Process for recovery of trace metals and salts from waste combustion residues

A method for continuously treating air pollution control residue with an extractant salt solution to remove lead, cadmium, chromium, cobalt, calcium, copper, aluminum, nickel, zinc, metal sulfates and metal chlorides therefrom, wherein said residue is from a single source and is comprised of variable compositions, said method comprising the steps of:

• a) adjusting the pH of the salt solution to a value between 1 and 12;
• extracting lead therewith from a sample of said residue and measuring the percentage amount of the extracted lead relative to the original amount of lead in said sample;
• b) continuing to adjust the pH of the salt solution to different values in a range between 1 and 12 and extracting lead therewith from additional samples of said residue, at different pH values respectively within said range, until a maximum percentage amount of extracted lead relative to the original amount of lead in the respective sample is obtained, at a specific pH value, within said range;
• c) extracting lead from another sample of the residue, with the salt solution, at the specific pH value, for a period of time sufficient to reach a maximum state of lead extraction;
• d) recycling the salt solution at the specific pH value by successively extracting lead from successive additional samples for a number of times until the percentage amount of extracted lead relative to the original amount of lead in a respective sample declines from the percentage amount of extracted lead, relative to the original amount of lead, in the preceding sample;
• e) continuously extracting lead from a successive number of batches of the residue equal to one less than said number of times, with the salt solution at the specific pH value, and for said period of time for each batch;
• and
• f) continuously extracting at least one of the members of the group consisting of cadmium, chromium, cobalt, calcium, copper, aluminum, nickel, zinc, metal sulfates and metal chlorides, from a successive number of batches of the residue equal to one less than said number of times, with the salt solution at the specific pH value, and for said period of time for each batch.