Abstract: The present invention relates to a method for recycling waste water from a stainless steel slag treatment process wherein stainless steel slag is brought into contact with water, in particular to neutralize the free lime contained therein, thereby producing said waste water. This waste water contains heavy metals, including at least chromium, and has a pH higher than or equal to 11. In accordance with the invention, it is used as production water for manufacturing mortar and/or concrete. In this way, the heavy metals, which are dissolved in the waste water and thus readily available, become bound in the newly formed cement phases so that they are prevented from leaching. Moreover, it has been found that the workability of the fresh mortar or concrete and also the quality of the final mortar or concrete materials is not negatively affected by the use of this alkaline waste water and that an accelerated setting could be achieved during the first hours.

Abstract: The present invention relates to a method for purifying highly alkaline waste water from a stainless steel slag treatment process. This waste water contains between 0.5 and 5 mg/l of trivalent chromium (Cr(III)) and between 0.5 and 1.0 mg/l of molybdenum. To reduce the chromium and molybdenum content a trivalent iron is added to the waste water in the form of a water soluble ferric salt and the trivalent iron is allowed to co-precipitate with said chromium and molybdenum by lowering the pH of the waste water. It was found that by performing the co-precipitation at a pH of 3.5 to 5.7, both the chromium and the molybdenum content could be effectively reduced to a level of less than 0.5 mg/l, and this without having to provide large amounts of trivalent iron in the waste water, without having to repeat the purification process for several times, without having to add sulphide to the waste water, and without having to lower and raise the pH of the waste water for more than one time.

Abstract: The present invention relates to a process for preparing, starting from a slag material, a filler for construction materials which contain bitumen or a hydraulic binding agent. The slag used to prepare the filler contains ?-dicalcium silicate. The process comprises the step of removing from the slag material a finer fraction formed by particles of a size between 0 and at least 0.75 mm so as to reduce the ?-dicalcium silicate content of the slag material; and the step of finely milling at least a portion of the remaining coarser fraction of the slag to obtain the filler. The invention also relates to the obtained filler, to the use thereof for preparing construction materials and to concrete or mortar compositions and asphalt compositions containing the filler.

Abstract: The present invention relates to a process for producing a granular material 26 for mixing with at least a hydraulic binding agent and with water to produce mortar or concrete. This process comprises at least an aggregation step and a carbonation step. In the aggregation step, steel slag particles from at least a fine fraction 24 of steel slag, in particular a fine fraction of steel slag containing a significant amount of ?-dicalcium silicate, are aggregated into larger grains so as to form a coarser granular material 25. In the carbonation step, said aggregated particles in said coarser granular material 25 are carbonated by means of carbon dioxide so as to produce a carbonated granular material 26. The present invention also relates to a carbonated granular material of aggregated steel slag particles containing a significant amount of ?-dicalcium silicate, in particular at least 3 wt. %, preferably at least 5 wt. % and more preferably at least 7 wt.

Abstract: The invention concerns a method of treating an alkaline granular carbonatable material which contains aluminium metal and which has in particular a pH of at least 10. The method comprises an oxidation step wherein at least a portion of said aluminium metal is oxidized by contact with moisture. The aluminium should be oxidized to avoid swelling problems when using the granular material as aggregate. In the method according to the invention this oxidation is accelerated by providing at least one oxidizing agent in said moisture, which oxidizing agent has a higher redox potential than the water contained in said moisture. The method further comprises a carbonation step wherein the granular carbonatable material is at least partially carbonated to lower the pH thereof. In this way the formation of ettringite, which may also release aluminium ions which causing further swelling problems, can be avoided in the granular material or any ettringite present therein can be destabilized.

Abstract: The present invention relates to a method for recycling waste water from a stainless steel slag treatment process wherein stainless steel slag is brought into contact with water, in particular to neutralize the free lime contained therein, thereby producing said waste water. This waste water contains heavy metals, including at least chromium, and has a pH higher than or equal to 11. In accordance with the invention, it is used as production water for manufacturing mortar and/or concrete. In this way, the heavy metals, which are dissolved in the waste water and thus readily available, become bound in the newly formed cement phases so that they are prevented from leaching. Moreover, it has been found that the workability of the fresh mortar or concrete and also the quality of the final mortar or concrete materials is not negatively affected by the use of this alkaline waste water and that an accelerated setting could be achieved during the first hours.

Abstract: Process for preparing a foaming slag former for electric furnaces comprising the steps of aggregating solid slag particles into a coarser granular material and carbonating the solid slag particles to form the foaming slag former. The solid slag particles are preferably aggregated before carbonization, so that the carbonates form a solid matrix binding the particles together.

Abstract: The invention concerns a method of treating an alkaline granular carbonatable material which contains aluminium metal and which has in particular a pH of at least 10. The method comprises an oxidation step wherein at least a portion of said aluminium metal is oxidised by contact with moisture. The aluminium should be oxidised to avoid swelling problems when using the granular material as aggregate. In the method according to the invention this oxidation is accelerated by providing at least one oxidising agent in said moisture, which oxidising agent has a higher redox potential than the water contained in said moisture. The method further comprises a carbonation step wherein the granular carbonatable material is at least partially carbonated to lower the pH thereof. In this way the formation of ettringite, which may also release aluminium ions which causing further swelling problems, can be avoided in the granular material or any ettringite present therein can be destabilised.

Abstract: The present invention relates to a process for preparing a foaming slag former 40 for electric arc furnaces 1, with at least 20 wt. % of solid slag particles, to the product of this process, and to its use in electric arc furnaces 1. The process of the invention comprises the steps of aggregating solid slag particles into a coarser granular material 33 and carbonating them to produce said slag former 40. In a preferred embodiment, said solid slag particles are aggregated before said carbonation, so that the carbonates form a solid matrix binding the particles together.

Abstract: The present invention relates to a process for producing a granular material 26 for mixing with at least a hydraulic binding agent and with water to produce mortar or concrete. This process comprises at least an aggregation step and a carbonation step. In the aggregation step, steel slag particles from at least a fine fraction 24 of steel slag, in particular a fine fraction of steel slag containing a significant amount of ?-dicalcium silicate, are aggregated into larger grains so as to form a coarser granular material 25. In the carbonation step, said aggregated particles in said coarser granular material 25 are carbonated by means of carbon dioxide so as to produce a carbonated granular material 26. The present invention also relates to a carbonated granular material of aggregated steel slag particles containing a significant amount of ?-dicalcium silicate, in particular at least 3 wt. %, preferably at least 5 wt. % and more preferably at least 7 wt.

Abstract: The present invention relates to a process for preparing, starting from a slag material, a filler for construction materials which contain bitumen or a hydraulic binding agent. The slag used to prepare the filler contains ?-dicalcium silicate. The process comprises the step of removing from the slag material a finer fraction formed by particles of a size between 0 and at least 0.75 mm so as to reduce the ?-dicalcium silicate content of the slag material; and the step of finely milling at least a portion of the remaining coarser fraction of the slag to obtain the filler. The invention also relates to the obtained filler, to the use thereof for preparing construction materials and to concrete or mortar compositions and asphalt compositions containing the filler.