Selective Flocculation Research Articles

Recovery of Ultra-Fine Iron Ore from Iron Ore Tailings

Many attempts has been taken for further utilisation of the tailings and slimes through different routes i.e. beneficiation, agglomeration etc. Though the slimes and tailings contain huge ultra fines, conventional beneficiation methods many not be much effective for handling because of particle size limitations. Physicochemical method i.e. selective flocculation is a process for handling the ultrafine particles present in the tailings. Review shows that selective flocculation technique have very limited commercial application. Here the study focuses on the application of selective flocculation process for beneficiation of synthetic mixtures of iron ore and kaolinite as well as iron ore tailings. Results show that it is possible to achieve 65.78(%) of Fe, with 2.65% Al2O3, 3.66 SiO2 (%) in the concentrate using synthetic mixture feed and more than 60% of Fe is obtained from natural iron ore tailings.

Guar gum as a selective flocculant for the beneficiation of alumina rich iron ore slimes: Density functional theory and experimental studies

Current iron ore processing generates about 25% of very fine material called iron ore slimes. These slimes are being disposed into tailing ponds owing to their high alumina content (10–15%) despite having good iron values (45–60% Fe). Due to the rapid depletion of high grade iron ores, there is an urgent need to develop effective beneficiation processes for utilization of slimes. The very fine size of the slime particles (<150µm) makes selective dispersion-flocculation a promising route for their beneficiation. In this paper, we present our first principles density functional theory (DFT) results along with full factorial design of dispersion - flocculation experiments results on the beneficiation of iron ore slimes using guar gum as flocculant. DFT computations have been used to compute the interaction energies and explain adsorption mechanisms of guar gum with hematite, goethite, gibbsite and kaolinite surfaces – the main minerals present in the iron ore slimes. The computed results show that guar gum will be selective towards the hematite surface due to strong FeOguar gum chemical interactions as compared to only weak hydrogen bonds in the case of the other mineral surfaces. The experiments were designed to study the effect of the three key process parameters namely, pulp density, guar gum dosage and settling time on the beneficiation of iron ore slimes. The experimental data is used to develop models for prediction of yield, iron grade, % alumina and iron recovery in the concentrate. The models thus obtained are utilized to arrive at the optimized process parameters to achieve maximum iron recovery with acceptable iron grades with minimum alumina in the concentrates. These optimized process conditions shall form base line for further scale-up of the process at pilot/plant scale.

Recovery of iron from iron ore slimes by selective flocculation

Recovery of iron from iron ore slimes by selective flocculation

Selective Flocculation of Iron Ore Slimes: Results of Successful Pilot Plant Trials at Tata Steel, Noamundi

A significant portion of currently mined iron ores, that is, 15–20% of run of mine ore, typically ends up as slimes—a slurry of fine particles (<45 micron) with relatively higher alumina contents (7–15% Al2O3). The only viable option currently is to dispose these slimes in tailing ponds for water recovery and future use. Due to increasing demand for steel and rapid consumption of high grade ores, processing and utilization of these slimes has become an urgent necessity. Traditional gravity and magnetic separation is not very effective in the ultrafine size range (less than 45 microns) and hence most of the flowsheets have a desliming step ahead of gravity and magnetic separation. Selective dispersion—flocculation is commercially proven technology to accomplish efficient separation in this size range, provided appropriate selective reagents are available. Our earlier work in TRDDC laboratories has demonstrated that selective flocculation with starch and guar gum is sufficiently selective for the reduction of alumina contents and thus this process should be scaled up for the processing of alumina rich Indian iron ore slimes. TRDDC has also designed a portable set-up which can be used to run pilot plant trials in a continuous mode onsite in the mines. The successful pilot plant trials of a selective flocculation separation process were completed by us at Noamundi mines recently. The results of these plant trials, using a portable pilot plant set up, designed by TRDDC, are summarized in this paper. The slimes sample for these plant trials, was withdrawn from one of the slimes stream at the Tata Steel’s iron ore beneficiation plant at Noamundi mines. Though there was considerable variation in the grade and pulp density of the slimes sample, it was possible to produce a concentrate of consistent quality in a continuous mode. It was for example demonstrated that one can produce a concentrate assaying 65.3% Fe and 2.5% alumina with a yield of 80.4% from a relatively richer grade slime sample containing 60.3% Fe and 4.8% alumina. More importantly, the corresponding tails contained less than 39.7% Fe. For a leaner grade slime sample assaying 53.4% Fe and 7.3% alumina, the corresponding concentrate grade was 63.5% Fe and 3.1% alumina, tailings grade 35.7% Fe and the yield achieved during the plant trials was 63.5%.

Surface chemical properties and selective flocculation studies on alumina and silica suspensions in the presence of xanthan gum

The changes in the surface chemical properties of alumina and silica suspensions consequent to the addition of xanthan gum were studied. The adsorption density of xanthan gum for alumina was found to be maximum at pH 2, whereas nil adsorption was found for silica throughout the pH investigated. The isoelectric points (i.e.p.) of alumina and silica were found to be located at pH 9.1 and presumably less than pH 2 respectively. The addition of xanthan gum shifted the i.e.p. of alumina towards more acidic pH values, in proportion with the concentration of xanthan gum added, with a concomitant change in the zeta potentials to more electronegative or less electropositive values. The addition of xanthan gum beyond a certain concentration (>50ppm), increases the flocculation of alumina suspension to a higher value (∼92%), in the pH range of 2–9. The electrokinetic and flocculation characteristics of the silica were not altered much by the addition of xanthan gum, akin to the adsorption result. FTIR spectral investigations provide evidence in support of hydrogen bonding and chemical interaction forces between alumina and xanthan gum. Maximum separation efficiency of ∼93% for alumina-silica synthetic mixture was observed in selective flocculation tests.

Selective Flocculation Enhanced Magnetic Separation of Ultrafine Disseminated Magnetite Ores

Simple magnetic separation for a certain magnetite mine with ultrafine disseminated lean ores has resulted in low performance, as the fine sizes and aggregation of ground mineral particles have caused inefficient recovery of the ultrafine minerals. In this study, we attempt to increase the apparent sizes of target mineral particles, and improve the separation indices, by using a multi-stage grinding-dispersion-selective flocculation-weak magnetic separation process. The results showed that under the conditions of 500 g/t sodium hexametaphospate (SHMP) as dispersant, 750 g/t carboxymethyl starch (CMS) as flocculant, agitating at 400 rpm for 10 min, with slurry pH 11, and final grinding fineness of 93.5% less than 0.03 mm, the obtained concentrate contained 62.82% iron, with recovery of 79.12% after multi-stage magnetic separation. Compared to simple magnetic separation, the concentrate’s iron grade increased by 1.26%, and a recovery rate by 5.08%. Fundamental analysis indicated that, in a dispersed state of dispersion, magnetite particles had weaker negative surface charges than quartz, allowing the adsorption of negative CMS ions via hydrogen bonding. Consequently, the aggregate size of the initial concentrate increased from 24.30 to 38.37 μm, accomplishing the goal of selective flocculation, and increasing the indices of separation.

Selective adsorption of anionic polyacrylamide onto ultra-low ash coal and kaolinite

To study the selectivity of polyacrylamide in the selective flocculation flotation of fine coal, the adsorption of anionic polyacrylamide (PAM A401) onto ultra-low ash coal and kaolinite was studied, including the adsorption thermodynamics, floc size distribution and wettability changes. The thermodynamics of the adsorption process at the low concentration of 0-16 mg/dm of PAM A401 were studied at different contact times, doses, temperatures and pH values. Thermodynamic parameters of ΔG, ΔH, ΔS and Ea were evaluated to understand the nature of the adsorption process. The results indicated that PAM A401 was selectively adsorbed onto ultra-low ash coal rather than kaolinite. Physical adsorption was the predominant mechanism, and the adsorption of PAM A401 at 12 mg·dm-3 onto coal was 2.15 times larger than the adsorption on kaolinite. After the adsorption of PAM A401, the lipophilic hydrophilic ratio (LHR) of coal decreased from 9.23 to 7.28, indicating that the coal became less hydrophobic than before. In contrast, the LHR of kaolinite increased from 1.44 to 1.65. Floc size measurements showed that the d10, d50 and d90 of coal flocculated by PAM A401 (at 12 mg/dm , pH 6.5) were 3.18, 2.76 and 2.59 times of the corresponding levels of these parameters for kaolinite floc, respectively. Moreover, the efficiency index of the selective flocculation flotation (PAM A401 2 g/Mg) increased by 5.43 percent compared with the efficiency index of conventional flotation of fine coal.

Xanthate-functional temperature-responsive polymers as selective flocculants and collectors for fines recovery

A novel method to improve the recovery of fines in the flotation process involving the use of a temperature-responsive copolymer poly(N-isopropyl acrylamide-co-ethyl xanthate methacrylate) (PNEXMA) incorporating poly(N-isopropyl acrylamide) (PNIPAM) and xanthate functionality has been investigated. Above a lower critical solution temperature (LCST), the polymer functions as both a collector and flocculant, forming hydrophobic aggregates of the valuable fines that are amenable to beneficiation by flotation. The viability of using PNEXMA for the flotation of sulfide fines has been evaluated based on initial screening with adsorption, contact angle and aggregation studies followed by flotation tests. The studies were conducted at both temperatures below and above the LCST, and the results were compared with an industrial collector, potassium amyl xanthate (PAX). Adsorption isotherms indicate a strong polymer affinity for chalcopyrite surfaces. The quartz contact angles were found to remain relatively hydrophilic and unchanged in the presence of the PNEXMA and PAX, while the chalcopyrite surface turned hydrophobic with contact angles above 60°, comparable to PAX. Temperature-responsive reversible flocculation was also observed with the polymer on chalcopyrite, while no response was found with PAX or with quartz. Flotation studies with chalcopyrite confirmed that PNEXMA is able to act as a selective collector, with performances on par with PAX. However, no recovery improvement over PAX was observed in the −20μm fines fraction, which was attributed to the use of fully-liberated synthetic feed in the current work resulting in high fines recoveries with PAX not usually found in actual ground mineral ores.

Adsorption of anionic polyacrylamide onto coal and kaolinite: Changes of surface free energy components

ABSTRACTThe wettability of floc has a large effect on the selective flocculation flotation process of fine coal separation. The changes of thermodynamic characterization of coal and kaolinite have been investigated by Washburn dynamic method and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption of anionic polyacrylamide. Lipophilic hydrophilic ratio (LHR), surface free energy, and its components were calculated by Washburn equation combined with Van Oss–Chaudhury–Good theory according to the wetting curves of coal and kaolinite samples wetted by n-hexane, α-bromonaphthalene, formamide, and water. After PAM A401 adsorption, the peaks of hydrophilic functional groups of coal (the amide group, free-NH2, secondary amide N–H, C–N) were increased, while the peaks of the hydrophobic functional group, including methyl (-CH3) and methylene (–CH2–), was decreased. The LHR value of coal decreased from 9.23 to 7.28. The polar components of coal were increased, the non-polar components were decreased, and the surface free energy was increased from 39.92 to 40.43 mN m−1. The coal surface became more hydrophilic. For kaolinite, both hydrophilic and hydrophobic functional groups were increased, while its LHR values increased from 1.44 to 1.65. The polar component was decreased from 58.27 to 55.05 mN m−2. Results of FTIR were corresponding to the surface property.

Indian China Clays: Vagaries in Process and Flow Sheet Development

Process and flow sheet development for the beneficiation of China clay remains always unique to each deposit since the mineral characteristics changes from deposit to deposit. The difference in characteristics has got a great bearing on the geological formation, setting and the transformation of the resource over millions of years. Each clay deposit differs in its type and extent of impurities, particle size distribution, pH and other characteristics. Hence it is imperative that flow sheet for beneficiation for any clay can be made only after detailed laboratory processing studies. The present paper discusses about the above mentioned aspect by carrying out process development studies on five typical clays from different states of India, viz., Mamuara clay from Kutch (Gujarat), Thonnakkal Pink clay from Trivandrum (Kerala), Thonnakkal Grey clay from Trivandrum (Kerala), Koraput clay from Orissa and Guda clay from Bikaner, Rajasthan so as to bring out the vagaries in process and develop flow sheet. Studies shows that, besides the normal operations, high gradient magnetic separation and calcination are essential for Mamuara clay so as to get a premium grade calcined clay, reductive bleaching is unavoidable for Thonnakkal Pink clay, shear-floc flotation is required for Thonnakkal Grey clay to remove graphite and a non-conventional (pH controlled) water washing is required for Koraput clay even before blunging since it is highly acidic (pH 1.7). Finally, Guda clay responds only to magnetic separation and can not be upgraded to any premium grade. Incidentally, reductive bleaching, flotation and selective flocculation are not effective for Guda clay. Thus the investigations reveal that each deposit needs different unit operations and hence different beneficiation flow sheets.

Quantitative Estimation of Mineral Phases from Chemical Assays and Powder X-Ray Diffraction Rietveld Analysis: A Case Study on Selective Flocculation of Iron Ore Slimes

A generic method for quantitative estimation of mineral phases in ores and process streams has been illustrated in this paper with the help of an example taken from our own work on the selective flocculation of alumina rich iron ore slimes. The method used conventional bulk chemical assay data and information on phases present, as determined by powder X-ray diffraction (XRD) pattern analysis. Iron ore slime samples were subjected to selective dispersion–flocculation experiments and the feed, concentrate and tails were analyzed using this method. Chemical assays (iron, alumina, silica and loss on ignition) were determined by wet chemical analysis and mineral phases (hematite, goethite, gibbsite, kaolinite and quartz) were quantified by Rietveld analysis of XRD patterns. Considering the proportion of various elements present in the constituent minerals, the chemical assay data and the reconciliation of assays (as well as the mineral compositions determined by Rietveld analysis, if available), one could estimate the proportion of various minerals present in different process streams. The mineral compositions estimated based on this method matched reasonably well with those obtained by quantitative phase analysis by the Rietveld analysis. In case the Rietveld analysis results were also reconciled with the elemental assays, one could arrive at even a better estimate of the proportion of various minerals in the different process streams. The estimated mineral compositions in feed, concentrate and tails were also used to compute mineral wise recoveries. The approach presented in this paper would provide mineral engineers a simple and relatively easy method to convert elemental assays into mineralogical compositions and thus compute extremely useful and reliable estimates of the mineral-wise recoveries, grades and distributions in the various plant streams, which are necessary for plant optimization and control purposes.

Characterization and Beneficiation of Iron Ore Tailings by Selective Flocculation

In the present paper, an attempt has been made to beneficiate iron ore tailings by selective flocculation using guar gum and starch as flocculants along with sodium hexametaphosphate (SHMP) as the dispersant. The mineralogical studies carried out initially indicated the presence of hematite and goethite as major iron bearing mineral phases along with quartz and kaolinite as major gangue minerals. The selective flocculation process showed that the Fe grade could be enhanced from 58.24 to 65.32 % Fe using starch as flocculant with a recovery of 62.08 %. However, 63.2 % Fe with a recovery of 68.04 % was obtained using guar gum as the flocculant. The efficacy of the studies were analysed using separation efficiency which indicated higher separation efficiency with the tests employing starch as the flocculant along with SHMP.

A facile disposal of Bayer red mud based on selective flocculation desliming with organic humics

Humics flocculant was applied in the disposal of Bayer red mud based on selective flocculation desliming process. The parameters affecting selective flocculation behavior such as flocculant dosage, slurry pH and agitation intensity were studied. For flocculating mechanism analysis, the iron mineral and the flocs product were characterized by ζ-potential testing, settling experiments, optical microscope and SEM imaging. The results show that humics exhibits a good selective flocculation performance in the high alkaline pH range. With an optimal condition of 2% solid density, flocculant dosage 30mgL−1, Na2SiO3 dosage 200mgL−1, slurry pH 10.0 and agitation speed 1000rpm, the recovery of iron minerals of 86.25±1.31%, the iron grade of concentrate of 61.12±0.10%, the separation index of 0.69±0.02 can be obtained in the selective flocculation. It is found that the adsorption bridging of humics polymer dominates the selectively flocculating the iron minerals. Large flocs or aggregates with a better settling capacity are generated because of humics occurring. The maximum settling velocity of 38.23±1.51mh−1 is reached at pH 10. This work brings the easiness in directly recovering fine particle size of iron-bearing minerals from red mud.

FLOCCULATION/DISPERSION OF HEMATITE WITH CAUSTIC DIGESTED STARCH

Selective flocculation of hematite with starch is a process well-known in practice. However, the separation of hematite from other minerals depends strongly on the methods of starch digestion performed either as heating-digestion or alkali-digestion (different type and dosage of alkali). The purpose of this study is to identify possible influence of the alkali-digested starch on flocculation of ultra- fine hematite when the starch was digested at different concentrations of sodium hydroxide at room temperature. Adsorption of starch digested with sodium hydroxide at different concentration on hematite was investigated by abstraction and co-precipitation tests. Turbidities tests, settling rates, flocculation/dispersion measurement and Fourier transform infrared spectroscopic analysis (FTIR) have also been conducted. Based on the results of the above mentioned tests it is suggested that the flocculating power of caustic digested starch towards fine particles may be significantly weakened, while its dispersing ability starts to play a role instead, if the concentration of sodium hydroxide is high enough in starch digestion. When the weight ratio of NaOH /starch is lower than 2, incomplete gelatinization of starch granules may lead to coagulation of fine particles of hematite mostly due to non-selective electrostatic attraction. The weight ratio of NaOH /starch from 2 to 4 helps to flocculate mineral surfaces selectively and efficiently, assuring a complete digestion of starch granules and a small amount of acidic functional products on the starch chain. However, much smaller and homogenous short-chain granules resulting from higher concentration of sodium hydroxide (the weight ratio of NaOH /starch is more than 4) used to digest starch may weaken the flocculating capacity of the caustized starch for hematite and lead to its dispersion.

Development of a Statistical Model for Selective Flocculation of Iron Ore Slimes

In this study, an attempt has been made to identify the significant factors that affect the selective flocculation of iron ore slimes using full factorial design. For this purpose, three factors pH, pulp density, and the flocculant dose were investigated. A 23 factorial design was employed and the results were analyzed statistically. The result indicated that the pH, pulp density, and their interactions significantly affect the grade of the concentrate. Regression model using the design matrix showed that the predicted values are in well agreement with experimental values for grade and recovery. From the studies, it was possible to enhance the grade to 62.78% Fe with a recovery of 84.23% at pH 10, pulp density 1% and a flocculant dose of 0.03 mg/g.

Role of water chemistry in the selective flocculation and dispersion of iron ore

Fine-grained hematite ore can be concentrated by the process of selective flocculation and dispersion, which relies on proper reagent selection and control of water chemistry. While many previous studies have been performed analyzing the effects of different reagents on this process in a laboratory environment, this paper focuses on investigating the water chemistry within the process in a pilot-scale continuous deslime thickener. The pH, sodium concentration, calcium concentration and magnesium concentration were varied to determine their effects on the iron concentrate grade and recovery, and the phosphorus concentrate grade and rejection in the pilot-scale selective deslime thickener. The ideal pH for the iron grade and recovery of the process using a starch selective flocculant was found to be 10.5. Phosphorus rejection, however, was increased at lower pH values. Minimization of sodium concentration was shown to improve iron grade, iron recovery and phosphorus rejection. Calcium acted as a nonselective flocculant showing higher iron recovery, lower iron grade and lower phosphorus rejection with increasing concentration. Conclusions could not be drawn from the experiments that varied magnesium concentration. The zeta potential of the solid-liquid interface of particles in each sample taken was also analyzed to show relationships between zeta potential and process performance. In all cases, a maximization of the magnitude of zeta potential correlated with increased iron grade and recovery. This supports the hypothesis that a higher level of dispersion enhances the selective flocculation and separation process.

Flocculation/flotation of hematite fines with anionic temperature-responsive polymer acting as a selective flocculant and collector

A novel approach to the recovery of valuable fines is the use of temperature-responsive polymers such as poly (N-isopropyl acrylamide) (PNIPAM). These polymers act as dual-function flocculants and collectors to form hydrophobic aggregates improving particle–bubble collision and attachment. The aim of this study is to investigate the flotation performance of anionic PNIPAM for an iron ore sample containing fines compared to sodium oleate, an industrial collector for hematite. PNIPAM conditioned at room temperature (25°C, below the lower critical solution temperature (LCST)) and floated at 50°C (above the LCST) was found to provide improved hematite grade and recoveries for particles above 20μm, compared to sodium oleate. This was attributed to the increased selectivity and hydrophobicity of PNIPAM. Turbidity testing confirmed the flocculation of fines with PNIPAM, which deslimes the surface of the coarser particles. Below 20μm, the hematite fines were almost completely recovered with PNIPAM. However, this recovery was not selective, attributed to the entrapment of gangue in the hydrophobic aggregates. Furthermore, conditioning of the polymer above the LCST resulted in significant losses in grade and selectivity, as the polymer self-aggregates hydrophobically and precipitates unselectively onto the closest surface.

Production and characterization of bioflocculants for mineral processing applications

A comparative study of two bacterial strains namely, Bacillus licheniformis and Bacillus firmus in the production of bioflocculants was made. The highest bioflocculant yield of 16.55g/L was obtained from B.licheniformis (L) and 10g/L from B.firmus (F). The bioflocculants obtained from the bacterial species were water soluble and insoluble in organic solvents. FTIR spectral analysis revealed the presence of hydroxyl, carboxyl and sugar derivatives in the bioflocculants. Thermal characterization by differential scanning calorimetry (DSC) showed the crystalline transition and the melting point (Tm) at 90-100°C. Effects of bioflocculant dosage and pH on the flocculation of clay fines were evaluated. Highest bioflocculation efficiency on kaolin clay suspensions was observed at an optimum bioflocculant dosage of 5g/L. The optimum pH range for the maximum bioflocculation was at pH7–9. Bioflocculants exhibited high efficiency in dye decolorization. The maximum Cr (VI) removal was found to be 85% for L (bioflocculant dosage at 2g/L). This study demonstrates that microbial bioflocculants find potential applications in mineral processing such as selective flocculation of mineral fines, decolorization of dye solutions and in the remediation of toxic metal solutions.

Assessment and Mechanism Investigation of Selective Flocculation Process for Ultrafine Chromite Particle

During beneficiation of low-grade chromite ore, huge amounts of ultrafine tailings are generated and contain substantial metal values which need to be recovered. Selective flocculation technique is one of the processes for beneficiation of ultrafine particles. Here an attempt was made to establish selective flocculation process by using two types of synthetic mixtures. In addition to this, selective flocculation was also attempted on natural tailings. It was found that it is possible to enrich the chromite value using the selective flocculation process. The selectivity of the wheat starch to the chromite mineral was also investigated using image analysis, FTIR analysis, and zeta potential analysis.

Effects of Water Chemistry on Hematite Selective Flocculation and Dispersion

The only industrially proven method for the beneficiation of fine-grained (<25 µm) hematite ores is selective flocculation and dispersion desliming followed by reverse cationic flotation. This process is reliant upon both water chemistry and proper reagent selection and dosing for effective separation of the hematite from gangue minerals. This study was performed to assess the effects of water chemistry on the beneficiation process in a pilot-scale deslime thickener. Grade versus recovery curves were constructed at varying water chemistries. In each set of experiments the concentration of one water chemistry parameter was varied while all others were held constant. The varied parameters included pH, sodium concentration and calcium concentration.The optimal pH for the separation of hematite from silica was found to be around 10.5. This was hypothesized to be due to a maximization in starch selective adsorption. Minimization in the sodium concentration showed increases in both the grade and the recovery of iron. Minimization in the calcium concentration showed increases in the grade of iron but losses in the recovery of iron. This study showed that the most effective way at increasing both the grade and recovery of the process was to optimize the pH and minimize the sodium concentrations.