WO2013014318A1

WO2013014318A1 - Inertization of electric-arc furnace dust by means of the stabilizing integration thereof in a construction material

Info

Publication number: WO2013014318A1
Application number: PCT/ES2012/070564
Authority: WO
Inventors: Ana Inés FERNÁNDEZ RENNA; Luisa Fernanda CABEZA FABRA; Camila BARRENECHE GÜERISOLI; Josep Maria Chimenos Ribera; Fernando ESPIELL ÁLVAREZ; Mercè SEGARRA RUBÍ; Cristian SOLÉ CUTRONA
Original assignee: Universitat De Barcelona; Universitat De Lleida
Priority date: 2011-07-26
Filing date: 2012-07-25
Publication date: 2013-01-31
Also published as: ES2450765R1; ES2450765B1; ES2450765A2

Abstract

The invention relates to the fact that large amounts of electric-arc furnace dust or EAFD, regardless of origin, can be stabilized and used in a 2 mm, commercially valuable sheet made of solid material, which can be obtained by extrusion, calendering or hot pressing from a composite formulation by mixing: (i) one or more polymers able to form a solid polymer matrix, in an overall amount of 10-25%; (ii) one or more organic-type phase change materials (PCM), optionally accompanied by mineral oil, wherein the total amount of PCM plus mineral oil is 5-20%; and (iii) 40-80% of EAFD. The sheet made of solid material can be used in the construction industry to simultaneously provide acoustic insulation blocks and storage of thermal energy.

Description

Inertization of steelworks dust 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 refining iron in an electric arc furnace (EAF), in which heat is supplied by electric arcs between carbon electrodes submerged in molten metal. Melting 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 are 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 (XRD) and scanning electron microscopy (SEM) analyzes reveal that the major 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. Arsenic is also frequently found. Metal oxides

Alkaline earths 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 sending them to external managers for disposal or recycling. EAFD is listed as toxic and hazardous waste in most industrialized countries and is classified in the European Catalog of

Waste as a hazardous waste that needs treatment before its final discharge. Some of the industrial treatment processes of the 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. The

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 used less because they have high energy consumption. Methods can be used to encapsulate toxic metals, but these methods are not commercially interesting, since they involve

major investments and no metal recovery.

Extraction processes in an acid medium can be used to treat EAFD and dissolve the metals of interest. Since the pH inherent in a powder suspension is greater than 1 1, 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 form

relatively pure 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 for 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 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 has been described conformable and useful for sound insulation in the automotive industry (cf. M. Niubo et al., "A possible recycling method for high grade steels EAFD", Journal of Hazardous Materials 2009, vol. 171, pp. 1 139-1 144; 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, June 21-25, 2009). The composite formulation also uses barite (BaS0 ₄ ) and / or calcium carbonate (CaC0 ₃ ) 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 mercuno in the EAFD from carbon steel mills makes it impossible to use them as a polymer filler 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 less than 30% by weight, with an optimum 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 EAFD treatment are not satisfactorily resolved with 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 into 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%; (¡I) 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, 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 are used, and the ethylene-based plastomer resin sold under the Exact 8201 brand. 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 Rew ^' ews 201 1, vol. 15, pp. 1675-1695, and its references). In particular embodiments of the present invention, the organic PCMs in the composite formulations are paraffins (mixtures of aliphatic long chain hydrocarbons), especially those having 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

Composite formulation preparation. If necessary Further lubrication 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 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 hot pressing (typically at a temperature of about 150 ° C) of any of the composite formulations mentioned above. The sheet may have a thickness of 1-5 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 sound insulation properties and thermal energy storage properties. This fact, together with its relatively good mechanical properties, makes it useful to be incorporated into materials of

construction: 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 it comprises mixing the respective ingredients, under stirring conditions, and 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 to 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 amounts of material can be used

(quantities greater 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 steps. 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 aliquot was performed, with a wave dispersion X-ray spectrophotometer (X-ray dispersion wave spectrophotometer, WDXRF) Philips PW2400. The analysis was performed with optical emission spectrometry with inductively coupled plasma (inductively coupled plasma optical emission spectrometry, ICP-OES) in the solution resulting from the total acid attack of EAFD. High-angle X-ray scattering (WAXS) X-ray diffraction was used to elucidate the crystalline phases present, and the morphology of EAFD particles was observed by 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

Particle size distribution 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 polyethylene-co-vinyl acetate (EVA) copolymer with 18% vinyl acetate, EVA Alcudia PA-538 from Repsol YPF, with melt flow index (MFI) of 2 g / 10 min (190 ° C at 2.16 kg load) and a density of 937 kg / m ³ , and an Exact 8201 ethylene-based plastomer resin from Exxon Mobil Chemical, with an MFI of 1.1 g / 10 min (ASTM D 1238) and density 882 kg / m ³ 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 EAFD using zinc stearate as 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 yield limit a _y and the maximum elongation s _max .

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 (DSC822e) using hermetically sealed crucibles to prevent evaporation. The dynamic method was applied, and each sample was cycled 3 times with a speed of

heating 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 noise 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 chamber and L _e in the sending chamber. When the background noise L _b was considered, the noise level in the receiver was L _r according to the equation described below. The difference between the two levels is the index of

D insulation (dB), which was used to compare the acoustic properties of different formulations using the same device and conditions.

Physicochemical characterization of EAFD The results of semi-quantitative analysis of X-ray fluorescence 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

The major 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 particle size of the EAFD sample was 1 - 50 pm. The density measured with the He pycnometer was 4.93 g / cm ³ and the specific surface area was 4 m ² / 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, d ₅₀ and d ₉₀ , were 1, 621 and 8,365 pm, respectively.

Component Content Table 2 shows several of the composite formulations prepared. In a first stage, an experiment design 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 the samples with PCM above 20% had a greasy surface. This may be macroscopic evidence that migration from the inside to the outer surface of the sheets took place and that the macroencapsulation of the PCM was not fully effective. Thus, a preferred range for the PCM was 10 to 20%.

The ratio between the polymers was optimized to achieve the desired mechanical properties with the lowest cost and the highest EAFD content. This ratio, after several trials, was set at 3: 1 EXACTEVA. 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 sound insulation, while the mechanical properties

decrease

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 the present invention. For all samples the thickness is 3 mm and the surface density close to 7 kg / m ² Table 2: Component contents (%) of prepared composite formulations

The mechanical properties of the different formulations, shown in Table 3, did not differ significantly. Changes in the yield limit (σ _ν ) and elongation (s _max ) are the result of the combination of several factors: the high load content, the mineral oil and / or PCM content, and the ratio of polymers , and cannot be attributed to a single factor.

Table 3: Mechanical properties of prepared formulations

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 in 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)

(cp of Sapphire) for three of the composite formulations prepared

Acoustic properties The determination of the insulation index D (dB) vs. the frequency (Hz) for 6 samples of composite formulations

tested, showed that an increase in EAFD content leads to an increase in isolation.

Claims

one . 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%;

(¡I) 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 mill {electric are 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 10-20%.

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 (EVA) copolymers, 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 claims

above, where EAFD comes from carbon steel mills.

8. Composite formulation according to any of the claims

above, where zinc stearate is used as a dispersant in an amount of 0.05-1 .0%.

9. Composite formulation according to any of the claims

above, where PCMs comprise paraffins.

10. Composite formulation according to any of the preceding claims, wherein the melting points of the PCMs are within the range 15-30 ° C.

eleven . Composite formulation according to any of the preceding claims, wherein the mineral oil is absent.

12. Procedure for obtaining any of the formulations

composite as defined in any of claims 1 -1 1, 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. Method 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. Solid matten sheet obtainable either by extrusion, by calendering, or by hot pressing, of any of the composite formulations as defined in any of claims 1 -1 1, 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 solid matenal sheet as defined in any of claims 14 or 15, in a construction element for

simultaneously provide acoustic insulation and thermal energy storage.

17. Use according to claim 16, wherein the construction element is a partition.