Column leaching of nickel laterite agglomerates: Effect of feed size

Heap leaching is a promising, less costly, alternative technology for processing low grade nickel (Ni) laterite ores compared with traditional, energy intensive processes (e.g. autoclave/tank leaching). However, significant technical challenges remain with Ni laterite heap leaching, preventing its general adoption. This paper presents some highlights of laboratory column leaching studies undertaken to characterise, evaluate and optimise sulphuric acid leaching behaviour of Ni laterite agglomerates. The main focus of the paper is to assess the effect of the initial feed ore particle size to the agglomeration stage on the leaching behaviour of the resulting agglomerates. This type of investigation provides basic but valuable information regarding Ni laterite agglomerate robustness and leaching performance under industrially-relevant, continuous acid irrigation conditions. In particular, Ni, cobalt (Co) and other key metalsʹ (e.g. Fe, Mg, Al and Mn) extraction rates, acid consumption and bed slump were determined at a given acid percolation rate as a function of time > 100 days. The findings show that the particle size of the agglomerate feed ore has a significant impact on the subsequent column leaching performance. Ni and Co recoveries of 90% and 80%, respectively, were achieved over 100 days for − 38 μm size feed, 5–40 mm agglomerates, but these decreased by 10% for the agglomerates made from coarser feed particles (i.e., 2–15 mm). Potential implications of the findings for devising strategies for improved Ni laterite plant heap leach operations are discussed.