Page 145 November 15-18, 2006 São Paulo – Brazil IIBCC 2006 - Sao Paulo, Brazil. October 15 - 18, 2006. Universidade de Sao Paulo & University of Idaho: Sao Paulo, 2006. OPTIMAL USE OF FLOCCULANTS ON THE MANUFACTURE OF FIBRE CEMENT MATERIALS BY THE HATSCHEK PROCESS A. BLANCO, E. FUENTE, L.M. SANCHEZ, A.ALONSO, J. TIJERO AND C. NEGRO Chemical Engineering Department, Complutense University of Madrid, Avda. Complutense s/n. 28040 Madrid. Spain ABSTRACT In the Hatschek process used to produce fibre-cement products, it is necessary to use a suitable flocculant when asbestos is substituted by pulp fibres. The right selection of flocculant is crucial in the industrial process due to its effects on mineral fines retention, dewatering and formation and, as a consequence, on the overall efficiency of the machine. Therefore, the optimisation of the flocculation process during fibre cement production is a key issue for the fibre cement industry. Many companies face difficulties in optimising the flocculant dosage in real time, which leads to product strength losses. The presentation will be focus in the description of a new methodology for flocculant selection in the fibre- cement manufacture. Results show that this methodology gives an in-depth knowledge of flocculation process. A real-time methodology has been used to study size, shape, strength and reversibility of formed flocks, based on a focused beam reflectance measurement (FBRM) system. The results have been corroborated by particle vision and measurement (PVM) analysis. The influence of the molecular weight and the anionic charge of anionic polyacrylamides on the flocculation behaviour of fibre cement suspensions and on the bending strength of the final product will be reported. Finally, will be reported the feasibility of using artificial neural networks (ANNs) to establish correlations between flocculation data, in-line measured in a Hatschek machine by a focused beam reflectance measurement (FBRM) sensor, and mechanical properties of final composites. The results show a clear relationship between the mechanical properties of fibre cement composites and the flocculation process and that these are determined in real time. KEYWORDS: Fibre-cement; Hatschek process; flocculation; fibre/matrix bond, retention. INTRODUCTION Over the last few years, many research studies related to the substitution of asbestos for others raw materials have been published (Daniel, 1996). These mainly focus on natural cellulose fibres from wood (virgin or recycled (Souroushian, 2000)) or non-wood raw materials (Savastano, 1993 and 2003) and synthetic fibres, alone or as a mixture (Bohnemann, 1998; Hannant, 1995). Out of all these sources the softwood un-bleached Kraft fibres are the most widely used due to their strength characteristics, the high availability and the price. Asbestos is a naturally occurring fibrous silicate and the fibre’s size together with its chemical structure, make asbestos very compatible with cement. However, the different density, chemical composition and hygroscopic character of pulp fibres make the compatibility between cellulose fibres and cement much more complex and, therefore, new aspects need to be considered. In the Hatschek process, the behaviour of these fibres is different and therefore, a suitable flocculant is needed when using pulp fibres. The machine type determines the addition points for the flocculants. The right selection of flocculant is crucial in the industrial process due to its