PROCESS FOR THE PRODUCTION OF THERMO-FORMED PRODUCTS

DESCRIPTION

The present invention relates to a process for the production of thermo-formed products starting from mixtures comprising products consisting of waste susceptible to inertisation.

CN 103449744 describes the production of a geopolymer. This document mentions sodium tripolyphosphate in an environment with a pH of 10-13. In such a pH range, calcium phosphates are insoluble and therefore they could not perform a chelating function in relation to heavy metals and activate the surface of the aggregates to favor the subsequent reticulation with agglomerating mortar.

Wikipedia “Sodium triphosphate” (https:/

/en. wikipedia.org/wiki/Sodium_triphosphate) describes the properties of sodium triphosphate. This substance is not an aggregating substance but it is soluble, and performs a wetting detergent function and therefore it does not favor geo-polymerization and is not known as a geo-polymerization adjuvant.

JP H05254909 describes the production of a product using a hydraulic binder that can be disposed of in an oven and is therefore refractory. The document describes a specific reaction between blast furnace slags and reactants such as alkaline phosphates, an alkali metal hydroxide, an alkaline earth metal hydroxide.

JP 2011157253A discloses the use of NaAl (SC>4)2 which is a hydraulic setting accelerator or modulator. US 8795428 B1 describes the use of citric acid which is not a chelating agent but is an agent which forms soluble metal complexes which hinder geo polymerization.

CN 107140903A mentions the use of reagents such as iminodisuccinic acid, one of its sodium salt, sodium gluconate, EDTA acid. These complex substances perform a wetting and detergent function and do not favor geo polymerization.

A process in accordance with the present invention aims at increasing the use of waste, in particular waste produced by industrial processes or decontamination or purification processes, providing benefits both in economic terms in relation to the use of certain types of waste as raw materials, both in environmental terms in relation to both the lower consumption of virgin raw materials and the reduction of areas destined for the storage of non-reused waste.

These and further advantages and features of the present invention will be better understood by every person skilled in the art thanks to the following description.

A process in accordance with the present invention involves the production of products obtained from the preparation of a mixture comprising an agglomerating mortar and one or more aggregates, or agglomerates, consisting of substances, in particular waste, containing compounds of calcium or iron or aluminum.

The percentage by weight of the agglomerating mortar is comprised between 3% and 50% of the total weight of the mixture. Complementarily, the percentage by weight of the agglomerates is comprised between 97% and 50% of the total weight of the mixture.

The agglomerating mortar is produced using agglomerating substances and water and constitutes a shapeable mass that can be shaped by casting or pressing in a mold or by extrusion. The amount of water varies according to the desired density for the shapeable mass which therefore assumes a condition of greater or lesser plasticity depending on the amount of water used.

The agglomerating substances can be selected in a first group comprising hydraulic lime, portland cements types I, II, III, IV, V, clinker, mixture cements, aluminous cements, white cements, quick-setting cements, kaolinitic clays, kaolin, glass, glass-ceramic fibers, pozzolan.

More generally, the agglomerating substances are inorganic binders with pozzolanic behavior, that is, compounds containing calcium oxides which can be combined with silicates, silico-aluminates and calcium oxide ferrites. These substances are in the form of powders with a particle size comprised between 10 and 50 microns and exhibit pozzolanic behavior (the pozzolanic behavior of a material is its ability to react with calcium hydroxide to form hydraulic compounds similar to those generated during hydration of Portland cement clinker giving rise to geopolymer structures). The prefix "geo" indicates that geopolymers are characterized by a chemical composition and mineralogical structure that are completely similar to those typical of natural rocks, of which, therefore, they exhibit the main properties, namely hardness, chemical stability and longevity. It is noted that the production of geopolymers is similar to that of cements: it occurs by mixing a reactive powder (called base) with a water- based binder (called activator) and possibly a functionalizing charge. The reaction of a powdered solid aluminosilicate with a highly basic aqueous solution (generally consisting of sodium and potassium hydroxides and silicates) produces a synthetic alkaline aluminosilicate, i.e. the geopolymer, which is the amorphous or semi-crystalline analogue of zeolites.

During the geo-polymerization a gel is formed, that is a poly-mineral “resin” (the real geopolymer matrix) which consists of SiCri and AIO4 tetrahedra that are linked in alternating sequence. The gel acts as an adhesive for the aluminosilicate-based raw materials that have not reacted and fillers possibly added as reinforcement (fibers, metal particles, ceramic and glass powders, polymers) as occurs with organic resins. The process takes place, also depending on the materials used at low temperatures, between 25° C and 120° C, and with a quick consolidation, it takes from 5 to 10 hours, a time equal to that of quick-setting cements. In accordance with the present invention, the aggregates or agglomerates can be selected from a second group of substances comprising compounds of calcium or silicon, iron and/or aluminum present in waste or scrap materials or by-products. For example, the aggregates can be selected from a group comprising: silicates - aluminates - ferrites, sulphates and/or calcium carbonates and oxides of silicon, and/or iron and/or aluminum in the presence of minor amounts of oxides of other elements such as copper, sodium and/or magnesium. For example, the aggregates are: glass, glass-ceramic, waste glass- ceramic fibers; sands and powders and waste sludge derived from the primary and secondary processing of non-ferrous metals; coal fly ash; ashes, sands and steel sludge; chemical gypsum and refractory casting gypsum; exhausted flotation sludge produced in the refining processes of copper and precious metals, obsidians, crystallines and ceramic glazes; chemical or biological purification sludge mineralized with lime or flocculant, paper mill sludge, pulper waste from paper mills. The present process foresees a step of activation of the agglomerants by means of a reaction accelerator consisting, for example, of sodium and/or potassium silicate, (Na2 S1O3 , K2 S1O3) in a percentage ranging from 1-20 % by weight of the agglomerating mortar. Mainly, the present process involves the use of sodium silicate which is less expensive than potassium silicate.

The present process also comprises a step of adding the aggregates with a solution of calcium phosphates Ca(H ₂ P0 ₄ ) ₂ or CaHP0 ₄ buffered in a range of pH 2-9 with phosphoric acid (H3PO4), in a percentage ranging from 1-25% by weight of the aggregates.

The calcium phosphate solution captures and renders inert the heavy metal cations present in the aggregates, preventing them from giving rise to dangerous releasing of the finished product if exposed to leaching deriving from environmental washout. The use of the calcium phosphate solution entails further advantages deriving from the fact that these phosphates, in presence of metals of the second and third periodic groups (Be, Mg, Ca, Ba .... B, A1 , Ga,...), form crystalline structures that contribute to making the product more solid and thermally refractory. This function of the calcium phosphate solution can be equally performed by other solutions (for example, a solution of sodium or potassium phosphates) but the calcium phosphate solutions are preferred because they carry out a more evident chelating reaction towards heavy metals present in the aggregates. The calcium phosphates thus introduced also contribute to the cementation of the aggregates.

The forming process can be assisted by ultrasound sources. Both the forming mold and the extrusion die can be equipped with ultrasound sources arranged on the forming walls of the die or of the mold. Preferably, the ultrasound sources are oriented perpendicularly to the casting and/or extrusion direction, with the particular function of homogenizing the phases making up the mixture on a micrometric scale. This expedient is aimed at obtaining the thermodynamic condition of a system of minimum surface energy, which favors the formation of a more compact product, free from distortions and tensions which after the thermal consolidation process can result as micro cracks and characterize the typical fragility of ceramic materials.

The raw semi-finished product thus obtained can be subjected to a stabilization and consolidation phase by stationing in a confined environment in which the following can be regulated: temperature (in the range 10°C-90°C), partial pressure of carbon dioxide introduced into the conditioning environment (Pco2 comprised in the range 1 x 10 ⁴ Pa - 2 x 10 ⁶ Pa), dwell time in the air conditioning environment in the range 2h-300 h) . This is in order to neutralize the excessive alkalinity of the product, due to the presence of high concentrations of alkaline elements, alkaline earth elements (Na, Ca, Mg). The dwell time in a controlled environment essentially depends on the pozzolanic reaction rate of the mixture intended as the geo-polymerization rate, that is, the rate of formation of the aforementioned geo-polymeric structures.

The consolidated raw semi-finished product can be subjected to a specific heat treatment here defined as "hardening", depending on the composition in aggregates, and on the "aggregates/aggregating" ratio. Although distinct heat treatments are envisaged, which will be further described in the paragraph of the examples, it is possible to define the hardening process as a thermal process consisting of a thermal conditioning phase, during which the temperature is increased from 20° C to 120° C in a time interval between 5 min and 180 min. Possibly, in particular for mixtures rich in calcium carbonates, a deep decarbonation phase can be provided, carried out by bringing the semi-finished product to a temperature between 900° C and 1100°C maintained for a time between 30 min and 360 min depending on the mass of the semi-finished product. The subsequent cooling is carried out by gradually lowering the temperature up to 600° C, followed by a forced cooling phase with a jet of air at a temperature between 500°C and 300°C followed by a spontaneous cooling phase down to ambient temperature.

After this hardening phase, the semi-finished product can be subjected to a surface treatment using impregnating liquids, such as solutions and/or suspensions comprising calcium hydroxides, magnesium, barium, or alkaline silicates, acid calcium and magnesium carbonates, calcium di-hydro phosphate, iron and copper sulphate ( Ba(OH)2 , Ca(OH)2 , Mg(OH)2 , CaHCCb , Ca3(H2P04)3, FeSCri to ensure that the finished product, due to possible leaching, does not give rise to release of metals dangerous for the environment. Furthermore, this surface treatment can induce interesting variations in the physical properties of the product, such as: change in color, hardness or permeability, and better compliance with the standards that establish limits to the releases.

The aforementioned process phases can be carried out in different stations of the same production site or even in different production sites.

The product can be provided with an internal reinforcement.

The forming phase can be carried out using molds of polymeric material or steel with coating on the internal surface of which are applied release additives which transfer to the mixture in the molds.

The following description provides examples of implementation of a process in accordance with the present invention.

EXAMPLE 1

Preparation for production of parallelepiped-shaped tiles 50x50x6 cm. An agglomerating mortar is prepared comprising Portland cement, in a total percentage of 98% by weight, added with sodium silicate at 2% by weight, and water sufficient to obtain a plastic mass.

The aggregates (agglomerates) are made up of 40% by weight of recovery glass-enamel powders mixed with 60% by weight of chemical and refractory casting gypsum, with the addition of a solution of calcium phosphates buffered at pH7.

The two preparations are mixed in the ratio of 15% of agglomerating mortar and 85% of aggregates (percentages by weight of the mixture). The mixture is poured into a polymeric mold for tiles, equipped with ultrasonic sources, from which it is unmolded after about 30 minutes. Then the unmolded raw tile is subjected to maturation at a temperature of about 30° C for 48 hours.

The consolidated product is subjected to a heat treatment process with an increase in temperature from 20 to 120°C in about 60 min, followed by an increase in temperature up to 1000° C which remains stable for about 90 minutes, then gradual descent of the temperature until it reaches room temperature.

The product is wetted by a 5% barium hydroxide solution, then passed in a solution of calcium phosphates at pH 8, and left to dry slowly.

EXAMPLE 2

Preparation for production of parallelepiped tiles 50x50x6 cm. An agglomerating mortar is prepared comprising kaolin clay and pozzolan at 95% by weight added with an activator consisting of sodium silicate at 5% by weight and water in the quantity necessary to amalgamate these substances.

The aggregates consist of about 20% recycled glass-enamel powders, mixed with 80% sands and steel sludge with the addition of a pH 8 buffered calcium phosphate solution.

The two preparations are mixed in the ratio of about 20% agglomerating and 80% aggregates (agglomerates). The mixture is poured into a polymeric mold for tiles, equipped with ultrasonic sources, from which it is unmolded after 10 minutes, then subjected to curing at a temperature of 90° C for 3 h. This is followed by a stabilization phase in CO2 atmosphere at partial pressure Pco2 equal to 2 x 10 ⁵ Pa for about 2 h.

The consolidated product is subjected to a heat treatment process with an increase in temperature from 20 to 120°C in about 30' min, followed by an increase in temperature up to 900° C which remains stable for about 30 minutes, then gradual descent up to room temperature.

The tile is rapidly cooled and subsequently immersed in calcium carbonate acid solution, Ca(HC03)2 , then left to dry slowly.

EXAMPLE 3

Preparation for the production of gravel.

An agglomerating mortar is prepared comprising kaolin clay, in a total percentage of 99% by weight, added with sodium silicate at 1% by weight, and water sufficient to obtain a plastic mass.

The aggregates (agglomerates) are made up of 20% by weight of recovery glass-enamel powders mixed with 80% of exhausted flotation sludge from copper and precious metals refining with the addition of a buffered calcium phosphate solution at pH 6.

The two preparations are mixed in the ratio of 8% of agglomerating mortar and 92% of aggregates (percentages by weight of the mixture). The mixture is pored into a metal roto-mold, equipped with ultrasonic sources, which exerts a pressure of about 3 Kg/cm ² , for a few seconds, followed by de-moulding. The semi-finished products, of small size, are subjected to maturation at a temperature of about 50° C for 1 hour. The consolidated product is subjected to a heat treatment process with an increase in temperature from 20 to 120°C in about 10 minutes, followed by an increase in temperature up to 1100° C which remains stable for about 90 minutes, followed by a descent gradual temperature until room temperature is reached.

The product is immersed in a solution of calcium phosphates and a solution of acid carbonate Ca(HC03)2 , then left to dry slowly.

EXAMPLE 4

Preparation for production of parallelepiped-shaped tiles 50x50x6 cm.

An agglomerating mortar is prepared comprising Portland cement mixed at 96% by weight added with activator consisting of sodium silicate at 4% by weight and water in the quantity necessary to amalgamate these substances.

The aggregates consist of dust from sludge and pulper waste from paper mills at 70% by weight, mixed with sands and chemical-biological purification sludge stabilized with a float at 30% by weight, with the addition of a solution of calcium phosphates buffered at pH 3.

The two preparations are mixed in the ratio of about 20% by weight of binder and 80% by weight of aggregates (agglomerates). The mixture is thrown into a polymeric mold for tiles, equipped with ultrasonic sources, compressed to 2 Kg/cm ² , unmolded after 2 minutes, then subjected to maturation at a temperature of 30°C for 3 h. A stabilization phase in CO 2 atmosphere follows at partial pressure Pco2 equal to 2 x 10 ⁵ Pa for about 2 h. The consolidated product is subjected to a heat treatment process with an increase in temperature from 20 to 120° C in about 60 min.

The tile is cooled and subsequently immersed in a solution of calcium phosphates pH 9 and then calcium carbonate acid Ca (HC0 ₃ ) ₂ , then left to dry slowly.

EXAMPLE 5

Preparation by extrusion of a parallelepiped - shaped tile measuring 5x30x120 centimeters reinforced with an electro-welded steel mesh.

An agglomerating mortar is prepared comprising clinker and hydraulic lime at 98% by weight added with an activator constructed from sodium silicate at 2% by weight and water in the quantity necessary to mix.

The aggregates consist of glass-ceramic fibers at 10 % by weight, sludge and pulper waste from paper mills at 20% by weight, mixed with flotation sludge from copper and precious metals refining at 70% by weight, with the addition of a pH 5 buffered calcium phosphate solution. The two preparations are mixed in the ratio of about 15% by weight of binder and 85 % by weight of aggregates (agglomerates). The mixture is poured into a polymeric mold for tiles until it is filled, in which the reinforcement consisting of the electro- welded steel mesh is previously positioned, and subjected to pressure of 1 Kg/cm ² for about 12 minutes, then the semi-finished product is kept at a temperature of 90° C for 1 h. This step is followed by a stabilization phase in CO2 atmosphere at partial pressure Pco2 equal to 1 x 10 ⁵ Pa for about 6 h.

The consolidated product is subjected to a heat treatment process with an increase in temperature from 20° C to 120° C in about 20 minutes.

The tile is impregnated with a pH 7.2 solution of calcium phosphates, again subjected to an increase in temperature from 20°C to 120°C in about 20 minutes and subsequently immersed in a solution of calcium carbonate acid, Ca (HCC>3)2, then left to dry slowly.

EXAMPLE 6

Preparation by extrusion of a 10x20x150 cm parallelepiped - shaped tile reinforced with an electro-welded steel cage.

An agglomerating mortar is prepared comprising kaolin clay at 97% by weight added with activator constructed from sodium silicate at 3% by weight and water in the quantity necessary to mix.

The aggregates consist of glass and glass-ceramic fibers at 40% by weight, sludge and waste from paper mills at 60% by weight, with the addition of a solution of calcium phosphates buffered at pH 3.

The two preparations are mixed in the ratio of about 10% by weight of binder and 90% by weight of aggregates (agglomerates). The mixture is thrown into a polymeric mold for beams until filling, in which the steel reinforcement is previously positioned, and subjected to a pressure of 1 Kg/cm ² for about 10 minutes. The semi-finished product is then left kept at a temperature of 90°C for 1 h. This is followed by a stabilization phase in CO2 atmosphere at partial pressure Pco2 equal to 1 x 10 ⁵ Pa for about 1 h.

The consolidated product is subjected to a heat treatment process with an increase in temperature from 20°C to 120°C in about 20 minutes. This is followed by an increase in temperature up to 900° C which remains stable for about 30 minutes and then the temperature gradually decreases to room temperature.

The tile is impregnated with a solution of calcium phosphates at pH 7.2, again subjected to an increase in temperature from 20°C to 120°C in about 20 minutes and then immersed in a solution of calcium carbonate acid, Ca(HC03)2, then left to dry slowly.

From the foregoing description it is evident that a process in accordance with the present invention is a process for the production of manufactured articles obtained starting from the preparation of a mixture comprising an agglomerating mortar and one or more aggregates consisting of waste, scrap or by-products containing calcium compounds or silicon and/or iron and/or aluminum, in which the agglomerating mortar comprises agglomerating substances consisting of inorganic binders with pozzolanic behavior, and is added with a geo-polymerization reaction accelerator or hydraulic setting, in which the aggregates are added an agent that performs a chelating action against the heavy metals present, and favors their geo-polymerization with the agglomerating mortar, in which this mixture, in the plastic state, undergoes a forming phase by extrusion, or by introduction into a mold, and in which , after said forming step, the raw semi-finished product thus obtained is subjected to a predefined heat treatment.

Calcium dihydrogen phosphate Ca(H ₂ P0 ₄ ) ₂ and CaHPCri, which is indicated above as a solution of calcium phosphates, have a chelating - binding action on heavy metals, fixing them as insoluble phosphates to the crystal lattice of silico -aluminates of calcium and other crystalline structures of metals present in the aggregates and / or agglomerants used, as well as aggregation by cementing the relative crystalline structures together.

In practice, the details of execution may in any case vary as regards the individual steps described and the substances indicated without thereby departing from the idea of the solution adopted and therefore remaining within the limits of the protection granted by this patent in accordance with the attached claims.