tlydrometallurgy, 32 ( 1993 ) 99-109 99 Elsevier Science Publishers B.V., Amsterdam Active nickel catalyst from metallurgical waste M.A. Rabah and M.A. Barakat Extractive Metallurgy Department, CentralMetallurgical Research and DevelopmentInstitute (CMRDI), P.O. Box 87, Helwan, 11421, Cairo, Egypt (Received October, 1991; revised version accepted March 13, 1992 ) ABSTRACT Rabah, M.A. and Barakat, M.A., 1993. Active nickel catalyst from metallurgical waste. Hydrometal- lurgy, 32: 99-109. The recovery and preparation of active nickel catalysts from metallurgical wastes such as fly ash and spent catalysts have been studied. The results obtained show that the nickel content of these materials is 7.8 and 3.5% (by mass), respectively. Nickel was recovered by leaching with pure or acidified water. Other metallic ions such as Fe 2+ and V 5+ were removed before extracting the nickel ions as hydroxide, oxalate and acetate salts. These salts were thermally decomposed under hydrogen gas to yield finely divided nickel metal. The chemical activity of the nickel metal was monitored by cracking natural gas in the presence of steam at 1223 K. Maximum recovery of 96% of the nickel present is obtained by leaching with water followed by 33% HCI/HNO3 (aqua regia) for 30 min. The chemical activity of the samples meets standard specifications and increases in the order oxalate, acetate and hydroxide salts. Differential thermal analysis shows that at 658 K endothermic reactions take place yielding oxides which are subsequently reduced by hydrogen. The running costs of prepar- ing the catalyst are competitive with commercially available samples. INTRODUCTION Fly ash is the residual non-volatile portion of fossil fuels used in power stations. Organo-metallic inclusions in the fuel undergo a series of thermal decomposition reactions followed by the formation of inorganic compounds. Sulphate salts may be formed by the attack of sulphur dioxide on metal ox- ides. Spent catalysts are poisoned nickel catalysts which have been used for cracking natural butane gas. The spent catalyst is in the form of spherical pellets about 15 mm in diameter and is light grey in colour. The recovery of nickel from secondary resources has been reported using hydrometallurgical techniques. The process involved de-oiling the grinding waste followed by chloride-based dissolution. The resultant residue was treated by leaching with an alkaline solution [ 1 ]. Correspondence to: M.A. Rabah, Extractive Metallurgy Department, CMRDI, P.O. Box 87, Helwan, 11421, Cairo, Egypt. 0304-386X/93/$06.00 © 1993 Elsevier Science Publishers B.V. All rights reserved.