Dissolution Model of Multiple Species: Leaching of Highly Soluble Minerals
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DUCTION
THE dissolution of soluble species from solid matrices is a phenomenon present in a wide variety of processes and materials; among them are fertilizers, drugs, polymers, salts, and minerals. When different soluble minerals in a same matrix are solubilized at different rates, the description of the dissolution is complex. If in addition, the grade of these soluble species is high, the solid matrix undergoes physical changes that, depending on the dissolution level of each of the species (partial or complete), can produce appreciable variations in porosity, which may cause the collapse of the matrix. The collapsed material is a disaggregated solid formed by inert material and a fraction of the soluble materials that are not yet dissolved. Heap leaching is widely used because large amounts of low ore grade can be processed at lower cost.[1,2] Leaching agent is added at the top of the heap and the enriched solution is collected at the base of the heap for subsequent steps of concentration and/or separation. Although the ores are composed by more than one leachable species dissolving at different dissolution rates and with different solubilities, the leaching of them is frequently modelled assuming that only a single species is dissolving at an average dissolution rate or including
LUIS MORENO is with the Department of Chemical Engineering and Mineral Process, Universidad de Antofagasta, 1240000 Antofagasta, Chile, and also with the Department of Chemical Engineering and Technology, Royal Institute of Technology, 100-44 Stockholm, Sweden. JAVIER I. ORDO´N˜EZ and LUIS A. CISTERNAS are with the Department of Chemical Engineering and Mineral Process, Universidad de Antofagasta. Contact e-mail: javier.ordonez@ uantof.cl Manuscript submitted June 4, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
only the species with the highest dissolution rate. This is based on that the most abundant species with high dissolution rate frequently controls the release of the others species. As example, in caliche leaching, nitrate that is rapidly dissolved and one of most abundant species controls the dissolution process. The heap leaching modeling is complex and significant assumptions and approximations are usually made in order to maintain the model simple and transparent. Some of the frequent assumptions are to study only the dissolution of a single species, that particles are spherical and of the same size, and that mineral has homogeneous composition and constant properties such as porosity and density. Leaching models seek to simulate, design and optimize the operation.[3–6] Caliche is a mineral with a high proportion of water-soluble species mined in northern Chile, where nitrate (also called saltpeter) and iodine are the main valuable products, which are used as fertilizer, additive in industrial processes, in medicine applications among others.[7,8] This ore is mostly leached in heaps, since its soluble grade has declined considerably in recent decades; from a soluble composition, greater than 50 pct, to current grades of abo
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