Particulates in hydrometallurgy: Part I. Characterization of laterite acid leach residues
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I.
INTRODUCTION
HYDROMETALLURGICAL research is dominated by investigations that emphasize the applications of solution chemistry.t1-8] In contrast, studies that focus on the particulate nature of the feed materials and/or solid intermediates have received comparatively little attention. This situation is likely to change in the future, given the increasingly stringent environmental constraints and the continual depletion of high grade ores. The role of particle science and technology in hydrometallurgical processing is particularly evident in the solid/liquid separation step of the flowsheet, where leach residues are initially present as suspended solids and are removed from slurries by sedimentation and/or filtration. Hydrometallurgical systems based on oxidic starting materials tend to exhibit poor solid/liquid separation characteristics. Most of the important oxide ores (e.g., bauxites, laterites, and manganese nodules) either occur or are processed as highly divided particulates. For example, laterites possess specific surface areas of the order of 60 mZ/g,I91 while manganese nodules have high microporosities with specific surface areas of the order of 200 m2/g. v~ Since fine
A. BRICENO, formerly Graduate Student, Department of Materials Science and Engineering, The Pennsylvania State University, is with the Department of Mining, University of Oriente, Venezuela. K. OSSEOASARE, Professor and Program Chair, is with the Metals Science and Engineering Program, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted April 1, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
particles settle slowly and microporous solids can act as a fine sponge trapping leach liquors, solid/liquid separation proceeds with difficulty. Furthermore, since only very limited physical upgrading of oxidized ores is feasible, large-scale plants are necessary to achieve economic metal recoveries. The selective extraction of a small percentage of valuable metal from large amounts of already finely divided ores necessarily produces a large residue of colloidal or near-colloidal material. The presence of these slimes puts a considerable burden on the solid-liquid separation step, making it one of the most capital intensive operations in the process flowsheet. In the 1960s and 1970s, considerable research effort was directed at the development of new and improved extraction technologies for laterites and manganese nodules. I9-~41 For economic reasons, much of this activity never reached commercialization. However, given the fact that the world's largest resources of nickel and cobalt are to be found in oxide ores, it is expected that sooner or later, these resources will rise to the fore again.t14~ In anticipation of the eventual glorious future of oxide ores, a research program was initiated in our laboratory to undertake systematic investigations into the physical and chemical properties of laterite leach residues and the effects of these properties on dewatering b
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