The effects of saline water on the recovery of lead and zinc sulfide during froth flotation

In this study, we investigated the effects of water salinity on the flotation performance of pure lead and zinc sulfide mineral samples as well as a Pb/Zn complex sulfide ore by means of micro-flotation and batch flotation experiments. Our results showed higher PbS and ZnS recoveries in more concentrated NaCl salt solutions. The results for the experiments using seawater demonstrated that in the presence of additional ions, such as Ca2+ and Mg2+, the recovery of PbS and ZnS was significantly reduced. As part of this investigation, we developed and implemented a surface complexation model for ZnS based on the presence of two differently charged surface sites. Zeta potential measurements of ZnS particles were used to optimise the parameters of our model. It was found that the surface potentials calculated using this model were in good agreement with the experimental zeta potentials, validating the model for predicting the zeta potential behaviour of ZnS particles over a broad range of pH and NaCl concentrations. Additionally, total interaction free energies were determined as a function of separation distance, representing particle–particle and particle-bubble interactions of our study in different NaCl concentrations. The theoretical analyses showed that asymmetric Pb/Zn particle–particle interactions were repulsive at lower NaCl concentrations, before becoming purely attractive at higher NaCl concentrations. For the case of the symmetric particle–particle interactions, attraction controlled all interactions, regardless of NaCl concentration. The calculated PbS-bubble interactions were repulsive in lower NaCl concentrations but became increasingly attractive in higher NaCl concentrations. Strong repulsions controlled all ZnS-bubble interactions, and these interactions remained repulsive with increasing NaCl concentration. The theoretical projections presented in this study were in good agreement with the measured saline water flotation phenomena

Electro‐driven materials and processes for lithium recovery—A review

The mass production of lithium‐ion batteries and lithium‐rich e‐products that are required for electric vehicles, energy storage devices, and cloud‐connected electronics is driving an unprecedented demand for lithium resources. Current lithium production technologies, in which extraction and purification are typically achieved by hydrometallurgical routes, possess strong environmental impact but are also energy‐intensive and require extensive operational capabilities. The emergence of selective membrane materials and associated electro‐processes offers an avenue to reduce these energy and cost penalties and create more sustainable lithium production approaches. In this review, lithium recovery technologies are discussed considering the origin of the lithium, which can be primary sources such as minerals and brines or e‐waste sources generated from recycling of batteries and other e‐products. The relevance of electro‐membrane processes for selective lithium recovery is discussed as well as the potential and shortfalls of current electro-membrane methods

The electrochemistry of the leaching of pre-reduced nickel laterites in ammonia-ammonium carbonate solution

A fundamental study was undertaken in order to establish the mechanisms of the leaching of pre-reduced nickel laterites in ammonia-ammonium carbonate solution. Although the process has undergone various improvements since it was first introduced, the total recoveries are still relatively low, averaging at 80% for nickel and 45-50% for cobalt. The lack of sound fundamental information regarding the mechanisms and the kinetics of the dissolution of nickel and cobalt from iron-alloy grains produced by the reduction roasting of lateritic ores is seen as the main obstacle to establishing the reasons for the lack of adequate recovery and to defining alternative processing strategies which would lead to improved extraction and better process optimisation. Based on fimdamental electrochemical studies and bench scale leaching tests, as well as on-site measurements at an industrial plant where this process is applied, the work presented in the thesis introduces significant new evidence and sheds more light on the understanding of the mechanism of the dissolution process and on the reasons for the low extractions of nickel and cobalt. It has been established that the oxidative dissolution of the iron-alloy grains formed during the reduction roasting takes place primarily via a reaction involving reduction of dissolved cobalt (111) to cobalt (11), and also that the reduction of water is not a significant component of the reactions involved in the dissolution process. Open-circuit potential measurements with various metals and iron-alloys selected to model the reduced material in various solutions which simulated the leaching conditions were also conducted and revealed that passivation takes place during the leaching process. This brings to light a possible new reason for the low recoveries of nickel and cobalt which has not been previously considered. In addition, a kinetic study was conducted, in which the dissolution rates for the various metals, iron-alloys and solutions were measured as a function of time, and the results of which shed more light on the development of the process of passivation. The passivation itself is attributed to formation of iron-oxide on the surface of the dissolving iron-alloy grains, which restricts the transfer of electrons to the reduced metal and brings the oxidative leaching reaction to an end. It has been shown that the passivation can occur in two ways. On the one hand, particularly high concentration of dispersed and dissolved oxygen in the leaching reactors causes passivation by overcoming the limiting current density for the oxidation of iron to divalent iron ions and taking the potential to the region where the direct oxidation to trivalent ions becomes favourable resulting in the formation of an iron-oxide film on the surface. On the other hand, in normally aerated solutions, the passivation of the dissolving ironalloy grains occurs due to the formation of a cobalt and nickel sulphide layer, as a byproduct of the reduction of thiosulphate on the metal surface, which in turn gradually shrinks the area available for the oxidation of iron, again leading to a situation where the oxidising agents present in the solution under standard aerated conditions become sufficient to shift the mixed potential to the region where the iron-oxide forming reaction becomes favourable. The presence of thiosulphate has a decisive role in the second type of passivation. What is more, besides preventing further dissolution of the nickel and cobalt locked in the iron-alloy matrix, the loss of nickel and cobalt by precipitation in the presence of thiosulphate can further reduce the recovery of these metals. For this reason, a method was developed for the oxidation and removal of thiosulphate fkom the actual plant liquor

The effects of NaCl addition on the particle-bubble interactions of galena in the presence of xanthate

This work investigated the effects of NaCl addition on galena flotation in the presence of xanthate. The micro-flotation experiments were performed using NaCl solutions which also included xanthate, at pH 9 (±0.1). Our results indicated that galena recovery improved for higher NaCl as well as higher xanthate concentrations.A pH-dependent chemisorption model for the galena surface, with the addition of xanthate adsorption was calibrated using measured zeta potential values. We propose that xanthate adsorption on galena can take place via two separate mechanisms. The first mechanism involves direct xanthate chemisorption to specific surface sites. The second mechanism involves lead/xanthate complexes formed in the bulk solution. These lead/xanthate complexes attach on the galena surface as hydrophobic lead xanthate salts.The galena-air bubble interactions are repulsive in 1 mM NaCl, with or without xanthate, consistent with the lower galena recovery measured experimentally. An increase to 100 mM NaCl, irrespective of the xanthate addition, resulted in attractive galena-air bubble total interaction energies. The agreement with the experimental results shows the effectiveness of the charge regulated model for estimating the galena and air bubble behaviours during flotation in NaCl solutions