## 2 Methods and Material
### Laboratory-Scale Experiments
#### 2.5.2 Controlling Cooling  
Four different cooling methods were tested on two batches of slag of different basicities, 2.1 and 2.8, to see how the cooling rate impacts chromium leaching. The reference slag samples were specifically chosen for their representation of different basicities and chromium leaching. The composition of the slag samples is shown in Table 3. Ideally, only the basicity would differ between the two slags but there was also significantly more Al\({}_{2}\)O\({}_{3}\) in the slag at basicity 2.8 and more chromium in the slag at basicity 2.1. The sample with basicity 2.1 was at the targeted basicity and leached below 0.04 mg/kg. The sample at basicity 2.8 was chosen for the unusually high leaching of 4.5 mg/kg. Before the remelting experiments, the slag was crushed to less than 4 mm. The EAF at Ovako steel plant in Hofors produces about 100 tonnes of steel in each batch. One batch was fed by two scrap baskets, the second basket was added after 20 min. Normally, two batches of slag from the EAF were tapped into the same slag pot. The slag pot was cooled outside for two hours before transportation to the slag tipping site. There, the slag was tilted from a ramp onto a heap of slag from previous slag ladles. The ramp was water sprayed and cleared of slag once every 24 h. This procedure caused the slag to reheat every 2 h and the slag might retain heat for up to 24 h. The elevated temperature over time might allow for brownmillerite formation. Two of the cooling method experiments (the hold temperature and altering temperatures experiments) were created to simulate the worst case scenarios of the slag cooling process with respect to forming brownmillerite. The slags were remelted in MgO crucibles with nitrogen running through the furnace. The slag was heated at 6 \({}^{\circ}\)C/min to 1600 \({}^{\circ}\)C and the temperature was maintained for 1 h before the cooling procedures started. The cooling methods are described below and the temperature profiles for the different cooling rates can be seen in Figure 2. In the hold temperature experiment, the slag was cooled at 6 \({}^{\circ}\)C/min to 700 \({}^{\circ}\)C and the temperature was maintained for 24 h; thereafter, the furnace was cooled to room temperature at 6 \({}^{\circ}\)C/min. In the altering temperatures experiment, the slag was set to cool at 6 \({}^{\circ}\)C/min to 1000 \({}^{\circ}\)C and maintained for 1 h. The temperature was alternated between 1000 and 800 \({}^{\circ}\)C three times at a rate of 6 \({}^{\circ}\)C/min, to simulate the addition of new slag onto the ramp,. The temperatures 1000 \({}^{\circ}\)C and 800 \({}^{\circ}\)C were maintained for 0.5 h, which resulted in a two-hour cycle. After the third time the temperature reached 800 \({}^{\circ}\)C, the furnace was cooled to room temperature at 6 \({}^{\circ}\)C/min. As a set cooling rate, 4 \({}^{\circ}\)C/min was used. For the fast cooling rate experiment, a furnace with water cooling without an inert atmosphere of nitrogen was used. The temperature dropped to about 500 \({}^{\circ}\)C in 1 h and the sample was then removed from the furnace and cooled to room temperature within 1 additional hour. Since the slag with a basicity of 2.1 leached below detection limit of 0.04 mg/kg, it was pointless to reduce the chromium leaching further; therefore, the slag was excluded from the experiments with a set cooling rate and a fast cooling rate. As a result of the retained heat in the refractory of the furnace, cooling took longer than described and depicted in Figure 2. The slag was crushed to less than 4 mm before autoclave treatment and the following EN 12457-2 leaching test.