The invention relates to a method of handling ash from mu- nicipal waste combustion as defined in the preamble of claim 1, as well as to a product made by the method as defined in the preamble of claim 7 and to the use of the product as defined in the preamble of claim 13. In the production of electrical and thermal energy, a variety of combustion plants are generally used, the ash produced by them being further processed case-specifically in different ways. Said plants employ, as a fuel, i.a., coal, wood, bark, peat and other biofuels, as well as natural gas, oil and, increasingly, also municipal waste which also can be referred to as "mixed waste".

Depending on the fuel employed by the plant, the ash must be disposed of, i.a., for environmental reasons, in varying ways. When the plant operates as an incinerator, it usually employs said mixed waste as waste and produces, when incin erating the waste, slag, boiler and fly ash as well as APC waste which are, in general, harmful and even dangerous for the people and environment. APC is an abbreviation of Air Pollution Control. Said APC waste mentioned in this speci fication is a side-stream fly ash material from incineration, or a material equal thereto, also referred to as APC ash and APC fly ash hereafter in this specification. The utilization of APC ashes from incineration is complicated by the fact that they contain substances which are classified as dangerous. These APC ashes contain, i.a., heavy metals and salts. Therefore, APC ashes from mixed waste combustion cannot be disposed to landfills, for example, without spe cific investigations. Their disposal to landfills is possi ble only after specific eligibility criteria are fulfilled. If the eligibility criteria are not fulfilled, said APC ashes are classified as dangerous waste and need to be disposed of or destroyed at sites reserved for them. The disposal of APC ashes is an increasing problem.

However, all APC ash is not this dangerous throughout but harmful substances can be separated therefrom. By appropri ate processing, a major part of the APC fly ash, or the like, could be utilized, for example, as an additional constituent in cement, or by combining it with other side-streams to form a binder, with the result that the solubility values do not exceed the allowed threshold values. This allows the fly ash, which is difficult to dispose of, to be used safely and destroyed without problems.

Fly ash and cement can be blended together to obtain a binder usable as a building material and constituting a material suitable for use in earth construction and as a stabilizer, for example. The manufacture of iron and steel produces a variety of slag materials, such as high-grade steel slag, ladle slag, blastfurnace slag etc. In this specification, all of these slags produced in the manufacture of iron and steel are commonly referred to as "slag".

As an example, blastfurnace slag has also been used, after been ground and blended together with cement, i.a, as a earth construction material. This involves the use of the ground, granulated blastfurnace slag, together with pure cement, as a binder, the slag being coarse ground with a D95 particle size over 40 pm. It has not been known how to activate the slag to harden, i.e. cure, in any other way but by means of cement, and, in addition, it has been necessary to use sodium hydroxide (NaOH), commonly known as lye, as an activator. In the prior-art binders, the amount of cement in the slag is approximately 20 to 60 % by weight.

It is the use of cement that is the problem with the known solutions because the manufacture of cement causes consid erable CO2 emissions. Therefore, it is desirable to develop binders suitable for more eco-friendly earth construction materials and for other uses as well.

As wood dissolved in a cooking process at a pulp mill is burned, green liquor dregs are produced, resembling, in con sistency, to wood combustion ash but it is much more diffi cult to treat because of its moist state. Therefore, the green liquor dregs are usually regarded as a useless waste and treated accordingly. When getting wet, the green liquor dregs, unlike wood ash, do not get harder but softer. The green liquor dregs have a high content of lime but also of phosphor, magnesium, manganese, sulfur and trace elements, such as zinc. The green liquor dregs are produced in high amounts and a lot of it is disposed to landfills although attempts have also been made to find long-term alternatives for how to recycle it.

This invention aims at eliminating the above-mentioned draw backs as well as to provide an inexpensive and reliable method of handling ash from municipal waste combustion, as well as other materials that are difficult to dispose of. An objective of the invention is to provide a binder product produced by the method, resembling cement and employing ash from municipal waste combustion as a constituent. This binder has many uses and can also be used for earth construction. Further, an objective of the invention is to make it possible to maximize the utilization of ash from municipal waste com bustion, thus expanding the possibilities for the disposal of this harmful ash. Still another objective of the invention is to reduce the use of cement in the binder that can be used for building, or. i.a., for earth construction. Thus, the aim is to provide a binder where only a small amount cement, or no cement at all, is needed.

The method according to the invention is characterized in what is set forth in the characterizing part of claim 1. Correspondingly, the product produced by the method accord ing to the invention is characterized in what is set forth in the characterizing part of claim 7 while the use of the product is characterized in what is set forth in the char acterizing part of claim 13. The other embodiments of the invention are characterized in what is set forth in the rest of the claims.

Typically, the inventive method of handling ash from munic ipal waste, i.e. mixed waste, combustion produces a binder combination to partly or entirely replace cement, wherein fly ash from municipal waste, i.e. mixed waste, combustion, i.e. APC ash, is blended with ground slag and/or slag sorted by particle size, or with green liquor dregs, to form a curable binder usable for different purposes, such as for earth construction, or as a stabilizer or building material, or for easier disposal.

The cement-like binder combination according to the inven tion may contain a substantially harmless ground slag ap proximately 60 to 80%, preferably approximately 75 %, and fly ash from municipal waste, i.e. mixed waste, combustion, i.e. APC ash, in an amount of approximately 20 to 40 %, preferably approximately 25 %. The binder combination ac cording to the invention may also comprise fly ash from municipal waste, i.e. mixed waste, combustion, i.e. APC ash, in an amount of up to approximately 70 to 90 %, preferably approximately 75 %, and green liquor dregs from the combus tion of wood dissolved in a cooking process at a pulp mill, in an amount of approximately 10 to 30 %, preferably approx imately 25 %.

In the method according to the invention, slag, such as blastfurnace slag and green liquor dregs, is activated by means of APC ash. Thus, the APC ash, which contains calcium oxide (CaO) in an amount of up to approximately 70 % by weight, suitably approximately 70 % by weight and preferably over 40 % by weight, is blended, in dry form, with the slag or green liquor dregs which are powdered. In the binder prepared in this way, the APC ash is mixed in to act as an activator for the slag and green liquor dregs, to cause a curing reaction of the binder when blended with water.

The binder combination according to the invention may contain other constituents in addition to the APC ash and slag, or just the APC ash and green liquor dregs. In this case, the amount of the other constituents reduces the above-stated percentages .

A major advantage of the solution according to the invention is that it allows materials which are difficult to dispose of, such as ash from municipal waste combustion, i.e. APC waste combustion, as well as the above-stated slag and green liquor dregs, to be utilized as far as possible. This makes it possible to replace a part of the cement powder, which otherwise would be used as a binder for building materials, such as concrete, and for earth construction, with these production side-stream materials. As cement is not needed as a binder, a drop of the CO ₂ emissions from the cement manu facture is achieved. Omitting the cement and replacing it with the above-stated iron and steel production slag or green liquor dregs, for example, also gives the solution according to the invention a very good ecological footprint. Another advantage is that no lye is needed as an activator for curing the binder containing powdered granulated slag but the APC waste, when dosed suitably, acts as an activator to start a curing reaction of the slag.After been hardened, i.e. cured, the binder meets even the CEM III strength requirements.

Until now, it has not been possible to freely recycle or to freely dispose of fly ash originating from the combustion of municipal waste, more commonly mixed waste, i.e. APC ash, as it contains compounds harmful and dangerous to humans, ani mals and the environment. The applicant has been able to develop, based on his numerous studies and trials, a novel innovative solution for utilizing APC ash in an inexpensive and safe way. In this solution, APC ash is blended, prefer ably in dry form, with suitably prepared granulated and ground metal-production slag, such as blastfurnace slag, or, alternatively, with the above-mentioned dried green liquor dregs ground to a suitable degree of fineness. This results in a novel and innovative cement-like binder that can be cured to suit its intended use, as a mine filler, ground stabilizer for reinforcing loose soil, building material, for asphalt construction and other convenient purposes.

An especially preferable feature of the invention is that production side-stream materials that are harmful in dif ferent ways, such as APC fly ash, steel and iron production slags and green liquor dregs, which mostly are difficult to dispose of, can be blended together, based on the above- mentioned results of the inventor's studies and trials, in a unique proportion and composition, with the consequence that the resulting material, which, in this case, is the cement-like binder usable for many purposes, no longer is a harmful or dangerous material. As an example, although the APC fly ash acting as the source material contains dangerous substances, such as chloride, that are dissolved into the ground, the solubility values of the APC fly ash, after blending it, by following the teachings of the invention, with slag or green liquor dregs treated in accordance with the invention, no longer exceed the allowed threshold values in said mixture. This makes it possible to safely use APC fly ash, when blended with slag or green liquor dregs, for land improvements, for example.

It can be stated that the solution according to the invention comprises preparing and using a cement-like binder combina tion as well as, as a product, the binder combination itself, the binder combination comprising a given percentage of APC fly ash which preferably is sorted, and, if necessary, after been sorted, ground and re-sorted, as well as a given per centage of suitably prepared ground slag or green liquor dregs. In addition, said binder combination, briefly binder, may comprise a percentage of one or more of the following constituents: fly ash from bark combustion, fly ash from peat combustion, fly ash from wood combustion, fly ash from other biocombustion, fly ash from coal combustion. Said binder combination may further contain a variety of addi tives. In the method according to the invention, said powdered binder combination is prepared, preferably in dry form, by blending together ash from municipal waste, i.e. more com monly mixed waste, combustion, i.e. APC ash, and either ground slag produced in the manufacture of iron and/or steel or green liquor dregs, or green liquor dregs produced in forest industry processes, in an amount of N %.

Preferably, the APC ash is blended into the binder to be prepared, to act as an activator causing, as the binder is mixed with water, a curing i.e. hardening reaction of the binder. This eliminates the need of using sodium hydroxide (NaOH), for example, as an activator. An APC ash content not higher than approximately 20 % is enough to start a curing reaction of the slag containing binder, for example. Corre spondingly, an APC ash content under 70 % is enough to start a curing reaction of the green liquor dregs containing binder.

The above-mentioned percentage N of the APC ash is a per centage by weight and any percentage in the range of 20 to 80 %, suitably one at a time from the following integers and their decimals: 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67 , 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79. That is, more briefly, the percentage N may have any numerical value with decimals in the integer range of 20 to 80, these values being included when the APC ash is used alone. If the APC ash is used together with some other ap propriate constituent, blended with the slag or green liquor dregs, the amount of the APC ash can be less than 20 %. The numerous tests and trials of the inventor have revealed that not all ash types are equally suitable for preparing the binder according to the invention. Depending, among other things, on the combustion material and temperature, the com position of the ash may vary to a high degree. The feedstock of the mixed waste combustion and, consequently, the compo sition of the APC ash obtained therefrom, show a considerable variation.

Suitably, the APC ash used for preparing the binder according to the invention contains calcium oxide (CaO) in an amount sufficient for the purpose. Thus, the APC ash contains cal cium oxide in an amount of up to approximately 70 percent by weight, preferably approximately 50 to 65 percent by weight and more preferably over 40 percent by weight. If the amount of calcium oxide is too low, the mixture of the APC ash and the slag and green liquor dregs does not cause the right reaction and does not reach a degree of hardness required for its intended use.

If the ash that is used does not contain enough calcium oxide, other materials containing enough calcium can be used in the preparation of the binder. However, it is the end result that matters, i.e. that the binder according to the invention contains calcium oxide in an amount of up to ap proximately 70 percent by weight, preferably approximately 50 to 65 percent by weight and more preferably over 40 per cent by weight.

Preferably, the APC waste combustion ash used for the mixture according to the invention is sorted by particle size and, if necessary, ground. The ash can be treated by first sorting it and by grinding and re-sorting the coarser fraction there after. Suitably, the D95 particle size of the ash used in the mixture is 10 to 40 pm, preferably 20 to 25 pm. What is essential is that the APC ash is as uniform in particle size, and as suitable for its intended use, as possible.

In the step of sorting, it is easy to get rid of any heavy metals enriched in the smaller particle size fractions, as well as other toxic agents present in the ash, by moving all of the sorted smaller fractions to be used in some other way, as a hazardous waste, for example.

Preferably, the powdered green liquor dregs used for the mixture according to the invention is also pre-sorted to a particle size suitable for the purpose. Suitably, the D95 particle size of the green liquor dregs used in the mixture is 10 to 40 pm, preferably 20 to 25 pm and most preferably approximately 35 pm. Once again, what is essential is that the green liquor dregs are as uniform in particle size, and as suitable for its intended use, as possible. If the green liquor dregs constituting the source material is not ready- to-use for the mixture, in terms of its particle size, it is ground and sorted to the above-mentioned suitable particle size prior to blending.

Correspondingly, the D95 particle size of the slag used in the mixture is 10 to 40 pm, preferably 20 to 25 pm. If the the slag does not have this particle size, it must be ground, and for an optimum result, also sorted to be as uniform in particle size as possible. Preferably, the slag is granulated prior to blending. When preparing the binder according to the invention for the purpose of reinforcing soil and/or stabilizing road beds, it may be preferable to also add fiber, such as such textile shred, into the binder combination. This provides the mixture with toughness and tensile strength.

Preferably, the cement-like binder according to the inven tion is used as a constituent in a material used as a mine filler, ground stabilizer for reinforcing loose soil, build ing material, for asphalt construction and other purposes where a curable binder like this can be used.

The binder according to the invention can be prepared in any suitable place. The powdered constituents having a suitable particle size, i.e. the APC ash and the slag or green liquor dregs, can be blended together at a blending station or at the site of application as well.

It will be appreciated by a person skilled in the art that the different embodiments of the invention are not solely restricted to the examples given above but may vary within the scope of the accompanying claims. What is essential is that the invention allows fly ash from municipal waste, i.e. mixed waste, combustion, i.e. APC ash, which is expensive and difficult to dispose of, and hazardous as well, to be utilized and recycled by suitably blending it with selected other materials.

It will also be appreciated by the person skilled in the art that, if the calcium dioxide content of the ash used for preparing the binder according to the invention is too low to cause a reaction for curing the binder, for example, to an appropriate hardness, by merely blending this ash with slag or green liquor dregs, it is possible to use, in addi tion to said ash, some other ash or a similar material, such as waste gypsum having a sufficient calcium dioxide content, in the mixture. Thus, the combined calcium dioxide content of the mixed materials is sufficient to cause a reaction for curing the binder according to the invention, when it is used as a building material and for other convenient pur poses, to an appropriate hardness, while it also is environ mentally harmless. This may apply not only to calcium oxide but also to other substances present in the ash and possibly important for other features of the binder. Hence, if nec essary, a third material may adjust, if necessary, the cal cium oxide content, and also the content of other constitu ents, in the binder.

It will also be appreciated by the person skilled in the art that, depending on the composition of the APC waste, the APC waste does not have to be treated in any way for the binder combination. Hence, the ash constituting the APC waste can be blended as such with the above-mentioned slag or green liquor dregs. If prepared like this, the binder will cure but more slowly and its strength values will be lower than those given by ground and/or sorted APC ash.

It will also be appreciated by the person skilled in the art that, depending on the chemical composition of the source materials, the blending proportions of the materials blended together may differ from the above. It is also possible to even blend all of the three above-mentioned materials, i.e. the APC ash, the slag and the green liquor dregs, together in dry powder form. Preferably, the APC ash and/or the slag and/or the green liquor dregs are sorted and, if necessary, ground as well. Suitably, after been sorted, all of the three materials intended to be blended together have a D95 particle size in the range of 10 to 40 pm, preferably 20 to 25 pm. As stated above, it is preferable that the ash that is used has a high CaO content. Each of the three materials, i.e. the APC ash, the slag and the green liquor dregs, may have, in the mixture, a share of approximately 1/3 of the mixture, for example. Depending on the composition of the source ma terials, the maximum amount of the slag can be up to 80 %, leaving a combined minimum share of approximately 20 % for the APC ash and/or the green liquor dregs.