Surface characterisation,collector adsorption and flotation response of enargite in a redox potential controlled environment

We previously investigated oxidation of the surface of natural enargite (Cu₃AsS₄) under potentiostatic control and the formation of oxidation species at the mineral surface at selected applied potentials in the oxidative range. Here we further extended the research by incorporating flotation collectors into the system. Electrochemical techniques, X-ray photoelectron spectroscopy (XPS) and microflotation in a redox potential controlled environment were applied to examine surface properties, collector adsorption and flotation response of enargite in pH 10 solutions of sodium ethyl xanthate (SEX) and sodium dialkyl dithiophosphinate (3418A). The spectral details of XPS analysis of electrochemically treated enargite surfaces show significant adsorption of SEX and 3418A collectors onto enargite at an applied voltage of +516 mV, but no adsorption of both collectors at −400 mV. The results of XPS analysis agree with the floatability of enargite determined by microflotation, showing that the flotation recovery was highest at high oxidative potential (+516 mV), then decreased at low oxidative potential (+100 mV) and was very poor at −400 mV. These results confirm that enargite floatability can be efficiently controlled electrochemically.     

Adsorption of dithiophosphate and dithiophosphinate on chalcopyrite

Electrochemical behavior of chalcopyrite was investigated in the absence and presence of dithiophosphate (DTP) and dithiophosphinate (DTPI), selective thiols against Fe-sulfides in the flotation of sulfide ores, in potentiostatically controlled electrochemical condition. Diffuse reflectance Fourier transformation (DRIFT) spectroscopy was applied to determine the type of adsorbed collector species, and Hallimond tube flotation tests were performed to clarify the role of polarization potential and thiol collectors on the floatability of chalcopyrite. DRIFT spectroscopy study proposed that dithiolate of DTP, (DTP)₂, was the major surface compound formed under oxidizing potentials in slightly acidic and neutral conditions. However, DTP species formed on mineral surface in alkaline condition could not be determined possibly due to heavy surface coating of metal oxyhydroxides. DTPI species formed on chalcopyrite was found to be in the form of CuDTPI + (DTPI)₂. Additionally, presence of adsorbed DTPI, DTPI⁰, was also detected. Self-induced floatability was significantly high particularly in slightly acidic condition and decreased by increasing pH due to surface coating of metal oxyhydroxides. Addition of both collectors improved the flotation performance at all pH values. However, the positive effect of DTP at high alkaline pH values was lower than that of DTPI. This was attributed to weak collecting property and lower hydrocarbon chain length of DTP compared to DTPI. Effect of pulp potential could not be observed in slightly acidic condition, but it became apparent at higher pHs. Although better flotation responses were obtained in mildly oxidizing potentials, both collectors enlarged the floatability potential range of chalcopyrite.     

Adsorption mechanism of mixed anionic/cationic collectors in Muscovite – Quartz flotation system

The flotation separation of muscovite from quartz was investigated using mixed sodium oleate/dodecylamine acetate (NaOL/DDA) collectors. The experiments were conducted on single minerals and on a mixture of minerals, and their collecting performances were studied by means of Fourier transform infrared (FTIR) spectroscopy, zeta potential technique and X-ray photoelectron spectroscopy (XPS). The results show that neither muscovite nor quartz is floated with NaOL alone, while using DDA alone, they can be separated only at strong acid conditions (pH < 3). Mixed NaOL/DDA collectors exhibits excellent performance in the flotation separation of muscovite from quartz at pH 10. The ratio of the mixed collectors is found to be an important criterion in the flotation tests. The best separation result (muscovite recovery of 80% and quartz recovery of 10%) could be achieved with NaOL/DDA molar ratios of 3/1 and 2/1 at pH 10. The co-adsorption of NaOL and DDA is found on muscovite surface by strong electrostatic interaction, hydrogen bonding and chemical adsorption. This study may provide guidance for the flotation mechanism and application of mixed anionic/cationic collectors.     

Selective separation of fine albite from feldspathic slime containing colored minerals (Fe-Min) by batch scale dissolved air flotation (DAF)

In this study, the separation of feldspar minerals (albite) from slimes containing feldspar and iron containing minerals (Fe-Min) was studied using dissolved air flotation (DAF) technique whereby bubbles less than 100 μm in size are produced. Before the flotation experiments with slimes, single flotation experiments with albite and Fe-Min were carried out using DAF in order to obtain optimum flotation conditions for the selective separation of feldspar from the slimes. Flotation experiments were performed with anionic collectors; BD-15 (commercial collector) and Na-oleat. The two methods of reagent conditioning were tested on the flotation performance; traditional conditioning and charged bubble technique. In addition, the effect of pH, flotation time, rising time, and drainage time which influence the selective separation in the DAF system were studied in detail. Overall, the flotation results indicated that the separation of albite from Fe-Min can be achieved with DAF at 5 min of rising time and 5 min of drainage time. Interestingly, these results also showed that the conditioning of the particles with the charged bubbles increased the flotation recovery of Fe-Min compared to the traditional conditioning. Furthermore, the flotation tests with the feldspathic slime sample were carried out under the optimum conditions obtained from the systematic studies using the single minerals. The charged bubble technique produced an albite concentrate assaying 0.33% Fe₂O₃ + TiO₂ and 11.07% Na₂O + K₂O from a slime feed consisting of 1.06% Fe₂O₃ + TiO₂ and 10.36% Na₂O + K₂O.     

Flotation and adsorption of mixed cationic/anionic collectors on muscovite mica

The adsorption of dodecylamine acetate (DAA), sodium oleate (NaOL) and DAA–NaOL mixtures on muscovite mica were investigated through flotation tests, zeta potential measurements, and pyrene fluorescence tests. The results show that the muscovite mica has a negative charge over the pH range 2–12. The muscovite mica did not float in the presence of NaOL alone. However, the recovery of muscovite mica ranged from ca. 80% (at pH 2) to 50% (at pH 11) using DDA alone. In the presence of mixed DAA–NaOL, recovery ranged from ca. 80% (at pH 2) to 90% (at pH 11). The individual cationic collectors DAA can be adsorbed strongly onto the muscovite mica, but no significant adsorption of anionic collectors NaOL can be detected by zeta potential measurements. In the mixed systems, the adsorption of both the cationic and anionic collectors are enhanced due to co-adsorption. The presence of NaOL in the mixture decreases the electrostatic head–head repulsion between the surface and ammonium ions and increases the lateral tail–tail hydrophobic bonds. Molecular dynamics (MD) simulations were conducted to further investigate the adsorption of DDA, NaOL, and DAA–NaOL on the (0 0 1) basal planes of muscovite using Materials Studio 5.0 program. The conclusions drawn from theoretical computations are in good agreement with experimental results.     

Contact angle and bubble attachment studies in the flotation of trona and other soluble carbonate salts

Trona, Na₂CO₃ · NaHCO₃ · 2H₂O, is mined as the primary source for sodium carbonate production in the United States. Recent studies have shown that the flotation method can be used for pre-processing of trona ore to remove insoluble mineral contaminants for the production of soda ash (sodium carbonate). Studies with carbonate salts suggest that certain important factors can affect their flotation response, including viscosity of the brine and interfacial water structure. Flotation studies showed that contrary to the strong flotation of NaHCO₃ with both anionic and cationic collectors, Na₂CO₃ does not float at all. Based on the analysis of interfacial water structure in saturated brines, Na₂CO₃ was found to act as a strong water structure maker, whereas NaHCO₃ acts as a weak water structure maker. Bubble attachment time measurements suggest that collector adsorption at the surface of NaHCO₃ induces flotation; this is not the case for Na₂CO₃. Contact angle measurements indicated that the surface of Na₂CO₃ is hydrated to a great extent, whereas the NaHCO₃ salt surface is less hydrated. These results reveal that there is a strong relationship between the interfacial water structure and the contact angle of these salts. The less stable NaHCO₃ surface is ascribed to the interfacial water structure which allows for NaHCO₃ flotation with both anionic and cationic collectors.     

Influence of bromine modification on collecting property of lauric acid

Bromine atom with strong electronegativity was introduced to α-carbon position of lauric acid (LA) by solvent-free method (Hell–Volhard–Zelinski reaction) at ambient pressure in laboratory, and the synthesized product α-Bromolauric acid (CH₃(CH₂)₉CHBrCOOH, α-BLA) was used as a new type collector for the flotation of quartz mineral. The flotation properties of pure quartz using α-BLA as a collector were investigated by single mineral flotation tests. The adsorption mechanism of α-BLA collector on quartz surface was established by zeta potential measurements, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), in conjunction with the results of quartz micro-flotation tests. Pure mineral flotation results showed that the collector α-BLA exhibited an excellent performance at alkaline conditions (pH ⩾ 11.50), activator CaCl₂ concentration 1.0 × 10⁻⁴ mol/L, and collector concentration 1.5 × 10⁻⁴ mol/L in a relatively lower temperature 15 °C, where about 99.8% of the quartz could be floated out. Compared with collector LA, the new synthesized collector α-BLA is more tolerant to lower pulp temperature and fluctuations of the reagents dosages. The study revealed that the α-BLA collector had adsorbed on the surface of pure quartz in the forms of chemical interaction, electrostatic adsorption and hydrogen bonding adsorption based on the results of zeta potential measurements, FT-IR spectra, and XPS.     

On the nanobubbles interfacial properties and future applications in flotation

Nanobubbles, generations forms, basic studies and applications constitute a growing research area, included their usage in advanced mineral flotation. Yet, there are investigation needs for sustainable generation procedures, stability and understanding the nanobubbles interfacial properties and structures. Results proved that a reduction in pressure makes the super-saturated liquid suffers cavitation and nanobubbles were generated. Medium pH and solutions tested were adjusted, in the air saturation vessel, before the nanobubbles were formed, and this allowed to control (in situ) the surface charge/zeta potential-size of the forming nanobubbles. Measurements obtained with a ZetaSizer Nano equipment showed zeta potential values, in the presence of 10⁻² mol L⁻¹ NaCl, displaying sigmoidal pH behaviour between pH 2 (+26 mV) and 8.5 (−28 mV); an isoelectric point was attained at pH 4.5 and were positively charged (up to 23 mV) in acidic medium, a phenomenon which has not been previously observed. In alkaline medium, bubbles were highly negative zeta potential (−59 mV) at pH 10. The double layers appear to play a role in the formation of stable nanobubbles providing a repulsive force, which prevents inter-bubble aggregation and coalescence. Accordingly, the sizes of the nanobubbles depended on their charge and increased with pH, reaching a maximum (720 nm) around the isoelectric point (±5 mV). Highly charged and small nanobubbles (approximately 150–180 nm) were obtained in the presence of surfactants (10⁻⁴ mol L⁻¹ of alkyl methyl ether monoamine or sodium dodecyl sulphate); the zeta potential values in these experiments followed a similar trend of other reported values, validating the technique used with the nanobubbles sizes varying with pH from 150 to 400 nm. Thus, charged and uncharged stable nanobubbles can be tailor-made with or without surfactants and it is expected that their use will broaden options in mineral flotation especially if collectors coated nanobubbles (“bubble-collectors”) were employed. A detailed and updated review on factors involving stability, longevity and coalescence of nanobubbles was made. It is believed that future trend will be on sustainable formation and application of nanobubbles at industrial scale contributing to widen applied research in mineral, materials processing and liquid effluent treatment by advanced flotation.     

The effect of reagents on selective flotation of smithsonite–calcite–quartz

In this paper the effects of sodium sulphide, sodium hexa methaphosphate (SH), sodium fluoric, starch and sodium silicate adsorption on smithsonite, quartz and calcite surfaces at various pH values, and using Armac C and oleic acid as collectors were investigated through microflotation. Also, the effects of various primary amine collectors (Armac C, Armac T, Flotigam SA, Flotigam TA and Armeen TD) were investigated for smithsonite flotation. The flotation tests were performed using purified samples from Angooran mine by the microflotation technique. The cationic flotation results showed that the maximum recovery of smithsonite could be improved to 92% using 400 g/t Armac C and 500 g/t sodium sulphide at pH 11. Also, the quartz and calcite recoveries reached 98% and 89%, respectively, at the above mentioned conditions. Moreover, using 1250 g/t SH and 1500 g/t sodium silicate as a depressant, the quartz and calcite recoveries decreased to 70% and 20%, respectively, and also the smithsonite recovery was reduced to 82%. Furthermore, the experiments showed that the behavior of sodium fluoric as a quartz depressant is similar to that of sodium silicate. Flotation results using oleic acid revealed that the maximum recovery of 90% occurs at pH 9 and 500 g/t oleic acid. Also, the quartz and calcite recoveries reached 26% and 87%, respectively, in the anionic flotation conditions. Increasing amount of sodium silicate to 2000 g/t caused a decrease in the smithsonite recovery to 87% and also decreased the calcite and quartz recoveries by 10% and 15%, respectively.     

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 20 μm, 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 20 μm, 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.     

Fundamental aspects of hematite flotation using the bacterial strain Rhodococcus ruber as bioreagent

Previous research showed the effectiveness of bacterial strains as flotation reagents on Hematite beneficiation. The aim of this work is to study and evaluate Rhodococcus ruber as a biocollector. The sample was conditioned with the biomass suspension by stirring under specific conditions as particle size, biomass concentration, pH solution and conditioning time. The results showed a change in hematite zeta potential profile after interaction with R. ruber, and its adhesion onto the mineral surface was higher at pH 3 and at concentration of 0.60 g/L (10⁹ cells/mL). Flotation studies were carried out in a 0.23 L modified Partridge–Smith cell flotation, and the highest floatability (84%) was achieved at size fraction −53 μm +38 μm under the conditions mentioned before. Complementary floatability studies were performed using the conventional frother Flotanol D24 combined with the R. ruber biomass, finding interesting results for the bigger particle size range. Thus, this research aims to evaluate the efficiency of bioflotation of minerals, particularly hematite, and the potential use of R. ruber as biocollector, projecting its future application in mineral flotation industry.     

Flotation behaviors of ilmenite,titanaugite, and forsterite using sodium oleate as the collector

The flotation behaviors of ilmenite, titanaugite, and forsterite using sodium oleate as the collector were investigated using microflotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR) analyses, X-ray photoelectron spectroscopy (XPS) analyses and the artificially mixed minerals flotation experiments. The results of the microflotation experiments indicate that ilmenite exhibits good floatability when pH > 4.0. Titanaugite possesses a certain floatability at pH 4.0–6.0 and pH > 10.0, and forsterite possesses certain floatability at pH 5.0–7.0 and pH > 9.0. The results of FT-IR and XPS analyses indicate that sodium oleate mainly interacts with Fe, resulting in ilmenite flotation; that the Ca and Mg on the titanaugite surface chemically reacted with sodium oleate, and that the Mg on the forsterite surface chemically reacted with sodium oleate under acidic condition. However, sodium oleate mainly reacted with the Ca and Mg on the titanaugite surface, whereas sodium oleate mainly reacted with the Mg on the ilmenite and forsterite surfaces under alkaline conditions. The results of the artificially mixed minerals flotation experiment demonstrate that the concentrate of TiO₂ grade increases from 16.92% to 30.19% at pH 5.4, which represents the appropriate conditions for the flotation separation of ilmenite from titanaugite and forsterite under weak acidic conditions.     

Separation of amine-insoluble species by flotation with nano and microbubbles

Amines (alkylamines–ether amines) are employed on a large scale to separate iron ores by reverse flotation of the gangue particles (mostly quartz and silicates). Quartz gangue particles coated with amine collector are dumped in tailings dams as concentrated pulps. Then, the fraction of the amines that detach from the surfaces and the portion that is soluble in water, contaminate surface and ground-water supplies. This work presents a novel flotation technique to remove decyl-trimethyl-ether-amine (collector employed in Brazilian iron mines) from water. This amine forms precipitates at pH > 10.5 which are removed by flotation with microbubbles (MBs: 30–100 μm) and nanobubbles (NBs: 150–800 nm). Bubbles were generated simultaneously by depressurization of air-saturated water (P_sat of 66.1 psi during 25 min) forced through a flow constrictor (needle valve). The flotation by these bubbles is known as DAF-dissolved air flotation, one of the most efficient separation technologies in water and wastewater treatment. Herein, best results (80% amine removal) were obtained only after selective separation of the MBs from the NBs exploring the fact that while the NBs remain dispersed in water, the MBs rise leaving the system. The MBs, because of their buoyancy, rise too rapidly and do not collide and adhere appropriately at the amine colloids/water interface, even causing some precipitates breakage. It was found that the “isolated” NBs attach onto the amine precipitates; aggregate (flocculate) them and entrain inside the flocs before rising by flotation. Because of the low residual amine concentration in water (6 mg L⁻¹), it is believed that this flotation technique have potential in this particular treatment of residual amine-bearing effluents.     

A mixed collector system for phosphate flotation

Flotation has been used in industry for more than a half century as the primary technique for upgrading phosphate. While the flotation of phosphate was inefficient when oleic acid was used alone as a collector, therefore a mixed collector of oleic acid (HOl), linoleic acid (LA) and linolenic acid (LNA) was employed to improve the recovery of phosphate flotation. The batch flotation results showed that the optimal composition of the mixed collector was 54 wt.% HOl, 36 wt.% LA and 10 wt.% LNA. Additionally, the effect of pH on the mixed collector application was studied while considering the surface tension, contact angle and micro-flotation. The results showed that the mixed collector should be used at a pH of 9.5. Above a pH of 9.5, the adsorption of fatty acids dimers on the apatite surface hindered phosphate flotation. The influence of the mixed collector assembly on apatite flotation was also investigated. It was demonstrated that due to its low critical micelle concentration, a sufficiently hydrophobic apatite surface could be generated at a collector concentration of 60 mg/L. In addition, zeta potential experiments suggested that collector adsorption was governed by chemisorption. FTIR and XPS spectra studies further indicated that the chemical reaction involved the carboxyl groups of fatty acids and Ca species at the apatite surface for each fatty acid in the mixed collector.     

Detachment of coarse composite sphalerite particles from bubbles in flotation: Influence of xanthate collector type and concentration

The force required to detach sphalerite ore particles from air bubbles has been measured in flotation concentrates, for particles in the size range of 150–300 μm and 300–600 μm with different degrees of liberation. An electro-acoustic vibrating apparatus, that produces typical force conditions experienced in a flotation cell, was used to measure particle–bubble detachment as a function of the vibrational acceleration. Sodium isopropyl xanthate (SIPX) and potassium amyl xanthate (PAX) collectors were used in flotation, at different concentrations. At a fixed frequency of 50 Hz, the maximum vibrational amplitude at which a particle detaches from bubble was used to calculate the particle detachment force. It was shown that changes in surface hydrophobicity (contact angle), due to variations in reagent conditions have significant impact on particles detaching from bubbles. On average, detachment of particles from oscillating bubble correlated well with xanthate concentration and hydrocarbon chain length of xanthate ions. Particles (300–600 μm) with high contact angle obviously required higher force to detach from bubbles than similar particles with lower contact angle. This correlated well with the flotation response at the different reagent conditions. SEM analysis of particles after detachment showed that fully liberated particles attached to bubbles more readily and also gave higher detachment force than composite particles. Moreover larger detachment forces were observed, on average, for particles with irregular shape compared to particles with rounded shape of the same size range.     

The mechanism of pyrite depression at acidic pH by lignosulfonate-based biopolymers with different molecular compositions

Electrochemical studies, adsorption isotherms and contact angle measurements were conducted to compare the effect of three lignosulfonate-based biopolymers (DP-1775, DP-1777 and DP-1778) as pyrite depressants in flotation at acidic pH. The adsorption isotherms showed that DP-1775 and DP-1778 had a higher adsorption capacity than DP-1777. The contact angle of pyrite particles was reduced by the three biopolymers in the order of DP-1778 > DP-1777 > DP-1775 at a similar adsorbed amount. These results are in accordance with biopolymers’ ability to inhibit collector adsorption in electrochemical studies. The depressing effect of these biopolymers was related to the biopolymer composition. It was found that the biopolymer molecular weight determined its adsorption capability and surface coverage. The content of functional groups was responsible for the change in contact angle. While a higher molecular weight led to greater pyrite depression, calcium ion as a counterion in the biopolymer structure also played a role.     

Prediction of the metallurgical performances of a batch flotation system by image analysis and neural networks

It is now generally accepted that froth appearance is a good indicative of the flotation performance. In this paper, the relationship between the process conditions and the froth features as well as the process performance in the batch flotation of a copper sulfide ore is discussed and modeled. Flotation experiments were conducted at a wide range of operating conditions (i.e. gas flow rate, slurry solids%, frother/collector dosage and pH) and the froth features (i.e. bubble size, froth velocity, froth color and froth stability) along with the metallurgical performances (i.e. copper/mass/water recoveries and concentrate grade) were determined for each run. The relationships between the froth characteristics and performance parameters were successfully modeled using the neural networks. The performance of the developed models was evaluated by the correlation coefficient (R) and the root mean square error (RMSE). The results indicated that the copper recovery (RMSE = 2.9; R = 0.9), concentrate grade (RMSE = 1.07; R = 0.92), mass recovery (RMSE = 1.94; R = 0.94) and water recovery (RMSE = 3.07; R = 0.95) can be accurately predicted from the extracted surface froth features, which is of central importance for control purposes.     

The role of citric acid in the flotation separation of rare earth from the silicates

The Nechalacho project is the most advanced large heavy rare earth elements (HREE) project outside of China. Open circuit and locked cycle flotation tests along with pilot plant testing of rare earth elements (REE) concentration from the host rocks are accomplished with collectors of alkyl phosphates and the modifier of citric acid. In this study, the function of citric acid in the separation of rare metals against silicates is investigated by a combination of micro-flotation tests and time of flight secondary ion mass spectrometry (ToF-SIMS) surface chemical analysis. It was observed that there was little effect of citric acid on the REE recovery in the micro-flotation tests conditioned with de-ionized water (DIW). To evaluate the flotation response with excess secondary ions in the pulp, micro-flotation tests were performed to look at changes in recovery as a result of adding Al ions and the subsequent presence of citric acid. The results from three micro-flotation tests (DIW, DIW with the addition of 100 mg/L Al and DIW + 100 mg/L Al and 500 g/t citric acid) revealed that the addition of Al ions led to a decrease of REE grade, a lower REE minerals recovery and/or an unexpected promotion of silicates to the concentrate. Citric acid reduced the negative effect generated by the Al ions in the flotation, which was shown by an improvement in REE grade. ToF-SIMS surface analysis of undifferentiated grains from the tests with and without citric acid revealed that grains reporting to the concentrate are doing so in response to collector attachment in combination with having more secondary Al on their surface. Citric acid may partially form aqueous soluble metal–ligand complexes resulting in less Al ions on the grains surface, which were rejected to the tailings. Citric acid also may form chelation competing for adsorption on gangue minerals, resulting in a diminished effectiveness of the activation site.     

Electrokinetic behavior and flotation of kaolinite in CTAB solution

The electrokinetics and flotation behavior of kaolinite in cetyltrimethylammonium bromide (CTAB) solution were studied. The point of zero charge (PZC) of kaolinite is 4.3. The possible mode of CTAB adsorption on kaolinite is due to Coulombic and Van der Waals forces revealed by zeta-potential and FTIR measurements. The negative zeta potential of kaolinite and the adsorption of cationic collectors on kaolinite were higher in alkaline media than in acidic media. However, the flotation tests show that the kaolinite exhibited much better floatability in the acid range than in the basic pH range in the 2 × 10⁻⁴ M CTAB solution. The surface charge of the basal plane is negative and that of the edge is positive in the acid pH range. The aggregation occurs possibly by electrostatic interaction between particles because of different charged based plane and edges, and makes floatability of kaolinite better in an acid pH range.