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A digital imaging based
approach to characterize arsenic minerals in colemanite ores
The presence of considerable amount of arsenic in borate concentrate
produces penalty in marketing and makes its removal necessary. In this
perspective, an automated procedure based on structural and textural
characterisation of a colemanite ore, in order to evaluate the degree of
liberation of the arsenic minerals, adopting image analysis techniques, is
presented. Samples of a colemanite (Ca2B6O11•5H2O)
concentrate coming from Turkey have been collected. It has been revealed the
occurrence of colemanite in different sizes and shapes, most commonly in
nodules (up to 50cm), sometimes with thin discontinuous layers of clay. The
samples are affected by relevant concentration of two arsenic minerals,
realgar (AsS) and orpiment (As2S3). Polished sections have been submitted to
scanning electron microscopy (SEM) and optical microscopy in order to
acquire suitable digital images. The arsenic minerals have been found either
as disseminated crystals or in veinlets along colemanite fractures with a
very thin size (up to 100μm). In order to characterise and quantify the
complex and variable distribution of the As minerals, fully imaging based
strategies have been set up and applied. The obtained results enabled to
define suitable and reliable comminution strategies in order to liberate the
arsenic minerals. The developed procedure can be successfully applied to
other ores, constituted by mineral association characterised by complex
textures. |
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