A PROPOSAL OF CYCLONE SEPARATORS FOR A GRADE CLASSIFICATION OF FINE AGGREGATES IN RECYCLING UNITS OF CONSTRUCTION AND DEMOLITION WASTE

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1 A PROPOSAL OF CYCLONE SEPARATORS FOR A GRADE CLASSIFICATION OF FINE AGGREGATES IN RECYCLING UNITS OF CONSTRUCTION AND DEMOLITION WASTE Renato Augusto NASCIMENTO, Civil Eng. 1 José Renato Baptista de LIMA Dr. Eng. 2 Sílvia Maria de Souza SELMO Dr. Eng. 3 1 Civil Construction Engineering Department - PCC, Escola Politécnica, University of São Paulo, Av. Prof. Almeida Prado, trav. 2 nº 83, São Paulo, , Brazil, renato.nascimento@poli.usp.br 2 Mining and Petroleum Engineering Department - PMI, Escola Politécnica, University of São Paulo, Av. Prof. Mello Moraes, 2373, São Paulo, , Brazil, jrblima@usp.br 3 Civil Construction Engineering Department - PCC, Escola Politécnica, University of São Paulo, Av. Prof. Almeida Prado, trav. 2 nº 83, São Paulo, , Brazil, silvia.selmo@poli.usp.br Keywords: cyclone separator, hydrocyclones, construction and demolition waste (CDW), recycling, aggregate classification, fine aggregates. Abstract The economical use of construction demolition materials as an alternative to natural raw materials has been studied in the last decades in many research centers for the purpose of avoiding solid waste deposition, and to contribute to the sustainable development of the country. The waste recycling process basically involves phase separation by screening (size separation) to sort the recyclable materials out of the mound and grinding them using appropriate equipment, thus making it possible to produce aggregates for use in mortars, concrete, and even for manufacturing construction blocks and bricks. The process for the separation of the various materials out of the construction and demolition waste (CDW) is very similar to operations used in mineral processing and mine exploitation, and it is carried out in order to make possible the production of quality raw materials at industrial scale for use in building construction. This paper describes a low cost wash method under development in a plant for the recycling of construction and demolition waste. A possible process is shown which includes the classification of the fine fraction of aggregates, and also the retrieval of water for reuse in the process

2 1. Introduction The mandatory need for a sustainable management of construction and demolition waste (CDW) implies the responsibility of the public and private sectors to create mechanisms that will make feasible the disposal of construction waste, to regulate the practice of generators of such waste, and to foster the development and use of recycled products. This work is part of a series of research works undertaken at a CDW collecting and recycling company based in Socorro, SP, Brazil, with financial support from a government institution for research financial assistance, drawing on Miranda s (2001) work for a Doctor s degree about plastering and renderings made with recycled fine aggregate. With but simple and rudimentary installations the company has given support to the development of research using aggregates obtained from CDW for the production of mortars, concrete, blocks and bricks. Ongoing activity in that plant, according to published work by Miranda & Selmo (2003, 2004) point to the need of introducing washing processes in the recycling of waste for obtaining better quality fine aggregates. According to Levy (2001) the use of recycled aggregates on the industrial level has not yet become established practice in Brazilian cities, and there is the need for creating recycling units with daily production and defined quality standards. It can be seen that there is much difficulty for such units to be created, both by the government (town halls) and the private enterprises, but some cities have been trying to get organized in the sense of adopting some management policy of their solid waste in order to turn this, from a business standpoint, into recycled aggregates. Also, upon knowing the nature of the Brazilian waste and the availability of equipment in the country for the separation of the various components of waste, the availability and qualification of manpower and local market conditions, there comes the need for developing pilot plants to assess the efficiency of the separation processes (Coelho, 2003). The selection of the equipments and the operation of the recycling system depend on the initial characteristics of the waste and degree of processing, which is determined by the specific application of the recycled aggregate. Detailed literature on the adequacy of equipments and projects for each type of process is available. In the recycling process, the equipments can be considered similar to the ones used for the production of natural aggregates. Nowadays the waste recycling systems can be classified according to the criteria and accuracy that will be considered in the elimination of contaminants (Carneiro et al., 2001). Sands for construction should fulfill a series of requirements in order to conform to the different existing specifications, whether in the technical standards or from clients requirements (Martins, 2004). Out of the many possible specifications, the limit quantity of fines, or more specifically grains smaller than mm can be taken for reference, for instance. Once the hydrocyclone separator proves to be a remarkable classifier in operations that require separation between and mm, its use is recommended to conform to specifications of sands with a large quantity of fines. This operation is called de-sliming, and turns out to be one of the main applications of hydrocyclone separators in sand mining. According to Lima (1997), the spread in the use of hydrocyclones allows greater use of mineral deposits with large quantities of fine fractions, thereby reducing the environmental impact of the disposal of ultra fines in mining and several other productive sectors, and offering an important tool for the treatment of fine solids generated in any industrial process. 2. Recycled fine aggregate production 2.1 Plant description The plant under discussion is located in Socorro, SP, Brazil, a town with approximately 30 thousand inhabitants, about 140 km from the Capital, São Paulo. According to the owner of the unit, around 1,200 ton/month of waste from construction is generated in that location. An amount of about 300 ton/month is collected by dump trucks of that unit and brought to it. From the moment the trucks are dumped in the yard, the production line of the unit is composed of the following stages: - visual assessment of the quality of the waste discharged; - manual separation of materials unusable as aggregates (wood, metal, paper, kraft paper, burlaps); - feeding the milling equipment with the previously selected waste by an operator using a shovel; - production of aggregates of different grading by using separation and classification equipments. Feeding of the circuit is kept at a rate of about 2 m 3 /h.

3 2.2 Washing process studied In this research a pilot plant was developed to produce basically aggregates for use in plastering and rendering. The results of Miranda (2000) research have pointed the need for the removal of fines in the aggregate recycling process so that the aggregates turn out suitable for that end use. The milling and screening process consist of the following stages, according to modifications introduced by Miranda; Selmo (2004) in a pilot plant presented in Fig.1: - As it passes through the jaw crusher, the waste is transported on a conveyor belt to a sieve shaker; - Screening is done on dry material using sieves of 4.8 mm opening, resulting in a passing percentage of material that is stockpiled for further use as laying mortar; - The percentage retained on the 4.8 mm sieve is sent to a hammer mill; - The sieve with 1.2 mm opening receives the milled material, and the retained material goes back to the mill; the percentage passing is screened in a sieve of 0.15 mm opening, washed by spraying water over the sieve area, and eventually the artificial washed sand is stockpiled. - The material passing in the sieve of 0.15 mm opening is loaded into decanter tanks. JAW CRUSHER SIEVES HAMMER MILL CDW WATER SIEVES AGGREGATE STOCKPILE >1.2 mm WASHED AGGREGATE > 0.15 mm < 1.2 mm < 0.15 mm WATERCOURSE Fig. 1. Flow chart of the aggregate production process under study by Miranda; Selmo (2004) at the Socorro-SP recycling plant. Next, the research focused on the washing process, as shown in Fig. 1, and a screw washer was used, and then the control of fines in the recycled sand was better than by using the process shown in Fig. 1. The other possibility, as proposed in this paper, is the use of cyclones in a simultaneous process of washing and classification of solids under suspension in the recycling slime, which should permit and broaden the end uses for the recycled material, and that is a great advantage of the use of cyclones instead of using screw washers. The authors do not know of any construction and demolition waste recycling units that have yet operated using cyclones, therefore it is important to bring this subject into discussion into this meeting in order to find other researchers with same experience or purposes. It is important to stress that washing processes in mineral CDW recycling have been studied not only in Brazil, as is the case of Miranda; Selmo (2004) research, but also more thoroughly by Weimann; Müller (2004).

4 3. Cyclone separators According to Chaves (2002), classification is the separation of some source population (the feed) into two other populations that differ by the relative distribution of their particle sizes. As for the process, the classifier is an apparatus that has a feeder containing particles of different sizes that sorts them out into two fractions or products: the underflow, which contains the largest proportion of coarse particles, and the overflow, where finer particles are concentrated. Last, in the field of mineral treatment this operation is always done in a moist state, that is, the feed is some slurry a suspension of solid particles in water. This way, Chaves (2002) states that the name cyclone separator is more adequate, as it is equipment for the classification of solid particles in a liquid medium; therefore the use of the expression hydrocyclone separator is redundant. A cyclone separator is a gadget of extremely simple mechanics, without any moving parts. It is made up of a vase, partly cylindrical and partly conical, with a diameter varying from 0.01 m to 1.3 m or more. It has a tangential feeding orifice called inlet and two outlets, one of them called apex, at the end of the cone where the coarse particles will be discharged. The other outlet, called vortex finder, is located at the end of the cylindrical part where the fine particles will be discharged. Fig. 2 shows a schematic exploded view of a cyclone separator. The dimensions of the cyclone separator are defined based on a series of parameters, such as pressure drop, particle size distribution and density, and solids content of the slurry. Nevertheless there are a number of variables that are empirically estimated, so as to define the cyclone capacity and separating diameter (called cut size) (Tarr Junior, 1985). Fig. 2. Schematic (exploded) view of a cyclone separator under operation (Tarr Junior, 1985). According to Storolli (2002), the cyclone separator is one of the main equipments used in classification processes of solid particles in mineral treatment units, and in most moist processing routes they are used in at least one of the stages of the concentration process, whether it is at the classification stage or in the desliming stage, or even in the washing of a product before the subsequent stage takes place.

5 4. Proposed use In CDW recycling, more than in any other process, the great challenge is to develop sustainable processes and systems with an optimization of the energy and non-renewable resources. In this particular research work cyclone separators were used for the classification of aggregates, as discussed previously in this paper, with the main following objectives: - to recover particles smaller than 0.15 mm unsuitable for use in mortars but suitable for use in the production of bricks and other applications; - to reduce the environmental impact of the disposal of the ultra fine fraction diluted in the process water, and also to make possible the reuse of such water in the process itself; Fig. 3 illustrates the proposed aggregate production process by using cyclone separators, which is to be tested in the same pilot plant of Miranda & Selmo (2004). Another possibility is to change the spiral classifier for the grain size separation in the range 4.8 mm to 0.15 mm by using another cyclone. In both cases (with or without a spiral classifier) the waste would be treated by at least one cyclone in order to make it a feasible production process. The scope is to recover the fine fractions of the waste so as to promote the reuse of water, and also to use the fine solids recovered in the process for the production of bricks. JAW CRUSHER SIEVE SHAKER HAMMER MILL CDW SIEVE SHAKER AGGREGATE STOCKPILE >1.2 mm WATER > mm WATER FOR REUSE CYCLONE overflow feed < 0.15 mm SPIRAL CLASSIFIER WASHED AGGREGATE > 0.15 mm < 1.2 mm underflow MUD < mm Fig. 3. Flow chart of the proposed recycling unit with a cyclone separator. 4. Conclusions This paper aimed at showing the need for using appropriate technology for the production of materials and for the use of the discarded fine fractions in the production and processing of CDW, and cyclones present excellent potential nowadays for more valued end uses, such as the production of plastering and rendering systems, or bricks for construction. As a logical sequence in the evolution of this work, it will be necessary to carry out the following steps:

6 - Mathematical modelling, with which it will be possible to describe and to study the improvement process; - An adjustment on such models with a set of input and output data, preset and representative of the system being studied, aiming at making the parameters ( constants ) of the model adequate to the process under analysis, by using the output data (LIMA, 1997); - A simulation to predict the phenomenon or process being analyzed, by using the output data; - An optimization looking for the best performance of the operation or process; - Closed circuit tests at the laboratory, in order to test and prove the efficiency of the studied models. Many of such tests take on a critical role in the option for certain equipment or supplier, being in some cases decisive in the decision making of the sequence of projects (Storolli, 2002). References Carneiro, A.P. et al. 2001, Características do entulho e do agregado reciclado. In Reciclagem de entulho para a produção de materiais de construção Projeto Entulho Bom. CEF, pp Chaves, A.P. 2002, Teoria e prática do tratamento de minérios. Signus Editora. Coelho P.E. 2003, Reciclagem de Entulho - O melhor ainda está por vir. Artigo publicado na internet, ( em 30/11/2003. Levy, S.M. 2001, Contribuição ao estudo da durabilidade de concretos, produzidos com resíduos de concreto e alvenaria. Tese de Doutorado - Escola Politécnica da Universidade de São Paulo. Lima, J.R.B. 1997, Estudo da modelagem matemática da microciclonagem. Tese de Livre Docência - Escola Politécnica da Universidade de São Paulo. Martins, M.A.S. 2003, Ciclones nas minerações de areia. Boletim Sindareia, 42. Artigo publicado na internet, ( em 24/08/2004. Miranda, L.F.R., 2000, Estudo de fatores que influenciam na fissuração de revestimentos de argamassa com entulho reciclado. Dissertação de Mestrado - Escola Politécnica da Universidade de São Paulo. 172 p. Miranda, L.F.R., 2001, Desenvolvimento de metodologia para controle de produção de argamassas em usinas de reciclagem. Projeto de Pesquisa Doutorado FAPESP. Miranda, L.F.R.; Selmo, S.M.S. 2003, Construction and demolition waste variability and its influence on masonry and plastering mortars properties. In Proceedings of the International Conference on the environmental and technical implications of construction with alternative materials WASCON 2003: Progress on the Road to Sustainability, ISCOWA / ISNASMET, pp Miranda, L.F.R.; Selmo, S.M.S. 2004, A case study on the variation in the quality of mortars using CDW recycled sands. In Proceedings of the International RILEM Conference on the Use of Recycled Materials in Buildings and Structures. RILEM Publications, PRO 40, pp Storolli, F.A.P., 2002, Análise comparativa do desempenho de ciclones com base em simulações prévias e ensaios em escala industrial. Dissertação de Mestrado - Escola Politécnica da Universidade de São Paulo. Tarr Junior, D.T., 1985, Hydrocyclones. In Weiss, N. L. (ed.), SME mineral processing handbook, SME/AIME, pp.3d-10/3d-38. Weimann, K.; Müller, A. 2004, Properties of building materials gained from wet-processed crushed concrete fines. In Proceedings of the International RILEM Conference on the Use of Recycled Materials in Buildings and Structures. RILEM Publications, PRO 40, pp