LU88471A1 - Method for treating slag from incineration ovens for household waste and refuse - Google Patents

Description

PROCESS FOR THE TREATMENT OF SLAG OF FOODS FROM THE INCINERATION OF HOUSEHOLD WASTE AND GARBAGE

The present invention relates to a method for treating slag from incineration ovens for household waste and refuse.

During the incineration of waste such as household waste, approximately one third of the initial quantity remains in the form of slag from incineration ovens.

Given their chemical composition, their reactivity and above all their very high quantity, these slags present an increasingly serious disposal problem. To date, this waste has been dumped on a landfill. No revaluation took place, this mainly for reasons of dimensional stability (risk of expansion) and for environmental reasons due to the possibility of leaching of water-soluble compounds. Various methods and devices have been proposed to solve the problems encountered during the removal of slag from household waste incineration ovens.

Thus, German patent application DE-24 58 265 A1 describes a process for treating slag intended to use it in the construction of road foundations. The slag is cooled, dried and mixed with Portland cement or other hydraulic binder to improve their mechanical properties.

In the process described in European patent application EP-1 241 635 A2, the slag is subjected to a continuous mixing and sieving in order to remove the fine particles in order to obtain a material with a reduced content of dangerous products. and toxic. This material could then be used in road construction or as gravel for the winter service of roads and sidewalks.

PCT patent application WO89 / 11912 proposes a process and a device for purifying slag by eliminating harmful substances and impurities. The slag is washed with approximately neutral water, the hazardous substances pass into the aqueous phase and the solid residues largely freed from their hazardous substances can be used in construction.

The method and the device for treating slag described in PCT patent application WO89 / 12609 recommend cooling the slag directly at the outlet of the furnace, without sudden cooling in an aqueous bath, then separating it into at least two fractions, of which one gathers the particles of a size lower than 2 mm.

Although the slag obtained by the processes described above has a lower content of harmful substances than that of untreated slag, the residual quantity of these elements still represents a potential risk for the environment if these slag is used in construction near the water tables.

The object of the present invention is to provide a method for treating slag from incineration ovens for refuse and household waste which makes it possible to minimize the leaching of salts and other compounds harmful to the environment. The objective is achieved by a process for treating the slag from incineration dumps for refuse and waste, essentially characterized in that the slag is subjected to a maturing step under atmospheric conditions, is dried to a moisture content residual between 5% and 20, are mixed with a bitumen emulsion, and in that all the particles are coated with a thin layer of bitumen so as to minimize the leaching of salts and other compounds harmful to the environment.

The slag treated by this process can be used as a building material and must no longer be stored in a landfill.

The physical properties of the slag thus treated are obviously more interesting than those of the untreated slag. The coated slag has properties similar to conventional coated materials. So we can compact them easily. Swelling on contact with water is minimized because water can no longer penetrate inside the particles. The slag obtained has mechanical characteristics and sufficient dimensional stability to allow its use in the different layers and different levels of road construction in particular and of backfilling in general. In view of the mechanical properties of the slag thus treated, it will be possible to use it not only in the lower parts of the road but also in the tie layers, which are no longer in contact with water coming from a groundwater table. The risk of accidental leaching is thus significantly reduced.

According to a first advantageous embodiment, the coating of the slag is carried out with a basic bitumen emulsion. The advantage of using a basic bitumen emulsion is that the rupture of the emulsion can be controlled, thus facilitating the coating and storage.

If the materials are used immediately after coating, a cationic bitumen emulsion can be used instead of the basic emulsion.

According to another preferred embodiment, a bitumen emulsion of the following composition is used: 45 to 65% by weight - penetration bitumen 180-200 (1/10 mm, 25 ° C, 100 g, 5s), emulsifiable - 35 to 55% by weight aqueous phase containing between 0.1 and 0.4% of caustic potash as well as suitable emulsifiers.

Alternatively, the coated slag can be subjected to a second coating after adding products such as stones and sands. The second coating can be done directly in the mixer. Depending on the properties desired for the final product, the same emulsion will be chosen for the second coating or else a different emulsion.

Example 1

After removal from the oven and after spraying with water, the slag is screened and the fraction containing particles larger than about 30 mm is separated. It is subject to manual selection and the unburnt materials are returned to the incineration plant. The rest must be treated separately.

The fraction of particles smaller than 30 mm is first of all freed of metallic particles by means of magnetic tapes or rollers, then stored in the open air. The slag can thus undergo a maturation, i.e. unburnt items can swell and organic matter can decompose. The infiltration water is collected to be treated in a treatment plant because, in general, this water is contaminated.

After the maturation stage, which can take a few months, the slag is poured into a buffer hopper. It is important to emphasize that the slag should not be subjected to drying before its treatment. Indeed, they have a natural humidity level which is between 5% and 20%. Once dosed, they are directly introduced into a mixer and following a premix, the binders are introduced after gravimetric dosing. Preferably a batch mixer with two axes is used. The mixing time is a function of the starting particle sizes of the materials used. The emptying of the mixer is accompanied by a visual inspection to check the effectiveness of the coating. Slag coated in this manner can be stored before being used in road construction. The bitumen-type emulsion used in this first example has the following properties: - Emulsifiable bitumen with penetration 180-200 1/10 mm (25 ° C, 100 g, 5 s), 55% by weight - aqueous phase containing 0.2 % of caustic potash: 45% by weight and as an emulsifier for products like tall oil or similar.

The characteristics of the product obtained can be summarized as follows:

The composition of the leaching water on the DURIEZ cylinders after 2 x 24 h stirring in ultra-pure water are:

Thus we have measured Zn contents of less than 0.02 mg / 1, Pb of less than 0.4 mg / 1, and of cd of less than 0.02 mg / 1.

The slag thus treated can be used as it is in road construction, or it can be mixed with other products, stones, sand etc. and undergo a second coating. The double coating thus increases the mechanical properties of the resulting product and significantly reduces the leaching. It is important to emphasize that one can use the same emulsion for the second coating or a different emulsion.

Claims (6)

1. A method of treating slag from incineration dumps for refuse and waste in which, after removal from the oven, the metal particles are separated from the slag which is then sieved, characterized in that the slag is subjected to a step of maturing under atmospheric conditions, are dried to a residual moisture content of between 5% and 20, are mixed with a bitumen emulsion and in that all the particles are coated with a thin layer of bitumen emulsion so as to minimize leaching of salts and other compounds harmful to the environment. 2. Method according to claim 1 characterized in that a basic bitumen emulsion is used. 3. Method according to claim 1 characterized in that a cationic bitumen emulsion is used. 4. Method according to claim 1 or 2 characterized in that a bitumen emulsion of the following composition is used: 45 to 65% by weight - emulsifiable bitumen of penetration 180-200 (1/10 mm, 25 ° C, 100 g, 5s), - 35 to 55% by weight aqueous phase containing between 0.1 and 0.4% of caustic potash as well as suitable emulsifiers. 5. Method according to any one of claims 1 to 4 characterized in that the coated slag is mixed with products such as stones, sand etc. and in that it is coated a second time with the same emulsion. 6. Method according to any one of claims 1 to 4 characterized in that the coated slag is mixed with products such as stones, sand etc. and in that it is coated a second time with a different emulsion.