Citric acid earths

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

A composition for dissolving filter-cake deposits left by drilling mud in wellbores is composed of an aqueous solution of citric acid and potassium chloride, alkali metal formate, acid tetraphosphate, alkaline earth chloride, and alkali metal thiophosphate [1012]. 

Most divalent and trivalent ions, with the exception of the alkaline-earth metals, are effectively chelated by the hydroxycarboxylates citric and tartaric acid, and citric acid will also sequester iron in the presence of ammonia. Another hydroxycarboxylate, gluconic acid, is especially useful in caustic soda solution and as a general-purpose sequestering agent. 

Eluants.—Citric acid buffered with ammonium citrate is the first eluant to be used in the separation of rare earths by ion exchange process. It is also the most extensively [85—89] investigated eluant. At low pH the individual rare earths move down the column at different rates. A plot of volume of eluted portion vs. concentration shows typical bell-shaped curves (Fig. 2) with widely spaced maxima characteristic of elution chromatography, although the system makes use of a chelating agent. 

The application of cellulosic anion exchanger in the separation of trace amounts of rare earths has also been investigated. Diethylaminoe-thyl cellulose paper and 0.026M citric acid were found to be the most satisfactory. A separation factor of 2.6 between Eu and Ce was obtained [123]. It has been found [124] that a mixture of HC1 and various aliphatic alcohols can be successfully used as eluant for the separation of rare earths by paper chromatography (Whatman No. 1). 

The extraction methods for aflatoxins are based on the solubility of these toxins in organic solvents, mainly chloroform, methanol, acetone, benzene, and acetonitrile. For more complex matrices, the addition of diatomaceous earth or citric acid is required. From matrices of vegetable origin, water is usually added in the extraction step, since it facilitates solvent penetration into substrates, improving the percentage of extraction of the toxin. 

Ion exchange has many preparative and analytical uses for example, the separation of the rare earths is usually achieved by cation exchange followed by elution of their complexes with citric acid. 

This method is well-known and is used for the synthesis of homogeneous multicomponent metal oxide materials it includes a combined process of metal complex formation and in situ polymerization of organics. It relies on the development of complexes of alkali metals, alkaline earths, transition metals, or even nonmetals with bi- and tridentate organic chelating agents such as citric acid [40],... 

The oil is loaded into the reactor, shown with both an agitator and a pumped circulation-spray loop, and heated under vacuum (110-130°C) to reduce water and peroxide contents. Next, the oil is cooled to 70-90°C and the catalyst is added as dry powder at 0.05-0.15 percent or suspended in dry oil. Randomization requires about 30 min, with an additional 15-30 min allowed for completioa After the reaction is complete, the batch is transferred to a postbleacher where the process is arrested by inactivating the catalyst by addition of water or an (phosphoric or citric) acid solution. Bleaching earth, added to absorb the inactivated catalyst and soaps removed by filtration and the oil sent to blending or deodor-ization. Losses from the formation of FFA and FAME are —10 times the catalyst weight, with... 

Poiishing fiitration Free fatty acids Odor and flavor compounds Bieaching earth Citric acid Carbonaceous materiai tank to deodorizer Pumping from deodorizer to poiish fiiter to oii cooier to storage tank 204-274 (400-525) 50-70 (122-158) 60-66 (140-151) 60-66 (140-151) Nitrogen or air Nitrogen or air... 

Citric acid is incompatible with potassium tartrate, alkali and alkaline earth carbonates and bicarbonates, acetates, and sulfides. Incompatibilities also include oxidizing agents, bases, reducing agents, and nitrates. It is potentially explosive in combination with metal nitrates. On storage, sucrose may crystallize from syrups in the presence of citric acid. 

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