To surely recover valuable metals from secondary fly ash of incineration at a low cost by adjusting the pH of the soln., which is obtd. by mixing the secondary fly ash and water, dissolving the valuable materials into the soln. and subjecting the soln. to a sepn. of solid from the liquid at need, then bringing metal zinc into contact with this soln., separating the soln. to cement and tailing and obtaining zinc hydroxide and aq. chloride soln. by adjusting the pH of this tailing.

The most of the valuable metals in the secondary fly ash are chlorides and nearly the entire amt. thereof relatively easily dissolves in the water. The greater part of the valuable metals and alkaline metals are, therefore, included in the aq. soln. The pH of the soln. is adjusted to 4 to 6.5 after the sepn. of the solid from the liquid and the metal zinc is brought into contact therewith to form the components electrochemically nobler than the zinc into an insoluble metal form. Consequently, lead, chromium, mercury, thallium, etc., deposit as the cement. The pH of the tailing from which the cement is separated is adjusted to 9 to 11 and while the remaining valuable metals are codeposited, the zinc is precipitated in the form of the zinc hydroxide. The soln. of the alkaline metal chlorides which do not contain harmful materials is thus obtd.