ES2450765B1 - INERTIZATION OF STEEL POWDER THROUGH ITS STABILIZING INTEGRATION IN A CONSTRUCTION MATERIAL - Google Patents

Abstract

Inertization of steel dust by stabilizing integration into a building material # Large quantities of steel dust (Electric Arc Furnace Dust, EAFD), regardless of their origin, can be stabilized and used on a sheet of solid material, 2 mm and with commercial value, obtainable either by extrusion, either by calendering, or by hot pressing, of a composite formulation obtainable by mixing: (i) one or more polymers capable of forming a solid polymer matrix, in an overall amount of 10 -25%; (ii) one or more phase change materials (PCM) of the organic type, optionally accompanied by mineral oil, where the total amount of PCM plus mineral oil is 5-20%; and (iii) EFDA by 40-80%. The solid material sheet can be used in the construction industry, to simultaneously provide acoustic insulation and thermal energy storage to the partitions.

Description

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DESCRIPTION

Steel powder inertization through its stabilizing integration into a building material.

This invention relates to the field of environmental chemistry, specifically to the inertization of a dangerous byproduct of the steel industry.

STATE OF THE TECHNIQUE

One way to produce steel is by means of iron refining in an electric arc furnace (EAF), in which heat is supplied by electric arcs between carbon electrodes submerged in the molten metal. Fusion and refining occur simultaneously after the solid charge is submerged under a layer of molten metal. This process is mainly used for the refining of scrap steel and for the direct reduction of iron. Very high temperatures are generated in the arc by plasma and volatile species are effectively removed from the metal. Dust, called steel powder (electric arc furnace dust; EAFD) is generated during the process. Millions of tons of EAFD are generated worldwide, and the amount of EAFD generated is expected to increase.

The EAFD has a complex mineralogy. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) analysis reveal that the main components of EAFD are mainly iron oxide, zinc oxide and zinc ferrite, with the presence of well defined peaks of sodium chloride and potassium chloride. Because calcium oxide is added to desulfurize and remove silicon oxide from steel in EAF, calcium compounds are present in various concentrations in EAFD. Chloride can exist in a phase of calcium chloride with magnesium, iron, zinc, lead and cadmium. The arsenic is also frequently found. Oxides of alkaline earth metals make EAFD suspensions highly alkaline.

Since EAFD contains toxic metals such as lead, cadmium and arsenic, treatment for steel manufacturers is a costly and time-consuming problem. The most common ways to manage EAFDs are to send them to external managers for disposal or recycling. The EAFD is classified as toxic and hazardous waste in most industrialized countries and is classified in the European Waste Catalog as a hazardous waste that needs treatment before its final discharge. Some of the industrial treatment processes of EAFD that have been proposed are mentioned in the following paragraphs.

The stabilization / solidification techniques have been used for the treatment of EAFD before its final discharge into landfills. Portland cement stabilization is the most economical alternative, but there are problems with the dissolution of metals due to the high pH of the leachate. Vitrification processes are less used because they have high energy consumption.

Methods can be used to encapsulate toxic metals, but these methods are not commercially interesting, since they involve significant investments and there is no recovery of metal.

The acid extraction processes can be used to treat EAFD and dissolve the metals of interest. Since the pH inherent in a powder suspension is greater than 11, excessive amounts of acid are required in this process. Thus, the commercialization of acid extractions from EAFD is not widespread.

Pyrometallurgical processes are used to remove lead and zinc from EAFD by volatilization and condensation of metals in a relatively pure form. However, with pyrometallurgical processes there is no recycling of iron to the EAF process. In addition, small particles of lead or lead oxide are difficult to completely remove from the steam outlet. Therefore, a concern with this process is lead contamination in neighboring areas.

Caustic processes in which the leaching and dissolution stages employ simple chemistry that takes advantage of the amphoteric nature of zinc, lead, tin, arsenic, selenium and aluminum, can be used to treat EAFD, but its commercial interest is less.

The process of incorporating EAFD as a filler in a polymer matrix has been described to obtain a composite formulation (name taken from the English composite, usually used to designate a composite material, also called simply "composite") that results in a heavy sheet conformable and useful for acoustic insulation in the automobile industry (cf. M. Niubo et al., "A possible recycling method for high grade steels EAFD", Journal of Hazardous Materials 2009, vol. 171, pp. 1139-1144; M. Niubo et al., "Study of the effect of EAFD and polymer composites using DoE", in Eurofillers 2009 Symposium; "From macro to nanofillers for structural and functional polymer materials"; Alessandria, 21-25 Jun 2009). The composite formulation also uses barite (BaSO4) and / or calcium carbonate (CaCO3) as fillers. This technique has the limitation that only the EAFD generated in the manufacture of high quality steels can be used, since the resulting EAFd has small contents of zinc, lead and arsenic. The presence of elements such as lead, chromium, cadmium and / or mercury in the EAFD from carbon steel mills makes it impossible to use them as polymers for this application since the products thus obtained exceed the limits required for automotive components. In addition, the content of this specific EAFD in the composite formulation is

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less than 30% by weight, with an optimal around 25%. This treatment process is therefore not suitable for incorporating large amounts of EAFD, or for other grades of EAFD.

Thus, apparently the environmental problems of the treatment of EAFD are not satisfactorily solved with the current technology.

EXPLANATION OF THE INVENTION

The present invention refers to the problem of obtaining an economically viable alternative treatment of large amounts of EAFD, regardless of the origin of the latter. This is achieved through a stabilizing integration of EAFD in a new and valuable composite formulation that p. ex. can be used massively in the construction industry.

Thus, one aspect of the present invention is related to the provision of a composite formulation obtainable by mixing a set of materials comprising the following ingredients, in the amounts indicated, expressed as mass percentages with respect to the total weight of the formulation: (i) one or more polymers capable of forming a solid polymer matrix, in an overall amount of 10-25%; (ii) one or more phase change materials (PCM) of organic type, optionally accompanied by mineral oil, where the total amount of PCM plus mineral oil is 5-20%, preferably 10-20%; and (iii) EAFD, by 40-80%, preferably 50-75%, with the proviso that the total sum of the amounts of ingredients is not more than 100%

In particular embodiments, polymers capable of forming a solid polymer matrix comprise thermoplastic elastomers. In preferred embodiments the thermoplastic elastomers are from the group of: polyethylene-co-vinyl acetate (EVA) copolymers, ethylene-based plastomer resins, styrene copolymer rubbers, ethylene-octene copolymers, ethylene-propylene-diene monomers ( ethylene-propylene-diene monomers, EPDM), and linear low-density polyethylenes (LLDPE). In the embodiment illustrated in the detailed description, mixtures of an EVA with vinyl acetate, and the ethylene-based plastomer resin sold under the Exact 8201 brand are used. The solid polymer matrix acts as a binder of EAFD particles. To mix the polymers, a small amount of dispersant can be used. A small amount of zinc stearate (0.05-1.0%, preferably 0.1-0.3%) is especially suitable.

The use in the PCM construction industry, both organic and inorganic, is well known (cf. eg LF Cabeza et al., "Materials used as PCM in thermal energy storage in buildings: A review", Renewable and Sustainable Energy Reviews 2011, vol. 15, pp. 1675-1695, and its references). In particular embodiments of the present invention, organic PCMs in composite formulations are paraffins (mixtures of aliphatic long chain hydrocarbons), especially those that have melting points within the range 15-30 ° C (human comfort temperature). Other organic PCMs, such as fatty acid esters with similar melting points, can be used. In addition to increasing the thermal inertia of the building element, PCMs also act as lubricants during the preparation of the composite formulation. In the event that more lubrication is necessary throughout the preparation procedure, PCMs can be supplemented with some mineral oil. However, formulations of composites without mineral oil are preferred.

The composite formulation of the present invention allows the incorporation of a high amount of EAFD, thus making an important contribution to the inertization of this toxic by-product. Although EAFD loads as high as 80% can be achieved, in a particular embodiment the load is 50-75%. EAFDs can come from any steel mill, unlike other treatments known in the art. Thus, the composite formulation of the present invention is especially advantageous when the EAFD comes from carbon steel mills, with a relatively high content of zinc, lead, chromium, manganese, cadmium, mercury and / or arsenic. All its highly toxic elements are stabilized when EAFD is incorporated into the composite formulation, and the latter is subsequently transformed into a sheet of solid material, either by extrusion, by calendering, or by hot pressing.

Thus, another aspect of the present invention is related to a sheet of solid material that can be obtained either by extrusion, by calendering, or by hot pressing (typically at a temperature of about 150 ° C) of any of the mentioned composite formulations previously. The sheet may have a thickness of 15 mm, with a thickness of about 2 mm being preferred.

As illustrated in the attached detailed description, the solid material sheet of the present invention simultaneously has good acoustic insulation properties and thermal energy storage properties. This fact, together with its relatively good mechanical properties, makes it useful to be incorporated into building materials: floors, ceilings and particularly partitions. This use is also an aspect of the present invention. As expected, the higher the PCM content in the composite formulation, the greater the energy storage properties of the solid material sheet.

Another aspect of the present invention is related to a process for preparing the aforementioned composite formulation, which comprises mixing the respective ingredients, under stirring conditions, and

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of sufficient addition rates to form a homogeneous mixture. Depending on the mixture used, some heating may be necessary. In a particular embodiment, this process comprises the steps of: (a) melting the respective mixture of polymers capable of forming a solid matrix of the polymer, including zinc stearate, where appropriate; (b) add the respective PCM, including the mineral oil where appropriate; and (c) add the corresponding EAFD.

Compared with other industrial EAFD treatment processes known in the art, the treatment of the present invention has the technical and economic advantages of providing a commercial material with a high EAFD load, which is useful in an industry - the industry of the construction - where large quantities of the material can be used (larger quantities than eg in the automobile industry). In addition, the energy expended in the manufacture of commercial material is relatively low, compared p. ex. with the vitrification processes.

Throughout the description and the claims, the word "comprises" and variations of the word are not intended to exclude other technical characteristics, additives, components or stages. Other objects, advantages and features of the invention will be apparent to those skilled in the art after an examination of the description or can be learned with the practice of the invention. The following detailed description is provided by way of illustration, and is not intended to be limiting of the present invention. The present invention encompasses all possible combinations of particular and preferred embodiments described herein.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Physicochemical characterization of EAFD

In order to evaluate the composition of the EAFD a sample of 5 kg was quartered (1/16), and an X-ray fluorescence of an alfcuot was performed, with an X-ray wave dispersion X-ray spectrophotometer spectrophotometer, WDXRF) Philips PW2400. The analysis was performed with inductively coupled optical emission spectrometry (inductively coupled plasma optical emission spectrometry, ICP-OES) in the solution resulting from the total acid attack of the EAFD. High-angle X-ray scattering (WAXS) X-ray diffraction was used to elucidate the crystalline phases present, and the morphology of the EAFD particles was observed using SEM, using a Quanta 200.

Density and specific surface area were determined with a He pycnometer and using the BET single point method, respectively. The distribution of particle sizes was evaluated with a Beckman Coulter LS 13 320 particle size analyzer with optical model.

Preparation of composite formulations by melt mixing

The polymer matrix was a mixture of copolymer of polyethylene-co-vinyl acetate (EVA) with 18% vinyl acetate, EVA Alcudia PA-538 from Repsol YPF, ^ on melt flow index (MFI) of 2 g / 10 min (190 ° C at 2.16 kg load) and a density of 937 kg / m, and a plastomer resin in Exax 8201 ethylene bath from Exxon Mobil Chemical, with an MFI of 1.1 g / 10 min (ASTM D 1238) and density 882 kg / m.

All samples were prepared at 150 ° C, using a paddle mixer with a speed of 55 rpm. The polymer pellet was mixed with the desired amount of EAFDs using zinc stearate as a dispersing agent. The PCM used were hydrocarbons based on n-paraffins and Rubitherm waxes, which acted as lubricating agents. Some formulations were prepared with the addition of mineral oil. Initially different compositions were formulated to assess processability. After mixing, the composite formulations were hot pressed, using a heated plate press at 150 ° C. For each formulation a heavy and homogeneous 2 mm thick sheet was obtained, from which samples were prepared for mechanical, thermal and acoustic tests.

Characterization of composite formulations

Physical and mechanical properties. The density of composite formulations was calculated by determining the mass and volume of the samples. Tensile tests were performed using a Mecmesin machine with a constant travel speed of 100 mm / min. The stiffness of composite formulations was evaluated

using the limit of transfer Oy and the maximum elongation Smax.

Thermal properties. Specific heat curves vs. temperature, and enthalpy curves vs. Temperature were necessary to know the energy stored in the material in a defined temperature range. The results were obtained by cycling the sample in a differential scanning calorimeter (differential scanning calorimeter, DSC822e) using hermetically sealed crucibles to prevent evaporation. The dynamic method was applied, and each sample was cycled 3 times with a heating rate of 0.5 ° C / min from 5 to 50 ° C.

Acoustic properties An experimental device based on the UNE-EN-ISO140 standard was used to measure airborne insulation and represent the insulation index (dB) vs. frequency (from 100 to 16000 Hz). The sample size was 30x30 cm. The noise level was recorded in each camera: L r in the receiving camera and Le

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in the broadcasting camera. When the background noise Lb was considered, the noise level in the receiver was Lr 'according to the equation described below. The difference between the two levels is the insulation index D (dB), which was used to compare the acoustic properties of the different formulations using the same device and conditions.

L

10 x log

(L 1010

v

4 \ 1010

)

Physicochemical characterization of EAFD

The results of semi-quantitative X-ray fluorescence analysis for EAFD are shown in Table 1. The chemical composition for each element is given in the form of its most stable oxide. Fe and Zn were the majority elements, and Ca, Si, Pb, Mn, S, K, Na and Al were minor elements. If the opposite is not said, all percentages are by weight (w / w).

Table 1. Results obtained with X-ray fluorescence of EAFD components

 Comp.

 % (w / w)

 Fe2O3

 40.23

 ZnO

 31.35

 CaO

 7.14

 SiO2

 4.06

 PbO

 3.32

 MnO

 1.98

 SO3

 1.95

 K2O

 1.83

 Na2O

 1.67

 Al2O3

 1.41

 MgO

 0.918

 Cr2O3

 0.453

 CuO

 0.425

 P2O5

 0.281

 TiO2

 0.203

The majority phases identified by DRX corresponded to iron oxides (franklinite, magnetite and hematite) and zinc oxides (zincite). EAFD particles were analyzed by SEM. It was observed that EAFD particles covered a wide range of sizes, with particles of different appearance, shape, etc. The size of the EAFD sample f ^ e from 1-50 pm. The density measured with the He pycnometer was 4.93 g / cm and the specific surface area was 4 m / g. On the other hand, homogeneity was favored by a small particle size and narrow distribution. It was observed that the solid had a volumetric distribution of bimodal particle size. The representative values of the distribution of the particles, d50 and d90, were 1,621 and 8,365 pm, respectively.

Component Content Table 2 shows several of the composite formulations prepared. In a first stage, a design of experiments was used to evaluate the effect of each component on each response. One of the main responses is a significant effect on the enthalpy curve vs. temperature. In composite formulations with a PCM content of less than 10%, the effect of storage due to phase change was not noticeable. Therefore, this 10% is a preferred lower limit. The appearance of all prepared samples was checked after 60 days. It was observed that samples with PCM above 20% had a greasy surface. This may be macroscopic evidence that migration from the interior to the outer surface of the sheets occurred and that the macroencapsulation of the PCM was not fully effective. Thus, a preferred range for the PCM was 10 to 20%.

The relationship between the polymers was optimized to achieve the desired mechanical properties with the lowest cost and the highest EAFD content. This ratio, after several tests, was fixed at 3: 1 EXACT: EVA. The lower the EAFD content, the better the processability of the mixture. However, in order to have a high EAFD load, all prepared samples contained at least 50% EAFD, this being a preferred lower limit. A preferred upper limit, depending on the viability of the processing, was set at 70%. It was observed that an increase in EAFD content above 70% does not lead to a proportional increase in acoustic insulation, while mechanical properties decrease.

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The preferred range for the polymer matrix content was 15 to 20%. A higher content improves the mechanical properties, but does not affect the thermal and acoustic properties, however increasing the cost of composite formulations.

Mechanical properties. Table 3 shows the results of the mechanical properties of some formulations prepared in as examples of l | present invention. For all samples the thickness is 3 mm and the surface density close to 7 kg / m.

Table 2: Component contents (%) of prepared composite formulations

 Ref.

 PCM EVA 18 EXACT EAFD Zn stearate mineral oil

 21.09

 --- 4.0 9.0 12.5 74.2 0.3

 17.11

 --- 3.9 8.8 11.8 70.1 0.1

 18.11

 6.7 4.2 5.2 10.3 73.8 0.1

 06.12

 8.6 10.6 2.9 9.7 68.0 0.2

 19.08

 6.2 7.5 2.3 7.9 75.9 0.2

 20.08

 7.2 9.3 3.4 10.3 69.6 0.2

 25.08

 --- 10.7 8.9 26.5 53.6 0.3

 26.08

 --- 19.9 4.9 14.8 60.1 0.3

The mechanical properties of the different formulations, shown in Table 3, did not differ

significantly. Changes in the limit of transfer (ay) and elongation (Smax) are the result of the combination of several factors: the high load content, the mineral oil and / or PCM content, and the ratio of the polymers, and They cannot be attributed to a single factor.

Table 3: Mechanical properties of prepared formulations

 Ref.

 ay (MPa) Smax (%)

 21.09

 5.6 13.1

 17.11

 7.5 13.8

 18.11

 8.6 15.8

 06.12

 6.8 15.0

 19.08

 5.7 7.1

 20.08

 5.2 7.8

 25.08

 6.8 10.5

 26.08

 7.0 11.2

Thermal properties. Enthalpy curves vs. Temperature were recorded in four samples. For each sample, there was a heating and cooling curve, with an average resulting from the application of 3 cycles with a dynamic method. It was observed that the increase in PCM content leads to a clear inflection in the curve, showing greater thermal inertia. Table 4 shows the experimentally found values for the specific heat at constant pressure (cp, of Sapphire) of the samples studied. An increase of the cp was observed around 22 ° C due to the phase change and according to the content of the PCM.

Table 4. Experimental values of specific heat at constant pressure (cp) (Sapphire cp) for three of the

prepared composite formulations

 cp (J / g.K)

 T (° C)

 19.08 20.08 25.08

 5

 0.94 1.06 1.20

 10

 1.20 1.32 1.48

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 1.46 1.68 1.66

 twenty

 1.52 2.11 1.93

 25

 1.10 1.27 2.21

 30

 1.01 1.09 1.83

 35

 1.02 1.13 2.07

 40

 1.1 1.19 1.88

 Four. Five

 1.09 1.17 1.71

 fifty

 1.12 1.21 1.72

5 Acoustic properties. The determination of the insulation index D (dB) vs. The frequency (Hz) for 6 samples of the composite formulations tested showed that an increase in EAFD content leads to an increase in isolation.

Claims (17)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 60 65 ES 2 450 765 A2 1. Composite formulation obtainable by mixing a set of materials comprising the following ingredients, in the amounts indicated, expressed as mass percentages with respect to the total weight of the formulation: (i) one or more polymers capable of forming a solid polymer matrix, in an overall amount of 10-25%; (ii) one or more phase change materials (PCM) of organic type, optionally accompanied by mineral oil, where the total amount of PCM plus mineral oil is 5-20%, (iii) steel powder (electric arc furnace dust, EAFD) by 40-80%; with the proviso that the total sum of the quantities of the ingredients is not more than 100%. 2. Composite formulation according to claim 1, wherein the total amount of PCM plus mineral oil is 1020%. 3. Composite formulation according to any one of claims 1 or 2, wherein the polymers capable of forming a solid polymer matrix comprise thermoplastic elastomers. 4. Composite formulation according to claim 3, wherein the thermoplastic elastomers are selected from the group consisting of: polyethylene-co-vinyl acetate copolymers (EVA), ethylene-based plastomer resins, styrene copolymer rubbers, ethylene copolymers octene, ethylene-propylene-diene monomers (ethylene-propylene-diene monomers, EPDM), and linear low-density polyethylenes (LLDPE). 5. Composite formulation according to claim 4, wherein the polymers capable of forming a solid polymer matrix are a mixture of a polyethylene-co-vinyl acetate (EVA) and an ethylene-based plastomer resin. 6. Composite formulation according to any of the preceding claims, wherein the amount of EAFD is 50-75%. 7. Composite formulation according to any of the preceding claims, wherein the EAFD comes from carbon steel mills. 8. Composite formulation according to any of the preceding claims, wherein zinc stearate is used as dispersant in an amount of 0.05-1.0%. 9. Composite formulation according to any of the preceding claims, wherein the PCMs comprise paraffins. 10. Composite formulation according to any of the preceding claims, wherein the PCM melting points are within the range 15-30 ° C. 11. Composite formulation according to any of the preceding claims, wherein the mineral oil is absent. 12. Method of obtaining any of the composite formulations as defined in any of claims 1-11, which comprises mixing the indicated amounts of the respective ingredients, under conditions of agitation and of sufficient addition rates to form a homogeneous mixture . 13. Procedure according to claim 12, comprising the steps of: (a) melt mixing the respective mixture of polymers capable of forming a solid matrix of the polymer, including zinc stearate where appropriate; (b) add the respective PCM, including the mineral oil where appropriate; Y (c) add the corresponding EAFD. 14. Laminate of solid material obtainable either by extrusion, by calendering, or by hot pressing, of any of the composite formulations as defined in any of claims 1-11, with a thickness of 1-5 mm. 15. Solid material sheet according to claim 14, wherein the thickness is 2 mm. 16. Use of a sheet of solid material as defined in any of claims 14 or 15, in a construction element to simultaneously provide acoustic insulation and thermal energy storage. 17. Use according to claim 16, wherein the construction element is a partition.