Establishing nickel laterite agglomerate structure and properties for enhanced heap leaching

Producing robust agglomerates with desirable structural properties is key to the success of the heap leaching of complex, low-grade nickel (Ni) laterite ores. The agglomerate microstructure characterization is essential for greater understanding and correlation with its key properties (e.g., porosity, permeability, strength) and performance during heap leaching. In this study, computed X-ray tomography and scanning electron microscopy are used with compressive strength and re-wetting integrity/stability analyses to establish links between Ni laterite agglomerate strength/stability, microstructure (e.g., porosity, inter-particle bridges), formulation of agglomeration medium and granule drying/curing condition. It is shown that both the agglomeration medium (e.g., tap water vs. 30% w/w H2SO4) and agglomerate drying/curing play pivotal roles in structural changes within the agglomerates and hence significantly impact on the agglomerateʹs physicochemical and microstructural properties. Acidic medium, in contrast to tap water, leads to significant leaching of Ni, Co and gangue from the ore during mixing. Upon agglomerate drying, solidified/crystallized leached species form strong intra-granular solid bridges which lead to greater agglomerate compressive strength. The strength of dry agglomerate is markedly greater for acid- than for water-bound agglomerates at equivalent residual moisture content. Structural stability/integrity of cured agglomerates upon contact with acidic solution, however, decreases dramatically due to greater internal pore volumes and the acid solubility of solid bridges. These findings are useful in shedding more light on agglomerate structure.