Quartz Collector Research Articles

Mechanism of action of the novel reagent dodecyl trimethyl ammonium chloride on magnesite and quartz surfaces

Silica impurities are one of the key factors that reduce the quality of magnesite. In this experiment, dodecyl trimethylammonium chloride (KDMP) was used as a quartz collector for silica-magnesium separation, and mineral flotation tests demonstrated that KDMP can effectively desiliconize and purify magnesite under the conditions of 20 mg/L and pH 5.0. Contact angle and Zeta potential measurements show that KDMP alters quartz’s characteristics more than magnesite. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) tests show that KDMP works on quartz and adsorbs solely on its surface, not on magnesite. Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) images revealed that the KDMP collector adsorbed exclusively on the quartz surface, forming a layer of adsorption structure, but was weak on the magnesite surface. As a result, the KDMP collector is a highly intriguing flotation collector that can efficiently separate magnesite from quartz while also introducing a new form of collector for the separation and purification of low-grade magnesite.

Effective flotation separation of malachite from quartz with a selective collector: Collection ability, separation performance and adsorption mechanism

In this study, we focused on the collecting features and sorption mechanism of stearyl diethanolamine (SDA) used as a novel collector towards the surfaces of quartz and malachite, to recover efficiently malachite from quartz. The flotation results demonstrated that DSA displayed an excellent collection performance for quartz but not for malachite. At pH 6.50, with 8 mg/L SDA, effectively recovering malachite from quartz was achieved by reverse flotation, in which 92.71 % of malachite was recovered and 91.91 % of quartz was removed, coupled with a high separation efficiency (SE) of 84.63 % and a high concentrate Cu grade of 52.52 %. Surface wettability studies suggested that SDA significantly improved the surface hydrophobicity of quartz but not malachite, as evidenced by the significantly increased contact angle of quartz (from 24.16° to 97.16°), which resulted in the excellent floatability of quartz. Adsorption amount detection results revealed that the adsorption density of SDA on quartz was much higher than that on malachite, namely 0.065 mg/g for quartz and 0.0049 mg/g for malachite, which enhanced the hydrophobicity of quartz. Zeta potential characterization and FTIR detection evidenced that apart from the strong electrostatic attraction interaction of the positively charged SDA+ with the quartz surface with negative charge, the strong adsorption of SDA onto quartz also depended much on the hydrogen bonding interaction between quartz’s Si-OH groups and SDA’s hydroxyl groups. Therefore, SDA can be regarded as a highly selective quartz collector to realize the effective recovery of malachite.

Selective collection performance of an efficient quartz collector and its response to flotation separation of malachite from quartz

In this study, laurylamine ethoxylate with fifteen ethoxylate units (LAEO-15) was employed as a quartz collector for the recovery of malachite from quartz via reverse flotation. Its collecting performance and adsorption mechanism were evaluated by flotation tests and surface analyses. The results of flotation tests suggested that LAEO-15 had an intense ability to collect quartz instead of malachite, and displayed a high flotation selectivity, which promoted the significant floatability differences of both minerals. XPS confirmed that quartz adsorbed a much larger quantity of LAEO-15 than malachite, resulting in the selective collection of quartz with LAEO-15. Zeta potential and FTIR characterization further uncovered that the strong adsorption of LAEO-15 was driven by hydrogen bonding and electrostatic attraction, while electrostatic repulsion hindered the LAEO-15 adsorption on the surface of malachite. As a result, the effective separation of malachite and quartz was realized with 20 mg/L LAEO-15 at pH 6.30 via reverse flotation, in which 92.54% of malachite was recovered and 92.72% of quartz was removed, coupled with a high SI value of 12.57 in concentrate. Therefore, compared with conventional collector dodecylamine, LAEO-15 exhibited high selectivity and purification effectiveness for the separation of malachite from quartz.

Differential adsorption of a high-performance collector at solid–liquid interface for the selective flotation of hematite from quartz

Different adsorption behaviors of the collector on the mineral surface play a crucial part in the flotation separation of different minerals by selectively modifying the wettability of mineral surfaces. In this investigation, to effectively remove quartz from hematite via reverse flotation, decaethoxylated stearylamine (DEOSA) was first introduced as a high-performance collector for quartz. The selective collecting performance and differential adsorption mechanisms of DEOSA for both hematite and quartz were studied by flotation experiments and surface analysis. Flotation results suggested that DEOSA displayed excellent collecting capacity for quartz against hematite and the effective removal of quartz from hematite was achieved. Adsorption capacity measurements and surface wettability analysis demonstrated that much larger amounts of DEOSA adsorbed onto quartz than hematite significantly enhanced the quartz surface hydrophobic whether the depressant starch was present or not, which resulted in the excellent flotation performance of quartz. Surface electrical characterization and Fourier transform infrared (FTIR) analysis further proved that the combination of hydrogen bonding and electrostatic attracting force enhanced the strong adsorption of DEOSA onto the quartz, achieving the efficient collection performance of DEOSA for quartz. Based on these findings, DEOSA can be used potentially as a strong-collection and high-performance quartz collector for recovering hematite from quartz via reverse flotation.

An HPLC Method for the Determination of Amines in Flotation Pulp Based on Derivatization

Alkyl amines are surfactants used as quartz collectors in the reverse flotation of phosphate ores. It is important in both research and industrial practice to quantify amine concentration in the solution and/or wastewater. A simple and rapid method using high-performance liquid chromatography (HPLC) was developed to quantitatively determine the concentration of amine collectors (including dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine) in a mineral flotation system. The method involved a sample derivatization procedure with 9-fluorenyl methoxycarbonyl chloride (FMOC-Cl) and separation/determination by HPLC coupled with a fluorescence detector. The calibration curves showed good linearity (R2 > 0.9956) in the range of 0.20–5.00 µg/mL, and the recoveries of dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine were in the ranges of 84.93–97.64%, 89.93–101.92%, 85.29–98.37%, and 93.57–103.26%, respectively. The method was successfully used to quantify amines in wastewater from flotation experiments and artificial flotation wastewater (amine solution after activated carbon adsorption). The results from the analysis of four amines in the solution demonstrated that the proposed method is suitable for the simultaneous determination of amines in flotation pulp and wastewater.

Differences in Etheramines Froth Properties and the Effects on Iron Ore Flotation. Part I: Two-Phase Systems

ABSTRACT Etheramines are quartz collectors and also play a role as frothers in cationic reverse flotation of iron ores. While the adsorption of this surfactant on quartz surface has been widely investigated, the impact of its foam/froth properties on the selectivity in iron ore flotation has not yet been addressed in detail. The structural differences between ethermonoamine and etherdiamine result in distinct adsorption and frothing properties, offering versatility in the concentration of hematite. This study addressed the effect of the etheramine type on flotation selectivity, focused on the analysis of frothing properties. The characterization of the surfactants in the pure state and in two-phase systems (liquid/air) was conducted to investigate the behavior of etheramines concerning foam forming and stabilization. The surface tension measurements showed greater activity of etherdiamine at the liquid–air interface in comparison with ethermonoamine, which was more effective to prevent bubble coalescence and produce smaller bubbles, despite the reagent’s higher critical coalescence concentration. Ethermonoamine presented faster foamability for concentrations greater than the observed critical coalescence concentration values as well as greater water recovery in foam, whereas the double CH2 group and higher molecular weight imparted strong lipophilic character to etherdiamines, producing drier, voluminous, and more stable foams, with longer lifetime. These results are fundamental for the evaluation of three-phase systems, which will be presented in a subsequent paper.

Investigation of nanobubble enhanced reverse anionic flotation of hematite and associated mechanisms

Hematite is commonly upgraded in China using a reverse anionic flotation process with starch as depressant for hematite, Ca2+ as activator and fatty acids as collector for quartz. The Anshan type of hematite is well known for its low grade, fine dissemination, difficulty in upgrading, and huge reserve in China. To investigate effects of nanobubbles and different reagents on the flotation process of this particular hematite, batch flotation tests were conducted with a mechanical flotation cell integrated with a cavitation device that generates nanobubbles under different process parameters including corn starch dosage, lime (CaO) dosage, collector dosage, and air flow rate through the nanobubble generator. Significant improvements in hematite flotation performance was achieved in the presence of nanobubble. The nanobubble flotation results and associated mechanisms are discussed based on up-to-date chemistry of hematite flotation and unique nanobubble characteristics.

Reverse flotation separation of quartz from phosphorite ore at low temperatures by using an emerging Gemini surfactant as the collector

Quartz, the gangue of phosphorite ore, is challenging to be separated at low temperatures. In this work, an amine-typed Gemini surfactant, N,N’-bis(dodecyldimethyl)-1,4-butane dibromide (BBD) was recommended as an emerging collector for reverse flotation separation quartz from phosphorite ore. Its collecting ability for quartz and selectivity for phosphorite were also compared with the corresponding unimolecular surfactant 1-dodecylamine (DA) under various experimental conditions. The flotation test results indicated that the BBD, which exhibited a forceful collecting function to quartz and preeminent selectivity for phosphorite at room temperature (25 °C), was a better collector than the conventional DA collector. With 2 × 10-5 mol/L dosage, the quartz recoveries with BBD and DA were 99.0% and 64.5%, respectively. Meanwhile, the phosphorite recoveries of two were not more than 16.0%. When the environment temperature descended, the separating power of the BBD collector for quartz exhibited a more definite stable trend. The recovery of quartz with BBD as a collector raised notably from 61.5% to 93.0% with temperature ranging from 0 °C to 15 °C. However, in the same conditions, the recovery with DA as a collector only raised from 19.5% to 49.5%. At 0 °C, DA lost the vast majority of its collector performance, while BBD still showed high performance. Therefore, BBD presented a better flotation ability for separation of quartz than DA at low temperatures.

Smart collectors: Control of the wettability and floatability of quartz with UV irradiation

Quartz is a hydrophilic mineral that usually associates with other ores. In this paper, the effect of UV stimuli on the wettability and floatability of quartz was studied. An azobenzene-containing surfactant was synthesized and its structure was identified by 1H NMR. We used UV–vis and 1H NMR spectra of the surfactant to study its photoisomerization. After UV irradiation of the surfactant molecular, the trans isomer concentration decreases and the cis isomer concentration increases; both the aromatic protons of the azobenzene moiety and aliphatic protons experience an upfield shift, indicating that the surfactant molecular isomerizes from the trans isomer to the cis form. We used contact angle measurements to demonstrate that UV irradiation decreases the hydrophobicity of the quartz and increases the adhesion tension of the surfactant on quartz. The results of flotation tests demonstrate that the azobenzene-containing surfactant has higher performances than alkyl amine salt, and UV irradiation improves the selectivity of the azobenzene-containing surfactant in the flotation of quartz. This study demonstrates that the azobenzene-containing surfactant can be used as a light-responsive collector for quartz in the flotation of phosphate ores.

Optimization of Reverse Cationic Flotation of Low-Grade Iron Oxide from Fluorspar Tails Using Taguchi Method

Due to gradual depletion of high-grade iron ores, there is a need to investigate the treatment of low-grade iron ores. Current procedures are time and cost intensive. Batch laboratory scale reverse cationic flotation was employed to concentrate low-grade Fe ore, found in fluorspar tails in the form of hematite. This study used two types of depressants (soluble starch and dextrin) and two types of amines (primary mono-amine and tertiary mono-amine). Optimisation of the process investigated parameters such as pH, collector type and dosage, depressant type and dosage, conditioning time, solids content, agitation speed and air flow rate. Owing to the high number of experiments when all possible combinations are investigated, Taguchi design of experiment method was utilised to streamline the number of experiments and optimize parameters using orthogonal array and signal–noise ratio (SN). The SN was used to determine the optimum conditions and analyse the relative significance of parameters studied. The results showed that both depressants were efficient for hematite depression; however, soluble starch produced better results when compared to Betachem 30D. Both Betacol 373 and Dodecylamine collectors were efficient as quartz collectors; however, Dodecylamine produced better results when compared to Betacol 373. Ranking of parameter using SN ratio showed that pH was the most critical parameter in obtaining higher Fe grade concentrate and the optimum pH is 10. De-slimming leads to low recoveries during reverse flotation of iron ores. The main conclusion is that Taguchi method can be used to optimise a reverse cationic flotation process of a low-grade iron ore.

Flotation of quartz using ionic liquid collectors with different functional groups and varying chain lengths

The application of imidazolium, ammonium, and pyridinium based ionic liquids (ILs) as the flotation collectors of quartz has been investigated. The flotation studies have been carried out for pure quartz, quartz-hematite synthetic mixture and a low grade banded hematite quartzite (BHQ) ore while the trend of floatabilities has been explained in terms of the structural differences of the ILs. The flotation of pure quartz using the ammonium and pyridinium based IL collectors has exhibited an excellent performance; where about 100% quartz could be floated at a collector concentration of 5∗10−5M. The results are found better compared to the imidazolium ILs and conventional quartz collectors like dodecylamine (DDA) and cetyl trimethyl ammonium bromide (CTAB). The ammonium and pyridinium based collectors also show better iron grade and recovery compared to the imidazolium collectors during the reverse flotation of the synthetic hematite-quartz mixture and BHQ ore. Using these collectors, an iron ore concentrate of ∼62% Fe at ∼75% recovery could be obtained from the BHQ ore containing ∼38% Fe. In the Fourier Transform Infra Red spectroscopy (FTIR), the peak intensity at 2900cm−1 due to the presence of alkyl groups signifies the extent of adsorption of the collectors on quartz. The N/Si ratio and CC peak area as determined by the X-ray photoelectron spectroscopy (XPS) results show the relative adsorption of the IL collectors. The pyridinium based IL collector show better adsorption strength compared to all others ILs under study. The better flotation results in the case of the ammonium and pyridinium collector are attributed to the presence of higher alkyl chain length inducing better hydrophobicity.

Ionic liquids as novel quartz collectors: Insights from experiments and theory

Application of quaternary ammonium based ionic liquids (IL’s) as flotation collectors of quartz has been investigated. Effect of number of carbon atoms in the four identical alkyl chains of the IL’s has been studied. The adsorption behaviour of the IL’s on the quartz surface is ascertained through FTIR, XPS and molecular modelling. The FTIR peak at 2900cm−1 indicates the adsorption of the IL’s onto the quartz surface, which is further substantiated by the appearance of the N (1S) peak in the X-ray photoelectron spectra (XPS). Curve splitting data of C (1S) suggests the maximum adsorption for the IL tetrahexylammonium iodide (THEX). Flotation results of pure quartz using ionic liquids are found to be better compared to the conventional collectors such as dodecylamine (DDA) or cetyltrimethylammonium bromide (CTAB). It is possible to float 92–100% quartz by using a THEX concentration of 4.8 × 10−5M. IL collectors are further applied in the flotation of a low grade banded hematite quartzite (BHQ) iron ore with ∼38% Fe. It is possible to achieve an iron concentrate of 63.6% Fe at 63.2% recovery by using THEX as the collector. Molecular simulations using the COMPASS forcefield explains the IL–quartz adsorption mechanism comprising of both electrostatic and van der Waals forces. Floatability of quartz has been correlated with the surface coverage and adsorption energy calculations. The IL’s used here are found to be better quartz collectors than the conventional ones as they show better collecting efficiency in lower dosages. Flotation using these IL’s does not require frothers which is an added advantage compared to the conventional collectors.

Fate and Transport of Molybdenum Disulfide Nanomaterials in Sand Columns.

Research and development of two-dimensional transition metal dichalcogenides (TMDC) (e.g., molybdenum disulfide [MoS2]) in electronic, optical, and catalytic applications has been growing rapidly. However, there is little known regarding the behavior of these particles once released into aquatic environments. Therefore, an in-depth study regarding the fate and transport of two popular types of MoS2 nanomaterials, lithiated (MoS2-Li) and Pluronic PF-87 dispersed (MoS2-PL), was conducted in saturated porous media (quartz sand) to identify which form would be least mobile in aquatic environments. The electrokinetic properties and hydrodynamic diameters of MoS2 as a function of ionic strength and pH were determined using a zeta potential analyzer and dynamic light scattering techniques. Results suggest that the stability is significantly decreased beginning at 10 and 31.6 mM KCl, for MoS2-PL and MoS2-Li, respectively. Transport study results from breakthrough curves, column dissections, and release experiments suggest that MoS2-PL exhibits a greater affinity to be irreversibly bound to quartz surfaces as compared with the MoS2-Li at a similar ionic strength. Derjaguin-Landau-Verwey-Overbeek theory was used to help explain the unique interactions between the MoS2-PL and MoS2-Li surfaces between particles and with the quartz collectors. Overall, the results suggest that the fate and transport of MoS2 is dependent on the type of MoS2 that enters the environment, where MoS2-PL will be least mobile and more likely be deposited in porous media from pluronic-quartz interactions, whereas MoS2-Li will travel greater distances and have a greater tendency to be remobilized in sand columns.

Aliquat-336 as a novel collector for quartz flotation

The study illustrates the first ever use of Aliquat-336 (C25H54ClN), an ionic liquid, in the flotation separation of quartz from hematite. Laboratory flotation studies of hematite, quartz and their synthetic mixture have shown selective collecting action of Aliquat-336 toward quartz. At an Aliquat-336 dosage of 280g/t, 97% quartz is floated at slightly alkaline pH (∼8), whereas hematite recovery is only 8%. Flotation of the synthetic mixture of hematite: quartz (1:1), with Aliquat-336 as the quartz collector and starch as the hematite depressant, has resulted in an iron concentrate of 63–65% Fe with 85–88% recovery. The reverse flotation behavior of the low grade banded hematite quartzite (BHQ) using Aliquat-336 as the collector has been investigated. It is observed that, iron values up to ∼65% Fe with 60% recovery can be achieved from the ore containing ∼38% Fe. Surface potential measurement and FTIR spectra lead to the indication of electrostatic adsorption between Aliquat-336 and quartz.

Use of Chemically Modified Nanocelluloses in Flotation of Hematite and Quartz

Nowadays, there are strong economical, ecological, and social incentives to develop novel green chemicals from renewable resources to reduce the environmental impact of processing. Cellulose, which is the most abundant natural polymeric source, offers one promising green alternative that could replace the present synthetic chemicals. In this study, two types of modified nanocelluloses (amphiphilic and hydrophilic) were produced and tested to understand their ability to function as collectors and depressants in the mineral flotation process for pure hematite and pure quartz. Hydrophilic nanocellulose (called dicarboxylic acid nanocellulose (DCC)) was observed to be a more selective depressant for hematite than for quartz. DCC seems to be most effective at a pH level of 6. Amphiphilic nanocrystalline celluloses (ANCCs) work as collectors. ANCCs were pH-dependent collectors, and they worked well at a pH value of 10 in the case of the investigated oxides (hematite and quartz). This research indicated that nanocelluloses functioned already at least at the same level as a commercial starch depressant for hematite and as an ether amine collector for quartz.

Use of the ionic liquid-tricaprylmethyl ammonium salicylate (TOMAS) as a flotation collector of quartz

Tricaprylmethyl ammonium salicylate (TOMAS), an ionic liquid has been employed as a collector for the flotation of quartz. The sign reversal of zeta potential of quartz from negative to positive values and increase in contact angle from 80 to 700 by the addition of TOMAS have substantiated the interaction of TOMAS with the quartz surface. The change in morphology as indicated in SEM and two peaks at 2933 and 2857cm−1 owing to the vibrations of CH2 and CH3 as seen in FTIR spectra support the adsorption of the reagent on quartz. The N(1s) peak as observed in the XPS spectra of the quartz treated with TOMAS, and the curve fitting data of C(1s) corroborate the reagent-mineral interaction. A comparative study of adsorption of DDA and TOMAS using classical molecular mechanics also suggests stronger adsorption of the latter on the hydroxylated quartz surface. Flotation studies of quartz at natural pH indicate ∼100% quartz recovery at a TOMAS concentration of 8*10−5M. Flotation of the natural occurring BHQ iron ore containing 38.7% Fe and 43.8% SiO2 concludes that a TOMAS concentration of 3.71*10−5M is sufficient to achieve 67.3% Fe with 66.6% iron recovery. TOMAS stands out as a better quartz collector, when compared with DDA.

Effect of amine and starch dosages on the reverse cationic flotation of an iron ore

In iron ore concentration, reverse cationic flotation of quartz has been successfully employed for particles below 150μm previously deslimed. Amine and starch are used, respectively, as quartz collector and iron oxides depressant. Understanding the mechanisms of reagents interaction is relevant to improve the separation selectivity, especially for high amine dosages. The term clathrate was used to explain this interaction, meaning a molecular compound in which molecules of one species occupy the empty spaces in the lattice of the other species, resulting in the depression of hydrophobic minerals. Laboratory scale experiments were carried out with itabirite iron ore in three different size ranges. The clathrate formation between molecules of amine and starch may explain the increase of SiO2 content in the concentrates of the coarse size range (−150+45μm) due to an increase in amine dosage.

Adhesion of Escherichia coli onto quartz, hematite and corundum: Extended DLVO theory and flotation behavior

The adhesion of Escherichia coli onto quartz, hematite and corundum was experimentally investigated. A strain of E. coli was used that had the genes for expressing protein for silica precipitation. The maximum cell adhesion was observed at pH <4.3 for quartz and at pH 4.5–8.5 for corundum. For hematite, cell adhesion remained low at all pH values. The microbe–mineral adhesion was assessed by the extended DLVO theory approach. The essential parameters for calculation of microbe–mineral interaction energy (Hamaker constants and acid–base components) were experimentally determined. The extended DLVO approach could be used to explain the results of the adhesion experiments. The effect of E. coli on the floatability of three oxide minerals was determined and the results showed that E. coli can act as a selective collector for quartz at acidic pH values, with 90% of the quartz floated at 1.5 × 10 9 cells/ml. However, only 9% hematite and 30% corundum could be floated under similar conditions. By using E. coli and no reagents, it was possible to separate quartz from a hematite–quartz mixture with Newton's efficiency of 0.70. Removal of quartz from the corundum mixture was achieved by E. coli with Newton's efficiency of 0.62.

Role of Solution Chemistry and Ion Valence on the Adhesion Kinetics of Groundwater and Marine Bacteria

The role of solution chemistry on bacterial adhesion has been investigated using a radial stagnation point flow (RSPF) system. This experimental system utilized an optical microscope and an image-capturing device to directly observe the deposition kinetics of a groundwater bacterium, Burkholderia cepacia G4g, and a marine bacterium, Halomonas pacifica g. Experiments were carried out under well-controlled hydrodynamic and solution chemistry conditions, allowing for the sensitivity of bacterial adhesion behavior to be examined under a range of ionic strength and valence (KCl vs CaCl2) simulating groundwater and marine environments. Complimentary cell characterization techniques were conducted to evaluate the electrophoretic mobility, hydrophobicity, surface charge density, and viability of the bacteria under the same range of conditions. Solution chemistry was found to have a marked effect on the electrokinetic and surface properties of bacteria and the quartz collector, as well as on the resulting rate of bacterial deposition. Comparable adhesion trends were observed for B. cepacia G4g and H. pacifica g. Specifically, the deposition rates of the two bacteria species in both KCl and CaCl2 solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which considers the combination of van der Waals and electrostatic double-layer interaction forces. However, in some cases, experimental results showed bacterial deposition behavior to deviate from DLVO predictions. On the basis of the systematic investigation of bacterial cell characteristics, it was found that Ca2+ ions play a distinct role on bacterial surface charge, hydrophobicity, and deposition behaviors. It is further suggested that bacterial adhesion is determined by the combined influence of DLVO interactions, electrosteric interactions associated with solution chemistry, and the hydrodynamics of the deposition system.

Exploiting the dual functions of polymer depressants in fine particle flotation

Fine hydrophilic particles are known to be entrained with water in flotation of many ores. Flocculation of the hydrophilic particles by polymer depressants could potentially reduce the mechanical entrainment of these particles. This paper reports testwork completed on fine particles of several solids, iron oxide, hydroxyapatite and sphalerite, as well as on a relatively coarse quartz sample (− 75 + 38 μm). Dodecylamine was used as a collector for quartz, and several dispersants and polymer depressants, including sodium silicate, sodium metaphosphate, zinc sulfate, cornstarch, corn dextrin and carboxymethyl celluloses (with molecular weights of both 700,000 and 80,000) were used as flotation modifiers. The major part of the testwork involved flotation tests in a 200 mL flotation column. It was observed that flocculation of the fine hydrophilic particles significantly reduced their mechanical entrainment, while dispersion severely aggravated it. Thus, in the flotation separation of synthetic mixtures of the − 75 + 38 μm quartz and fine (reagent grade) iron oxide or hydroxyapatite, polymer depressants that caused flocculation performed better than those that did not cause flocculation.