Behavior of metals in discard nickel smelter slag upon reacting with sulfuric acid

Abstract

Characteristics of two nickel smelter slags (one fresh and one 30‐years old) and their leaching behavior in sulfliric acid were investigated. X‐ray diffractogram revealed that both slags were mainly iron silicate glass, with a small fraction of crystalline fayalite (Fe₂SiO₄). The fresh slag contained a very small fraction of maghemite (y‐Fe₂O₃) in addition. In the 0.1 M sulfuric acid solution, over 35% of Ni and 45% of Co were extracted from the slag (L/S = 10) within 5 hours. Over 65% Ni and 75% Co extraction were reached after 20 hours. Higher acid concentrations accelerated the leaching process. No selective leaching of Ni and Co was observed in the acid at concentrations of 0.05 M or above. The fraction of Fe extracted was comparable to Co. The additives, including NH4⁺ and Cl^‐, showed little effect on the selectivity under the condition studied. Further decrease in the acid concentration, however, resulted in a preferential leaching of Ni and Co, which may explain the deficit of Ni and Co in the weathered old slag.

Key words:

• Discard smelter slag
• sulfliric acid
• extraction
• nickel
• cobalt