Hydrometallurgical recycling of steel grinding swarf via hydrochloric acid leaching and precipitation for production of high purity iron chloride coagulants and hydrogen gas

Grinding swarf is a hazardous waste from the steel and manufacturing industry which is difficult to recycle due to its low value, heterogeneity, and distributed production across numerous workshops. Thousands of tons of grinding swarf are today landfilled, and the aim of this work was to propose an alternative recycling strategy and process for producing iron chloride water treatment coagulants from this waste. Two samples were leached with hydrochloric acid at pH 2 and 60°C for 3 h to extract up to 95% iron from the swarf by forming soluble ferrous chloride (FeCl 2 ). The slurry pH was thereafter increased to 4 by adding more swarf, at which point chromium, aluminium and molybdenum were precipitated via hydrolysis. Nickel, cobalt, and copper could also be separated from FeCl 2 by precipitation but were instead found to be cemented onto the swarf’s metallic iron surface. Nickel and cobalt cementation was facilitated by high chloride concentrations in the slurry. The investigated leaching and precipitation techniques were combined to propose a simple yet flexible process for producing water purification grade iron chloride from grinding swarf. Around 4.2 tons of 34% FeCl 2 solution and 24 kg of hydrogen gas can be produced per ton of swarf as valuable products, promoting recycling and contributing towards zero-waste in the steel value chain.