Methods for removing an oxyanion from an aqueous source containing said oxyanion, comprising contacting said aqueous source with an aqueous-insoluble hydrophobic solution containing an oxyanion extractant compound dissolved in an aqueous-insoluble hydrophobic solvent to result in formation of an oxyanion salt of said extractant compound and extraction of said oxyanion salt into said aqueous-insoluble hydrophobic solution, wherein said extraction results in an extraction affinity (D) of said oxyanion of at least 1, wherein D is the concentration ratio of said oxyanion in the organic phase divided by the concentration of said oxyanion in the aqueous phase; wherein said extractant compound has the following composition: ##STR00001##
wherein at least one of R.sup.1-R.sup.10 is or contains a hydrocarbon (R) group containing at least 4, 5, 6, 7, 8, 9, 10, 11, or 12 carbon atoms.

A method for extracting a rare earth element from a rare earth-containing substance, the method comprising mixing the rare earth-containing substance with a protic ionic liquid, such as:

##STR00001##

wherein R.sup.1 is selected from hydrogen atom and hydrocarbon groups containing 1 to 6 carbon atoms; R.sup.2 and R.sup.3 are independently selected from hydrocarbon groups containing 1 to 12 carbon atoms; and X.sup. is an anionic species; to produce a composition of the formula (RE)(amide).sub.yX.sub.z at least partially dissolved in the protic ionic liquid, wherein RE is at least one rare earth element having an atomic number selected from 39, 57-71, and 90-103; y is 2-6; z is a number that charge balances the total positive charge of RE; and the amide is the conjugate base of the cationic portion of the protic ionic liquid of Formula (1) and has the following formula:

##STR00002##

Hydrometallurgical compositions are described in which organic amine-based lixiviants and organic amine-based pre-lixiviants are utilized in the selective recovery of rare earth elements. The lixiviant species can be regenerated in situ, permitting the organic amine to be used in substoichiometric amounts.

Hydrometallurgical compositions are described in which organic amine-based lixiviants and organic amine-based pre-lixiviants are utilized in the selective recovery of rare earth elements. The lixiviant species can be regenerated in situ, permitting the organic amine to be used in substoichiometric amounts.

Methods and compositions are described in which amine-based compounds are utilized in the recovery of rare earth elements from solution. The rare earth elements are recovered selectively and sequentially.

Methods and compositions are described in which amine-based compounds are utilized in the recovery of rare earth elements from solution. The rare earth elements are recovered selectively and sequentially.

A method for extracting a rare earth element from a rare earth-containing substance, the method comprising mixing the rare earth-containing substance with a protic ionic liquid, such as: ##STR00001##
wherein R.sup.1 is selected from hydrogen atom and hydrocarbon groups containing 1 to 6 carbon atoms; R.sup.2 and R.sup.3 are independently selected from hydrocarbon groups containing 1 to 12 carbon atoms; and X.sup. is an anionic species; to produce a composition of the formula (RE)(amide).sub.yX.sub.z at least partially dissolved in the protic ionic liquid, wherein RE is at least one rare earth element having an atomic number selected from 39, 57-71, and 90-103; y is 2-6; z is a number that charge balances the total positive charge of RE; and the amide is the conjugate base of the cationic portion of the protic ionic liquid of Formula (1) and has the following formula: ##STR00002##

A method for extracting a rare earth metal from a mixture of one or more rare earth metals, said method comprising contacting an acidic solution of the rare earth metal with a composition which comprises an ionic liquid to form an aqueous phase and a non-aqueous phase into which the rare earth metal has been selectively extracted.

A process for recovering chromium from hexavalent chromium-containing wastewater comprises the following steps: (1) extracting hexavalent chromium in wastewater to an organic phase by using an extracting agent, and separating hexavalent chromium from a water phase, so as to acquire a hexavalent chromium-loaded organic phase; (2) reducing the hexavalent chromium-loaded organic phase by using an aqueous solution of an organic reducing agent, reducing hexavalent chromium into trivalent chromium, reversely extracting trivalent chromium into the water phase, and separating the organic phase from the water phase to acquire a solution of the trivalent chromium and a renewable organic phase, wherein the organic reducing agent is one or a mixture of alcohols, aldehydes and carboxylic acids having the carbon atom number ranging 1 to 3; and (3) performing solvent evaporation on the solution of trivalent chromium, catalyzing, and recovering the trivalent chromium.

A method for recovering scandium is provided, which is capable of recovering highly-pure scandium from nickel oxide ore in a simple and efficient manner. The method for recovering scandium according to the present invention includes a scandium elution step S2 of passing a solution containing scandium through an ion exchange resin to obtain an eluted liquid containing scandium from the ion exchange resin, a neutralization step S3 of adding for neutralization a neutralizing agent to the eluted liquid, a solvent extraction step S4 of solvent-extracting the neutralized eluted liquid using an amine-based extracting agent, and a scandium recovering step S5 of obtaining a scandium precipitate from residual liquid separated by the solvent extraction, and then roasting the precipitate to obtain scandium oxide.