To recover valuables from a waste generated when removing a core sand by dipping a cast-metal molding obtained by using a core consisting essentially of calcium carbonate into a nitric acid solution, and recovering the waste liquid formed by dissolving the core sand forming the core as a lime nitrate.

A cast-metal molding cast by using a core consisting essentially of calcium carbonate is dipped into a nitric acid solution (a) in a tank T after mechanically removing the core sand. A waste liquid obtained by dissolving the core sand forming the core is recovered as a lime nitrate solution (v) and utilizing the recovered lime nitrate solution (v) as a fertilizer. A carbon dioxide gas generated when dissolving the core sand in the tank T is liquefied at a gas-treating device G comprising a compressor, etc., and optionally recovered and utilized as a dry ice.