High Floatability Research Articles

An investigation of the effect of clay type on coal flotation along with DLVO theoretical analyses

ABSTRACTCoals generally exist with clay minerals, which are very fine-sized minerals, and adversely affect the flotation of coal. For instance, they make the coal surface hydrophilic by coating coal surfaces and therefore, they inhibit bubble-particle attachment. Clay minerals can also cause over-consumption of reagents due to their high surface area. Additionally, clay minerals can transfer into the concentrate during the flotation process by entrainment because of their low weight and small particle size, and thus, increase pulp viscosity and changing froth stability. In this study, the influence of various clay minerals (kaolinite, illite, and bentonite) on the flotation behavior of coal sample was studied in detail by conventional flotation tests. In addition, the values obtained from flotation tests were correlated with theoretical energy barrier values established with classical DLVO theory based on zeta potential values of coal and clay samples measured at different pH values. According to the results of this study, no significant effect of clay minerals was observed on coal flotation. This was probably because of the high floatability of the coal used for this study. Both the results obtained from the experiments and theoretical analysis, DLVO calculations, showed that the type of clay mineral is the main indicator parameter for coal flotation.

Effects of Xanthate on Flotation Kinetics of Chalcopyrite and Talc

This paper investigated the effects of using or not using potassium butyl xanthate (PBX) as a collector on the flotation kinetics of talc and chalcopyrite. By means of atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), a contact angle measuring instrument and particle size analyzer, the underlying causes behind the flotation rate changes of talc and chalcopyrite are analyzed. Experimental results showed that in collectorless flotation, the law of change in the flotation rate constant (k) of the two minerals over time is independent of pH, and k values of chalcopyrite are much smaller than those of talc. In the presence of PBX, the flotation speed of chalcopyrite greatly increases, and the k values of chalcopyrite are far larger than those of talc. This is mainly because the amount of xanthate adsorbed on the surface of chalcopyrite is large and the adsorption is in the form of chemisorption, while the adsorption of xanthate on the talcum surface is in very small amounts and in the form of physical adsorption. Simulation results indicated that the collectorless flotation of chalcopyrite conform to the classical first-order kinetics model and the Kelsall model, whereas that of talc only conform to the latter, which is due to the layered structure of talc. In the presence of the collector, talc flotation conforms to the two model, because talc has a higher floatability and particle morphology has less influence on the flotation rate.

The effects of microwave irradiation on the floatability of chalcopyrite, pentlandite and pyrrhotite

Research into the application of microwave irradiation in the comminution of ores has made great progress in recent years, creating a demand to understand the effects of this technique on downstream processes, especially flotation. The present work investigated the floatability of untreated and microwave-treated chalcopyrite, pentlandite and pyrrhotite samples using potassium amyl xanthate and sodium oleate as collectors. The effects of the exposure time on each mineral’s recovery at different concentrations, pH and particle sizes were studied through microflotation, and the adsorption of the collectors was analyzed by electrophoretic zeta potential measurements. Microwave irradiation led to the decrease in the floatability of chalcopyrite and pyrrhotite in the presence of xanthate, at the pH values investigated, whereas no significant change was observed for pentlandite. The flotation of the microwave-treated minerals required greater sodium oleate concentration. The treated and non-treated pentlandite and pyrrhotite samples did not float at pH 10. Although the treated chalcopyrite and pentlandite displayed low recoveries at all pH values, the treated pyrrhotite displayed high floatability at acidic and neutral pH. The recovery of the microwave-treated sulphide minerals was more affected by the particle size in the tests with potassium amyl xanthate than with sodium oleate. The overall results presented by this work indicate potential conditions to achieve selectivity between the microwave-treated chalcopyrite, pentlandite and pyrrhotite.

Physico-chemical properties of extruded aquafeed pellets containing black soldier fly (Hermetia illucens) larvae and adult cricket (Acheta domesticus) meals

Fish farming is faced with the challenge of high cost of feeds because of the cost of high quality protein needed for formulation of the feeds. Thus, there is urgent need for alternative protein sources. The effects of substituting freshwater shrimp meal (FWSM) with black soldier fly larvae meal (BSFM) or adult cricket meal (ACM) on physico-chemical properties of hot-extruded fish feed pellets were investigated. The FWSM protein in a 26 g/100 g protein fish feed formulation was substituted at 0, 25, 50 and 75%, and moisture content of the formulated blends adjusted to 10, 20 or 30 g/100 g prior to extrusion. Floatability, expansion rate, bulk density, durability index, water absorption index, water solubility index, and water stability of extruded pellets were determined. Sinking velocity and the total suspended and dissolved solids in water were determined for the optimal pellets. Pellet floatability was not influenced by the type of insect meal but the interaction between level of inclusion and moisture content of the feed at extrusion. Pellets with high floatability >90% were produced from all feed blends at 30 g/100 g moisture content. Expansion ratio, was not influenced by type of insect meal or the level of inclusion but by the moisture content whereby feed blends extruded at 30 g/100 g moisture gave pellets with high expansion ratio ~60%. Bulk density was influenced by the interaction of the three factors. Pellet durability and water absorption indices were not influenced by the investigated factors or their interactions. Processed pellets were generally highly durable (99%) out of water, but the stability in water was significantly influenced by the interaction of type of insect meal level of inclusion and moisture content at extrusion. Water solubility increased with increasing extrusion moisture. Overall, it was possible to process good quality extruded pellets with 75% BSFM or 75% ACM at 30 g/100 g feed moisture.

Surface properties and physiology of Ulmus laevis and U. minor samaras: implications for seed development and dispersal.

Plant surface properties influence solid-liquid interactions and matter exchange between the organs and their surrounding environment. In the case of fruits, surface processes may be of relevance for seed production and dispersal. To gain insight into the relationship between surface structure, chemical composition and function of aerial reproductive organs, we performed diverse experiments with the dry, winged fruits, or samaras, of Ulmus laevis Pall. and Ulmus minor Mill. both at the time of full maturity (green samaras) and of samara dispersal (dry samaras). Samaras of both elm species showed positive photosynthetic rates and absorbed water through their epidermal surfaces. The surface wettability, free energy, polarity and solubility parameter were lower in U. laevis than in U. minor and decreased for dry samaras in both species. Ulmus laevis samaras had a high degree of surface nano-roughness mainly conferred by cell wall folds containing pectins that substantially increased after hydration. The samaras in this species also had a thicker cuticle that could be isolated by enzymatic digestion, whereas that of U. minor samaras had higher amounts of soluble lipids. Dry samaras of U. laevis had higher floatability and lower air sustentation than those of U. minor. We concluded that samaras contribute to seed development by participating in carbon and water exchange. This may be especially important for U. minor, whose samaras develop before leaf emergence. The trichomes present along U. laevis samara margin may enhance water absorption and samara floatability even in turbulent waters. In general, U. minor samaras show traits that are consistent with a more drought tolerant character than U. laevis samaras, in line with the resources available both at the tree and ecosystem level for these species. Samara features may additionally reflect different adaptive strategies for seed dispersal and niche differentiation between species, by favoring hydrochory for U. laevis and anemochory for U. minor.

Study of the natural floatability of molybdenite fines in saline solutions and effect of gypsum precipitation

The floatability of molybdenite fines in saline solutions was investigated through microflotation studies using a modified Hallimond tube. In addition, the effect of pH and gypsum precipitation from calcium ions (Ca2+) and sulfate ions (SO 4 2− ) ions in saline water on the recovery of the molybdenite was analyzed. It was found that the floatability of molybdenite fines significantly increased with the ionic strength of the saline solutions and is independent of pH above 0.5 mol/L ionic strength. The high floatability of molybdenite in saline solutions is explained as being due to the low electrostatic repulsion between bubbles and the edges of molybdenite particles, which is exceeded by interactions due to van der Waals and hydrophobic forces. The precipitation of Ca2+ and SO 4 2− ions as gypsum had a detrimental effect on the natural floatability of molybdenite because of gypsum crystal attachment on the faces of the molybdenite particles. This precipitation phenomenon may be initiated in copper-molybdenite flotation circuits that use recycled saline water, like seawater containing Ca2+ and SO 4 2− ions.

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 0.60g/L (109cells/mL). Flotation studies were carried out in a 0.23L modified Partridge–Smith cell flotation, and the highest floatability (84%) was achieved at size fraction −53μm +38μm 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 Behavior of Arsenopyrite and Pyrite, and Their Selective Separation

This study investigated the effect of pH and pulp potential (EH) on the floatability of arsenopyrite and pyrite, which are single minerals, in Hallimond tube, by using xanthate as a collector. On this basis, the study further investigated the selectivity index of arsenopyrite and pyrite, using a mixed sample of arsenopyrite and pyrite. To examine the flotation behavior of each mineral by pH change, flotation was carried out at pH 4 and pH 10. The test results showed arsenopyrite had higher floatability at pH 4, regardless of the potassium ethyl xanthate (PEX) concentration. This is because xanthate ion was oxidized to be stable dixanthogen, which was well adsorbed onto arsenopyrite surface, due to the high EH of pulp. Meanwhile, arsenopyrite had relatively lower floatability at pH 10 than at pH 4, which was because the dixanthogen remained unstable, and was not adsorbed onto the arsenopyrite surface, due to the relatively low EH of pulp. Pyrite had low floatability at both pH 4 and pH 10. Just as for arsenopyrite, the result for pH 10 was caused by the low EH of pulp. Yet, interestingly enough, different from the case of arsenopyrite, pyrite at pH 4 had low floatability, despite its high EH. FTIR analysis was performed, to examine the reason for such contradictory behavior. The analysis result showed that this was caused by poor adsorption with xanthate, due to sulfate ion (SO4) that was generated by the oxidation of pyrite surface in reaction with oxygen in pulp at pH 4. To further investigate the selectivity index (i.e., the pyrite recovery/ arsenopyrite recovery ratio) of arsenopyrite and pyrite, additional flotation tests were carried out on mixed sample of the two minerals. Different from the flotation behavior of single minerals, the results showed that the recovery of arsenopyrite was lower than that of pyrite, and the selectivity index of arsenopyrite and pyrite was the highest when the PEX concentration was the lowest. Such a different trend in flotation behavior of the mixed sample from the flotation behavior of the single minerals was because the surface oxidation reaction of arsenopyrite, which was more affected by EH among the mixed arsenopyrite and pyrite, generated ferric arsenate, a hydrophilic compound, on the surface of arsenopyrite, resulting in poor adsorption with xanthate; in turn, this depressed the floatability of arsenopyrite. [doi:10.2320/matertrans.M2014369]

Biosorption of Pb2+ from Natural Water using Date Pits: A Green Chemistry Approach

Removal of Pb2+ ions from aqueous solutions by adsorption onto Date Pits (DP) has been investigated. The date pits (sorbent) may represent an environmental problem. The characteristic parameters (solution pH, initial concentration of Pb2+, sorbent dose, shaking time and temperature) influencing the adsorption process have been examined. pH=7 is found the best one having high floatability of 6 g l-1 dose of DP. The Freundlich and Langmuir were applied. The change in Gibbs free energy change (ΔGo), enthalpy (ΔHo) and entropy (ΔSo) were also calculated. Under the optimum experimental conditions employed, the removal of ~95% of Pb2+ was attained. The procedure was successfully applied to remove Pb2+ from natural water samples. The SEM image of DP before and after lead adsorption shows complete adsorption.

Floatability of polymer materials modulated by frothers

Flotation tests of 35 polymer materials were carried out to investigate their floatability modulated by frothers. Results of flotation tests demonstrated that polymer resins and soft PVC showed high floatability, floatability of hard PVC plastics was relatively low and was related to the frothers, and there exists significant difference in the floatability of different post-consumer plastics. Flotation rate of post-consumer plastics varies from 0% to 100%. Furthermore, three-category low-energy surface (LES) was defined based on the hydrophile index of the materials involved in this paper, and an adsorption model was proposed to explain the results of flotation and to discuss the floatability of polymer materials modulated by frothers. Frother molecules are prone to adsorb on the surface of bubble rather than LES at relatively low concentration, bubble adsorbed by frother molecules is prone to approach first-category LES rather than third-category LES, and the structure of liquid film is formed on the first-category LES at large concentration. Floatability of polymer materials modulated by frothers is further discussed: frothers increase the floatability of the first-category LES but decrease the floatability of the third-category LES, while the floatability of the second-category LES is related to the type of frothers.

Study on Application of Intensifying Depression Talcum in the Copper Sulphide Flotation

Talcum is a common gangue with which sulphide ores are associated, it has an adverse impact on sulphide ores flotation and product index due to its high natural floatability. In this paper it takes talcum-bearing copper sulphide ores from DongChuan in Yunnan province as experimental samples, and a series of tests on depressing talcum in the copper suphide ore flotation were carried out. Results show that when took the composed CMC and sodium hexametaphosphate as depressant with respective dosage 200g/t and 300g/t, it obtained a favourableeffect. In addition, depression effect can get improved with the dosage of collector increasing properly, it shows that when took the composed CMC and sodium hexametaphosphate as depressant, it can make the flotation process stable.It employed rougher-scavenger-three cleaners system as the closed-circuit flowsheet, and attained a Cu concentrate product of whom grade and recovery is 16.16%, 78.78% respectively.The results might contribute to dispose some similar talcum-bearing sulphide ores in the future.

Electrokinetic properties of smithsonite and its floatability with anionic collector

The effect of the smithsonite/water interface properties on the floatability of the mineral without and in the presence of sodium carbonate was examined through zeta potential measurements, microflotation tests, and the concentration of Zn2+ ions measurement, in the pH range from 7 to 11. The isoelectric point value of the mineral was achieved at pH 8.0, and the species Zn2+, OH−, HCO3−, CO32−, and H+, as well as the reabsorption of hydrolysis products would determine the smithsonite–solution interface properties. Smithsonite presents high floatability with sodium oleate (1.5×10−4mol/L) between pH 7.0 and 8.0. Above pH 8.0, the smithsonite floatability decreases abruptly, and the polymeric zero-charged Zn(II) hydrolyzed species [Zn(OH)2(H2O)2]n0 is proposed for depressing the floatability of smithsonite. With the sodium carbonate added into the solution, the isoelectric point value of the mineral was achieved at pH 8.2. The smithsonite interface, having more surface cation sites and zinc species in the Stern layer, gives rise to the floatability in the pH range from 7.0 to 8.7. Due to the formation of Zn(CO3)22−, the decrease of the concentration of the hydrolyzed species [Zn(OH)2(H2O)2]n0 makes smithsonite more floatable than that without the Na2CO3 at 8.7<pH<10 (flotation recovery from 30% to 75% at pH 9.5). The results show that the anionic flotation of smithsonite is a promising route to recover Zn with the sodium carbonate.

Influence of the roughness and shape of quartz particles on their flotation kinetics

Surface roughness and shape play an important role on the behavior of particles in various processes such as flotation. In this research, the influence of different grinding methods on the surface roughness and shape characteristics of quartz particles as well as the effect of these parameters on the flotation of the particles was investigated. The surface roughness of the particles was determined by measuring their specific surface area via the gas adsorption method. The shape characteristics of the particles were measured and calculated by images obtained by scanning electron microscopy via an image analysis system. The flotation kinetics was determined using a laboratory flotation cell. The results showed that the particles of rod mill products have higher roughness and elongation ratio and lower roundness than the particles of ball mill products. The flotation kinetics constant of the particles increased with their surface roughness increasing. Particles with higher elongation and lower roundness indicated higher floatability. In addition, the influence of the surface roughness on the flotation kinetics was greater than that of shape parameters.

Study of the sorption of petroleum and petrochemicals from the water surface by polystyrene foam-based Sorbents

The kinetic behavior of sorption of petroleum and petroleum products from the water surface by polymeric sorbents based on a foamed polystyrene formula has been studied. It has been found that the sorbents have good sorption properties, high floatability, and hydrophobicity. The effect of the environmental temperature and the apparent density of the sorbents on their sorption properties in a medium of crude petroleum and petroleum products has been shown.

Electrokinetic properties of wavellite and its floatability with cationic and anionic collectors

The reverse apatite flotation with fatty acids has been widely used for the reduction of phosphorus content of magmatic origin iron ores. However, the occurrence of phosphorus intensely disseminated as secondary minerals such as wavellite renders the anionic reverse flotation a challenge. Zeta potential measurements and microflotation tests of wavellite with the use of anionic and cationic collectors were carried out in this work. The wavellite’s IEP value was achieved at pH 4.5. Below the IEP value, the surface positively charged sites are made up of aluminum ions. The species H+,Al(OH)2+,Al(OH)2+,Al3+,OH-,H2PO4-,HPO42-, and PO43- play a role in the protonation and deprotonation reactions that will determine the wavellite-solution interface properties. The highest values of wavellite’s floatability under basic pH conditions were achieved in the presence of cationic collectors (1×10−4molL−1). The formation of surface complexes and the precipitation of insoluble salt of aluminum onto wavellite surface seems to be the most likely hypothesis for the chemical nature interactions between amines and wavellite. The surface formation of aluminum oleate on the wavellite’s surface seems to be the most probable hypothesis for the adsorption mechanism and the resultant high floatability of wavellite between pH 7.5 and pH 10.0 in the presence of sodium oleate (1×10−4molL−1). The results showed that the cationic reverse flotation of secondary phosphates is a promising route to reduce the phosphorus content of iron ores from deposits that underwent a supergene enrichment process, since wavellite floatability in the alkaline pH range, using amine as collector, was not significantly affected by the presence of corn starch.

Detached aquaculture buoys in the SE Pacific: potential dispersal vehicles for associated organisms

Throughout the world's oceans a wide variety of floating plastics are found, among which buoys stand out for their high floatability and diversity and abundance of associated organ- isms. Between 2001 and 2005, we conducted 25 ship surveys in the Bay System of Coquimbo (BSC), during which we registered 34 detached buoys floating between 1 and 45 km from the coast. The objective of this study was to infer the possible origin of these buoys, identify the associated biota and characterize their biological traits. Short-term drift experiments (30 min) showed that buoys without rope responded primarily to the velocity and direction of the wind, while buoys with ropes (3 m length) followed surface currents. Using the wind velocity and direction during the 12 h before cap- ture of the detached buoys, we estimated the hypothetical trajectories of these buoys during that time period. Results indicated that most buoys originated from aquaculture facilities in the BSC. A total of 134 different species from 14 phyla was found on 18 anchored (91 species) and 22 detached (116 spe- cies) buoys sampled. Community composition was similar among buoys—54% of all species were common for anchored and detached buoys—but a higher number of rare species occurred on detached buoys. Buoys do not seem to lose but rather gain organisms after detachment. The most common functional groups on these buoys were mobile species, suspension-feeders and species with sexual reproduction, separate sexes, internal fertilization and direct or very short larval development. Fouling communities on detached buoys were mostly in advanced successional stages, comprising diverse species (including several non-indigenous species) adapted to the conditions at the sea sur- face. These results suggest that floating buoys may transport associated species over extensive distances, thereby also contributing to the spread of non-indigenous species.

Effects of Organo-mineral Complexes on Flocculation, Settlement and Vertical Distribution of Bioelements in Soil Suspensions

Soil organic matter that could be combined with soil particles into large aggregates, may reduce soil erosion. However, soil organic matter itself is a possible source of water pollution. The objective of the present study was to analyze organo-mineral complexes and their effects on flocculation and settling characteristics of soils. Particle-size fractionation and flocculation/settlement experiment were conducted by using 7 types of soil samples (smectic heavy clay soils with 5 types of agricultural practices, alluvial clay loam soil, and volcanic heavy clay soil). All the samples were taken from paddy fields in Japan. Particle size fractionation showed that short-term (4 years) organic matter application to the smectic soil had increased the number of coarse organic particles. Puddled ponding water in the smectic heavy clay field under 4 years of organic matter application led to the highest levels of total organic carbon and particulate organic carbon among the sampling fields. Therefore, the coarse organic particles were considered to be easily suspended by puddling. The high floatability of coarse organic particles was consistent with their low density and weak association with minerals. Flocculation/settlement experiments showed the significant effect of pH decrease by organic matter application on the settlement of the smectic soil particles. The alluvial soil, volcanic soil, and smectic soils under continuous (4 years and 19 years) organic matter application could form large floes even at 50 mM NaCl, while the smectic soils under conventional tillage, no-tillage, and no-puddling required more than 200 mM NaCl for rapid settlement. Sodium pyrophosphate treatment of the dispersive soils resulted in higher concentrations of carbon and nitrogen in the upper layer (0–4 cm) of their suspension after 8 h of settlement, although the treatment had reduced the organic matter content of the soils. The reduction in the hetero-flocculation of the soil particles with different charge characteristics was considered to be the possible process for the increased dispersibility of the soils by the removal of organo-mineral complexes, because the smectic soil did not show a rapid settlement at the average point of zero salt effect for the whole soil components. Based on the settlement profiles, we estimated that the reduction of nutrient losses (suspended load) from surface ponding water in puddled fields was 74–112 kgC ha−1 and 6–7 kgN ha−1 by 8 h of settlement, and at least 100–157 kgC ha−1 and 9–10 kgN ha−1 by 8 h of settlement with an improvement in the pH and electrolyte concentrations.

Dispersion of kaolinite and talc in aqueous solution: nano-morphology and nano-bubble entrapment

Nano-morphological structure of well-crystallised kaolinite, micronised talc and micronised talc ground in a ring mill has been compared using field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kaolinite and ground talc dispersed in water immediately after shaking whereas the majority of the micronised talc remains at the air–water interface. AFM micrographs revealed more three-dimensional details of growth steps and attached colloid particles on basal planes of the crystallites than high resolution SEM micrographs. Two-dimensional ordered surface structure on the molecular level was measured by AFM. There are major differences in nano-morphology and surface structure between these three samples. The compact, blocky kaolinite crystals show large, relatively flat (<1.5 nm) basal planes with distinctive step growth on their surfaces. The irregular, thin, curved platelets of the micronised talc have much less complex surface structure with flat, smooth basal surfaces. Micronised talc platelets have much larger aspect ratios than either kaolinite or the ground talc. For micronised talc, the total edge contribution to the specific surface area is 13% whereas ground talc and kaolinite edges contribute 21% and 30–50%, respectively. The low edge contribution to total surface area in micronised talc contributes to its poor dispersion. Highly porous re-entrants and folds are frequently displayed at the edges and between sheets of the micronised talc. These voids, observed in both SEM and AFM micrographs, are filled by air nano-bubbles causing poor dispersion and high floatability when the talc is mixed with water. After grinding, the micronised talc particles are smaller, have reduced aspect ratios and much reduced porosity at edges and between sheets. Hence, the morphological differences in aspect ratio and air entrapment in the porous structure of talc are possible causes for the poor dispersability of micronised talc in comparison to kaolinite and ground talc samples.

Selective flotation separation of plastics by chemical conditioning with methyl cellulose

The floatability of seven plastics (POM, PVC, PET, PMMA, PC, PS and ABS) in the presence of methyl cellulose (MC) and separation of plastics mixtures were investigated in this paper. It was found that the seven plastics can be separated into three groups by using the wetting agent MC. Group one includes POM and PVC. They are depressed at very low MC concentrations. Group two, including PET, PMMA and PC, has an intermediate floatability. Group three (ABS and PS) has a high floatability. They are almost not depressed within the given MC concentration range. In order to understand the mechanism of selective flotation of plastics and the chemical conditioning process, surface chemical factors, such as wettability of plastics and surface tension of flotation medium, and gravity factors, such as particle density and shape, were studied. It was found that the depressing effect of MC on plastics is ascribed mainly to its adsorption on the plastics surfaces. The MC molecules absorbed on plastics expose some of their polar groups oriented towards the aqueous phase, hence making the plastics surfaces hydrophilic. In addition, flotation selectivity for the plastics is dominated not only by wettability of plastics, but also by particle size, density and shape.

Surface Energy and Induction Time of Fine Coals Treated with Various Levels of Dispersed Collector and Their Correlation to Flotation Responses

Separation of fine coal in froth flotation relies upon the wettability difference between the coal-rich and mineral-rich particles in the aqueous solution. Two methods were used to measure the wettability of six ranks of coal as well as coal samples treated with various levels of dispersed collector in aqueous solution. Wettability was determined by measuring the distribution of critical wetting surface tension, i.e., surface energy, using the film flotation technique and by measuring the induction time, i.e., bubble-particle attachment time, of the material. The wetting of coal particles is strongly dependent upon the coalification processes and can be affected by ash content. For anthracite coal with a high ash content, very high surface energy and intermediate induction time were measured, but intermediate floatability with a very good ash rejection was obtained. Sub-bituminous coal with low mineral inclusion was found to have a relatively low surface energy, and thus a high floatability, but very poor selectivity was observed, which was reflected in lengthened induction time. When dynamics of flotation behaviors are involved, flotation results can be better interpreted by induction time. For dispersed collector-treated coal samples, an increase in collector dispersion (i.e., a decrease in kerosene droplet size), by direct liquid collector mechanical agitation, ultrasonic energy emulsification, or atomization, caused decreases in surface energy and induction time and closely matched the increase of flotation recovery and selectivity. With similar particle density, mineral liberation conditions, and particle size, the induction time was found to be closely related to the mean critical surface tension for untreated coal samples and for HV-bituminous coal samples treated by various levels of dispersed collector.