Introdjjctjgn

The present invention relates to a method for treatment of an alkaline waste mainly comprising one of fly ash and slag from metal production, or a combination thereof. The present invention also relates to a combination of an alkaline waste and a flowable solidfier, and an underwater structure made therefrom.

Fly ash is a residue generated in large amounts from combustion, such as from coal, waste and etcetera. Slag is a residue generated from metal production after that the desired metal has been separated from the ore. Both the fly ash and the slag contain considerable quantities of dangerous substances, such as dioxin and heavy metals. Furthermore, the fly ash and the slag are highly alkaline.

The fly ash and the slag have traditionally been deposited in landfills. However, due to stricter regulatory requirements, special deposit arrangement are necessary in order not to contaminate the surrounding environment. Alternatively, the pollutants in ash and the slag may be removed by various separation processes. A disadvantage with such special deposit arrangement and separation processes are that they are costly in view of the large amounts of fly ash and slag to be treated.

Yet another problem when depositing the alkaline waste is that the waste may be in form of powder or small pieces, which enables the alkaline waste to be dislocated away from the intended waste deposit. This problem is in particular pronounced when depositing the alkaline waste in the sea. When the alkaline waste is deposited in the sea, the waste spreads when sinking towards the sea bottom and covers a large area of the sea bottom around the location of the waste deposit. Furthermore, even after being deposited, currents in the water may spread the alkaline waste along the sea bottom. The spread of the alkaline waste may severely influences the algaculture at the sea bottom around the waste deposit. The problem is also present at land deposits, where the alkaline waste is spread by the wind.

ID201301721A discloses a method for making a geopolymer composite that comprises Ti0 ₂ . The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. In particular, a first object of the invention is to provide a method for treatment of fly ash and slag that allows the fly ash and the slag to be deposited with reduced leakage of dangerous substances. A second object of the invention is to provide a method for treatment of fly ash and slag that allows the fly ash and the slag to be deposited submerged in water, such as in a lake or the sea. A third object of the invention is to provide a method for treatment of fly ash and slag that allows the waste to be deposited without being displaced from the deposit.

These objects are achieved through features, which are specified in the description below and in the claims that follow. In particular, these objects are achieved by means of a method for treatment of an alkaline waste mainly comprising one of fly ash and slag from metal production, or a combination thereof. The method comprises

- adding the alkaline waste and a flowable solidifier to a container, wherein the flowable solidifier comprises one of a flowable geopolymeric former and a flowable cement former, or a combination thereof, wherein the flowable geopolymeric former possesses the ability to produce a geopolymeric reaction by itself or in combination with the alkaline waste in which a geopolymer is formed, wherein the flowable cement former possesses the ability to produce a cement solidifying reaction in which concrete is formed,

- combining the alkaline waste with the flowable solidifier into a formable combination, and

- solidifying the formable combination by allowing the geopolymeric reaction and/or the cement solidifying reaction to form a solidified combination.

By forming the solidified combination of the alkaline waste and the flowable solidifier, the alkaline waste is at least partly enclosed in the combination. Thereby, the direct exposure of the alkaline waste to the surrounding environment is reduced. Furthermore, after that the formable combination has solidified, the flowable solidifier acts as a barriers against leakage and diffusion of dangerous substances, such as dioxin and heavy metals, from the alkaline waste.

Accordingly, the method of the invention results in reduced leakage of the dangerous substances from the alkaline waste when the solidified combination is stored in a deposit. The reduced leakage of dioxin and heavy metals from the alkaline waste is particular pronounced when the combination is deposited submerged in water. The method enables the solidified combination to fulfil the increasingly stricter environmental requirements from the authorities on deposition of the alkaline waste. Furthermore, by means of the combination of creating the geopolymer from the alkaline waste, the alkaline waste is combined to a larger unit. Accordingly, it can be assured that the alkaline waste is maintained at the location of the deposit.

The term geopolymeric reaction relates to the chemical process in which the flowable geopolymenc former solidifies, also denoted geopolymerization. The geopolymeric reaction may relate to one of a process of repeating units, such as silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-AI-0-), ferro- silico-aluminate (-Fe-O-Si-O-AI-O-) or alumino-phosphate (-ΑΙ-0-Ρ-0-), and etcetera.

The term cement solidifying reaction relates to the chemical process in which the flowable cement former solidifies. The cement solidifying reaction may relate to one of a process of hydration and carbonatation in which the flowable cement former solidifies.

According to an embodiment of the invention, the flowable solidifier mainly comprises the flowable geopolymeric former that is configured in combination with the alkaline waste to produce the geopolymeric reaction that solidifies the formable combination into the solidified combination. Preferably, the flowable solidifier comprises more than 90% of the flowable geopolymeric configured accordingly.

According to an embodiment of the invention, the flowable geopolymeric lacks sufficient high pH for the geopolymeric reaction, wherein the alkaline waste is added to an amount that provides sufficient high pH to the flowable geopolymeric for the geopolymeric reaction. By forming the geopoly- mer, the alkaline property of the alkaline waste is utilized at the same time that the dangerous substances of the alkaline waste are enclosed.

According to an embodiment of the invention, the alkaline waste comprises a first portion and a second portion, wherein the flowable geopolymeric former is configured in combination with the first portion of the alkaline waste to produce the geopolymeric reaction, and wherein the second portion of the alkaline waste is combined with the flowable solidifier so that the second portion of the alkaline waste is at least partly enclosed by the combination of the flowable geopolymeric former and the first portion of the alkaline waste.

The first portion of the alkaline waste is combined with the flowable geopolymeric former to the geopolymer that is produced by the geopolymeric reaction. The second portion of the alkaline waste is at least partly encapsulated by the formed geopolymer. By means of the combination of creating the geopolymer from the first portion of the alkaline waste and encapsulating the second portion of the alkaline waste by the geopolymer, a large amount of the alkaline waste can be combined together. Accordingly, it can be assured that the dangerous substances of the alkaline waste are enclosed. It is further assured that the alkaline waste is maintained at the location of the deposit.

According to an embodiment of the invention, the flowable solidifier mainly comprises the flowable geopolymeric former that is configured to react by itself to produce the geopolymeric reaction that solidifies the formable combination into the solidified combination. Preferably, the flowable solidifier comprises more than 90% of the flowable geopolymeric former configured accordingly.

By means of the combination of the flowable geopolymer former with the alkaline waste, the alkaline waste is combined to larger units. Accordingly, it can be assured that the alkaline waste is maintained at the location of the deposit. Furthermore, the exposure of the alkaline waste with the environment is reduced resulting in reduced leakage of the dangerous substances from the alkaline waste.

According to an embodiment of the invention, the flowable solidifier mainly comprises the flowable cement former that is configured to react by itself to produce the cement solidifying reaction that solidifies the formable combination into the solidified combination. Preferably, the flowable solidifier comprises more than 90% of the flowable cement former configured accordingly.

By means of the combination of the flowable cement former with the alkaline waste, the alkaline waste is combined to larger units. Accordingly, it can be assured that the alkaline waste is maintained at the location of the deposit. Furthermore, the exposure of the alkaline waste with the environment is reduced resulting in reduced leakage of the dangerous substances from the alkaline waste.

According to an embodiment of the invention, the alkaline waste is combined with the flowable solidifier so that the flowable solidifier mainly encloses an outer surface of the alkaline waste.

According to an embodiment of the invention, the method further comprises

- forming the combined alkaline waste and the flowable solidifier into pellets.

According to an embodiment of the invention, the alkaline waste is combined with the flowable solidifier in the pellets so that the flowable solidifier mainly encloses an outer surface of the alkaline waste.

By arranging the solidified combination of the alkaline waste and the geopolymeric former into pellets, the deposition of the combination is facilitated and the deposition facilities can be utilized to high degree in that the pellets allow a high degree of packing density. The pellets are preferably configured with a size that prevents them from being displaced by interaction of streams of water, wind, and etcetera. The pellets may be arranged in various of forms, such as spherical, cylindrical, and etcetera.

According to an embodiment of the invention, the method further comprises

- depositing the combined alkaline waste and flowable solidifier.

According to an embodiment of the invention, the combined alkaline waste and flowable solidifier are deposited after that the combination has solidified.

According to an embodiment of the invention, the combined alkaline waste and flowable solidifier are deposited after that the solidified combination has reached a compressive strength of more than 2 MPa, preferably more than 5 MPa. The flowable solidifier may after being fully solidified have a compressive strength of 10 MPa or higher, such as 25 - 55 MPA under favourable conditions. However, even before being fully solidified, the flowable solidifier provides a reduction of leakage of dangerous substances from the alkaline waste.

According to an embodiment of the invention, the method of forming the formabie combination of the alkaline waste and the flowable solidifier is performed on a vessel. Preferably, the method of forming the formabie combination of the alkaline waste and the flowable solidifier is performed on a vessel during transportation from the mine or extraction site to the waste deposit. By performing the method of forming the solidified combination of the alkaline waste and the flowable solidifier during transportation, the overall cost of the deposition is reduced. According to an embodiment of the invention, the method further comprises

- covering an area or object at the seabed by depositing the combined alkaline waste and the flow- able solidifier. The object may for example be a wreck or other structure. The area may for example be an area comprising contamination.

According to an embodiment of the invention, the method further comprises

- filling a bore of a well with the combined alkaline waste and the flowable solidifier. For example, a bore of an offshore well.

According to an embodiment of the invention, the method further comprises

- forming the combined alkaline waste and the flowable solidifier into a breakwater structure for reducing coastal erosion or providing safe harbourage.

According to an embodiment of the invention, the method further comprises

- depositing the combined alkaline waste and flowable solidifier submerged in water.

By depositing the combination of the alkaline waste and the flowable solidifier in a lake or the sea, the cost of the deposition is reduced compared with land based deposition facilities.

According to an embodiment of the invention, the method further comprises

- forming the combined alkaline waste and flowable solidifier combined alkaline waste into an underwater structure for increasing fish yield or for algaculture.

According to an embodiment of the invention, the flowable geopolymeric former is one of a slag- based geopolymer, a rock-based geopolymer and a fly ash-based geopolymer, or a combination thereof.

According to an embodiment of the invention, the flowable geopolymeric former comprises water and at least one of silicon dioxide (Si0 ₂ ), aluminium oxide (Al ₂ 0 ₃ ) and calcium oxide (CaO), or a combination thereof.

According to an embodiment of the invention, the flowable geopolymeric former comprises mining waste.

According to an embodiment of the invention, the mining waste has a grain size in the range of 5 - 0,001 mm, preferably 0,15 - 0,05 mm.

According to an embodiment of the invention, the mining waste comprises depleted mining waste of at least one of the mineral rutile and ilmenite, or a combination thereof.

According to an embodiment of the invention, the mining waste constitutes 50 - 95 % of the mass of the formable combination, preferably, 60 - 80 % of the mass.

The objects of the invention are further achieved by means of a combination of an alkaline waste and a flowable solidifier, characterized in that the combination is manufactured by a method according to any of claim 1-22.

The objects of the invention are further achieved by means of an underwater structure for increasing fish yield or for algaculture, characterized in that the underwater structure comprises a combination of an alkaline waste and a flowable solidifier according to claim 23.

The objects of the invention are further achieved by means of use of a combination of an alkaline waste and a flowable solidifier according to claim 23

Detailed description

In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

Fig. 1 discloses a flow chart of a method for treatment of alkaline waste according to an embodiment of the invention.

Fig. 2a discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a first embodiment of the invention.

Fig. 2b discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a second embodiment of the invention.

Fig. 2c discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a third embodiment of the invention.

Fig. 2d discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a fourth embodiment of the invention.

Fig. 3 discloses a vessel for transporting and forming the combination of the mining waste and the flowable solidifier.

In fig. 1 an example of a method for treatment of alkaline waste according to an embodiment of the invention is disclosed. The alkaline waste comprises mainly one of fly ash and slag from metal production, or a combination thereof

The method is initiated in a step 100 by adding the alkaline waste to a container and in a step 110 by adding a flowable solid ifier to the container. The alkaline waste and the flowable solidifier may be added in any order or simultaneously.

The alkaline waste is preferably in a form that enables it be mixed and coated with a flowable geo- polymeric former. The flowable geopolymeric former is preferably arranged flowable with a viscosity that enables the geopolymeric former to cover an outer surface of the alkaline waste. Preferably, also mining waste is added to the container, such as depleted mining waste of at least one of the mineral rutile and ilmenite, or a combination thereof. According to an embodiment of the invention, the mining waste constitutes 50- 95 % of the mass of the formable combination, preferably, 60 - 80 % of the mass.

In a step 120, the method further comprises combining the alkaline waste with the flowable solidifier. The combination is done by mixing the alkaline waste with the flowable solidifier in a mixing device, such as a by means of a concrete mixer comprising a revolving drum for mixing the alkaline waste with the flowable solidifier. Preferably, the alkaline waste with the flowable solidifier is mixed until the alkaline waste is homogeneously distributed in the flowable solidifier. By means of step 120, the flowable solidifier encloses the alkaline waste into a formable combination. Preferably, the method further comprises steps of dividing the formable combination into pellets of similar size and form.

In a step 130, the method further comprises solidifying the formable combination by allowing the geopolymeric reaction and/or the ceramic reaction to form a solidified combination of the alkaline waste and the flowable solidifier.

The solidified combination of the alkaline waste and the flowable solidifier is arranged so that the flowable solidifier mainly encloses the alkaline waste, preferably the flowable solidifier completely encloses the alkaline waste. Thereby, the exposure of an outer surface of the alkaline waste with the surrounding environment is reduced and possible leakage or diffusion of the dangerous substances are reduced.

According to a preferred embodiment of the invention, the method steps of 100 - 30 are performed on a vessel during transportation from the mine or extraction site to the waste deposit, for example on a ship when transporting the mine waste for deposition submerged in water. In shall be understood that the method steps of 100 - 130 also may be performed during the vessel is in an idle position, such as when being anchored at sea or at a harbour.

In a step 140, the method comprises depositing the combined alkaline waste and flowable solidifier. Preferably, the combined alkaline waste and flowable solidifier are deposited after that the combination has at least partly solidified. The solidified combination of the alkaline waste and the combined alkaline waste and flowable solidifier provides the advantage of allowing the alkaline waste to be deposited without that the alkaline waste is displaced by interaction from steams of water, wind, and etcetera. Accordingly, the environmental effect of depositing the alkaline waste is reduced.

The solidified combination of the alkaline waste and the combined alkaline waste and flowable solidifier further provides the advantage of allowing the alkaline waste to be deposited with reduced leakage or diffusion of the dangerous substances, such as dioxin and heavy metals, and without changing the pH of the environment at an in vicinity of the deposit. Thereby, the solidified combination can be deposited at more simple deposit facilities or submerged in water while fulfilling the environmental requirements from the authorities. Accordingly, the overall cost of the deposition by means of treatment of the alkaline waste using the method is reduced.

The flowable solidifier is one of a flowable geopolymeric former and a flowable cement former, or a combination thereof. In the following, an example of the flowable geopolymeric former will be presented.

According to a preferred embodiment, the formable combination is made by mixing the following components in regards to their weight, 75 % mining waste, 15 % fly ash and/or slag, 5 % potassium silicate, 1 % sodium hydroxide, 4% water. Accordingly, the flowable geopolymeric former comprises above components excluding the fly ash and/or the slag. The components are mixed together to the formable combination that is divided into pellets and allowed to solidify.

In the following, an example of the flowable cement former will be presented. According to a preferred embodiment, the flowable cement former is a Portland cement. Preferably, the cement comprises one of type I, type II, type III, type IV and type V Portland cement according to ASTM C150, wherein the alkaline waste and/or residual waste from titanium production constitutes 50 - 95 % of the composition, preferably 70 - 80 % of the composition.

Fig. 2a discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a first embodiment of the invention. In the disclosed embodiment, the flowable solidifier comprises mainly the flowable geopolymeric former that is configured in combination with the alkaline waste to produce the geopolymeric reaction in which a geopolymer is formed that solidifies the formable combination into the solidified combination. In the following embodiment, the flowable geopolymeric former has been added to an amount that enables it to form the solidified combination by a geopolymeric reaction mainly between the geopolymeric former and the alkaline waste. By means of the geopolymeric reaction, the alkaline waste becomes a part of a solidified geopolymer 200. In fig. 2a, the solidified combination is illustrated by a first hatching.

Fig. 2b discloses a schematic overview of the microstructure of a combination of alkaline waste and a f!owable solidifier according to a second embodiment of the invention. In the disclosed embodiment, the flowable solidifier comprises again mainly the flowable geopolymeric former that is configured in combination with the alkaline waste to produce the geopolymeric reaction in which a geopolymer is formed that solidifies the formable combination.

In contrast to the embodiment in fig. 2a, the flowable geopolymeric former has been added to an amount that enables it to form the solidified geopolymer 200 with only a first portion of the alkaline waste. A second portion of the alkaline waste is enclosed by the combination of the flowable geopolymeric former and the first portion of the alkaline waste. In fig. 2b, the solidified geopolymer 200 is illustrated by the first hatching together with enclosure of grains 210 of the second portion of the alkaline waste. The grains 210 of the second portion of the alkaline waste are preferably uniformly distributed in the structure.

Fig. 2c discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a third embodiment of the invention. In the disclosed embodiment, the flowable solidifier comprises mainly a flowable cement former that possesses the ability to produce a cement solidifying reaction in which a concrete structure 205 is formed. Grains 210 of the alkaline waste are enclosed in the solidified combination of the flowable cement former and the alkaline waste. In fig. 2c, the solidified concrete structure 205 is illustrated by a second hatching. The grains 210 of the second portion of the alkaline waste are preferably uniformly distributed in the structure.

Fig. 2d discloses a schematic overview of the microstructure of a combination of alkaline waste and a flowable solidifier according to a fourth embodiment of the invention. In the disclosed embodiment, the flowable solidifier comprises partly a flowable geopolymeric former and a flowable cement former. The flowable geopolymeric former has been added to an amount that enables it to form the solidified combination with a first portion of the alkaline waste by a geopolymeric reaction between the geopolymeric former and the first portion of the alkaline waste. The structure in fig. 2d further comprises partly a flowable cement former that possesses the ability to produce a cement solidifying reaction in which a concrete structure 205 is formed. In the disclosed embodiment grains 210 of a second portion of the alkaline waste are enclosed in the combined geopolymer 200 and concrete structure 205. In fig. 2d, the solidified combination is illustrated by the first and the second hatching together with enclosure of the second portion of the alkaline waste. The grains 210 of the second portion of the alkaline waste are preferably uniformly distributed in the structure.

Fig. 3 discloses a vessel 300 for transporting and forming the combination of the alkaline waste and the flowable solidifier. In the disclosed embodiment of the invention, the vessel 300 is a ship and the combination of the alkaline waste and the flowable solidifier is adapted to be deposited in the sea.

The vessel 300 is configured with means for manufacturing the formable combination of the alka- line waste and the flowable soiidifier. The means comprises arrangement for adding the alkaline waste and the flowable soiidifier to a container 310, such as a first conveyor belt 315, combining the alkaline waste with the flowable soiidifier into a formable combination, such as by rotating the container 310, and dividing the formable combination into pellet that are allowed to solidify. The vessel 300 further comprises a plurality dispiaceable boxes 320 for holding the alkaline waste, the flowable soiidifier or components of the flowable soiidifier, and pellets of the formable combination or solidified combination.

Preferably, the vessel 300 further comprises a second conveyor belt 325 that is adapted to transport the formable combination while being solidified to a discharging arrangement 330 for discharging the combination from the vessel 300. The discharging arrangement 330 comprises for example a pipe or similar for guiding the combination of the alkaline waste and the flowable soiidifier to the intended position of deposit at the seabed. Preferably, the second conveyor belt 325 is provided with a layer of granular solid material, such as sand, gravel, etcetera, for preventing the formable combination from sticking to the second conveyor belt 325. In the disclosed example the container 310 is arranged in the bow of the vessel 300.

Preferably, the solidified combination is deposited submerged in water is such a way that an artificial reef is constructed. The artificial reef is arranged with forms and hollow spaces that are desirable for increasing fish yield or for algaculture. The solidified combination may also be used for covering an area or object at the seabed, such as a wreck or other structure, or for covering an area of the seabed that comprises contamination. The solidified combination may also be used as a filling material for a bore of an offshore well. Furthermore, the solidified combination may be used as material in a breakwater structure for reducing coastal erosion or providing safe harbourage. it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.