Method for utilizing PH control in the recovery of metal and chemical values from industrial waste streams

A method for the recovery of metal and/or chemical values from waste material streams which comprise zinc, cadmium, and lead compounds, comprising the steps of:

• a. treating said waste material stream with an ammonium chloride solution at an elevated temperature to form a first product solution which comprises dissolved zinc, cadmium, and lead compounds, and a first undissolved material;
• b. separating said first product solution from said first undissolved materials;
• c. determining the pH of said first product solution and if the pH of said first product solution is greater than 6.3 then adding an effective amount of a first compound to said first product solution to obtain a pH of less than about 6.3;
• d. adding zinc metal to said first product solution whereby any lead and cadmium ions contained within said first product solution are displaced by said zinc metal and precipitate out of said first product solution as lead and cadmium metals, leaving a second product solution;
• e. separating said second product solution from the lead and cadmium metals;
• f. adding an effective amount of a second compound to said second product solution to obtain a pH of about 6.5 to about 7.0;
• and
• g. lowering the temperature of said second product solution thereby precipitating the zinc compounds as a mixture of crystallized zinc compounds, leaving a third product solution.