Method for purifying aqueous alkaline solution

A method for purifying an aqueous alkaline solution, comprising:

• bringing a fibrous activated carbon into contact with an aqueous alkaline solution to remove a metal component other than alkali metals and alkaline earth metals from the aqueous alkaline solution,
• wherein the aqueous alkaline solution is an aqueous alkaline solution which comprises at least one hydroxide of at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and further comprises the at least one metal component other than alkali metals and alkaline earth metals,
• wherein the aqueous alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution,
• wherein the metal component other than alkali metals and alkaline earth metals contained in the aqueous alkaline solution contains at least one metal selected from the group consisting of iron, nickel, molybdenum and copper,
• wherein a concentration of metal hydroxide comprised in the aqueous alkaline solution is 10 to 55% by weight, and wherein the fibrous activated carbon has an average aspect ratio of 50 or more, a specific surface area of 2000 m2/g or more and a pore volume of 0.75 ml/g or more, and
• wherein the metal component other than alkali metals and alkaline earth metals contained in the aqueous alkaline solution are reduced to 200 ppb or less.