A Study on the Electric Surface Potential and Hydrophobicity of Quartz Particles in the Presence of Hexyl Amine Cellulose Nanocrystals and Their Correlation to Flotation

Abstract

In this work, the study of hexyl amine cellulose nanocrystal (HAC) as a renewable and environmentally-friendly reagent for the flotation of quartz (QRZ) is expanded with a focus on the changes of electrical states at the solid-liquid interface, the range of solid-gas interactions, and their impact on flotation operations under a turbulent regime. Furthermore, particle-bubble attachment probabilities were measured with the recently engineered automated contact timer apparatus (ACTA), a versatile technique used to deduce the wettability of microparticles and potentially predict their floatability. Therefore, the findings of the ACTA proved that, with sufficiently hydrophobic QRZ (i.e., HAC concentration ≥ 0.667 mg HAC /m 2 QRZ), stable particle-bubble attachments occur at particle-bubble distances in the range of tens of micrometers. The distances for the successful attachment of HAC-coated QRZ particles exceed the range of interactions reported in literature so far and imply the existence of structural or hydrodynamic phenomena acting between particle and bubble surfaces. The occurrence of so-called non-compressive particle-bubble attachments is shown to correlate with a significant increase in the floatability of QRZ, where recoveries up to 90% were obtained. Based on the experimental results, some insights on the nature of the long-range interactions responsible for the particle-bubble attachment of hydrophobic particles are provided.

On the Colloidal Behavior of Cellulose Nanocrystals as a Hydrophobization Reagent for Mineral Particles

“…60%, even recoveries higher than 85% were obtained for a concentration of 50 g/t using a similar HAC sample. 16 This indicates the first advantage on the use of nanocellulose particles as a collector.…”

“…For the purposes of this work, a size fraction for ACTA and flotation experiments was prepared as reported earlier. 16 In short, about 100 g of quartz was ground for 10 s in a ring mill (Fritsch PULVERISETTE, planetary micro mill) made of tungsten carbide. It is expected that no contamination of samples results from grinding.…”

“…Recently, our research group studied the influence of HACs on the floatability of quartz by monitoring fundamental particle-bubble attachments with an automated contact timer apparatus (ACTA) and their correlation with recovery in bench-scale flotation. 16 It was found that HACs increase the bubble-particle attachment probability and the recovery of quartz in a flotation cell, upholding its effectiveness as a hydrophobization agent. Unlike the characterization techniques used by the other authors, bubbles in the ACTA are formed on a needle tip and subsequently approach a particle bed, consisting of micrometer-scale particles, during a controlled time.…”

“… 15 This balance of surface groups with different behaviors is exemplified by hexylamine cellulose nanocrystals (HACs), which have showed a promising performance as a collector for quartz in recent studies with recoveries of up to 80 or even 90%, depending on the type of flotation cell and flotation conditions. 7 , 8 , 16 Hence, HACs have shown a high potential to replace water-soluble amine-based collectors, e.g., in reverse flotation of iron ores. Simultaneously, due to its relatively simple chemical composition, quartz was considered as a suitable substrate for further investigations on the behavior of HACs as the hydrophobization reagent.…”

“…Nevertheless, an interesting feature of nanocellulose is that several functional groups may be incorporated onto their surface, allowing for the design of collectors with finely tuned properties. − To obtain an optimal collector one should focus on the modification of the surface groups of nanocellulose to reach a balance between mineralophilic and hydrophobic sites, to simultaneously attach on a mineral species while rendering it sufficiently hydrophobic to allow orthokinetic attachments to bubbles, i.e., the formation of permanent aggregates . This balance of surface groups with different behaviors is exemplified by hexylamine cellulose nanocrystals (HACs), which have showed a promising performance as a collector for quartz in recent studies with recoveries of up to 80 or even 90%, depending on the type of flotation cell and flotation conditions. ,, Hence, HACs have shown a high potential to replace water-soluble amine-based collectors, e.g., in reverse flotation of iron ores. Simultaneously, due to its relatively simple chemical composition, quartz was considered as a suitable substrate for further investigations on the behavior of HACs as the hydrophobization reagent.…”