Sludge recycling within cemented paste backfill: Study of the mechanical and leachability properties Mostafa Benzaazoua a, * , Jean-Franc ¸ois Fiset b,1 , Bruno Bussie `re a , Mathieu Villeneuve a , Benoı ˆt Plante a a University of Quebec in Abitibi-Te ´miscamingue, Canada Research Chair on ‘‘Integrated Management of Sulphidic Tailings using Fill Technology’’, Industrial NSERC Chair Poly-UQAT in ‘‘Mining environment’’, 445 boul. De l’Universite ´, Rouyn-Noranda (Que ´bec), Canada J9X 5E4 b Natural Resources (CANMET-MMSL), 555, Booth Street, Ottawa (Ontario), Canada K1A 0G1 Received 30 June 2005; accepted 27 September 2005 Available online 11 November 2005 Abstract Cemented paste backfill (CPB) technology has become widely used in Canada and around the world. While most of the studies related to CPB have concentrated on the mechanical, physical, rheological and economical aspects, very few studies have been conducted on metal leachability. The objective of this study was to investigate the mechanical and environmental behaviour of a novel CPB technique consisting of incorporating various treatment sludges within the conventional paste mixture. For the CPB studied, the binder PC10-50 50/50 offers higher mechanical resistance than the slag-based cement. While PC-based binders are more or less penalized by the addition of sludge, slag-based cement benefits from this additive. In terms of leachability, the results show that PC and slag-based binders were efficient in minimizing the release of Zn and Mn even at a low binder proportion. The addition of 0.15% and 0.30% of three different sludges to the tailings paste backfill did not have any negative impact on metal leachability. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Acid rock drainage; Tailings disposal; Paste backfill; Sludges; Leaching 1. Introduction Daily, the mining industry produces different types of waste such as mill tailings, waste rock, and water treatment sludge (Aubertin et al., 2002). Various techniques are com- monly used in the mining industry to dispose of its waste. Waste rocks are usually stored at the surface in stacks called waste rock piles; they can also be used as under- ground backfill material (cemented or uncemented rock fill). Tailings can be stored in a surface tailings pond or can be used as backfill material (as hydraulic fill or paste backfill) to fill underground open stopes. Tailings and waste rocks can also be stored in old mine shafts, workings and abandoned open pits with subsequent flooding (Ledin and Pedersen, 1996). The main concerns with tailings and waste rock disposal are the physical stability of the surface storage area and the reactivity of the sulphide minerals often contained in the mine waste. The acid mine drainage (AMD) generated by sulphide oxidation due to the action of oxygen and water is treated by active treatment using generally lime addition. This pro- cess allows meeting the regulations in terms of discharged water quality but producing a certain amount of sludges containing toxic elements. Water treatment sludge from mine operations contains usually between 1% and 30% sol- ids depending on the treatment method (Aubertin et al., 2002). In Canada, it is estimated that as much as 6.7 mil- lion cubic meters of sludge are produced annually (Zinck and Aube ´, 2000). Canadian mining companies usually dis- pose of their sludge in ponds or lagoons, or they combine 0892-6875/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2005.09.055 * Corresponding author. Tel.: +1 819 762 0971x2404; fax: +1 819 797 6672/4727. E-mail addresses: mostafa.benzaazoua@uqat.ca (M. Benzaazoua), jefiset@nrcan.gc.ca (J.-F. Fiset). 1 Tel.: +1 613 995 4641; fax: +1 613 996 9041. This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 19 (2006) 420–432