Impurities, effect caking

The newly formed y-Mn02 actually coats the surfaces of the particles of the soHd phase the MnSO dissolves in the Hquid phase, along with the majority of the ore impurities. The effective surface area is expanded by the etching action of the sulfuric acid. Following the acid treatment step, the slurry is filtered and the cake is carefiiUy washed and dried at a controlled temperature. 

Washing in a continuous decanter is fairlv effective on solid particles larger than 80 jlrn (200 mesh), provided the particles are reasonably uniform in size with porous structure, Othenvise, the vv ash tlovvvs across the cake surface with little penetration because the pores at the cake surface are plugged bv fines. Rinsing efficiency, the proportion of soluble impurities displaced from the solids, is in the range of 50 to 80... 

The efficiency of rejecting impurity via crystallization is reduced if impurities are preferentially absorbed on the crystal surface. For resolution of chiral compounds or CrystaUization of pure bulk pharmaceuticals, trace levels of adsorbed impurities could be detrimental if not properly treated. Fortunately, surface impurities can generally be removed with proper cake cash. Therefore, an effective wash to remove the adsorbed impurities is highly desirable. 

When mixtures of anthracene and phenanthrene, such as are obtained by removing carbazole from anthracene press cake by caustic fusion, arc oxidized, mixtures of phthalic anhydride and anthraquinone result. A separation of these valuable products is effected by washing out the acids with an alkali solution and recovering as sodium salts or as acids by addification subsequent to removal of anthraquinone by filtration. The products may be distilled or sublimed to separate from any unoxidized material that may be present. Maleic acid may also be present in the products to a small extent and is recovered with the phthalic anhydride from which it must be removed as an impurity.88... 

The chemical composition of fertilizers has an effect on the caking tendency. For example, it has been shown that the caking tendency of ammonium nitrate-based and urea-based NPK fertilizers is greater than that of ammonium sulfate-based and ammonium phosphate-based NPK fertilizers [87,88,89,901. Even impurities may affect caking. Fertilizer products made from wet-process phosphoric acids characteristically contain significant proportions of iron and aluminum phosphate impurities, which have been shown to... 

Since caking is a surface phenomenon, impurities in the salt can have a disproportionate effect. Section 7.1.5.1 referred to the fact that the magnesium chloride impurity in solar salts tends to be at the surfaces of the particles. With its low critical humidity ( 29%), MgCl2 is more likely than NaCl to attract moisture from the air. The surfaces of solar salt particles, even if initially dry, tend to be wet when stored in the open. This does not necessarily mean that solar salts have more tendency to cake that requires humidity cycles. If the humidity seldom drops below the critical level, caking will not occur. Calcium chloride, with a critical humidity of about 35%, acts the same way and is added to certain specialty salts by spraying onto the surface partly to achieve this effect. Because the impurity is concentrated at the surface but at a low overall concentration, the absorption of water is limited, and the particles do not dissolve but maintain their wet feel and resist caking. 

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