Original Research Paper Mechanical strength and rewetting stability of nickel laterite pellets Danfeng Xu a , Lian X. Liu b,⇑ , Jonas Addai-Mensah a , David J. Robinson c a Ian Wark Research Institute, The ARC Special Research Centre for Particle and Material Interfaces, University of South Australia, Mawson Lakes, SA 5095, Australia b JKMRC, Sustainable Minerals Institute, The University of Queensland, Brisbane, QLD 4072, Australia c CSIRO Minerals Down Under National Research Flagship, Australian Minerals Research Centre, PO Box 7229, Karawara, Western Australia 6152, Australia article info Article history: Received 19 December 2012 Received in revised form 18 March 2013 Accepted 23 March 2013 Available online 11 April 2013 Keywords: Nickel laterite pellets Pellet strength Leaching Rewetting abstract The stability of agglomerated/pelletized ores is one of the key properties for successful heap leaching of complex, low-grade nickel laterite minerals. In this paper, single pellets of saprolitic and goethitic nickel laterite with controlled binder type (tap water and 44 wt.% H 2 SO 4 ), binder content and pre-set porosity were made by a pellet press and subjected to mechanical strength and rewetting stability tests. The effect of fine/coarse particles ratio on the mechanical strength was also investigated using siliceous goethitic ore. The failure strength of the pellets under different drying conditions was measured and the time taken for the pellets to disintegrate under saturated (soaking) and leaching conditions was recorded. The results showed that, with the same type of nickel laterite, the time taken to disintegration during leaching test is proportional to the pellets tensile strength. Pellets with water as binder are more stable under soak con- ditions. Furthermore, failure strength for oven dried pellets is greater than that of air dried. With sapro- litic nickel laterite (SAP) pellets, their mechanical strength and re-wetting stability can be enhanced by drying the wet pellets or by increasing the binder content in the pellets. The pellets mechanical strength was found to be a good indication of their stability under leaching conditions as well. However, no rela- tionship between the two was observed for goethitic nickel laterite pellets. Ó 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction Today there is an increasing focus on the processing of the huge reserves of nickel-rich laterite ores, which are exceptionally com- plex, low grade and expensive to treat using conventional smelting and high temperature/pressure autoclave methods due to the declining global reserves of nickel laterite ores. Heap leaching is a process employed in the minerals industry to extract valuable met- als from low-grade ores at relatively low capital and operational cost. Practically all heap leaching operations use agglomeration as an intermediate stage between mineral crushing and its stacking [1–3]. The main objective of agglomeration is to form a relatively uniform and highly permeable bed by eliminating the migration of fine particles in the heap. Pelletization, granulation, and agglomera- tion are common terms describing the size enlargement processes. There are four types of bonding mechanisms involved in the binding process: solid bridges, mobile liquid binding, intermolecular and electrostatic forces, and mechanical interlocking, among which the first two are most common in the agglomeration of crushed ores [2]. Optimum conditions (moisture content, binder type, porosity) are needed in the agglomeration step to prevent agglomerate break- down when the ore is moistened by the leaching solution [4]. Poor quality agglomerates and size segregation will lead to deteriorated permeability, causing ponding and partial or non-existent liquid percolation will consequently reduce recovery, and increase cost. Good agglomerates in a heap should survive the aggressive acid leaching conditions without disintegration over a long period. So far, there is no standard, quantitative method for evaluating agglomerate stability in the literature. Some stability tests con- ducted include soaking agglomerates in water [5,6] and observing the slump of the ore bed in percolation columns [7]. As one of the Cluster parties of a 3-years, collaborative research program executed with the CSIRO Minerals Down Under (MDU) Flagship Cluster project, we have selected West Australia Ni laterite ores, generically classified and named ‘‘siliceous goethite’’ (SG), ‘‘goethite’’ (G) and ‘‘saprolitic’’ (SAP). The mineralogy of the three ore types is generally consistent with that of range of laterite depos- its round the world. The extent of weathering determines the rela- tive abundance of oxide/hydroxide (most weathered) near the surface and clays (least weathered) mineral content at depth, with Ni mobilising and deporting to a broader range of mineral phased with depth. In our previous paper [8], the mechanical strength of siliceous goethitic (SG) nickel laterite pellets and their stability un- der soaking and leaching conditions was reported. In this paper, the stability of single pellets made from saprolitic (SAP) and goethitic 0921-8831/$ - see front matter Ó 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. http://dx.doi.org/10.1016/j.apt.2013.03.014 ⇑ Corresponding author. Tel.: +61 7 33658591; fax: +61 7 33654199. E-mail address: l.liu@uq.edu.au (L.X. Liu). Advanced Powder Technology 24 (2013) 743–749 Contents lists available at SciVerse ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt