Preparation and Characterization of Cadmium Oxide and some By-products from Residual Fly Ash

Galal  Mahmoud Abd El Wahab

Nuclear Materials Authority, P.O.Box 530 El Maadi, Cairo, Egypt.

Summary: The chemical analysis of residual fly ash resulted from Egyptian electrical power stations revealed the presence of some economic metals; one of the most important of them is Cd which assays 65 mg/kg as well as 45 g/kg of Zn and 48 g/kg of S. A hydrometallurgical process has been performed to prepare pure CdO together with some by-products namely; ZnS and elemental S. Leaching conditions such as: H₂SO₄ concentration, solid/liquid (S/L) ratio, leaching time and temperature were investigated to prepare suitable sulfate leach liquor.     Chemical analysis of the latter shows the presence of 6.4 mg/L of Cd with achieved leaching efficiency of 99% at the applied optimum conditions.

Direct precipitation technique was conducted for the separation of (CdS + elemental S) cake from the prepared sulfate leach liquor by using 1% Na₂S at pH 0.6. The latter cake was dissolved in 10% HNO₃ solution and treated with 5% NaOH solution at pH 8.5 to precipitate Cd(OH)₂. By calcinations at 850^°C for 1 h and washing, pure CdO has been prepared.