Inorganics freeze concentration

Concentration. This group consists of those processes in which water is removed and the dissolved substances are left behind. Examples are freeze concentration, lyophilization (freeze-drying), vacuum distillation, and membrane processes such as reverse osmosis and ultrafiltration. A common disadvantage of these methods is that inorganic species are concentrated along with the organic constituents. 

The subject of salt effects on the freezing process is not new. Nevertheless, despite many years of study, it is still an inadequately understood process (12). Recent applications of the freeze concentration technique to inorganic recovery from water have been reported (2, 9, 10, 16). Many of these studies were prompted by a communication (J5)... 

Dissolved inorganic solids have been shown to inhibit organic recovery eflBciency by freeze concentration from aqueous solution (4). Similarly, increased salt content reduces cationic recovery (Figure 7). As ionic concentration increases at the interface, there is an increase in tendency toward dendritic growth and associated entrapment, changes in surface tension and induced interfacial potential, and impedance of specific ionic migration. 

The occurrence of selective ion incorporation has precluded the use of an internal standard as an indicator of the overall recovery eflBciency, a technique apphed successfully to the concentration of organics (4). Because of this inabihty at the present time to quantify the eflBciency of concentration, the application of the freeze concentration technique solely for the determination of trace inorganics is impractical. There are more precise methods available for inorganic concentration—e.g., evaporation or solvent extraction. Further refinement of the freeze concentration technique for cations may be achieved by washing the ice after transfer of the residual liquid. This point is being confirmed by current studies. 

The study is a direct outgrowth of a continuing investigation of the freeze concentration of organic microcontaminants in water. The concentration of inorganic constituents is being monitored by atomic absorption... 

Farad. Boc. xiv. 10,1921) for the composition of the sols and gels of the inorganic colloidal hydroxides, e.g. zirconia produced by the hydrolysis of zirconium oxychloride. By electropotentiometric measurements of the hydrogen and chlorine ion concentrations of sols formed by hydrolysis as well as freezing point, conductivity and transport number determinations he has shown that a series of salts are formed of the types ... 

Humic substances have been concentrated by vacuum distillation. This method is carried out at low temperatures, which avoids decomposition and chemical reactions within the sample (Jolley et al., 1975), and is faster than freeze-drying (Katz et al., 1972). All solutes are concentrated by this method, and coprecipitated organic matter must be further extracted from precipitated inorganic salts (Katz et al., 1972). Vacuum distillation of humic substances to dryness is not recommended because it results in a dense product that is not easily removed from the drying vessel and may be difficult to dissolve. 

Baker, R. A. (1967). Trace organic contaminant concentration by freezing. I. Low inorganic aqueous soiutions. Water Res. 1, 61-77. 

Freezing is considered to be an acceptable preservation method for wet sediments collected for the determination of inorganic constituents (Forstner, 2004). It has been shown that rapid deep-freezing can best maintain sample integrity, thus enabling reliable evaluation of contaminant concentrations. The lower the deepfreezing temperature the better a minimum temperature of —80°C was suggested. 

Nitrous oxide (laughing gas) [10024-97-2] M 44.0, b -88.5. Wash the gas with concentrated alkaline pyrogallol solution, to remove O2, CO2, and NO2, then dry it by passing it through columns of P2O5 or Drierite, and collecting in a dry trap cooled in liquid N2. It is further purified by freeze-pump-thaw and distillation cycles under vacuum [Ryan Freeman J Phys Chem 81 1455 1977, Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 484-485 1963]. 

---