Abstract
Complex gangues and low-quality waters are a concern for the mining industries, particularly in water shortage areas, where the closure of hydric circuits and reduction in water use are essential to maintain the economic and environmental sustainability of mineral processing. This study analyzes the phenomena involved in the water recovery stage, such as sedimentation of clay-based tailings flocculated with anionic polyelectrolyte in industrial water and seawater. Flocculation–sedimentation batch tests were performed to ascertain the aggregate size distribution, the hindered settling rate, and the structure of flocs expressed through their fractal dimension and density. The aggregates’ properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The impact of the type of water depends on the type of clay that constitutes the suspension. For quartz/kaolin, the highest performance was obtained in industrial water, with bigger aggregates and faster settling rates. However, the tailings composed of quartz/Na-montmorillonite reversed this trend. The type of water impacted the efficiency of primary-particle aggregation. The trials in industrial water generated a portion of non-flocculated particles, which was observed through a bimodal distribution in the unweighted chord-length distribution. This behavior was not observed in seawater, where a perceptible fraction of non-flocculated particles was not found. The additional cationic bonds that offer seawater favor finer primary-particle agglomeration for all tailings types.
Highlights
Mining tailings are residual suspensions that come from froth flotation stages and are made up of non-valuable minerals, such as silicates and phyllosilicates
The results showed increased salinity reduced kaolinite sedimentation, but the salinity slightly accelerated the settling rate for montmorillonite and illite
HPAM interacts with the kaolin surface through the nitrogen of the acrylamide group with the deprotonated oxygen of the surface, while in quartz, the nitrogen of the acrylamide group interacts with the oxygen from the hydroxide on the surface
Summary
Mining tailings are residual suspensions that come from froth flotation stages and are made up of non-valuable minerals, such as silicates and phyllosilicates. Kaolinite of the composition Al2Si2O5(OH) is a non-swellable clay in freshwater, whose structure is composed of an octahedral sheet of aluminum hydroxide and a tetrahedral sheet of silica joined to form a basic unit of 1:1 repeat (see Figure 1). The central layer contains octahedrally coordinated Al and Mg in oxides and hydroxides, and is surrounded by two outer layers formed by tetrahedrally coordinated silicon oxides In this structure, the water molecules enter the middle of the layers and cause swelling and modification in the mineral structure [8]. The subsequent reduction in electrostatic repulsion reduces the separation distance between sheets, which prevents the entry of water molecules into the clay [10]
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