Browsing by Author "Manono, Malibongwe"

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    A determination of the effect of changing collector chain length under varying Water Quality
    (2025) Natalia Sinjani, Taonga Mchirwa; Corin, Kirsten; Manono, Malibongwe; Manenenzhe, Resoketswe
    The mineral processing industry needs to recycle process wastewater to decrease the detrimental effects of its discharge into the environment. This is of high importance in regions where water availability is restricted. Recycling process water leads to differences in water quality such as changes in pH, ionic strength (IS), and the concentration of total dissolved solids (TDS). The froth and pulp zones in the flotation cell work interactively to recover minerals and changes to water quality affect both zones. The factors affect the behavior of minerals and chemical reagents, impacting flotation performance. According to literature, collector behavior can be impacted differently by certain ions. An increase in the IS and TDS of water can result in a decrease in mineral recoveries and grades. This is due to gangue and ions that either coat or create precipitates that passivate mineral surfaces, preventing collector adsorption. However, it is also known ions are capable of activating valuable minerals and gangue. Anincrease in collector chain length leads to an increase in the strength of the collector due to an increase in hydrophobicity. However, this order of strength may be affected by pH and IS as these affect the collector adsorption. The selectivity of collectors increases with a decrease in the collector chain length. pH also affects the selectivity of collectors as an increase in pH results in a decrease in grade. However, the stability of collectors is independent of chain length. A high collector dosage may not imply an increase in flotation performance as there is a risk of over-dosage. This may result in other reagents being overpowered in the pulp, leading to decreases in grades and recoveries. The first objective of this study was to investigate the differences in flotation performance when collectors of different chain lengths are used in synthetic plant water with increasing ionic strength. The second objective was to determine the interactive effects between collector chain length, collector dosage, and ionic strength of synthetic plant water on flotation performance. To address the objectives, a two-phase factorial design of experiments was created, with Phase one utilising SEX and Phase two, SIBX. The factors selected for investigation were the collector chain length, dosage and the ionic strength of synthetic plant water. Batch f lotation on a Merensky ore was utilised to obtain copper and nickel grades and recoveries which illustrated flotation performance. Additionally, batch flotation was used to obtain the entrainment factors of the two collectors at the different ionic strengths of SPW. Zeta potential measurements on chalcopyrite were utilised to determine changes to the mineral surface potential when the factors were varied. Sedimentation tests on the tails samples of the batch flotation tests provided information on the behaviour of the fines, and UV/Vis spectroscopy determined the concentration of residual xanthates present after flotation. i The study found that the longer chained collector, SIBX, behaved atypically to what has been observed in other studies. It obtained lower solids and recoveries than SEX in water with low ionic strengths. Furthermore, under these conditions, SIBX achieved the highest copper and nickel grades. Interestingly, as the ionic strength of the water increased, the trend was reversed. The copper recoveries were independent of the changes made to all the factors, however, the nickel recoveries did show slight variations. Both an increase in the ionic strength and collector chain length resulted in a decrease in the entrainment factor. Additionally, an increase in the ionic strength resulted in a less negative zeta potential. It was determined that there were interactive effects among the factors that were varied and concluded the factor with the largest impact on the flotation response (i.e. solids and water recovery and the recovery and grades of copper and nickel) was the ionic strength of the water. These conclusions emphasise the importance of investigating the effects of recirculating water within the flotation process. The determination of the effects on flotation performance by different collectors under varying water quality will provide more knowledge into the optimisation of reagent usage in mineral processing in the presence of recycled water. Subsequently, this will provide plant operators with more control over the performance of the process as reagent control may compensate for changes in water quality.
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    An investigation into the impact of residual reagents on flotation in response to process water recirculation
    (2023) Khan, Saahil; Manono, Malibongwe; Corin Kirsten
    In the mineral pulp phase of the flotation process, water makes up about 80-85% of the constituents, thus making water an important component. The increasing scarcity of water has resulted in greater environmental restrictions which have led to the necessity of mine operations recycling water from tailing dams, thickener overflow, dewatering and filter products. However, water quality is found to influence the process of ore flotation, the results of various studies investigating the effects of water and recirculating water have seen an adverse effect on flotation selectivity. The particular focus of the study was to consider the impact of dewatering reagents which may have been present in water recycled from the tailings back into the flotation process. The ore was from the Merensky reef which is found in the Bushveld Igneous Complex (BIC). The complex contains the world largest deposits of platinum group elements. About 75% of the world's platinum reserves and 50% of the world's palladium reserves are in the bushveld igneous complex, making it one of the most economically significant mineral deposit complexes in the world. The primary dewatering reagents considered were flocculants and coagulants. There are two mechanisms by which flocculation occurs: the polymer bridging theory and the patch model. Polyacrylamides (PAM) are the most common flocculants. Coagulants use a charge neutralisation mechanism to take effect with the most common type being used are salts containing highly charged cations such as Al 3+ and Fe3+ . The experimental design chosen was a factorial with midpoint analysis. Three factors that were considered at varying dosages; the depressant, flocculant and coagulant. The two levels were high and low (where low was no addition of the respective reagent and high was equivalent to the concentrate seen on site recirculated process water). The key performance parameters used to determine effects were solid recovery, water recovery, copper and nickel mineral recovery, copper and nickel mineral grade, residual concentrations of collector and depressant pre and post flotation as well as particle settling of the tails. For all test conditions relative to the base condition where none of the varied reagents were added, the solid and water recovery increased, the nickel recovery increased slightly while its grade decreased, the copper recovery was unaffected, but the grade decreased, there was no impact on the residual concentration of the collector and depressant pre and post flotation. The settling of the tailings also remained unaffected. The solids and water recovery increased due to the agglomeration of finer particles in the system which resulted in the particles having better momentum for particle bubble attachment and faster recovery rates. There may have been a slight effect of the increase in ionic concentration of the water caused by the presence of additional reagents which resulted in a more stable froth and may have increased the recoveries of the solids. The recoveries of the value bearing minerals did not change, the grade however decreased because the increase in solids recoveries is attributed to increased gangue recovery owing to the fine particle size, which, in the presence of dewatering agents would have a faster recovery rate. The residual reagents concentration did not change as the primary impact on their adsorption would have iv been a change in the surface area due to an increase in particle size, which was not varied by grinding in this study. However, owing to the addition of dewatering agents, the particles may have agglomerated and hence become larger. The depressant adsorption may have been unimpacted owing to the inability of the depressant to fully cover the particle surfaces under standard flotation conditions. The collector adsorption was unimpacted and this is assumed to be owing to the concentration of the dewatering agents used within this study not being high enough to compete with the collector for mineral surface area. The settling of the tails remained unaffected as the finer particles which, in the presence of dewatering agents reported to the concentrate and had little impact on the composition of the tails. It can be deduced from the results that the possible introduction of the dewatering reagents into the flotation system due to recycling of tailings water may be detrimental to the system. The primary impact of flocculants and coagulants in the flotation process was the introduction of more gangue in the concentrate which decreases the grade of the concentrate and will need to be further refined downstream. Furthermore, there is no positive impact on the settling of the tails, implying that the flocculant and coagulant action is suppressed during flotation and further flocculant and coagulant would need to be added during dewatering but may need careful screening prior to the recirculated water entering the milling and flotation stages for a mineral processing circuit
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    Considering the action of frothers under degrading water quality
    (2020) Tetlow, Sarah; Corin, Kirsten; Manono, Malibongwe
    Froth flotation is a highly water-intensive process which is under scrutiny due to scarce fresh water supplies and increasingly strict environmental regulations with regards to polluted water discharge. This is driving the mining industry to use recycled water for their operations, which is usually sourced from tailings dams or concentrator thickeners. This means that the recycled water can contain elevated levels of dissolved solids which consist of various ions and other contaminants such as residual reagents. This presents a problem in the flotation circuit as these dissolved solids tend to affect the water quality and can impact the efficiency and performance of flotation operations. The stability of the froth is known to strongly affect flotation performance and thus the grade and recovery of the valuable minerals. Literature shows that both frothers and ions reduce bubble coalescence, and stabilise the bubbles that form, resulting in greater froth stability. Considering that the level of ions in process water is on the rise, and both variables act on the froth in a similar manner, it is becoming increasingly important to understand how frothers behave under conditions of increased ionic strength. If it can be determined how these variables interact, then it may be possible to manage frother dosage in operations that recycle process water with the aim of reducing the quantity and cost of frothers and limiting the need for large amounts of fresh water, while still maintaining flotation performance. Therefore, this study was undertaken to investigate how frother dosage and ionic strength, both individually and simultaneously, affect the froth stability and therefore flotation performance. This study was limited to varying the frother type, frother dosage and ionic strength whilst keeping all other experimental conditions constant. Batch flotation tests were carried out involving the bulk flotation of chalcopyrite and pentlandite. Flotation performance was evaluated by examining the water, solids, copper and nickel recoveries, and the grades of both copper and nickel. The ore used for this study was Kevitsa ore from Finland. Both the individual effects of frother dosage and ionic strength and their simultaneous action were analysed. It was found that increasing the frother dosage stabilised the froth and increased the recovery of water and solids but had no impact on the recovery of copper and only a slightly positive influence on the recovery of nickel. At the same time, the grades of both copper and nickel were found to decrease, likely due to increased gangue recoveries. Increasing the ionic strength also stabilised the froth which increased the recovery of water and solids, but both the recoveries and grades of copper and nickel were not significantly affected. Examining both variables simultaneously revealed that ionic strength was more influential than frother dosage in the recovery of water with the opposite being true for the solids recoveries. This means that a simultaneous increase in ionic strength and decrease in frother dosage by the same amount will increase the water recoveries and decrease the solids recoveries. It will also slightly decrease the nickel recoveries while having no effect on the copper recoveries. The grades of both will either increase or remain the same. Overall, managing the frother dosage under conditions of increased ionic strength, while still maintaining flotation performance, is possible and could result in a decrease in the quantity and cost of frothers required for flotation. It may also allow the mining industry to recycle more of their water without the need for extensive cleaning which in turn will reduce the amount of fresh water required for flotation and reduce environmental discharge. However, because ionic strength and frother dosage have varying levels of influence and therefore must be monitored, the amount by which the ionic strength of the water is allowed to increase, and the amount by which the frother dosage is decreased, need to be tailored to suit the needs of the plant with regards to water recovery and the recoveries and grades of the valuable minerals.
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    Editorial for Special Issue “Water within Minerals Processing”
    (Multidisciplinary Digital Publishing Institute, 2022-03-14) Corin, Kirsten; Smart, Mariette; Manono, Malibongwe
    The products of mining are key to the technology development of the future [...]
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    Evaluation and optimisation of the performance of a multi-integrated lab-scale plant for the treatment of dairy wastewater
    (2025) Ramsuroop, Jyestha; Basitere, Moses; Manono, Malibongwe
    South Africa's dairy sector, producing 3.4 million tonnes of milk in 2019, generates significant wastewater, estimated at 2.5 times the volume of processed milk, or approximately 8.5 million tonnes annually. This wastewater poses serious environmental risks due to its high organic content, potentially leading to eutrophication and hypoxic zones in water bodies. Effective treatment methods are essential to mitigate these impacts. This study evaluates the performance of a lab-scale wastewater treatment plant, combining various biological processes previously used for abattoir wastewater (AWW), given the similarities between AWW and dairy wastewater (DWW) in terms of high organic and fat content. In anticipation of the challenge of clogging which has been prevalent in previous studies, an investigation was done into the use of okra as a biological coagulant which could possibly be integrated with the system. The research focuses on optimizing individual treatment units and assessing their collective performance in treating DWW. Initial challenges included operational errors, such as the overuse of Morma in pre-treatment, leading to increased biomass production and elevated Chemical Oxygen Demand (COD). Despite subsequent corrections improving system stability, fluctuations persisted, particularly in the Expanded Granular Sludge Bed Reactor (EGSBR). COD removal rates ranged from 60% in week 3 to 26% in week 5, highlighting the system's potential but falling short of traditional anaerobic digestion (AD) systems, which can achieve up to 90% COD removal. However, the system performed better with higher raw COD levels, indicating its efficacy in treating wastewater with elevated COD content. EGSBR stability issues were attributed to clogging and biomass washout, exacerbated by a reduced pre-treatment hydraulic retention time (HRT) of 12 hours. Analysis of fat, oil, and grease (FOG) removal revealed inconsistent performance, with the highest removal rates occurring in weeks with FOG content exceeding 6000 mg/L DWW. FOG removal rates ranged from 27% to 94%, surpassing those of previous AD reactor studies. The observed correlation between FOG content and system performance warrants further investigation. Total Suspended Solids (TSS) removal rates served as indicators of reactor stability issues, with increased TSS indicating biomass washout. Decreasing pre-treatment HRT adversely affected reactor stability, highlighting the importance of optimizing pre-treatment parameters. Additionally, the use of okra seeds as a coagulant was explored, showing promising results in reducing TSS and COD from DWW. The optimal dose was 5g per 2L of DWW, achieving the highest removal rates for both TSS and COD. This suggests that okra seeds offer an eco-friendly alternative to traditional coagulants like alum. Integrating coagulant treatments with biological agents could enhance the removal of solids and FOGs, addressing the stability issues observed in the EGSBR and improving overall system performance.
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    Investigating the effect of water quality on the adsorption of a xanthate collector in the flotation of a sulphide ore
    (2018) Manenzhe, Resoketswe; Corin, Kirsten; Wiese, Jennifer; Manono, Malibongwe
    Environmental concerns necessitate the recycling of process water within mining operations. On average, recycled water contains more dissolved solids than fresh water. Since water is used as both a transportation and process medium, it is expected that changes in its quality will affect plant processes. Flotation is a process that is acutely sensitive to the immediate conditions of the system. Literature suggests that the efficiency of flotation separation is driven by the hydrophobicity that can be achieved by the mineral particles meant to be floated. The hydrophobicity is in turn driven by the adsorption of specialised reagents i.e. the collectors. Since collectors are added such that they adsorb at the liquidparticle interface, it stands to reason that changing the chemical composition of the aqueous phase will affect the collector adsorption, and hence the flotation response of target minerals. In this study, a sulphide copper ore from the Zambian Copperbelt was floated in synthetic plant waters of varying ionic strengths, and with different concentrations of the collector sodium isobutyl xanthate (SIBX). The synthetic plant waters were prepared by adding varying concentrations of inorganic salts to distilled water in order to achieve process water compositions that reflect water compositions typically found in mining plants. Additionally, a nickel-copper ore from Lapland Finland was floated in the synthetic plant waters as well actual plant waters. To account for the latter ore’s polymetallic nature, the collectors aerophine and sodium isopropyl xanthate (SIPX) were used sequentially. The objective of the study was therefore to investigate the effect of water quality on collector adsorption in the flotation of sulphide ores. The study showed that water quality has a quantifiable effect on SIBX and SIPX adsorption. The respective effects of water quality and collector adsorption on ore flotation could not be irrefutably decoupled. However, it could be concluded that of the tested waters, the copper thickener overflow was the least conducive to xanthate adsorption and valuable mineral recovery. On the other hand, collector adsorption was favoured by waters such as the raw and standard process. However, increased adsorption did not necessarily result in improved grades and recoveries. The study further showed that in the case that the dissolved ionic species are identical, increasing the ionic strength of water yields a linear decrease in xanthate adsorption, and that recycling SIPX retained in flotation waters resulted in reduced separation selectivity.
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    Recirculated Process Water in the Flotation of Sulfides
    (2023) Ngau, Michael; Manono, Malibongwe; Corin Kirsten
    Water scarcity has affected the availability, quality, and quantity of water available for use at water-intensive mineral processing concentrator plants. In response, more sustainable water reuse strategies have gained traction and proved beneficial by reducing used water effluents and freshwater withdrawals through the recycling of effluent water. The performance of concentrates using recycled water has been a headline topic of research. However, water recycling leads to a change in water quality in terms of species present in solution and physio-chemical properties, to the detriment of the flotation performance of sulfide ore. Froth stability is the ability of the foam to resist bubble coalescence and bubble bursting and is an integral property of the pulp with implications for flotation recovery and selectivity. This study investigates the impact of a change in water quality through the consecutive recycling of recovered tailings water, using a filter press to separate the tailings solids from batch flotation tests of a UG2 ore. The study investigated the impact of the addition of recycled water to the sequential milling and batch flotation tests of a UG2 ore on the froth stability of the tailings slurry and recovered water samples from the tailings and concentrate slurry. The experimental methodology developed in this paper was developed to: (1) monitor the accumulation of compounds and elements in the process water through the comminution and flotation facilities; (2). Investigates the impact of point of addition of recirculated water (i.e. to the mill or the float cell.). (3) Investigate the impact water recirculation on froth stability, pulp chemistry, mass and water recovery, coagulation and the grade and purity of sulphide concentrates. The techniques utilized in the project were as follows: (1) Pulp chemistry analysis using a multiprobe meter to analyse electrical conductivity (EC), pH, Dissolved Oxygen (DO%); Oxidative Redox Potential (mV) (2) Compound and elemental analysis and coagulation through UV/Vis and X-Ray fluorescence (3) Foam and Froth stability measurements of the tailings pulp and recovered water samples. The technique used to evaluate froth stability was a dynamic froth stability tests that observes the build-up of a set sample volume of slurry or recovered water sample in a non-overflowing froth column, agitated and aerated with a constant air feed of 7 L/min, measured and monitored for 20 minutes. The Bikkermans stability parameter and kinetic models of build-up were developed from experimental values to establish theoretical maximum froth height, bubble lifetime, and gas holdups of foams and froths was developed. Water recirculation leads to a change in the water quality and an increase in froth and foam stability due to the increase in the concentration of ions reducing the electrostatic stabilisation, leading to the formation of smaller bubbles with an improved resistance to coalescence and rupture, developing high froths visible from the different in maximum froth. The change in water quality also impacts the bubble lifetime, leading to longer bubble lifetimes, which slow down the froth development visible in the kinetic models developed. The point of addition of recirculated leads to a difference in the foam and froth stability, with recycling to the float cell achieving a higher froth stability due to higher ionic concentrations. Water recirculation lead to a increase in the solids and water recovery compared to baseline tests with float recirculation recovering 20 % more solids and 17 % more water as compared to mill recirculation at a higher recovery rate. Concurrently higher Cu recoveries when using recycled water, especially when recycled to the float cell, however reduced the grade of sulphides recovered due to an increase in gangue entrainment. This due to the higher ionic strength of the recycled water as observed in the higher concentrations of Ca2+, Mg2+, SO4 2- , Cl- , and higher EC, which are especially higher in float cell recirculated water. In addition, the residual reagent concentrations present in the tailings water samples were at ppm level due to high reagent mineral interaction. The significant decrease in DO% in mill recirculation's shows the impact of galvanic interactions on the pulp chemistry. In conclusion water recycling is a viable and efficient water reuse strategy that should be employed due to the improved recoveries, with keen monitoring of grades achieved.
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    Simulating the Effect of Water Recirculation on Flotation through Ion-Spiking: Effect of Ca2+ and Mg2+
    (2020-11-19) Dzingai, Mathew; Manono, Malibongwe; Corin, Kirsten
    Froth flotation is a multifaceted complex process which is water intensive. The use of recycled water as an alternative source of water to meet water demands of the process may introduce deleterious inorganic ions that affect the mineral surface, pulp chemistry, and reagent action, hence the need to establish whether threshold ion concentrations exist beyond which flotation performance will be adversely affected. This is of paramount importance in informing appropriate recycle streams and allowing simple, cost-effective water treatment methods to be applied. Here we report that increasing ionic strengths of synthetic plant water (SPW); 3, 5, and 10 SPW respectively, resulted in an increase in water recovery in the order 0.073 mol·dm−3 (3 SPW) < 0.121 mol·dm−3 (5 SPW) < 0.242 mol·dm−3 (10 SPW), indicating an increase in froth stability as higher water recoveries are linked to increased froth stabilities. This behavior is linked to the action of inorganic electrolytes on bubble coalescence which is reported in literature. There was, however, no significant effect on the valuable mineral recovery. Spiking 3 SPW to 400 mg/L Ca2+ resulted in higher copper and nickel grades compared to 3 SPW, 5 SPW, and 10 SPW and was deemed to be the Ca2+ ion threshold concentration for this study since 3 SPW spiked with further Ca2+ to a concentration of 800 mg/L resulted in a decrease in the concentrate grade. The spiking of 3 SPW with Mg2+ resulted in higher copper and nickel grades compared to all other synthetic plant water conditions tested in this study.
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    The effect of flotation reagents on the coagulation and dewatering of flotation tailings
    (2025) Chidzala, Unaswi; Manono, Malibongwe; Corin, Kirsten
    Sustainable water management in mining operations is necessary due to South Africa's water scarcity, especially in PGM mining, where flotation tailings pose serious difficulties. Water constitutes 80-85% of the mineral pulp in the flotation process, emphasising the significance of its role. However, water recycling from tailings dams and dewatering systems is becoming increasingly essential, yet it is impeded by the adverse effects of residual reagents on flotation selectivity. Utilising Merensky ore from the Bushveld Igneous Complex (BIC), this study examines how flotation reagents, including coagulants, flocculants, depressants, and collectors, affect the coagulation and dewatering of flotation tailings. The BIC has 75% of the world's platinum reserves and 50% of palladium reserves, making it one of the most commercially significant mineral deposits. The effects of different reagents, their combinations, and their effects on sedimentation, turbidity reduction, and particle size distribution (PSD) were assessed in a set of 15 tests. The study investigates coagulants (e.g., Fe2⁺ salts), that operate by charge neutralisation, and flocculants (e.g., polyacrylamides), that work through polymer bridging or patch processes. Systems which comprise flocculants or coagulants demonstrated higher settling rates, achieving turbidity reductions beyond 500 NTU/min within the initial five minutes, significantly exceeding the performance of systems utilising of only collectors or depressants. The combination of flocculants and coagulants in two-component systems resulted in the most fast settling rates, emphasising their synergistic effect. PSD analysis indicated that collector or depressant only systems retained particles under 200 μm, whereas flocculant and coagulant systems had broader distributions (up to 1100 μm), which corresponded with effective sedimentation. To improve polymer adsorption performance, tailored reagent optimisation exploited optimal particle size distributions and doses to overcome the obstacles presented by ultrafine particles (<1 μm). Rheological analyses demonstrated shear-thinning behaviour in coagulant-flocculant systems, decreasing slurry viscosity under shear to improve flowability, pumping efficiency, and dewatering. According to microstructural investigations (PSD, SEM), larger flocs improved sedimentation and reduced water entrainment, which is consistent with Stokes' law. These results demonstrate that flotation reagents can be strategically applied to improve dewatering efficiency and effectively tackle water recirculation challenges. The study stresses the optimisation of reagent combinations to enhance water quality for reuse in flotation and to promote dry stacking methods, hence facilitating sustainable mining in regions with limited water supplies.
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    The effect of ion accumulation owing to water recycling on flotation performance
    (2019) Dzingai, Mathew; Corin, Kirsten; Manono, Malibongwe
    With the drive to reduce water usage globally, the mining sector must reassess its water usage as it has in the past contributed greatly to environmental degradation due to effluent discharge, tailing disposal and process water seepage into the water-table. Mineral beneficiation entails different unit operations; amongst them is froth flotation. Froth flotation is a multifaceted complex process which is water intensive and to manage water usage, the global mining industries are now recycling water. The recycled water may contain deleterious ions that affect the mineral surface, pulp chemistry and reagent action, hence the need to establish whether threshold concentrations exist beyond which the flotation performance will be adversely affected. This is of paramount importance in informing appropriate recycle streams and allowing simple, cost-effective water treatment methods to be applied. To better understand the influence of water recycling in flotation, a low-grade Cu-Ni-PGM sulphide ore was used. This study investigated the effects of increasing ionic strength as well as increases in specific ion concentrations to determine whether these selected ions had beneficial or deleterious effects on the flotation process. Copper and nickel were the target metals, floated as chalcopyrite and pentlandite, respectively. Their recovery and grade under different conditions was used as a measure to quantify whether a threshold ion concentration existed. The key performance indicators used were: (a) water recovery, (b) solids recovery, (c) valuable metal recovery, (d) grade of the recovered concentrates and (e) electrical conductivity. While a complex background water chemistry of 3 SPW was maintained for the spiking tests, ion spiking was intended to mimic the recycling of water and the most prevalent ions which would likely be recycled and therefore accumulated, such ions as: Ca2+, Mg2+, NO3 - , SO4 2- and S2O3 2-. These ions were chosen based on speculation from relevant literature that they might impact the flotation performance due to their influence on pulp chemistry and reagent interaction. This was achieved by conducting sequential batch flotation and electrical conductivity (EC) tests. Batch flotation tests were performed to investigate the effect of different ionic strength conditions on the overall flotation performance. The same ionic strengths and spiking concentrations were used for froth (or foam) column studies with a focus on tracking the ion concentration distribution between the froth and the slurry (or solution) by means of measuring the EC of each of the froth and the pulp (solution) phases. The differences implied whether the ions were selectively concentrated at the air-water or solids-water interphases in a 3-phase system or likewise at the v bubble surface or within the solution for a 2-phase system. This distribution of ions was linked to the other key performance indicators. Increasing ionic strength; 3, 5 and 10 SPW respectively, resulted in an increase in water recovery in the order 3 SPW < 5 SPW < 10 SPW, indicating an increase in froth stability due to inhibition of bubble coalescence at high ionic strength. There was, however, no significant effect on the valuable metal recovery. Most of the nickel was recovered in the copper circuit which was expected as on-site conditions were not maintained at the laboratory scale, no lime was added to adjust the pH in the copper circuit and an EDTA chelating agent was not included in the nickel circuit. Spiking 3 SPW with 800 ppm Ca2+ results in considerably higher water recovery per unit solids recovered compared to 3 SPW, 5 SPW, 400 ppm Ca2+, 350 ppm Mg2+, 700 ppm Mg2+. 400 ppm Ca2+ resulted in the highest copper and nickel grade and was deemed the threshold for this study while for Mg2+ threshold lies outside of the range considered for this study. 10 SPW shows a decrease in the copper and nickel grade while the copper and nickel recoveries were not significantly impacted. The presence of the Ca2+ and Mg2+ at high concentrations leads to gangue activation which as a consequence will result in decreased grade. 880 ppm NO3 - gave the highest copper and nickel grade compared to 3 SPW while increasing the S2O3 2- from 60 to 78 ppm resulted in an increase in nickel grade. 1200 ppm SO4 2- and 880 ppm NO3 - were deemed the threshold concentration for these anions, above which the flotation performance declines, while for S2O3 2- the threshold lay outside the range considered for this study. This study has shown that the accumulation of ions within plant water, owing to recycling, is, in general, beneficial to flotation. This study has also shown that there is a concentration for each ion beyond which it is no longer beneficial to flotation. While this finding is clearly ore and ion dependent, it gives an indication as to the need for water treatment and considering the threshold concentrations found, may direct operations to suitable treatment methods for their systems.
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    Water quality effects on the bubble-particle attachment of sulfide minerals
    (2021) October, Lisa Louise; Corin, Kirsten; Manono, Malibongwe
    probability, mass of particles recovered in the ACTA and further validation with microflotation recovery that bubble-particle interaction increases as the ionic strength of the plant water increases. This was the case with both chalcopyrite and galena particles. Literature would suggest that this result of an increase in particle recovery and bubble-particle attachment may be due to the increase in concentration of inorganic electrolytes; which leads to the compression of the electrical double layer and the subsequent faster rupturing of the film at the air – water and solid – water interfaces resulting in faster bubble-particle attachment. Zeta potential measurements showed that the surface charge of the particles became less negative as the ionic strength of the water increased; this indicates the adsorption of cations on the particle surface. Furthermore, at the pH these tests were conducted (pH 6.5 to 7), the surface potential was closer to 0 mV as the ionic strength increases. A surface charge of 0 mV is known to result in particle agglomeration; therefore, in addition to faster rupturing of the film between the bubble and particle, particle agglomeration may also be responsible for the increase in bubble-particle attachment with increasing ionic strength of the plant water. Adsorption studies across all minerals showed that less xanthate adsorbs on the mineral surface as the ionic strength of the plant water increases; this indicates that the increase of inorganic electrolytes hindered xanthate adsorption on the mineral surface. Intuitively it is expected that this decrease in xanthate adsorption with water of higher ionic strength will translate to lower recoveries and bubble-particle attachment; the opposite was shown to be the case. The effect of the synthetic plant waters at pH 11 on bubble-particle attachment was also studied in this work. Zeta potential measurements showed a distinct increase in surface charge of all minerals with the three waters at pH 11; it was thus thought to be of interest to investigate this effect on bubble-particle attachment. Speciation diagrams of these waters show oxyhydoxyl constituents present at pH 11. Therefore, the presence of these species on the mineral surface is the reason for the increase in mineral surface charge. At pH 11, poor mineral recoveries regardless of the water type were observed as compared to the recovery with these waters at the natural pH (pH 6.5 to 7). It can thus be concluded that these oxyhydroxyl species hinder the flotation of the pyrrhotite particles as well as processes such as collector adsorption and the action of the electrical double layer. Another objective of this study was to ascertain whether certain ions within the plant water existed that either have a negative or positive effect on the bubble-particle interactions. If it is the case that one specific ion has a negative effect on bubble-particle attachment, then the removal of this ion would be a more cost effective and environmentally friendly exercise compared to treating the water or bringing in fresh water. Microflotation and ACTA studies with chalcopyrite, galena and pyrrhotite showed that Ca2+ containing solutions resulted in lower recoveries and attachment probabilities respectively. While the NaNO3 solution resulted in the highest recoveries and attachment probabilities across the three sulfide minerals. These results were observed both in the presence and absence of SIBX. Studies in literature have shown that the stability of the hydration layer in monovalent solutions of high ionic strength result in shorter induction times and thus improved bubble-particle attachment. This study also showed that the monovalent Na+ showed higher attachment probability and mineral recovery. Less xanthate was adsorbed on the sulfide mineral surfaces in Ca2+ containing solutions, hence the poorer bubble-particle attachment with the fundamental attachment timer and microflotation systems. The increased zeta potential and therefore high surface charge on the mineral surface in Ca2+ containing solutions may hinder the adsorption of xanthate as other authors have proposed that the collector adsorption reaction is driven by the electrical double layer and high surface charges may hinder this reaction. Therefore, it may be that the passivation of Ca2+ on the mineral surface may hinder the action of collector; as Ca2+ may compete with collector ions for sites on the mineral or that the high surface charge may be hindering the collector – mineral reaction. This work produced a number of outcomes. The validation of the use of the ACTA as a means of measuring mineral floatability through comparison with classical microflotation tests was displayed. The importance of showcasing both the attachment probability and mass of particles collected when taking measurements with the ACTA was evident in this work. This work also showed that the performance of bubble-particle attachment under ionic solutions was attributed to underlying factors such as the surface charge and collector – mineral adsorption. The adsorption of xanthate decreased in waters of high ionic strength and Ca2+ containing solutions. Waters of higher ionic strength further resulted in more positive surface potential and possible particle agglomeration resulting in higher recoveries. Bubble-particle attachment was also seen to reduce dramatically at pH 11 under the various synthetic plant waters; this was attributed to the presence of oxyhydroxyl species depositing on the mineral surface inducing surface hydrophilicity. Ca2+ was identified as resulting in lower mineral recoveries and attachment probabilities; Ca2+ passivated the sulfide minerals' surface more than Na+ and less collector adsorbed on the mineral surface in the presence of this ion. The latter result alludes to the fact that higher attachment probabilities and recoveries may be achieved by the removal of Ca2+ in recirculated plant water. The ACTA was constructed with the intent of it being a quick diagnostic tool on flotation plants to assess the bubble-particle efficiency under varying conditions; the outcome of this work showed that this instrument is a viable option as a measure for particle floatability. It is further believed that the findings of this work will provide flotation operations with an understanding of how specific ions within plant water affect bubble-particle attachment; which will allow for the water quality to be tailored towards achieving high mineral recoveries.
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    Open Access
    Water Quality Impact on Flotation Response: A Focus on Specific Ions and Temperature
    (2022) Charamba, Apollonia Anesu; Corin, Kirsten; Manono, Malibongwe
    Factors such as water scarcity and environmental restrictions have brought about the need to recycle process water within the mining industry. This recycling however causes an accumulation of ions in the process water which may affect plant processes since processing routes are water-intensive. Seasonal temperature differences affect the water quality through variation of the available recycled water within the plant between the summer and winter seasons. Literature highlights that flotation efficacy is reliant on the differences in mineral surface properties. Chemical reagents are used to increase the separation of valuable mineral (which is usually hydrophobic) from unwanted gangue (which is usually hydrophilic). Literature also highlights that different ores and different minerals react differently to temperature variation. The presence of certain species in process water with water variation has been seen to impact the flotation response. It stands to reason that simultaneously varying the temperature and specific ions concentrations will affect the interaction of minerals and reagents thus affecting the flotation response of target minerals. This is a temperature-controlled flotation chemistry study that adopted a three-level-four-factor (3 4 ) factorial experimental design to evaluate the simultaneous effects of temperature and specific ions; Ca2+, SO4 2- and S2O3 2- as well as determined the possible interactive effects between the chosen parameters. A low-grade copper-nickel platinum group element (Cu-Ni-PGE) ore from the Kevitsa Igneous Complex in Lapland, Finland was floated in a complex water matrix that mimics onsite process water. This ore is remarkably similar to the Merensky ore in South Africa, meaning that the results of this study may apply to the South African mining industry. Sequential batch flotation tests were conducted, targeting copper flotation with Aerophine 318A as the copper collector. Consequently, followed by targeting nickel flotation with sodium isopropyl xanthate (SIPX) used as the respective collector. Carboxymethylcellulose (CMC) was the depressant used and Nasfroth 240 was the frother used. The objective of this study was therefore to investigate the effect of specific ions and temperature, relevant to onsite process water recycling and temperature variations brought about by seasonal changes, on the separation of gangue from valuable minerals in batch flotation of a low-grade Cu-Ni-PGE ore. The study demonstrated that there are specific ion concentration ranges beyond which flotation performance was adversely affected and other ranges beyond which no observable effect on flotation was visible. Based on this understanding, it may be possible to predict the ideal operating conditions for the number of water recycles in a plant. The effects of single variables and the interactions between variables were reflected in some responses. The higher ionic concentrations and their corresponding ionic strengths resulted in a more stable froth in comparison to lower ionic concentrations and consequently an improvement in the recoveries. Water and solids recoveries were impacted by the interaction of Ca2+ and SO4 2- . At high SO4 2- concentration an increase in Ca2+ increased the mass of water and solids recovered. An increase in SO4 2- alone caused an increase in copper recovery whilst decreasing the copper grade. S2O3 2- alone affected the nickel recovery. An increase in S2O3 2- caused an increase in nickel recovery whilst the nickel grade was affected by the interaction of S2O3 2- and temperature. Furthermore, copper showed similar trends as those observed for nickel in the responses for the mineral grade. At high S2O3 2- concentration there was no observable change in the nickel and copper grades when temperature increased. At low S2O3 2- concentration, an increase in temperature decreased the nickel and copper grades. In addition to the interactive effect of temperature and S2O3 2- , nickel was more temperature sensitive in comparison to copper. It may thus be concluded that the postulated hypotheses are supported by this work.