Iron Ore Flotation Research Articles

Froth Flotation of Iron Ores

With the depleting reserves of high-grade iron ore in the world, froth flotation has become increasingly important to process intermediate- and low-grade iron ore in an attempt to meet the rapidly growing demand on the international market. In over half a century's practice in the iron ore industry, froth flotation has been established as an efficient method to remove impurities fro m iron ore. In this chapter, the industrial practice and fundamental research activities of iron ore flotation are reviewed. The latest innovations in iron ore flotation at major iron ore operations around the world are introduced. The development of flotation routes fro m direct an ionic flotation to reverse cationic flotation, and the rising of reverse anionic flotation in China in recent years is discussed. Although direct anionic flotation was the first flotation route employed in the iron ore industry, it was later largely replaced by the more efficient reverse cationic flotation route. The application of reverse anionic flotation in Ch ina in recent years effectively overcomes some flaws of reverse cationic flotation such as high reagent cost and high metal loss in desliming. The reagents used in iron ore flotation, including starch, amines and fatty acids, and the mechanisms of their interactions with the minerals in iron ore are examined. The p resence of some specific impurities other than quartz in iron ore, such as alu mina containing minerals, i.e. kaolinite and gibbsite, and phosphorous, is detrimental and attracts penalties. The removal of these specific impurit ies has received increasing attention in the iron ore industry. The industrial pract ice and latest research activities in this area are closely reviewed.

Effect of Slimes on Iron Ores Flotation

The presence of slimes is, in general, harmful to the flotation of iron ores, affecting the selectivity and the quality of the concentrates, besides causing an increase in reagents consumption. This work describes the behavior of different iron ore types from the Iron Quadrangle, Brazil, with respect to desliming in hydrocyclones and flotation, including a study on the dispersion degree as a function of pH. Flotation experiments were performed at different slimes contents (designated as by-pass) aiming at assessing the influence of this variable on the selectivity. The different ore types present differences in chemical and mineralogical composition and also in size distribution. The content of slimes not removed in the desliming stage (by-pass) affects differently the selectivity of each ore type. Some ores keep the selectivity constant for all levels of by-pass, but present a reduction in phosphorus grade in the concentrate for reduced by-pass levels. Other types respond to the reduction of by-pass with increased selectivity. As a general rule, by-pass levels lower than 4% lead to a stable behavior concerning selectivity, yielding low phosphorus content in the concentrate. The behavior of each ore type is related to the chemical and mineralogical composition and size distribution of the slimes and also to the dispersion degree of the ore. Preliminary tests indicated that the specific surface area of samples with different by pass levels can explain the flotation behavior.

Role of Water Structure-Making/Breaking Ions in the Cationic Flotation of Kaolinite: Implications for Iron Ore Processing

Australia is the largest exporter of iron ore in the world. The high Al content in Australian hematite/goethite ores is detrimental to blast furnace and sinter plant operations. Of the Al containing minerals in iron ore, kaolinite is a common gangue mineral frequently found in iron ore deposits. In iron ore flotation pulp, various ions exist and may inter- fere with the flotation performance when their concentration is high enough. In this work, the role of a water struc- ture-making ion, i.e. Na + , and a water structure-breaking ion, i.e. K + , in the flotation of kaolinite under reverse cationic flo- tation conditions, the most widely used flotation route of iron ore in the world, was studied in a series of laboratory batch flotation tests. It was found that K + , a water structure breaker, can better reduce the zeta potential of kaolinite and thus causes higher flotation recovery of the clay mineral, in comparison to Na + , a water structure maker. The different effects of the alkali metal cations on kaolinite flotation are attributed to the different aggregation degree of kaolinite particles in the presence of these cations.

Interfacial properties of natural magnetite particles compared with their synthetic analogue

Understanding of the interactions between iron oxides and flotation reagents is important both for flotation and agglomeration of iron ore. Model systems comprising synthetic iron oxides and pure chemical reagents are commonly applied in experimental work in order to obtain high quality data and to ease the interpretation of the empirical data. Whether the results obtained using model systems are valid for iron ore minerals and commercial reagents is a question seldom addressed in the literature. It is shown in this work that previously reported results obtained from a model system, concerning adsorption of a carboxylate surfactant and sodium metasilicate onto synthetic magnetite nanoparticles, as obtained by in situ ATR-FTIR spectroscopy and contact angle measurements, are applicable to adsorption of flotation reagents on magnetite concentrate. Additionally, the problem of restoring magnetite wetting after flotation is addressed since good wetting of a magnetite concentrate is required to produce iron ore pellets by wet agglomeration. The results from the present work indicate that the wettability of both synthetic magnetite coated with surfactant and magnetite concentrate after flotation can be improved by adsorbing a hydrophilizing agent such as silicate or polyacrylate.

Effect of starch type on selectivity of cationic flotation of iron ore

Cationic flotation is one of the most widely accepted technologies for upgrading siliceous iron ore using polysaccharides (mainly starches) as depressing agents for iron bearing minerals while floating silica with amines. In this paper, a group of starches are investigated as depressants for haematite. These starches are wheat, corn, rice, potato and dextrin. The role of starch type on the selectivity of the separation process has been studied through zeta potential, adsorption measurements as well as flotation tests. The effects of type of starch and pH of the medium have been studied. The results indicate that the selectivity of the separation process is strongly affected by the type of starch used, where better results are obtained with corn starch or wheat starch in comparison to the other types. Fourier transform infrared spectroscopy measurements indicated that the interaction between starches and haematite surface is intermolecular interaction.

The effect of polymer adsorption on the wetting properties of partially hydrophobized magnetite

Upon reverse flotation of iron ore, the surface of the iron ore concentrate may become partially hydrophobized due to adsorption of flotation collector, which is facilitated by the calcium ions present in the process water. Hydrophobic areas on the concentrate surface may introduce problems in subsequent pelletization of the concentrate. A possible way to restore the wettability of the surface could be by modifying the surface with a hydrophilic polymer. The effect of hydrophilic polymers of different types, viz. cationic, anionic, and non-ionic, on the wettability of the magnetite surface after adsorption of a surfactant was investigated. Although all the polymers could adsorb on magnetite at pH 8.5, the contact angle measurements revealed that only anionic ammonium polyacrylate could decrease the contact angle of synthetic magnetite after surfactant adsorption to a level close to that of as-synthesized magnetite. Such effect was probably achieved due to shielding of the hydrophobic surfactant chains from the aqueous phase by hydrophilic polyacrylate molecules. The fact that polyacrylate adsorption on magnetite occurred via calcium ions makes polyacrylate suitable for application in calcium-rich process water. The results presented in this work illustrate that ammonium polyacrylate could be successfully used to improve the wettability of magnetite after adsorption of surfactants.

Comparative studies of reverse cationic/anionic flotation of Vale iron ore

The comparative studies of reverse cationic/anionic flotation routes were conducted using Vale iron ore in batch scale flotation tests. The effect of slimes on the performance of the two flotation routes was also studied. After desliming, the overall Fe recovery in reverse anionic flotation is significantly higher than reverse cationic flotation at the same concentrate grade. For ultrafine particles (< 10 μm), the metal loss in reverse cationic flotation is over 92% due to the entrainment of hematite ultrafine particles. However, in reverse anionic flotation, metal loss is as low as 42% in the particle size range of 5 to 10 μm, while rejecting almost all the quartz ultrafine particles at the same time. In the coarse particle size range (> 210 μm), the performance of reverse cationic flotation is slightly better than reverse anionic flotation, with more quartz coarse particles rejected. The major advantage of reverse anionic flotation over reverse cationic flotation was found to be its excellent capability to selectively separate ultrafine particles of quartz and hematite.

The effect of calcium ions, sodium silicate and surfactant on charge and wettability of magnetite

Anionic carboxylate surfactants and sodium silicate are used in the reverse flotation of iron ore to separate magnetite from apatite. In this work, consecutive adsorption of sodium silicate and an anionic surfactant on synthetic magnetite modified with calcium ions was studied in the pH range 7.5–9.5 using in situ ATR-FTIR spectroscopy. The effect of these chemicals on the zeta-potential and wetting properties of magnetite was also investigated. While adsorption of silicate increased with increasing pH, subsequent surfactant adsorption went through a maximum at pH 8.5. Surfactant adsorption in the presence of calcium ions was not affected by the amount of silicate adsorbed on magnetite. Calcium ions were found to render the magnetite surface positive in the pH range 3–10 and could reduce the dispersing effect of silicate in flotation of apatite from magnetite. While treatment with calcium chloride and sodium silicate made magnetite more hydrophilic, subsequent adsorption of the anionic surfactant increased the water contact angle on the magnetite surface from about 10° to 40–50°. Although the latter values are not high enough to make magnetite float, the hydrophobic areas on the magnetite surface could result in the incorporation of air bubbles inside the iron ore pellets produced by wet agglomeration, lowering the pellet strength.

Efeito da dispersão em polpas de minérios itabiríticos

A flotação reversa do minério de ferro é antecedida de uma operação de deslamagem, cuja eficiência aumenta com o uso de um reagente que promova a dispersão da polpa. O trabalho avaliou a influência do tipo e da concentração do dispersante na eficiência da dispersão e nos resultados da flotação. Os resultados foram avaliados em termos de tamanho das partículas da lama, grau de dispersão e Índice de Seletividade de Gaudin, obtido na flotação. Os resultados mostram a importância da dispersão antes da deslamagem e sugerem que o reagente escolhido, como dispersante, não pode ser depressor para o quartzo. O hidróxido de sódio parece ser a melhor alternativa entre os reagentes testados.

Using Polyoxyethylene Reduction the Flotation Temperature of Fatty Acid

The separation of quartz from hematite adding the polyoxyethylene ether to the fatty acid has been investigated. The main factors affecting flotation temperature were found to be constitutes of collector and surfactants. The results indicate that the temperature of fatty acid anion reverse flotation of iron ore could be reduced to 22 from 45 . It can achieve purposes of saving energy and lowering carbon let.

Effect of a low-molecular-weight polyacrylic acid on the coagulation of kaolinite particles

Kaolinite is of very fine particle size in nature and thus its dispersion plays a key role in the successful removal of kaolinite in iron ore flotation and selective flocculation processes. As the most widely used dispersant in the world, sodium silicate has been used as a standard dispersant in iron ore industry. However, in the author's previous work, the actual effect of sodium silicate on the colloid stability of kaolinite particles was found to be weak under the typical conditions of iron ore flotation and selective flocculation. In this work, the dispersive effect of a low molecular weight polyacrylic acid on kaolinite particles was systematically investigated through electrophoretic mobility and colloidal stability studies. The results demonstrate that interactions between polyacrylic acid and kaolinite take place over the entire pH range studied in this work, from pH 5 to 10.5, with stronger interactions observed at neutral and acidic pH. This indicates that polyacrylic acid adsorbs on both positively and negatively charged sites on kaolinite, although the presence of positively charged sites on the clay surfaces at low pH and in CaCl 2 and MgCl 2 solutions at high pH significantly enhances its interactions with kaolinite. The strong dispersive effect of polyacrylic acid on kaolinite in the presence of CaCl 2 and MgCl 2 shows that polyacrylic acid is a promising dispersant for kaolinite under the typical conditions of iron ore flotation and selective flocculation.

Role of hydrolyzable metal cations in starch–kaolinite interactions

The effect of hydrolyzable metal cations, i.e. calcium and magnesium, present in mineral suspensions on starch–kaolinite interactions was studied through zeta potential, adsorption and turbidity measurements. The results demonstrate that hydrolyzable metal cations in mineral suspensions can significantly affect starch adsorption on kaolinite under typical conditions of iron ore flotation and selective flocculation. The effect of calcium and magnesium on starch adsorption on kaolinite surfaces correlates to their abilities to reduce the electrostatic repulsion between the anionic starch molecules and the negatively charged kaolinite particles. The hydrolyzable metal cations cause fast coagulation of kaolinite particles at pH 10.5 by reducing the repulsive electrostatic forces between kaolinite particles, when their concentration is ≥ 0.001 M. The presence of starch further enhances such effect at low dosages, but re-disperses kaolinite particles at high dosages by inducing steric forces between the kaolinite particles coated with starch.

Investigation on alternative depressants for iron ore flotation

Iron ore concentration through flotation represents an important application of reagents in mineral processing. Nowadays all Brazilian iron ore concentrators use starch as iron oxides depressant. This study evaluated the application of other depressants, which are commonly used in other flotation systems. Six carboxymethylcelluloses, three lignosulphonates, one guar gum, and four humic acids samples were investigated in the reverse cationic flotation. Laboratory flotation tests showed that only two polymers (one carboxymethylcellulose and guar gum) reached the same performance as starch. The superior performance of these reagents was due to the presence of the glucopyranose ring. The use of polymers blends led to promising results.

Evaluation of novel Georgia Pacific clay binders in iron ore flotation

Reverse cationic flotation is the most widely utilized flotation method for concentrating iron ore. In this process, quartz is often floated with ether amines (R-(OCH2)3-NH2) partially neutralized with acetic acid. However, it is well known that the cationic flotation of quartz does not work well if a certain amount of slime is present in the ore slurry. To improve flotation performance, starch is often added to the flotation feed to selectively floc-culate and depress the iron minerals and sodium silicate is used to disperse the silica gangue. The present study was conducted to improve the efficiency of iron ore flotation by the use of a new type of depressant for clay and iron minerals, Georgia Pacific (GP) clay binder. The GP clay binder minimizes slime adsorption on quartz and hematite particles by agglomerating clay particles to reduce their surface area. It also helps depress hematite flotation due to its unique chelating action on iron ions. The results from this study show that the GP clay binder is an effective depressant in iron ore flotation. When it was used as a substitute for corn starch, it increased concentrate grade from 60.78% to 67.67% and increased iron recovery from 71.96% to 72.90%. The combined use of GP clay binder with corn starch produced even better flotation performance, increasing iron recovery to 78.15%, while the concentrate grade remained stable at 67.08%.

Biodegradation studies on fatty amines used for reverse flotation of iron ore

Bacteria present in effluents from the process of iron ore flotation were isolated and identified in an attempt to identify the microorganisms responsible for fatty amine degradation. Water samples collected at the tailings dam led to the identification of the bacterial species Serratia marcescens as the microorganism responsible for degradation, while in laboratory flotation conditions, a strain of Enterobacter cloacae was shown to be the biodegrading agent. Both S. marcescens and E. cloacae are Gram-negative, non-sporulated, mobile and facultative anaerobic bacteria. Monitoring of the effluent had shown that after 5 days, around 34% of amine was already consumed, increasing to 75% after 10 days; these data are important for testing the reuse of the fatty amines contained in effluents. Biodegradation experiments carried out with S. marcescens revealed the significant role of temperature and concentration on the biodegradation rate of the etheramine EDA 3B. For the concentration of 10 mg L −1, amine biodegradation rates are very close at all temperatures. However, as amine concentration increases, the influence of temperature can be better observed, mainly for concentrations of 40 and 60 mg L −1. This isolate will be potentially useful in biotreatment of wastewaters and bioremediation of contaminated soils.

The use of collectors mixture in the reverse cationic flotation of magnetite ore: The role of Fe-bearing silicates

The paper describes effective reagent combinations for removal of silicates by reverse cationic flotation from magnetic concentrate in magnetite ores processing. This work is based on a hypothesis that a further development in reverse cationic flotation of iron ores implies, a more detailed consideration of the nature of the Fe-bearing gangue minerals. Thus, the choice of reagent regime has been determined by the similar physicochemical properties of iron oxides and silicates such as amphiboles due to inclusion of iron into their crystal lattice. Zeta-potential studies of Fe-oxides, quartz and Fe-bearing amphibole samples have shown that amines of different molecular structure are equally well adsorbed both on the surface of Fe-oxides and on the surface of silicates within рН range of 4–10. Flotation studies of quartz and Fe-bearing amphibole samples have revealed that the use of starch as a depressant of Fe-oxides has a hydrophilic effect on the surface of Fe-bearing silicates and significantly decreases their flotation by ether amines. Flotation of these minerals is not possible by primary monoamines in the presence of starch due to the adsorption layer formation. The experimentally selected mixtures of ether amines with primary monoamines or with alcohols provide formation of a hydrophobic adsorption layer on the surface of amphiboles and magnetite–silicate aggregates, even in the presence of starch in the system. A total hydrophobic effect is sufficient for an effective flotation of the entire silicate complex and producing of magnetite concentrates with SiO 2 content <1.0% and Fe content up to 70.3% from magnetic concentrate with SiO 2 content ∼3%.

Geometrical optimization of the structure of carboxylic acids vis-à-vis their effectiveness toward iron ore flotation

Saturated and unsaturated fatty acids are used in the flotation of iron values present in iron ore. Among the several fatty acids, oleic acid and its sodium salt are widely used. To substantiate the flotation results, the quantum chemical calculations of a few such acids have been carried out by adopting the semi-empirical AM1 method. These acids have been further optimized in the presence of an iron atom. The electronic interaction of the polar carboxylic head group of oleic acid with the iron atom is higher compared to the other acids. The numerical results support the flotation behavior of iron ore with oleic acid.

Colorimetric determination of ether amine greases utilized in the flotation of iron ore

Ether amine greases are commonly used in the flotation of iron ore, and after use are discarded in the tailings dams. The aim of this work was to quantify a commercial ether amine using the bromocresol green dye in chloroform. The statistical data obtained show that the method is characterized by satisfactory accuracy and precision with a detection limit below 1 mg/L. The recovery obtained was 98.53%, in average. In addition, the method presented here provided a recovery of ether amine contained in effluents and solids higher than 98%.

Reciclagem de aminas na flotação de minério de ferro

O presente trabalho tem por objetivo investigar a possibilidade de reutilização de aminas residuais provenientes do processo de flotação de minério de ferro. Os testes de flotação em bancada foram realizados em pH 10,5, tendo o amido como depressor dos óxidos de ferro e as aminas Flotigam EDA 3B e F2835 como coletores para a sílica. Cada rejeito desses ensaios foi submetido à separação sólido/líquido através de filtração a vácuo. O líquido contendo amina residual foi reutilizado em um segundo ensaio de flotação, onde foi investigada a dosagem de reagente novo. Utilizando-se a água contendo amina residual, juntamente com quantidades novas dos coletores, observou-se que há a possibilidade de diminuir o consumo desse reagente em até 50%. Foi realizado também teste de dessorção das aminas contidas em rejeitos sólidos, adicionando-se água ao resíduo em diferentes valores de pH e massa do resíduo. Os resultados revelaram que mais de 95 % da amina adicionada pode ser recuperada.

Residual amine in iron ore flotation

The possibility of recovering residual amine present in the water phase of tailings pulps of the reverse cationic flotation of iron ore was investigated. The samples collected in the tailings from mechanical and tank cells and also from flotation columns were kept under rest to promote the separation between the water and the solid particles. The water was used for determination of the residual amine concentration and for flotation tests. The residual amine concentration was determined through indirect quantitative analysis using a spectrophotometer. The flotation tests were performed using, separately, each tailings water and a composition of them. Four sets of tests were carried out. The first three sets indicated the strong possibility of reusing the amine present in the water. As a consequence, the dosage of amine was reduced and the residual amine concentration of three out of four collection points was below the detection limit in the sampling for the last set.