Wet extraction

Measured concentrations of 2-ADNT and 2,4-DANT in spiked sediments at the end of a short mixing period (up to 4 h) were also substantially lower than nominal concentrations [8,9,13], as expected based on the description of the fate of those compounds in sediment [7], Spiking of TNB to sediment resulted in the formation of l-amino-3,5-dinitrobenzene, also called 3,5-dinitroaniline [13]. Similar to TNT, reduced transformation products of TNB can form covalent bonds with the sediment and resist solvent extraction, thus explaining the substantial difference between the analytically determined concentrations of extractable compounds and the expected concentrations. Similar to TNT, air-drying of sediment spiked with TNB or 2,4-DANT prior to solvent extraction appears to promote a decrease of the extraction efficiency of parent and transformation products, as lower extraction efficiencies were observed with air-drying [8] than without air-drying [13] for those compounds in separate studies. A direct comparison of the extraction efficiency of spiked sediment extracted wet and air-dried, conducted for 2,6-DNT [12], should be performed for other major explosives for validation of the recommendation of wet extraction [12] of sediments contaminated with explosive compounds. 

Liang, L., Horvat, M., Fajon, V., Prosenc, N., Li, H., and Pang, P., Comparison of Improved Combustion/Trap Technique to Wet Extraction Methods for Determination of Mercury in Crude Oil and Related Products by Atomic Fluorescence, Energy Fuels, Vol. 17, No. 5,2003, pp. 1175-1179. 

For the wet-extraction of copper, the chalcopyiite (CxiFeS2) is usually used as the raw materials, and the leaching reagent is the ferric sulphate. Its leaching reaction is... 

If the source of the polyunsaturated acid is a tissue rather than a pure fat or oil, the total lipid must first be extracted by some method of wet extraction. For example, Holman and Greenberg (1953) employ ethanol, or ethanol-ether, as a solvent, or separate the acid after digestion of the tissue with 30% potassium hydroxide. It is important to protect the sample as much as possible during all stages of preparation, and for this reason the reactions are generally carried out as far as is practicable under nitrogen. After isolation of the lipid mixture, the material is saponified (if this step has not been previously carried out), and the acid is freed, washed, and dried. 

A significant part of the wet extraction processes for minerals invedves either the removal of oversi/e materials from a suspension or the division of a suspension inlo two fractions by particle size. For these purposes, the decanter, operating in classiticatinn mode, is an ideal processing tool. 

Coconuts have a solid as well as a liquid endosperm. Solid endosperm is the white coconut kernel which is used to extract coconut oil. The extraction process can be categorized based on the nature of coconut kernel and the methods used to obtain oil from coconut kernel. If dry coconut kernel is used for the extraction of coconut oil, the process is called dry process. Fresh coconut kernel is used in the wet extraction process. Here, a water emulsion of coconut kernel is prepared by mixing crushed or scraped coconut kernel with water. The resultant white-colored, milk-like emulsion, usually known as coconut milk is used for the extraction of coconut oil. 

In addition to the separation of coconut oil from a coconut milk emulsion, enzyme treatment can also be used to extract coconut oil from finely divided copra meal. Coconut oil extraction based on the enzymatic action of polygalacturonases, a-amylase and proteases on a diluted coconut paste has been tested (McGlone et al., 1986). After the reaction with enzymes, the mixture gave three phases upon centrifugation. The upper phase contained high quality coconut oil and the middle layer and the lower layer contained water and coconut meal respectively. This process gave a yield of 80%, which is a much higher yield compared to other traditional wet extraction methods. Enzyme assisted extractions have also been used to extract coconut oil from powdered copra. The crude commercial enzyme used in this study contained a-amylase, neutral protease, acid protease, cellulase/hemicellulase, and pectinase. The enzyme treatment in this process can be considered as a pretreatment of copra prior to the oil extraction. The enzyme was added 1% rate of the copra and allowed to stand for 30 min. After enzyme treatment, the meal was extracted by hot water and the emulsion was boiled to evaporate water. This enzyme pretreatment of copra prior to the extraction improved the yield of coconut oil by 50% compared to the same extraction procedure without enzyme... 

The higher phenolic antioxidant contents of eoeonut oil prepared at high temperatures can be easily explained by considering the polarities of phenolic substances and coconut oil. Coconut oil can be considered as a non-polar substance and oil dissolves in nonpolar solvents such as hexane. On the other hand phenolic substances are polar substances and, therefore, the solubility of polar phenolic substances in nonpolar coconut oil is low. More phenolic substances are incorporated into coconut oil when oil is extracted by wet extraction with prolonged boiling of coconut milk emulsion. High temperatures improve the solubility of phenolic substances in coconut oil. In the cold extraction methods, the phenohc substances are not properly ineorporated into eoeonut oil due to the mild temperature conditions. 

As the fatty acid composition of coconut oil is independent of the method of extraction, it can be assumed that any health effect purely connected to the fat content may not vary with the type of coconut oil. However, non-lipid components of coconut oil significantly vary with the method of extraction. As most of these minor compounds are polar in nature, then-solubility in coconut oil is higher at high temperatures. Therefore, coconut oil prepared by boiling coconut milk contains higher amounts of phenolic antioxidants compared to other coconut oils. Virgin coconut oil produced under cold conditions can also retain thermally unstable non-lipid matter such as vitamins, some phenolic compounds and several other compounds such as sterols. Copra oil contains lower amount of important non-lipid compounds. Therefore, coconut oil prepared by wet extraction under cold or hot conditions seem to confer better beneficial health effects compared to copra oil. 

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