Time-dependent leaching of coal fly ash by chelating agents

Leaching rates of transition metal ions from coal flyash by ph 7.4 solutions of the chelating agents citric acid, EDTA, histidine, and glycine were measured. The results were compared with leaching of the same flyash by 0.5 M HCl, 0.10 M ph 7.4 Tris buffer, 0.5 M NH 4oh, and canine serum. Canine serum is a better leaching agent than was predicted on the basis of its concentrations of citrate and histidine. The trace elements zinc, manganese, chromium, nickel, and copper revelaed initial leaching rates with 0.5 M HCl range from 350-850 mg/g/day of metal. Rates dropped by 1-2 orders of magnitude within 24 hours and level off at 1-10 ppm/day. EDTA and citric acid leach over 50% of acid-soluble vanadium compared with only 10-35% of the other transition metals.