Abstract
Particle size distribution (PSD) determination is a typical practice for the characterization of the slurries generated in a precipitation plant. Furthermore, the precipitates generated in these processes form colloidal or aggregated suspensions. Nevertheless, the conventional methods used to estimate PSD (e.g., laser diffraction and/or a cyclosizer) have not been designed to measure particles that tend to aggregate or disaggregate, since they include external forces (e.g., centrifugal, agitation, pumping and sonication). These forces affect the true size of the aggregates formed in a unit operation, thereby losing representativeness in terms of aggregates particle size. This study presents an alternative method of measuring the size distribution of particles with aggregation behavior, particularly, by using non-invasive microscopy and image processing and analysis. The samples used were obtained from an experimental precipitation process by applying sulfidization to treat the cyanide-copper complexes contained in a cyanidation solution. This method has been validated with statistical tools and compared with a conventional analysis based on laser diffraction (Mastersizer). The PSD results obtained with optical microscopy show a bi-modal behavior of the precipitates. However this behavior could be not determined when using the laser diffraction technique. The PSD obtained for the sample tested by microscopy had a mean of 119.7 μm, a median of 147 μm and a 90% distribution reached a particle size of 312.5 μm. These values differ with those obtained by the laser diffraction technique. Our results show significant differences between the methods analyzed, demonstrating that the image processing and analysis obtained by optical microscopy is an excellent and non-invasive alternative to obtain size distributions of aggregates in precipitation processes.
Highlights
Our results show significant differences between the methods analyzed, demonstrating that the image processing and analysis obtained by optical microscopy is an excellent and non-invasive alternative to obtain size distributions of aggregates in precipitation processes
A maximum precipitate generation of 99.97% was reached for the operational conditions assessed, and it was possible to obtain a precipitate quality with 67.69% w/w of copper content, as found in other SART studies or industrial plants [5]
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Summary
Minerals 2019, 9, 724 copper sulfide precipitation from acid mine drainage, using hydrogen sulfide [4] and copper sulfide precipitation from cyanide solutions in gold mining [5] These processes must accommodate a subsequent solid–liquid separation stage (i.e., thickeners and/or filters) to remove the solids generated from the solution. An appropriate characterization of the precipitates size is crucial for the selection and design of an adequate separation process In this context, there are some studies that characterize the precipitates formed in sulfidization processes for treating AMD [6,7] and cyanide solutions [9,10]. These studies determined the aggregate characteristics from metal sulfide precipitates and the dependence of pH and sulfide dosage (chemical solution characteristics) on aggregate size
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