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Nowadays, humankind undergoes intensive efforts to minimize the environmental pollution worldwide. One main challenge is the reduction of chemicals based on mineral oil and petroleum by the employment of sustainable and environment-friendly alternatives. A promising candidate is cellulose, which is a green, sustainable and abundant polymer. Cellulose can be treated physically and chemically to obtain tailored properties, which enable the employment of cellulose in industrial processes, such as flotation. Nonetheless, the structure of cellulose, which differs substantially from conventional flotation reagents, leads to different behaviour in ore dressing and in subsequent particle-bubble attachment. Therefore, the interactions between cellulose and the minerals under different conditions is investigated using the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory, comprising van-der-Waals and electrostatic interactions, and the results are put in context with flotation recoveries using a single gas capillary Hallimond tube. The results obtained indicate that van-der-Waals interactions are dominant at very close distances and electrostatic interactions at distances of several nanometres between cellulose and the minerals. Accordingly, this study illuminates that the occurrence of physisorption phenomena between cellulose and the minerals and efficient particle-bubble attachment depend on electrostatic interactions between them.

The fundamental formation of the three phase contact in flotation is an intensively and controversially discussed phenomenon and the contact angle method is usually employed to characterise the wettability of solid surfaces. A more recent technique to explore the hydrophobicity of solid particulate phases is inverse gas chromatography (iGC) which is used to quantify the wettability of solid surfaces through thermodynamic parameters. In this article, the recently introduced net free energy of interaction between particles and bubbles immersed in water ΔGpwb is derived from the surface free energy analysis and its correlation to the flotability of solid phases is evaluated. At the same time, a more detailed analysis on the action of flotation reagents is presented performing iGC measurements under dry and flotation experiments under aqueous conditions. In general, flotation reagents have to satisfy required features to adsorb selectively, render the solid surface wetting property sufficiently, and comply current regulations concerning the preservation of the environment. Consequently, many conventional reagents are increasingly subjected to restrictions. One potential alternative candidate is nanocellulose due to the versatile chemical composition and functionality. The synthesis of cellulose nanocrystals (CNCs) includes different mechanical and chemical modification routes to lower the crystal sizes and integrate specific functional groups and organic components into the cellulose structure. This study is concentrated on the investigation of aminated CNCs for the flotation of quartz in comparison to conventional reagents. The employment of CNCs as a renewable and sustainable alternative to conventional chemicals is challenging due to the more complex structure of cellulose crystals and leads to new perspectives regarding the action of flotation reagents at the interface of a mineral under dry and wet environments.

The time required for the attachment (tatt) between solid particles and bubbles in an aqueous phase is known to reflect the interfacial characteristics of the three-phase system. Although plenty of research has been performed on the use of induction timers to measure tatt, the derivation of quantitative parameters to determine the wettability of microparticles has not been reported so far. Indeed, the use of induction timers has been limited to the estimation of relative floatability of specific systems. Consequently, the objective of this work is to develop a sound methodology to overcome the current limitations of induction timers. In order to provide an adequate method for wettability characterisation, the present work offers a critical analysis on assumptions and experimental procedures previously reported in the literature regarding contact timers. The arbitrary definition of contact times at 50% bubble-particle attachment probability and the negligence of particle-bubble distance during attachment events are of particular concern. Using the novel Automated Contact Timer Apparatus (ACTA), it was found that, for a proper assessment of attachment due to interfacial forces, attachment probabilities should be measured within a zone of non-compressive attachment (NCA). In the absence of compression, only particles with a meaningful hydrophobic character present high attachment probabilities. It is also experimentally demonstrated that the probability of attachment as a function of contact time depends on the final distance between particles and bubbles. Using the right values of particle-bubble attachment probability, a method to deduce three-phase contact angles from induction timer experiments is proposed for the first time. The similarities between contact angles calculated from attachment timer results (i.e, 51° and 88°) and those of analogous flat surfaces with the sessile drop method (i.e, 49° and 78°) prove the applicability and high potential of this methodology to study the wettability of microparticles.