Recycling silicon solar cell waste in cement-based systems Lucia J Ferna ´ ndez a,n , R. Ferrer a , D.F. Aponte a , P. Ferna ´ ndez b a Departament de Construccions Arquitect  oniques I—Universitat Polit  ecnica de Catalunya, Spain b Departamento de Ingenierı ´a Civil: Ordenacio ´n del Territorio, Urbanismo y Medio Ambiente, Universidad Polite ´cnica de Madrid, Spain article info Article history: Received 23 April 2010 Received in revised form 15 December 2010 Accepted 18 January 2011 Available online 3 March 2011 Keywords: Solar cells Silicon Recycling New applications Building abstract This is a study of the recycling of crystalline solar cells by incorporating them in cement matrices. The hydration process of a mixture of calcium aluminate cement (CAC) and solar photovoltaic cell waste was researched and analyzed. The nature of the hydration products of various compositions of these mixtures was evaluated at a temperature of 20 1C by analyzing the samples through X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The total porosity and mechanical strength development of these materials were also determined. It was revealed that the presence of a solar cell residue of up to 5% in the cement matrices does not result in new hydration products that are different from those derived from the normal hydration of the CAC cement. Moreover, the material developed can be considered as an expansive cement blend because it releases H 2 at early stages. The presence of waste causes a decrease in the mechanical strength and an increase in the total porosity of this material, but it can be used for applications such as thermal insulation. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Photovoltaic (PV) energy is a renewable, versatile technology that can be used for almost anything that requires electricity. In the past 20 years, research and development have advanced PV technology and a new generation of low-cost products based on thin films of photoactive materials (e.g., amorphous silicon, copper indium diselenide, cadmium telluride and film crystalline silicon) deposited on inexpensive substrates has increased the prospects of rapid commercialization [1,2]. Decommissioning at the end of the life cycle of PV modules, which is expected to last around 30 years, is an important factor. There is also concern regarding their disposal as they may contain small amounts of regulated materials (e.g., Cd, Pb and Se). Research into the options for recycling manufacturing waste and used solar cells is currently underway [3]. Cement-based waste forms have been commonly used world- wide for the disposal of radioactive, hazardous and mixed wastes. The use of cement-based systems and the fixation capabilities of cementitious minerals have been extensively discussed [4]. In many cases the leaching susceptibility of these solidified wastes can be drastically decreased. For example, setting can be seriously delayed by the influence of zinc on the hydration of calcium silicates [5]. Therefore, many existing solutions are inadequate and the problem of stabilization remains, although it has been reported that the use of calcium aluminate cements (CAC) may be a suitable approach to eliminate such negative effects [6]. Nevertheless, silicon—particularly crystalline silicon wafers is the current dominant semiconductor used in PV cells. With PV systems becoming more numerous, recycling of the modules will gain in importance. However, the matter of how to dispose off used photovoltaic power generation systems, which would be of a substantial volume given large demand, has not yet been discussed. Many researchers have indicated the need for valuable materials from damaged and used photovoltaic modules to be re-used [4,5]. Blended cements have been noted for their properties in reducing CO 2 emissions [7]. For every ton of cement, roughly 1 ton of CO 2 is emitted. The CaO content of Portland cement is around 60%–65%, whereas in CAC the CaO content of the clinkers is lower, 40%–60%. Therefore, large drops in CO 2 are possible by incorporating supplementary cementitious materials in CACs. The normal CAC hydration with water leads to the formation of CAH 10 hydrated calcium aluminates at low temperatures, whereas C 2 AH 8 ,C 3 AH 6 and AH 3 are formed at intermediate and high temperatures [8–10]: CA+10H-CAH 10 2CA+11H-C 2 AH 8 +AH 3 3CA+12H-C 3 AH 6 +2AH 3 C 3 AH 6 and gibbsite are the stable phases in this system. Due to conversion, calcium aluminate cement (CAC) has been relegated from structural to only special applications. Rapid strength Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2011.01.033 n Corresponding author. Tel.: +34 934054247. E-mail address: lucia.fernandez@upc.edu (L.J. Ferna ´ ndez). Solar Energy Materials & Solar Cells 95 (2011) 1701–1706