Filtering the unfilterable: tuning the mesostructure of precipitating silica gels to improve the filterability of acidic lixiviation slurries
Résumé
Silica precipitation is a ubiquitous but deleterious phenomenon occurring in many hydrometallurgical processes. Indeed, silicon is often released during the dissolution of minerals under acidic leaching conditions. Eventually, it precipitates into a hard-to-filter silica gel, which has prompted some efforts to hinder silica precipitation through pre-treatment or extra dilution. However, these approaches are usually either mineral-specific or costly. Here, we propose a disruptive strategy based on controlling the gel's mesostructure, and therefore its filterability. We designed an alternative precipitation pathway consisting of adding extra silicate ions, but at basic pH. Using small-angle Xray scattering, we show that this pathway transforms the network of polymeric silica ('polymer gel') obtained in the very acidic leaching conditions into a network of dense silica particles ('particle gel'). This structural compaction at the mesoscopic length scales cascades to the macroscale and leads to a drastic improvement of filterability by two orders of magnitude. Furthermore, we demonstrate that this method is generic by applying it successfully to both a model and real ore systems.
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