Hydrometallurgical recycling of steel grinding swarf via oxidative leaching using ferric chloride

Abstract

Grinding swarf is a hazardous waste generated in hundreds of thousands of tons and currently has limited options for recycling. It is an environmental and economic burden for the manufacturing industry and new recycling processes are necessary for sustainable waste management. Ferric chloride (FeCl₃) is an oxidant which can be used to extract metals from steel scrap to produce ferrous chloride (FeCl₂) solutions. This was applied for recycling of grinding swarf containing 64% mostly metallic Fe by dissolving it in concentrated FeCl₃. Optimization of leaching conditions showed that up to 94% of Fe was recovered as FeCl₂ within 1 h of leaching with FeCl₃, but that reaction temperature was difficult to control due to highly exothermic reactions. In contrast, classical leaching with hydrochloric acid only recovered 41% Fe from swarf in 2 h and forms large volumes of flammable H₂. This improvement in efficiency was attributed to the leaching mechanisms of FeCl₃ which are kinetically superior and capable of circumventing lubricant components which otherwise protect the steel surface. These findings contribute to the development of a safe recycling process for valorisation of grinding swarf. Production of iron chloride solutions with applications in water treatment promotes recycling and reduces incineration and landfilling of this waste.