritation study. Br J Dermatol. 2004 151 1039 8. 

Nurcombe, V., Cool, S.M., 2007. Heparan sulfate control of proliferation and differentiation in the stem cell niche. Crit. Rev. Eukaryot. Gene Expr. 17 (2), 159-171. 

Sulfate control and remediation. Proceedings of 4th International Symposium on Environmental Geochemistry. Vail, Colorado. October 1997. 

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