Provided is a method for inhibiting extractant degradation comprising preparing step, extracting step and scrubbing step, the method including: (a) the preparing step of a DSX solvent by adjusting the extractant concentration of the DSX solvent to a specific range; (b) the extracting step of metal included in the feed solution by adjusting the ratio of the organic (solvent) and an aqueous (solution) as a feed solution; (c) the scrubbing step of adjusting the zinc concentration of the solution using zinc sulfate; and (d) stripping step.

Provided is a method for inhibiting extractant degradation by a diluent and an extractant input manner, the method including steps of: (a) determining and analyzing the total volume of the DSX solvent when the diluent and the extractant, which are the DSX solvents, are added in the DSX process and identifying the concentration of the extractant; (b) calculating an extractant concentration according to an amount of the diluent to be added based on the analysis value of step (a), and then adding the extractant; (c) determining the ratio between the extractants through analysis after adding the extractants; (d) adding the extractant to be needed when the ratio between extractants is out of the range; and (e) adding the diluent and analyzing the ratio between the extractants.

Provided is a method for inhibiting extractant degradation in the DSX process through the manganese extraction control, the method comprising: (a) stirring DSX solvent and DSX feed solution, which is a solution containing a valuable metal from which iron has been removed in an agitator, in which soda ash (Na.sub.2CO.sub.3) is further added to maintain a constant pH; and (b) scrubbing the manganese from the DSX solvent, extracted in step (a).

Provided is a method for inhibiting extractant degradation comprising preparing step, extracting step and scrubbing step, the method including: (a) the preparing step of a DSX solvent by adjusting the extractant concentration of the DSX solvent to a specific range; (b) the extracting step of metal included in the feed solution by adjusting the ratio of the organic (solvent) and an aqueous (solution) as a feed solution; (c) the scrubbing step of adjusting the zinc concentration of the solution using zinc sulfate; and (d) stripping step.

A method for processing lithium ion battery scrap according to this invention includes a leaching step of leaching lithium ion battery scrap to obtain a leached solution; an aluminum removal step of neutralizing the leached solution to a pH range of from 4.0 to 6.0, then performing solid-liquid separation and removing aluminum in the leached solution to obtain a first separated solution; and an iron removal step of adding an oxidizing agent to the first separated solution and adjusting the pH in a range of from 3.0 to 5.0, then performing solid-liquid separation and removing iron in the first separated solution to obtain a second separated solution.

A method of recovering metal compounds from solid oxide fuel cell scrap includes processing the solid oxide fuel cell scrap to form a powder, digesting the processed scrap, extracting lanthanum oxide and cerium oxide from a solution containing the digested processed scrap, extracting a zirconium compound from the solution after extracting the lanthanum oxide and cerium oxide, and extracting scandium compound from the solution extracting the zirconium compound from the solution.

A method for producing manganese(II) sulfate monohydrate includes a pulverization and washing step of pulverizing and washing a manganese-containing by-product, a leaching step of leaching the pulverized manganese-containing by-product after the pulverization and washing step to produce a leachate, a neutralization step of neutralizing the leachate produced in the leaching step, an impurity removal step of removing impurities from the leachate neutralized in the neutralization step, a solvent extraction step of recovering manganese in the form of an aqueous solution of manganese sulfate from a process liquid subjected to the impurity removal step by using a solvent extraction method, and a crystallization step of producing manganese(II) sulfate monohydrate by evaporating and concentrating the aqueous solution of manganese sulfate produced in the solvent extraction step.

A method of recovering metal compounds from solid oxide fuel cell scrap includes processing the solid oxide fuel cell scrap to form a powder, digesting the processed scrap, extracting lanthanum oxide and cerium oxide from a solution containing the digested processed scrap, extracting a zirconium compound from the solution after extracting the lanthanum oxide and cerium oxide, and extracting scandium compound from the solution extracting the zirconium compound from the solution.

A method for processing lithium ion battery scrap according to this invention includes a leaching step of leaching lithium ion battery scrap to obtain a leached solution; an aluminum removal step of neutralizing the leached solution to a pH range of from 4.0 to 6.0, then performing solid-liquid separation and removing aluminum in the leached solution to obtain a first separated solution; and an iron removal step of adding an oxidizing agent to the first separated solution and adjusting the pH in a range of from 3.0 to 5.0, then performing solid-liquid separation and removing iron in the first separated solution to obtain a second separated solution.

A method for producing manganese(II) sulfate monohydrate includes a pulverization and washing step of pulverizing and washing a manganese-containing by-product, a leaching step of leaching the pulverized manganese-containing by-product after the pulverization and washing step to produce a leachate, a neutralization step of neutralizing the leachate produced in the leaching step, an impurity removal step of removing impurities from the leachate neutralized in the neutralization step, a solvent extraction step of recovering manganese in the form of an aqueous solution of manganese sulfate from a process liquid subjected to the impurity removal step by using a solvent extraction method, and a crystallization step of producing manganese(II) sulfate monohydrate by evaporating and concentrating the aqueous solution of manganese sulfate produced in the solvent extraction step.