AU2010220974A1

AU2010220974A1 - Method for producing artificial lightweight aggregates using cold- or hot-rolled mill sludge

Info

Publication number: AU2010220974A1
Application number: AU2010220974A
Authority: AU
Inventors: Young Ho Jeong
Original assignee: CERAGREEN CO Ltd
Current assignee: CERAGREEN CO Ltd
Priority date: 2009-03-03
Filing date: 2010-03-03
Publication date: 2011-11-17
Also published as: CA2761252A1; CN102414141A; KR101165395B1; KR20100099494A; WO2010101412A3; WO2010101412A2

Abstract

The present invention relates to a method for producing artificial lightweight aggregates using cold- or hot-rolled mill sludge and clay as a main material. More particularly, the present invention relates to a method for producing artificial lightweight aggregates, in which the aggregates are produced from cold- or hot-rolled mill sludge and clay as a primary material, and the aggregates have an absolute dry specific gravity of 0.8 to 1.5 and an absorptance of 5 to 20%. As the artificial lightweight aggregates according to the present invention use cold- or hot-rolled mill sludge, which is a by-product of the steel industry, as a main material, the necessity of an additional foaming agent is eliminated, and steel wastes are reutilized to increase economical advantages, reduce wastes, and prevent environmental contamination.

Description

METHOD FOR MANUFACTURING ARTIFICIAL LIGHTWEIGHT AGGREGATE USING COLD AND HOT ROLLING MILL SLUDGE TECHNICAL FIELD 5 The present invention relates to a method of manufacturing an artificial lightweight aggregate using cold and hot rolling mill sludge and clay as main raw materials, and more particularly to a method of manufacturing an artificial lightweight aggregate using cold and hot rolling 10 mill sludge and clay as main raw materials, in which the artificial lightweight aggregate has an absolute dry specific gravity of 0.8-1.5 and a water absorption rate of 5-20%. BACKGROUND ART 15 Raw materials containing a foaming agent such as expanded shale and expanded clay are required to manufacture lightweight aggregates from natural materials according to the prior art. Because the quality of lightweight aggregates is determined according to the distribution and content of the 20 foaming agent, securing good-quality raw materials is significantly important for the manufacture of lightweight aggregates. Such raw materials are manufactured only in several countries, but are not manufactured in Korea. Thus, in order to obtain good quality lightweight aggregates, 25 components such as Fe 2 0 3 and C have been artificially added to 11 raw materials for manufacturing lightweight aggregates. Such components account for a significant portion of the production cost of lightweight aggregates as well as impose many restrictions on the manufacture of lightweight aggregates. 5 In recent years, researches are in progress to manufacture lightweight aggregates using industrial waste in a cost-effective manner. In general, steelmaking byproducts include slag (furnace slag and steelmaking slag), sludge (steelmaking sludge, lime 10 sludge, cold and hot rolling mill sludge, ash sludge, wastewater treatment area sludge, and continuous casting sludge), dust (sintered R/EP dust, sintered W/EP dust, lime B/F dust, steelmaking E/P dust, and steelmaking B/F dust) and bottom ashes. Such steelmaking byproducts comprise SiO 2 , A1 2 0 3 , 15 Fe 2 0 3 , CaO, MgO, Na 2 0, K20, TiO 2 , P 2 0 5 , Cr20 3 , MnO, C and the like, and are recycled in steelmaking processes, but the cold and hot rolling mill sludge is recycled at a significantly low rate, because it contains impurities such as oily components. In Korea, the cold and hot rolling mill sludge is generated in 20 an amount of more than about 200,000 metric tons each year and is mostly landfilled. Also, such cold and hot rolling mill sludge entails a problem in that the chemical components thereof mostly comprise heavy metals which are considerably harmful to the human body, and secondary environmental 25 pollution problems are caused upon the reclamation thereof. 2 Korean Patent Laid-Open Publication No. 2003-0069692 discloses a method of manufacturing a lightweight aggregate having an apatite crystal structure using wastewater sludge containing phosphate, wherein a steel sludge having an iron 5 content of about 60% is added as a foaming agent in an amount of 5-15% by weight in order to manufacture the lightweight aggregate. However, the above lightweight aggregate manufacturing method encounters a problem in that, when the amount of steel sludge added is more than 15% by weight, the 10 resulting product will have a thick block color which lowers the merchantability of the product, and thus the recycling of the steel sludge is significantly limited. In addition, Korean Patent Registration No. 662,812 discloses a method for manufacturing an artificial ultra 15 lightweight aggregate, which comprises adding 20-30 parts by weight of a dry steel sludge to a raw sewage sludge. Since raw sewage sludge has a water content of about 80%, it cannot be molded. To solve this problem, the method disclosed in Korean Patent Registration No. 662,812 aims to make it 20 possible to form the lightweight aggregate by adding the dry steel sludge dried to a water content of about 20-30%, thereby reducing the drying cost of the lightweight aggregate. In line with the general concept of the expansion of lightweight aggregates, when lightweight aggregates are 25 calcined, the thermal desorption of organic materials occurs, 3 and gas, carbonic acid, sulfur dioxide and trivalent iron oxide, which are generated by the thermal desorption, are reduced into bivalent iron oxide while they calcine the outer surface of particles surrounding the formed gas. If the gas 5 cannot come out of the calcined surface, the inside of the clay will expand and have somewhat uniform porosity, and thus become lightweight. The above-mentioned method of manufacturing the artificial lightweight aggregate using a combination of the raw sewage sludge and the dry steel sludge, 10 disclosed in the above prior art document, also uses a process similar to this concept. However, about 90% or more of organic materials contained in the raw sewage sludge form many pores during the calcining process, thus making difficult a reduction reaction of Fe 2 0 3 , and the surface of the lightweight 15 aggregate is excessively calcined or melted before the expansion process, which makes it significantly difficult to control the calcining process. In addition, it is difficult to ensure the quality uniformity of the manufactured lightweight aggregate. 20 In Korea, the steel industry accounts for a large portion of the entire industry, and thus waste, including sludge, is generated in large amounts. Such waste is disposed of by, for example, a method of landfilling solid bricks prepared from such waste, and the technology of disposing of such waste 25 remains at a very early stage. Steel sludge and the like 4 which are landfilled without being recycled can contaminate the surrounding environment and can cause serious problems such as soil contamination. Disposal of sludge involves a great deal of cost to increase the production costs, thus 5 weakening the competitiveness of companies. The above-mentioned patent documents suggest the method of recycling industrial byproducts containing iron, but the suggested method cannot be said to be an ultimate treatment method. Specifically, the disclosed materials serve either as 10 additives for expansion rather than serving to provide main raw materials for the manufacture of lightweight aggregates, or as water-controlling agents during the forming process. Further, the disclosed methods require a process of producing solid bricks, and a pelletizing process, followed by 15 landfilling. Accordingly, the recycling of the steelmaking byproduct sludge helps to prevent environmental pollution and enhancing national competitiveness, and thus many researches thereon and the positive use thereof are required. 20 Accordingly, the present inventors have made extensive efforts to recycle steelmaking byproducts and, as a result, have found that, when a cold and hot rolling mill sludge which is a byproduct of the steel industry is used as a raw material for manufacturing a lightweight aggregate, the expansion of 25 the aggregate during a calcining process can be easily 5 controlled, the average calcination temperature of the aggregate can be lowered to greatly save energy, and the recycling rate of steelmaking byproducts can be significantly increased, thereby completing the present invention. 5 DISCLOSURE OF INVENTION TECHNICAL PROBLEM It is an object of the present invention to provide an artificial lightweight aggregate manufactured using a mixture 10 of cold and hot rolling mill sludge and clay which are mixed at a specific ratio, and a method of manufacturing the artificial lightweight aggregate, in order to recycle steelmaking byproducts containing impurities, such as oily components, which make it difficult to recycle the byproducts. 15 TECHNICAL SOLUTION To achieve the above objects, in one aspect, the present invention provides an artificial lightweight aggregate which is manufactured using cold and hot rolling mill sludge and 20 clay as main raw materials, and has an absolute dry specific gravity of 0.8-1.5 and a water absorption rate of 5-20%. In another aspect, the present invention also provides a method for manufacturing an artificial lightweight aggregate having an absolute dry specific gravity of 0.8-1.5 and a water 25 absorption rate of 5-20%, the method comprising the steps of: 6 (a) mixing 5-90 parts by weight of a cold and hot rolling mill sludge and 10-120 parts by weight of clay; (b) molding the mixture; (c) drying the molded material; and (d) calcining the dried material. 5 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a process of manufacturing an artificial lightweight aggregate according to the present 10 invention. BEST MODE FOR CARRYING OUT THE INVENTION Other features and embodiments of the present invention will be more apparent from the following detailed descriptions 15 and the appended claims. In one aspect, the present invention is directed to an artificial lightweight aggregate which is manufactured using cold and hot rolling mill sludge and clay as main raw materials, and has an absolute dry specific gravity of 0.8-1.5 20 and a water absorption rate of 5-20%. In another aspect, the present invention is also directed to a method for manufacturing an artificial lightweight aggregate having an absolute dry specific gravity of 0.8-1.5 and a water absorption rate of 5-20%, the method comprising 25 the steps of: (a) mixing 5-90 parts by weight of a cold and 7 hot rolling mill sludge and 10-120 parts by weight of clay; (b) molding the mixture; (c) drying the molded material; and (d) calcining the dried material. As used herein, the term "cold and hot rolling mill 5 sludge" means a sludge containing large amounts of heavy metals, which is generated in cold and hot rolling processes in a steel mill. The artificial lightweight aggregate according to the present invention is manufactured using steel waste such as a 10 cold and hot rolling mill sludge. It does not require a separate foaming agent, because chemical components, such as Fe 2 0 3 and C, which are contained in large amounts in the cold and hot rolling mill sludge, serve as the key foaming agents during calcination of the lightweight aggregate as shown in 15 the following chemical equations: Fe 2 0 3 + C -- 2FeO + CO t ...... (1) 3Fe 2

O

3 + C -. 2Fe 3

O

4 + CO T ...... (2) 3Fe 2

O

3 -- 2Fe 3

O

4 + 1/2 CO T...... (3) 20 Thus, the present invention can solve the problems associated with the insufficient foaming components of raw materials which could not provide lightweight aggregates. At the same time, according to the present invention, the lightweight aggregate is manufactured using steelmaking waste 25 which has been landfilled, and the manufactured lightweight 8 aggregate is used as a raw material for high-value-added construction materials. Thus, the present invention significantly contributes to reducing environmental pollutants which become social problems. 5 In one embodiment of the present invention, the artificial lightweight aggregate is manufactured by mixing 5 90 parts by weight of the cold and hot rolling mill sludge with 10-120 parts by weight of clay, molding the mixture and calcining the molded material in an electric furnace at 1100 10 12000. The manufactured artificial lightweight aggregate showed an absolute dry specific gravity of 1.0-1.5 and a water absorption rate of 5-10%. In another embodiment of the present invention, the artificial lightweight aggregate is manufactured by mixing 5 15 90 parts by weight of the cold and hot rolling mill sludge with 10-120 parts by weight of clay, primarily molding the mixture using an extrusion molding machine, cutting the molded material, secondarily molding the cut molded material, and calcining the secondarily molded material in a rotary kiln at 20 950-11000. The manufactured artificial lightweight aggregate showed an absolute dry specific gravity of 0.8-1.5 and a water absorption rate of 12-20%, and no heavy metals were detected in the artificial lightweight aggregate as can be seen from the results of measuring the leaching of hazardous substances. 9 Such lightweight aggregates having various specific gravities can be used in a wide range of applications, including structural materials in the construction and civil engineering field, noise-reducing materials for buildings, 5 humidity-controlling materials for buildings, and horticultural applications. Hereinafter, the present invention will be described in further detail with reference to examples. It will be obvious to those skilled in the art that these examples are 10 illustrative purposes only and are not to be construed to limit the scope of the present invention. EXAMPLES Example 1: Measurement of chemical components of raw 15 materials The chemical components of red clay (Asan Industrial Co., Ltd., Hongsung, Chungcheongnam-do, Korea) and a cold-and hot rolling mill sludge (Posco Co., Ltd., Korea) required to manufacture an artificial lightweight aggregate were measured 20 according to the chemical analysis and testing method of KS L 4007 (chemical analysis method of clay). As a result, as shown in Table 1 below, the cold and hot rolling mill sludge had a Fe 2 0 3 content of 70% or more and an unburned carbon content of 10% or more, and such components 10 (Fe 2 0 3 and carbon) can provide sufficient amounts of foaming agents during the calcinations process. [Table 1] Type Ig SiO 2 A1 2 0 3 Fe 2 0 3 CaO MgO Na 2 0 K 2 0 TiO 2 ZrO 2

P

2 0 5 Cr 2 0 3 MnO C loss Red 9.0062.1016.81 6.20 0.511.160.812.350.77 - 0.09 - - clay Cold and hot rolling8.611.

2 6 5.13 70.220.820.040.010.010.02 - 0.850.130.2312.69 mill sludge _________________ 5 Example 2: Manufacturing of lightweight aggregate using cold and hot rolling mill sludge In Experimental Example 1, 10 parts by weight of a cold and hot rolling mill sludge was mixed with 90 parts by weight of clay, and the mixture was crushed and kneaded. Then, the 10 resulting material was manually formed into a pellet shape and calcined in an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an absolute dry specific gravity of 1.48 and a water absorption rate of 9.48%. 15 In Experimental Example 2, 20 parts by weight of a cold and hot rolling mill sludge was mixed with 80 parts by weight 11 of clay, and the mixture was molded in the same manner as in Experimental Example 1. The molded material was calcined in an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an 5 absolute dry specific gravity of 1.40 and a water absorption rate of 8.64%. In Experimental Example 3, 30 parts by weight of a cold and hot rolling mill sludge was mixed with 70 parts by weight of clay, and the mixture was molded in the same manner as in 10 Experimental Example 1. The molded material was calcined in an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an absolute dry specific gravity of 1.46 and a water absorption rate of 9.05%. 15 In Experimental Example 4, 40 parts by weight of a cold and hot rolling mill sludge was mixed with 60 parts by weight of clay, and the mixture was molded in the same manner as in Experimental Example 1. The molded material was calcined in an electric furnace at about 11500. The lightweight aggregate 20 manufactured according to this Experimental Example showed an absolute dry specific gravity of 1.08 and a water absorption rate of 9.59%. In Experimental Example 5, 50 parts by weight of a cold and hot rolling mill sludge was mixed with 50 parts by weight 25 of clay, and the mixture was molded in the same manner as in 12 Experimental Example 1. The molded material was calcined in an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an absolute dry specific gravity of 1.16 and a water absorption 5 rate of 7.44%. In Experimental Example 6, 60 parts by weight of a cold and hot rolling mill sludge was mixed with 40 parts by weight of clay, and the mixture was molded in the same manner as Experimental Example 1. The molded material was calcined in 10 an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an absolute dry specific gravity of 1.23 and a water absorption rate of 4.48%. In Experimental Example 7, 70 parts by weight of a cold 15 and hot rolling mill sludge was mixed with 30 parts by weight of clay, and the mixture was molded in the same manner as in Experimental Example 1. The molded material was calcined in an electric furnace at about 11500. The lightweight aggregate manufactured according to this Experimental Example showed an 20 absolute dry specific gravity of 1.11 and a water absorption rate of 5.79%. [Table 2) Comparison of specific gravity and water absorption rate between lightweight aggregates manufactured in electric 25 furnace Type Cold and hot clay Absolute Water 13 rolling mill dry absorption sludge specific rate(%) gravity Experimental 10 90 1.48 9.48 Example 1 Experimental 20 80 1.40 8.64 Example 2 Experimental 30 70 1.46 9.05 Example 3 Experimental 40 60 1.08 9.59 Example 4 Experimental 50 50 1.16 7.44 Example 5 Experimental 60 40 1.23 4.48 Example 6 Experimental 70 30 1.11 5.79 Example 7 Table 2 above shows the absolute dry specific gravity and water absorption rate of the lightweight aggregates manufactured according to Experimental Examples 1 to 7. The 5 physical properties of the lightweight aggregates using the mixtures of the cold and hot rolling mill sludge and clay were compared with each other, and as a result, the lightweight aggregates manufactured in the Experimental Examples all had an absolute dry specific gravity of 1.5 or less and a water 10 absorption rate of 10% or less. Example 3: Comparison of physical properties between lightweight aggregates manufactured in mass production process In Experimental Example 8, 30 parts by weight of a cold 15 and hot rolling mill sludge was mixed with 70 parts by weight of clay, and the mixture was crushed and kneaded. The 14 resulting material was primarily molded in an extrusion molding machine equipped with a mold having a plurality of perforated circular holes having a diameter of 5-11 mm. The molded material was cut to a specific length using a rotating 5 cutter and was transferred to a rotating drum in which the molded material was in turn secondarily molded into a pellet shape. Next, the secondarily molded material was dried, and then calcined in a rotary kiln at about 10000. The manufactured lightweight aggregate had an absolute dry 10 specific gravity of 1.44 and a water absorption rate of 13.98%. In Experimental Example 9, 40 parts by weight of a cold and hot rolling mill sludge was mixed with 60 parts by weight of clay, and the mixture was molded according to the method of Experimental Example 8. The molded material was dried, and 15 then calcined in a rotary kiln at about 10000. The manufactured lightweight aggregate had an absolute dry specific gravity of 1.29 and a water absorption rate of 15.76%. In Experimental Example 10, 50 parts by weight of a cold and hot rolling mill sludge was mixed with 50 parts by weight 20 of clay, and the mixture was molded according to the method of Experimental Example 8. The molded material was driedm, and then calcined in a rotary kiln at about 10000. The manufactured lightweight aggregate had an absolute dry specific gravity of 0.90 and a water absorption rate of 19.80%. 15 The absolute dry specific gravity and the water absorption rate of the artificial lightweight aggregates manufactured according to the above Experimental Examples were measured according to KS F 2503 (testing of density and water 5 absorption rate of coarse aggregate). [Table 3] Comparison of physical properties between lightweight aggregates manufactured in rotary kiln Cold and hot Absolute Water rolling mill clay dry . absorption sludge specific rate(%) _________ gravity Experimental 30 70 1.44 13.98 Example 8 Experimental 40 60 1.29 15.76 Example 9 1 Experimental 50 50 0.90 19.80 Example 10 10 Table 3 above shows the absolute dry specific gravity and water absorption rate of the lightweight aggregates manufactured according to Experimental Examples 8 to 10. The physical properties of the lightweight aggregates manufactured in the above Experimental Examples showed that the absolute 15 dry specific gravity thereof is less than 1.5. In particular, in case of Experimental Example 10, the lightweight aggregate showed an absolute dry specific gravity of 0.90, which is considerably low. This makes it possible to manufacture a general structural lightweight aggregate as well as an untra 16 lightweight aggregate which can be used for non-structural concrete As such, the fact that lightweight aggregates having various specific gravities can be manufactured means that they 5 are not limited to structural materials in the construction and civil engineering field, but can be used in a wide range of applications, including partition panels and noise-reducing materials for buildings, humidity-controlling materials for buildings, and horticultural applications 10 In addition, the leaching of hazardous substances of the lightweight aggregate manufactured according to Experimental Example 10 was measured by a waste processing test method, and no heavy metals were detected in the artificial lightweight aggregate as can be seen from Table 4 below. 15 [Table 41 Type The leaching of hazardous substances(mg/L) Pb Cd Cr Cu As Hg Zn Ni Experimental Example 10 lightweight none none none none none none none none aggregate Example 4: Measurement of compressive strength of concrete using lightweight aggregate comprising cold and hot 20 rolling mill sludge 17 Concrete was manufactured using the lightweight aggregate manufactured according to the present invention, and then the compressive strength thereof was measured. Preparation Example 1 in Table 5 below is concrete 5 manufactured using lightweight aggregate 1 of Experimental Example 9. Concrete specimens were manufactured according to KS F 2403 (method for manufacturing specimens for testing strength of concrete) and cured, and then the compressive strengths thereof were measured according to KS F 2405 (test 10 method for compressive strength of concrete). In the meantime, for comparison with Preparation Example 1, Comparative Example 1 in Table 5 is general crushed aggregate (Gwangcheon-eup, Hongseong-gun, Chungcheongnam-do, Korea) used in conventional concrete. Concrete was 15 manufactured using the aggregates of Comparative Example 1 in the same manner as in Preparation Example 1, and the compressive strengths thereof were measured in the same manner as in Preparation Example 1. As a result, as shown in Table 5 below, when the concrete 20 of Comparative Example 1 comprising conventional crushed aggregate was compared with the lightweight aggregate concretes of Preparation Example 1 comprising a cold and hot rolling mill sludge, the crushed aggregate concrete of Comparative Example 1 had a compressive strength of 23.0 N/mm 2 25 whereas the artificial lightweight aggregate concrete of 18 Preparation Example 1 comprising the cold and hot rolling mill sludge showed a compressive strength of 23.5.0 N/mm 2 , which was similar to or slightly higher than that of conventional crushed aggregate concrete. In addition, when the materials 5 used and the mixture ratio thereof are reviewed, the amount of cement used when manufacturing concrete using the general crushed aggregate is 330 kg/m 3 whereas the amount of cement used when manufacturing concrete using the artificial lightweight aggregate is 315 kg/m. Thus, it was determined 10 that the manufacturing cost of the concrete could be reduced. [Table 5] Materials used and the mixture Compressive Type ratio(kg/m 3 ) Type of Cre ssive Typestrength (N/in cement Fine Coarse S aggregate m 2 ) aggregateaggregate Comparative 330 811 918 47 55 Crushed 23.0 Example 1 aggregate Ecological Preparation 315 827 520 47 55 lightweight 23.5 Example 1 aggregate Accordingly, the artificial lightweight aggregate manufactured according to the present invention uses, as a 15 main raw material, the cold and hot rolling mill sludge containing, in large amounts, chemical components such as Fe 2 03 and C serving as foaming agents, thus making easy a reduction reaction of Fe 2 0 3 , so that since the expansion of the aggregate during a calcining process can be easily controlled, a 20 separate foaming agent is not required. In addition, the 19 average calcination temperature of the aggregate is 10000, which is lower by about 100-2000 than an existing calcination temperature to greatly save energy. Further, since the cold and hot rolling mill sludge is used in an amount of more than 5 50% as a main raw material of the lightweight aggregate, the recycling rate thereof can be remarkably increased. Although the present invention has been described in detail with reference to the specific features, it will be apparent to those skilled in the art that this description is 10 only for a preferred embodiment and does not limit the scope of the present invention. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof. 15 INDUSTRIAL APPLICABILITY The artificial lightweight aggregate according to the present invention is manufactured using, a main raw material, cold and hot rolling mill sludge, i.e., a steelmaking byproduct in the steel industry, so that a separate foaming 20 agent is not needed, steel wastes can be recycled to ensure high economic efficiency, and wastes can be reduced to solve environmental pollution problems. 20

Claims

4. The method according to claim 2, characterized in that the 25 calcining of step (d) is performed in an electric furnace or a rotary kiln. 21
5. The method according to claim 2, characterized in that the calcining of step (d) is performed at 950-1200 0. 22