Applications

Inorganic extractions are used in both analytical and industrial fields. Chelates form an important part of inorganic extractions and have extensive application in many areas of science and industry.

As discussed above, analytical applications include the separation and/or preconcentration of an analyte for determination. Another analytical application is the use of inorganic extraction techniques for reagent purification by removing trace metals (e.g. purification of aqueous buffers). Extraction of metals into nonpolar organic phases crosses many scientific disciplines. For example, crown ethers are used extensively as phase transfer catalysts. Crown ethers extract an element (e.g. K + ) from the aqueous phase into an organic phase. The K+ ion is engulfed (chelated) in the centre of the crown ether. A class of antibiotics, the ionophores (e.g. nonactin, valinomycin, gramicidin, etc.) work much like crown ethers: they alter the permeability (distribution) of bacterial cells to metal ions and thereby disrupt their metabolism.

An example of a large-scale inorganic metallurgical extraction, is the Purex process used to extract ura nium isotopes and plutonium. Once the uranium ore (e.g. carnotite) is crushed, it is concentrated by physical means; the uranium is then further concentrated by flotation methods. The ore is then roasted and leached with sulfuric acid (often with an oxidizing agent) and precipitates as sodium diuranate, a bright yellow solid called 'yellowcake'. This solid dissolves in nitric acid producing uranyl nitrate. The inorganic solvent extraction (Purex process) extracts the uranyl nitrate from the aqueous solution into tributyl phosphate in an inert hydrocarbon diluent: the impurities remain in the aqueous phase.

The aim of speciation studies is to identify and quantify all species that together combine to comprise the total element concentration. This is typically achieved by physicochemical techniques. A range of physicochemical separation techniques has been applied to speciation studies, including inorganic solvent extraction.

Inorganic chelate extractions are used extensively in industrial applications. A brief listing includes the following applications:

• Metallurgical extraction

o used in water softeners o boiler scale removal o industrial cleaning o soil metal micronutrient transport o food preservation

• The chelate: nitrilotriacetic acid (NTA)

o similar applications to those listed for EDTA

• Ion exchange resins can be chelates o water purification processes

• Zeolites are a type of chelating ion exchange resin o water purification processes

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