LD-Slag is an inevitable by-product of Linz-Donawitz (LD) process using the basic oxygen furnace for steelmaking. For successful recycling of the residual iron and iron oxides into the steel making process the amount of phosphorous in the slag has to be reduced. The present study investigates the separability of the phosphorous carrying phase by physico- chemical methods including the alteration of the liberation state by preconditioning of the slag.
The initial raw material´s analysis including microscopic and SEM investigations in property classes showed that the slag is constituted dominantly of dicalcium silicate (C2S) as well as calcium- and magnesium- ferrites in a wide range of elemental composition, iron and free lime. The phosphorous is mainly situated in the C2S phase, thus the limits of flotation and wet magnetic separation are examined in order to separate the diamagnetic silicates from the iron containing oxides. The liberation state is described combining automated mineralogy and conventional particle categorization by physical methods.
Pure CO2 gas was percolated through the pulp for C2S deconstruct and also pH conditioning for flotation in a controlled way.
The low phosphorous concentration in the filtrate of the carbonation process, which was detected by chemical assays, is an evidence for partly deconstruction of the C2S phase, while no phosphorous was detected in the filtrate of long term hydration process (162 hours) at the absence of CO2.
The effects on separability of partial leaching of C2S and precipitation of CaCO3 are discussed on the base of SEM investigations and lab scale separation tests.