Kernel functions to flotation bubble size distributions

Flotation modelling has advanced from deterministic single particle-bubble models into using such models to solve flotation systems by using modern computational techniques. The step from a single particle- single bubble event to multiple events taking place in the large computational volume like a flotation cell poises the challenge of handling bubble and particle distributions in all computational cells. The estimation of bubble size has either been omitted (constant size) or has been lately estimated by a population balance approach. The physical performance of flotation is excessively determined by the bubble size distribution (BSD). Therefore, the bubble size distribution estimate is crucial for modelling. Although the BSD can be measured, the underlying effects of different variables causing changes in break-up and coalescence rates producing changes in the measured BSD's are not well understood. This paper discusses the profound effects frothers have on both the coalescence and break-up of gas bubbles.Depending on the bubble surface stiffness caused by frother adsorption, the drainage rate of fluid between two approaching bubbles is very different. Frothers like DF200 and Pentanol have a higher coalescence rate than frothers like DF250 and NF240. Break-up is shown to be a function of the dynamic surface tension, not the static surface tension. Fast adsorbing frothers (DF200) have at very short time scales a higher rate of break-up. The paper suggests a division of frothers into two distinct classes for modelling purposes. Those with fast adsorption and desorption, which leave the gas-air interface mobile and those frothers that by slower adsorption and desorption create stiff interfaces. The effects in real systems may be more varied. The modelling of subtler frother effects will not substantially improve modelling quality.Peer reviewe

Automated contact time apparatus and measurement procedure for bubble-particle interaction analysis

The novel Automated Contact Time Apparatus (ACTA) presented in this paper serves as a diagnostic tool that allows the detection of changes in bubble-particle attachment probability and therefore floatability caused by alterations in the chemical environment and particle properties. The apparatus consists of six identical capillaries where bubbles with defined size are produced simultaneously in a measurement chamber. The bubbles at the needle tips are placed in contact with the submerged particle bed for specific time periods, controlled with the help of automatic actuators. The advantage of the instrument is that hundreds of bubble-particle contacts can be measured automatically within a short time period. Microscopy pictures of each measured bubble are taken while recording the movement of the bubble before, during and after contact with the solid particles. The recorded pictures can be used to determine the actual bubble size and its corresponding deviation, and to detect the attachment of particles. The attached particles are collected in a detachable chamber for subsequent characterization. Furthermore, the device is portable and can be taken to the mineral processing plants for quick evaluation of particle-bubble attachment efficiency with particles and process water sampled directly from real processes.Peer reviewe

Fundamental and flotation techniques assessing the effect of water quality on bubble-particle attachment of chalcopyrite and galena

| openaire: EC/H2020/730480/EU//ITERAMS Funding Information: This work is financed by the National Research Foundation of South Africa (NRF) [Grant number 103641] and this project has received funding from the European Union H2020 programme under grant agreement No 730480. Any opinion, finding and conclusion or recommendation expressed in this material is that of the authors and the NRF does not accept any liability in this regard. Further the financial and technical contributions from the South African Minerals to Metals Research Institute (SAMMRI) is also acknowledged. Publisher Copyright: © 2021 The Author(s) Copyright: Copyright 2021 Elsevier B.V., All rights reserved.Bubble-particle attachment has been studied in the most fundamental way from as early as 1934 by bringing a bubble into contact with a flat mineral surface and since then, techniques measuring this interaction have advanced. Water quality within flotation will impact the bubble particle attachment and as more operations recycle their water on site, an understanding of this process becomes vital. This study uses an Automated Contact Time Apparatus (ACTA) to assess the effect of water quality on bubble-particle attachment of selected sulfide minerals; galena and chalcopyrite, from a fundamental perspective. Classical microflotation tests are complemented with collector adsorption and mineral potential under degrading water quality to validate the ACTA and gain an understanding of the effect of water quality on bubble-particle attachment as well as subsequent flotation. This investigation showed that the results from the ACTA qualitatively showed similar trends as that of the classical microflotation technique for measuring floatability, however the quantitively these methods showed very different results. Due to the dynamic nature of the microflotation technique it may be assumed that plant recovery will resemble the results from this technique closer than that of the ACTA. Furthermore, this investigation showed an increase in zeta potential of both minerals as the concentration of inorganic electrolytes in the water increased. It can thus be speculated that the increase in bubble-particle attachment with increasing ionic strength of synthetic plant water may be attributed to electrical double layer compression and particle agglomeration.Peer reviewe

A fundamental study considering specific ion effects on the attachment of sulfide minerals to air bubbles

| openaire: EC/H2020/730480/EU//ITERAMSBubble-particle attachment is one of the most fundamental sub-processes in froth flotation. It is of critical importance in achieving the separation of value from non-value. This sub-process is affected by many factors such as the chemistry of the pulp, action of the reagents, hydrodynamics and operational factors. Understanding the effects of these factors on bubble-particle attachment is thus crucial as they may in turn affect the mineral recoveries attained. With the current drive towards zero effluent discharge on mineral concentrators water quality is an important factor to understand as it can change the pulp chemistry and subsequently affect mineral recoveries. This study thus considers the effect of specific ions found in process water on the bubble-particle attachment of chalcopyrite and galena. Adsorption studies and zeta potential measurements were conducted to interpret the outcomes of the bubble-particle attachment tests. Pulps containing Ca2+ resulted in lower bubble-particle attachment probability and recovery of galena and chalcopyrite. Adsorption studies complemented the bubble-particle attachment findings well and showed that in Ca2+ containing waters, less xanthate was adsorbed on both the chalcopyrite and galena surfaces. The zeta potential measurements showed an increase in mineral potential with Ca2+ containing salts compared to the very negative mineral potential in NaNO3. This work provides evidence of the passivation of the mineral surface with Ca2+; which hindered the adsorption of xanthate on the mineral surface in Ca2+ containing solutions and subsequently resulted in poor bubble-particle attachment.Peer reviewe