To provide a method for separation removal of arsenic existing as impurity in an acidic solution containing a metal, particularly etching waste- liquid collected in a copper etching process for a printed circuit board.

Arsenic existing as an impurity in an acidic solution containing a metal is separately removed with the separation of a basic salt of the metal by cooling a neutralized solution. In this case, particularly the liquid temperature of the neutralized solution is heated to 70-100°C, and cooled to 15-35°C to separate the basic salt, and arsenic is separately removed with the separation of the basic salt.