A study was carried out to improve the flotation selectivity between galena and sphalerite during the flotation of a Cu-Pb-Zn sulphide composite ore from the Rosh Pinah Mine (Namibia). Xanthate collectors were found to be unselective for the flotation of the Rosh Pinah composite sample. It was observed that the recovery of sphalerite increased with both the recovery of galena and the concentrate mass pull. In addition, the recovery of sphalerite increased after activation with Cu(II) ions while that of galena decreased when the composite was dry ground in a mild steel mill with mild steel grinding media. However, the recovery of galena was not affected after wet milling in a stainless steel mill. The recovery of Cu(II)-activated sphalerite was independent of the milling environment (wet or dry) and grinding media. The activation of sphalerite by cuprous cyanide complexes, which are present in the recycled water, was clearly shown in this study. Both batch flotation tests and XPS analysis have confirmed that sphalerite was activated by copper(I) from the cuprous cyanide complexes. The recovery of copper(I)-activated sphalerite increased further when the composite was dry milled as compared to wet milling. Batch flotation tests have shown that the use of cyanide alone is not efficient for the depression of sphalerite due to the mineralogical texture of the Rosh Pinah ore. A large quantity of galena locked and/or attached to sphalerite was observed in the lead concentrate. Their prevalence increased with increasing particle size. The use of both cyanide and zinc sulphate improved the depression of sphalerite much better than cyanide alone. A flowsheet has been proposed to improve selectivity between galena and sphalerite in the lead flotation circuit. It includes the regrinding of the lead rougher concentrate prior to the cleaning stage due to poor liberation between galena and sphalerite. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

A gradual depletion of high-grade ores, coupled with the growing demand for mineral commodities across the world has culminated in the increased exploitation of lean-grade ores with complex mineralogy. The mineral processing industry commonly uses an extensive range of inorganic, naturally derived or synthetic organic reagents in the separation of valuable minerals from the ore. Froth flotation is a commonly used separation technique to float or depress different sulfide minerals from the ore, based on their surface properties. In recent times, biological processes have been attracting attention in mineral processing and metal recovery operations due to a number of factors, especially lower operating costs, lesser energy consumption and their environment friendly nature. The use of microorganisms and their direct derivatives in mineral processing, hydrometallurgy and in the bioremediation of mineral industry discharges has led to the emerging area of “Mineral Bioprocessing”. In this study, a family of four microorganisms belonging to the Bacillus species, viz., Paenibacillus polymyxa, Bacillus circulans, Bacillus megaterium and Bacillus subtilis was used to ascertain the selective floatability of sphalerite from a sphalerite-galena mineral mixture. These bacteria are Gram positive, mesophilic, neutrophilic, aerobic and spore forming. The major objectives of the investigation include: a) Identification and characterization of bioreagents derived from Bacillus species for the flotation of sphalerite from a sphalerite-galena mixture b) Optimization of the flotation process for the enhanced recovery of sphalerite using specific bioreagent combinations c) Modes and mechanisms of bacterial adaptation to minerals and their consequent effects on the flotation of sphalerite and galena d) Elucidation of the mechanisms of microbe-mineral interactions and the role of extracellular secretions in sphalerite flotation column and their N-terminal residues were identified using Edmann N-terminal sequencing. Additionally, sequences of several internal peptides from both the proteins were determined using Tandem Mass Spectrometric techniques. A database search revealed that the sequences of these peptides are unique and have not been reported earlier. It was established that the bacterial cells give high flotation recovery of sphalerite under buffered conditions and that it took place only in the presence of anionic buffers. Additionally, the viability of the bacterial cells was not required for the flotation of minerals. A major finding of this study was that other than extracellular DNA (eDNA), none of the other bacterial surface components like teichoic acids, surface proteins, polysaccharides played a positive role in the flotation process. Nucleic acids, more particularly single stranded DNA (ssDNA), facilitated sphalerite flotation relative to double stranded DNA (dsDNA). A probable mechanism of ssDNA -mediated selective flotation of sphalerite has been presented. A negative role for non-DNA surface components was also observed. This led to the realization of the need for an optimum ratio of DNA to non-DNA components in the selective flotation of sphalerite from a sphalerite-galena mixture. It was found that the surface physiochemical properties of the mineral adapted bacteria differed significantly from that of the unadapted bacteria. Adaptation enhanced the flotation recoveries of the corresponding mineral vis-à-vis the unadapted bacteria. Sphalerite adapted bacteria secreted more extracellular proteins while the galena adapted bacteria secreted more polysaccharides compared to the unadapted bacteria. Sphalerite adapted bacteria selectively floats more sphalerite from the mineral mixture than the galena adapted as well as the unadapted bacteria. It was evident from the electrokinetic studies that the surface charge of the chosen sulfide mineral adapted bacteria was less negative relative to the unadapted bacteria. This phenomenon was observed with all the four bacterial species used in this study. A noteworthy finding was that the bacteria especially B.circulans induce a change in morphology from rod to sphere as a strategy during adaptation to a toxic mineral such as galena. This phenomenon has been shown to involve changes in crucial cell wall components as well as changes in the levels of expression of bacterial cytoskeleton elements involved in the maintenance of the rod shape. This aspect of the study involved the partial sequencing of the B.circulans homolog of the key cytoskeleton gene, mreB (B gene in murien cluster e), using the Polymerase Chain Reaction (PCR) followed by DNA sequencing. A Genbank search indicated that this is the first report of the sequence of B.circulans mreB gene. This was followed by measuring the hypothesized downward changes in the levels of expression of the mreB gene by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The possible mechanisms of the adaptive morphological changes and of the interaction of the chosen sulfide minerals with the family of microorganisms studied have been discussed with respect to their bioflotation efficiency.

Due to the increasing demand for processing low-grade ores, larger volumes of material are being processed. Therefore, the size of flotation equipment has significantly increased for the past decades. The studies related to scale-up are and will remain to be crucial in terms of designing larger flotation equipment. One of the most important factors for flotation scaling-up is the “flotation rate constant”. Hence, the main aim of this investigation was to understand the scale-up criteria when the size of different laboratory-scale cells increases, using the Outotec GTK LabCell®. This was done by assessing the influence of impeller speed, as a hydrodynamic variable, on the flotation performance. Recovery was found to increase with an increase in the cell area to rotor diameter ratio. Flotation rate and recovery increased with an increase in the impeller speed until a certain point that it eventually decreased for the 2 l and 7.5 l cells. For the 4 l cell, the flotation rate and recovery decreased with increasing the impeller speed. The impeller speed of 1200 rpm allowed a successful scale-up based on the flotation rate constants and recovery when increasing the size of the cells. Maintaining the impeller speeds constant at 1300 rpm increased the flotation rate constants and recovery when increasing the cell size from both the 2 and 4 l cells to the 7.5 l cell. A further increase in the impeller speed to 1400 rpm also produced the flotation rate constants and recovery to increase as the cell size increased from both the 2 and 4 l cells to the 7.5 l cell. However, when increasing the cell size from 2 l to 4 l, good results were also observed for all impeller speeds. The products concentrate seem to become finer when decreasing the cell size, with only a few exceptions. The recovery of particles larger than 38 μm was found to differ considerably less among the different scales.

No description available.

Thesis (DEng (Process Engineering))--University of Stellenbosch, 2005. / This dissertation covers research carried out over the past 25 years in the area of flotation. Flotation is one of the most widely used processes in the beneficiation of minerals. The process is characterized by a number of important sub-processes each with their own set of critical variables. These include: • The pulp phase which is influenced by variables such as pH, Eh, the nature of the chemical reagents used, the chemical state of the surface of the ore particles, etc. • The reactor in which the process occurs, viz. the flotation cell, which is influenced by factors such as aspect ratio, degree of agitation, mechanical design criteria, energy input, aeration processes, etc. • The froth phase which is arguably the heart of the process and probably the least well understood but which is influenced by factors such as size and shape of the solid particles in the froth, the nature of the surfactant used, the aeration rate, the water recovery rate, the froth depth, etc.

A dissertation submitted to the faculty of Engineering and the Built Environment, University of Witwatersrand in fulfilment of the requirements for the degree of Master of Science in Engineering 28 January 2017 / Batch scale laboratory testwork was conducted to evaluate collector and depressant addition on flotation performance of a nickel sulphide ore. The objectives of the study were to: 1. develop an understanding of the effects of collector and depressant dosage, and its interactive effects, on flotation performance and 2. determine the effect of stage dosing collector and depressant on flotation performance. Testwork was conducted on the Nkomati Main Mineralized zone orebody, a nickel sulphide orebody in the Mpumulanga Province of South Africa consisting of pentlandite, chalcopyrite, pyrrhotite, pyrite and magnesium bearing silicates. Characterisation testwork was conducted, including mineralogy on the major plant streams (by QEMSCAN) and a process survey. The results indicated that there was potential to increase the recovery of coarse pentlandite and that major nickel losses were observed in ultrafine pentlandite. Milling optimisation requires the minimisation of ultrafine generation while ensuring adequate liberation of the course nickel. Stage dosing of collector at nodal points (where more than one stream meets) is currently practiced on the plant, however, its effect had not yet been quantified on the plant or in the laboratory. Stage dosing of depressant is currently practiced on the cleaner flotation stage, however, this too has not been compared to upfront dosage on its own. Significant gangue depression was noted specifically for the cell at which stage dosing was done. The current study would provide an understanding of the current practices with the possibility of offering improvements. The addition of collector progressively improved the hydrophobicity of the sulphide minerals and gangue (with particular emphasis on magnesium bearing gangue), improving recovery significantly. As a result of additional gangue recovery at the higher collector dosages, increased depressant dosages were required to maximise nickel recovery. The collector improved valuable mineral recovery, however, gangue recovery was increased simultaneously, albeit at a reduced rate or in reduced quantities. Furthermore, increased gangue entrainment was evident at higher collector dosages from the increase in water recovery. Excessive depressant addition destabilised the froth phase by the rejection of froth stabilising gangue, which resulted in reduced recovery of the valuable minerals. Therefore, a careful balance must be maintained in order to maximise nickel recovery. Iron recovery was markedly increased at higher reagent dosages, indicative of increased pyrrhotite recovery. Pyrrhotite, although containing nickel, reduces the concentrate grade and may need to be depressed in the latter stages of flotation to ensure the final concentrate specification is achieved. This is an important observation as any improvement in nickel recovery in the roughing stages must be evaluated against the subsequent effect on the cleaning stages. Stage dosing both collector and depressant, individually and collectively, proved to be beneficial by improving the nickel recovery. Stage dosing of both collector and depressant produced higher recoveries than stage dosing of the reagents individually. The time at which the reagent is dosed also proved to have an effect on the performance with an increased dosage in the latter stages providing the highest recovery. The typical recovery by size performance for flotation is characterised by low recovery of fines and coarse with an optimum recovery of an intermediate size fraction. Stage dosing ensures that fine particles are recovered with minimal reagent addition upfront, thereby, coarser particles can be effectively recovered once the high reagent consuming fines are removed. The results have indicated that stage dosing improved the recovery of both coarse and fine particles, whilst reducing the recovery of the intermediate size fraction. Stage dosing can be implemented for two reasons: 1. maximising recovery 2. minimising reagent consumption to achieve the same recovery as upfront dosing A financial evaluation should be conducted to quantify the optimum operating solution. Minimising reagent consumption could be beneficial under conditions of very low commodity prices and excessive reagent costs. / MT2017

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfillment of the requirements for the degree of Mastel' of Science in Engineering Johannesburg 1998 / Impala's Minerals Processing Plant in the Rustenburg Area, South Africa, uses flotation to beneficiate precious metal bearing ores from the Bushveld Complex. Pyrrhotite is one of the sulphide minerals that is targeted but it is the least amenable to current flotation conditions having the lowest recovery. Electrochemical techniques (mixed potential measurements, cyclic voltammetry and current transient techniques) were used to study the relevant reactions on the surface of pyrrhotite mineral electrodes. Aspects investigated included the oxidation of the mineral in aqueous alkaline solutions, activation by copper sulphate, kinetics of oxygen reduction and the adsorption of isobutyl xanthate. Mixed potential measurements of mineral electrodes were taken in batch flotation test work. In addition a novel qualitative measure of hydrophobicity was investigated. The oxidised surface of pyrrhotite is likely to be covered with iron hydroxides and a sulphur rich sub-lattice. No direct evidence was found for the activation of pyrrhotite by copper sulphate in alkaline solutions. It was shown however that activation could be achieved in mildly acidic media and that the surface remained activated if subsequently exposed to alkaline conditions. When achieved under acidic conditions activation was observed to enhance the degree of interaction between the mineral and the xanthate collector. Also copper sulphate appeared to aid the formation of a more hydrophobic surface (as indicated by the hydrophobicity tests). Copper activation conducted in acidic media did not significantly enhance the kinetics of oxygen reduction, a reaction seen as crucial to the adsorption of xanthate. No evidence was found for the initial chemisorption of xanthate onto the mineral surface. However evidence was found for the oxidation of xanthate to dixanthogen at sufficiently anodic potentials. It Was concluded that the relatively poor flotation performance of pyrrhotite could be combated by minimising the extent of the oxidation, adding reagents as soon as possible before the mineral becomes extensively oxidised and by removing surface hydroxides through lowering the pH during conditioning. / MT2017

A seletividade e eficiência do processo de flotação não estão fundamentadas tão somente nas diferenças das propriedades físico-químicas das superfícies dos minerais, mas também na hidrodinâmica do sistema de concentração. Via de regra, a eficácia da flotação diminui quando o tamanho de partícula ultrapassa 150 micrômetros. Esta pesquisa visou estudar a influência de variáveis hidrodinâmicas sobre mecanismos de flotação de partículas grossas em células mecânicas e suas implicações cinéticas. Os ensaios utilizaram células com agitação mecânica e cada situação experimental esteve associada a um conjunto de variáveis hidrodinâmicas: números de hidrodinâmicos adimensionais, características geométricas do impelidor, velocidade mínima de suspensão da polpa, energia dissipada média e energia de preservação do agregado partícula-bolha. Desta forma, a influência dos parâmetros hidrodinâmicos na flotação de apatita e esferas de vidro (diâmetro médio248 micrômetros) foi determinada na presença de oleato de sódio e acetato de eteramina em pH 10. Em condições hidrodinâmicas pouco turbulenta, a recuperação de partículas grossas decresce em função da falta de suspensão de partículas, por outro lado para condições hidrodinâmicas mais severas a recuperação foi quase nula devido à destruição do agregado partícula/bolha. A cinética de flotação da apatita foi estudada em escala de laboratório sob severas condições de turbulência, os resultados indicaram que partículas grossas de apatita têm flotabilidade inferior a finas, corroborando que a flotação dessas partículas grossas não se ajustou ao modelo de primeira ordem. Estes resultados evidenciaram que grossas demandam um ambiente hidrodinâmico apropriado para flotar eficientemente. / Coarse particles badly float mostly because the bubbleparticle aggregates are not strong enough to prevent the particle detachment from the bubble surface caused by the particle weight and turbulence eddies during the rise of the aggregates in the pulp phase to the froth phase and then to the froth launder. The aim this work was to determine effects and degrees of significance of hydrodynamic variables on coarse particle flotation and their kinetic implications. The tests were carried out in flotation cells with mechanical stirring system and each experimental condition was related to group of hydrodynamic variables: hydrodynamic dimensionless numbers, impeller geometries, minimum impeller rotational speed, energy dissipation rate and detachment energy. The influence of hydrodynamic parameters on flotation of the apatite and glass spheres (diameter average248 micrometers) was determined in the presence of sodium oleate and etheramine acetate at pH 10. For more quiescent hydrodynamic conditions, recovery of coarse particles decreased due to a lack in particle suspension, on the other hand, in the most severe hydrodynamic conditions the recovery was almost nil because the bubbleparticle aggregates detachment. Flotation kinetics of apatite was studied in laboratory scale under strong hydrodynamic conditions, the results indicated that coarse particles of apatite float at a lower rate than finer particles and the flotation kinetics of coarse particles did not fit to first order model. Those results evidenced that coarse particles demand a suitable hydrodynamic environment to float efficiently.

Este trabalho aborda a caracterização da matéria orgânica existente num ácido fosfórico de pureza industrial (AFPI), oriundo do Marrocos, objetivando sua remoção através de flotação por ar dissolvido (FAD). O AFPI é um líquido escuro que exibe densidade (2020 kg/m³) e viscosidade dinâmica (1,94 x 10-² Pa.s at 20°C) muito mais alta do que os tipos mais puros de ácido fosfórico, como o grau alimentar e o de pureza analítica. Por outro lado, o AFPI apresenta tensão superficial mais baixa que o ácido de grau alimentício (55,2 mN/m versus 63,7 mN/m a 25°C), indicando a presença de espécies surfactantes dissolvidas (ácidos carboxílicos de cadeia aromática). O teor de 447ppm de carbono orgânico total (TOC) evidencia a alta contaminação do AFPI marroquino por matéria orgânica, que pode ocorrer dissolvida (ácidos carboxílicos aromáticos) ou na forma de minúsculas placas que exibem diâmetro (média aritmética ponderada) de 4µm. Ensaios FAD foram executados usando ar pressurizado a 3,5kgf/cm², que após alívio de pressão, produziu uma população de bolhas com diâmetro de 2,41 x 10`POT´-5m (média aritmética ponderada) e altíssimo desvio padrão (2,94 x10`POT´-5m). A medida do diâmetro de bolhas (db), através de difração de laser, somente foi factível com mistura contendo 40% de ácido fosfórico grau alimentar e 60% de água. Devido a isto, os valores reais de db nos ensaios FAD podem diferir os valores medidos. Ensaios DAF foram executados sob diferentes tempos de flotação (15-60 minutos), todavia a mais alta remoção de TOC (somente de 17,7%) foi obtida com 45 minutos de flotação. A remoção muito baixa de TOC (e também de As, Mg e sulfato) gerada pelos ensaios FAD pode ser explicada pela baixa eficiência de colisão (EC) exibida por minúsculas placas (partículas orgânicas suspensas no AFPI) que precisam colidir com bolhas de ar muito maiores para que possam aderir às mesmas, flutuar e serem removidas do AFPI. Esta possibilidade foi corroborada por um valor de EC da ordem de 0,04 (EC~0,04), que foi determinada pelo modelo de Yoon-Luttrell. / This thesis approaches the characterization of the organic matter which exists in a Moroccan phosphoric acid of industrial grade (PAIG), aiming at its removal via Dissolved Air Flotation (DAF). PAIG is a dark liquid which exhibits specific gravity 2020 kg/m³ (26°C) and dynamic viscosity 1.94 x 10-² Pa.s (20°C) very much higher than other purified types of phosphoric acid (food or analytical grade). Conversely it presents surface tension lower than phosphoric acid food grade (55.2 mN/m versus 63.7 mN/m at 25°C), indicating the presence of dissolved surfactants (carboxylic acids bearing aromatic chains). The content of 447ppm of total organic carbon (TOC) evidences its high contamination by organic matter, which may occur either as dissolved species (aromatic carboxylic acids) or suspended platy-shaped particles (weighed average diameter of 4Êm). DAF experiments were conducted using an air pressurization of 3.5kgf/cm², which, after pressure release, yielded a bubble swarm of weighed average size of 2.41 x 10-5m and a large standard deviation of 2.94 x 10-5m. Because bubble size (db) measurements were conducted via laser diffraction with a mixture of 40% phosphoric acid food grade plus 60% of water, actual values of db may be different from the measured ones. DAF tests were conducted under different length of time (15-60 minutes), but the highest removal of TOC (17.7%) was accomplished at 45 minutes of flotation time. The very low removal of TOC (and also Mg, As and sulfate) yielded by DAF experiments may be explained by a low efficiency of collision (EC) exhibited by small platelets (suspended organic particles) which must collide with bigger air bubbles in order to attach to them and be floated. This possibility was corroborated by efficiency of collision (EC) = 0.04, determined by Yoon-Luttrell Model.

Sammanfattning Boliden Mineral AB är intresserade av att göra en omfattande kartläggning av flotationskinetiken i alla sina anrikningsverk. Kartläggning av ett anrikningsverk är en viktig pusselbit för att förbättra processen, se eventuella flaskhalsar och utveckla framtida processmodeller. I en flotationsprocess är det önskvärt med höga utbyten, snabb flotation och ett högt tonnage. Syftet var att göra en kartläggning av flotationsprocessen i Garpenbergs anrikningsverk. Den praktiska delen av examensarbetet var att göra flotationsförsök i labbskala. Resultatet från flotationsförsöken anpassades med hjälp av Minitab för att se vilken första ordningens kinetikmodell som passar bäst. Genom att använda olika typer av kinetikmodeller så anpassas kinetiken till labbflotationsstudier, det är till för att förfina modellerna vid uppskalningsberäkningar och utvärderingar av nya malmlinser. De tre första ordningens kinetikmodeller som jämförts är den klassiska modellen, Klimpels modell och den fullständigt blandade modellen. Med dessa gjordes en kartläggning av flotationskinetiken i Garpenbergs anrikningsverk. Materialet som flotationsförsöken utfördes på är tagna från anrikningsverket, där värdemineralen är kopparkis, blyglans och zinkblände. Kartläggningen av flotationskinetiken i Garpenberg visas i resultatdelen för varje provtagningspunkt med en sammanfattande diskussionsdel om varje del av processen. Koppar- och blyflotationen visar att det är höga utbyten genom hela processen och att ommalningsdelen i kretsen ger en del förbättringar i utbytet. Vad resultatet visar är att verket går optimalt, och att nästan allt koppar och bly tas ut inom 10 minuters flotation. Modellen som passar bäst är den klassiska modellen för alla provpunkter, förutom för ingående malm där Klimpels modell passar bäst. Kartläggningen för zinkflotationen visar att det är höga utbyten genom hela processen. I sista steget i zinkflotationskretsen är provpunkten andra repeteringen, där är det svårt att flotera enbart zink eftersom det är lätt att gångartsmineral också floteras i detta steg. Övriga provtagningspunkter tyder på att verket går optimalt och att det mesta av Zn är uttaget inom 10 minuters flotationstid. Modellen som passar bäst är den klassiska modellen för alla provpunkter, förutom för andra Zn repeteringskoncentrat där Klimpels modell är bäst. Malkretsflotationens resultatdel visar en flotationskrets med bra utbyte, men på grund av den grövre partikelstorleken floterades det långsammare än övriga flotationstester. För bly passar Klimpels modell bäst och för koppar passar den klassiska modellen bäst.