Flotation Times Research Articles

Seed flotation in some widespread, oceanic‐dispersed trees and their island‐endemic congeners

AbstractVariation in plant dispersal capabilities strongly influences the assembly of island plant communities. Many tropical plants have seeds capable of long‐distance, often oceanic, dispersal; in some cases, these taxa speciate into island interior endemics with reduced dispersal capabilities, though whether this is a general pattern is debated. Flotation times are highly variable among plants with oceanic dispersal and between such plants and their inland congeners. Here, we experimentally compared salt‐water flotation in three woody plant genera in Palau, Micronesia, comparing broadly distributed and island endemic species within each genus. The widespread Calophyllum inophyllum (with oceanic and vertebrate dispersal), C. soulattri (vertebrate dispersal), and Terminalia catappa had substantially longer flotation than their inland endemic relatives C. pelewense and T. crassipes. This supports the “Loss of dispersal ability” hypothesis for Calophyllum though, for Terminalia, additional phylogenetic information is needed to determine T. crassipes' sister species. Seed flotation in the widespread, oceanic dispersed Pandanus tectorius did not significantly differ from that of the Palau endemics P. palawensis and P. aimiriikensis. Our results highlight that differences among taxa in dispersal modes, speciation modes, and their interactions may influence the assembly of island floras.

On the selection of the coarsest size class in flotation rate characterizations

This paper studies size-by-size batch flotation kinetics for the separation of Cu at particle sizes +75 μm, investigating the responses in the -150/+75 μm, -212/+150 μm, -300/+212 μm, -355/+300 μm and +355 μm size fractions. The kinetic results were analyzed to identify classes limited by the maximum achievable recovery or low flotation rates. Combinations of these classes were investigated, emulating the selection of the coarsest size in a kinetic study. The impact of compositing size classes was discussed, emphasizing implications in the identification of difficult-to-float components. The -212/+75 μm classes reached steady recoveries at long flotation times, whereas the -355/+212 μm classes presented sustained increasing recoveries at extended flotation times. Flotation rate distributions in the -212/+75 μm classes exhibited mound-shaped distributions, indicating low fractions of rate constants close to zero (R∞-limited case). Conversely, the -355/+212 μm classes presented reverse J-shaped distributions, with a high fraction of valuable minerals with flotation rates close to zero (rate-limited case). Combining several size classes in the definition of the coarsest size fraction in kinetic characterizations proved to hide the flotation patterns of the less massive constituents (+212 μm classes). The +75 μm and +150 μm cumulative retained classes trended towards steady recoveries, consistently leading to mounded flotation rate distributions. This study highlighted the need for reliable methodologies to select size fractions in kinetic characterizations, as their arbitrary definitions may lead to a misinterpretation of the mineral losses when compositing classes with different flotation responses.

Mathematical and Pharmacokinetic Approaches for the Design of New 3D Printing Inks Using Ricobendazole.

3D printing (3DP) makes it possible to obtain systems that are not achievable with current conventional methods, one of them, sustained release floating systems. Floating systems using ricobendazole (RBZ) as a model drug and a combination of polymers were designed and obtained by melt solidification printing technique (MESO-PP). Four different MESO-PP inks were formulated based on combinations of the polymers Gelucire 43/01 and Gelucire 50/13 in different ratios. For each of the formulated inks, physicochemical characterization was performed by thermal analysis (thermogravimetric analysis [TGA] and differential scanning calorimetry [DSC]), fourier transform infrared spectrophotometer (FTIR) and X-ray diffraction (XRD). Pharmaceutical characterization was performed by in vitro assays to determine pharmaceutically relevant parameters. These parameters were calculated by applying mathematical models developed to evaluate in vitro drug release profiles. On the other hand, a physiologically based pharmacokinetic (PBPK) model was developed to predict the in vivo performance of RBZ loaded in the different inks by determining the Cmax, and the AUC0-∞. By increasing the proportion of Gelucire 50/13 co-surfactant in the mixtures (the proportion in Ink 1 was 33%, while the proportion in Ink 4 was 80%), the dissolution capacity of RBZ increases substantially, decreasing flotation times. MESO-PP produced ink 1 (50% Gelucire 43/01, 25% Gelucire 50/13 and 25% RBZ), which has a zero-order release (RR = 0.180%/min) and the longest flotation time (545 ±23min), and in turn would produce a significant increase in oral absorption of the drug, with an AUC0-∞ 2.16-fold higher than that obtained in animals treated with RBZ loaded in conventional tablets.

Improving the flotation recovery of Cu from flash smelting slags by utilizing cellulose-based frother formulationss

• First published study using polymer-surfactant mixes as frothers in Cu slag flotation. • Using the PS-mix improved overall Cu recovery compared to commercial frother. • PS-mix significantly increased productivity, i.e. similar froth product in less time. • PS-mix demonstrated superior tolerance in performance when reducing xanthate dosage. Froth flotation is an operation currently used for the recovery of Cu from pyrometallurgical smelting slags due its simple operation and relatively low operational costs. While it has been utilized for many decades, it may be necessary to develop strategies that improve Cu recovery from slags, as the unprecedented increase in Cu demand has made industrial waste and side streams economically relevant sources of metals. This study presents a novel chemistry-based approach for the flotation of Cu from smelting slags by utilizing an amphiphilic cellulose-surfactant mixture as a flotation frother, hereby referred to as CellFroth. The present work pursues two main objectives: i) to improve the performance of flotation for the treatment of smelting slags and ii) to accomplish a first proof of concept for frothers produced from renewable sources in the context of industrial waste treatment. The flotation performance of CellFroth was compared with a commercially available additive (i.e., DowFroth250) and hydroxypropyl methyl cellulose (HPMC). The results showed significant advantages in performance for CellFroth. At the highest collector concentration, Cu recovery was higher with CellFroth compared to DowFroth 250 and pure HPMC (73%; 62% and 65% respectively). A 75% reduction in xanthate concentrations had negligible effects on Cu recovery for CellFroth (70%), while recoveries decreased drastically with DowFroth250 (47%) and pure HPMC (50 %). Finally, CellFroth consistently reached comparable concentrate productivity (grade and recovery) as DF250 within significantly shorter flotation times. The use of CellFroth thus offers the possibility of increasing the Cu recovery from flash smelting slags, while reducing the environmental impact of the process by using a frother produced from sustainable sources and simultaneously reducing xanthate consumption.

Electrocoagulation Treatment of Oily Wastewater in the Oil Industry

Electrocoagulation has turned out to be a rapidly growing area of wastewater treatment due toits ability to remove contaminants that are generally more difficult to remove by filtration orchemical treatment systems. These pollutants may include emulsified oil, petroleumhydrocarbons, suspended solids, and heavy metals. In this novel technology, metal cations arereleased into the wastewater through dissolving metal electrodes. Simultaneously, beneficialside reactions can help in removing flocculated material from the water.Oily wastewater represents a dangerous threat when discharged to the environment; thereforetreating it becomes vital in oil industry. This research has investigated electrocoagulation as asimple, effective and economic technique for treatment of such wastewater. Bench scale reactorwas used to evaluate the factors that may affect the treatment of oily wastewater. Aluminumwas used as a sacrificial anode. Electrodes were arranged at different configurations to selectthe optimal one. Other tested operation parameters include time of treatment, current density,distance between the electrodes, and the electrolyte concentration of the emulsion. Theexperimental results indicated that electrocoagulation was very efficient and able to achieve94% turbidity removal in less 60 min, pH:7, current density of 45 (A/m2).Also the effect of initial concentration of oil (100-1000 ppm) in wastewater, applied voltage(10-20 v), the dose of NaCl electrolyte (0-1 g) and temperature (35-60 oC) were optimized.What distinguishes this work is the the type of the electrodes configuration. Circular horizontalAl/Al electrodes (Ø12 cm) with 17 holes (Ø7 mm) have been found to give the bestelectrocoagulation environment and thus optimum results. The associated electrical energyconsumption is 1.6 kW h/m3 for flotation times of 60 min.

Developing buoyant and biocompatible nanoclays for the removal of hydrocarbon pollution from aqueous systems

There is a current need to develop buoyant and biocompatible nanoclays for removing oil pollution from the surface waters of rivers, lakes and oceans. Application of clay-based amendments should either aid dispersion, adsorption or biodegradation of hydrocarbons without introducing additional toxicity. Ultrathin (< 15 μm thick) nanoclay films of low density, in the form of cm-sized clay flakes, represent promising materials for enhancing all three of these remediating mechanisms. In this experimental microcosm study using brackish Baltic seawater and crude oil (MC252), smectite-talc mineral flakes were tested and compared against smectite-organoclay and smectite based mixtures. All three types of clay flake initially adsorbed significant volumes of oil before sinking with <10% of the original hydrocarbon remaining at the surface after 5 weeks of experimentation. Contact with the clay flakes furthermore increased oil droplet formation at the mineral-hydrocarbon interface and promoted detachment and dispersion of the oil phase. The presence of fertilizing agents (N, P, K) in the flakes also stimulated microbial activity within the brackish oil-contaminated water by up to 162% compared to control experiments. Due to their long period of flotation and attachment to the oil before sinkage, the smectite-talc flakes are considered to be the more favourable mixture despite being the least successful at stimulating microbial activity. Experiments indicate flotation times will be notably longer in more saline waters compared to brackish or freshwater systems due to the higher density and surface tension of saltwater. Although further improvements are required to enhance buoyancy, the use of potentially recoverable thinly filmed clay mineral flakes represents an important step in the application of eco-friendly nanoclay additives for cleaning up oil spills in aqueous systems.

Analysis of flotation rate distributions to assess erratic performances from size-by-size kinetic tests

This paper presents a size-by-size kinetic characterization for copper-lead separation from a complex ore. Batch tests are run under extended flotation times to obtain approximately steady recoveries (unscreened samples) at the end of the tests. The size-by-size time-recovery curves are fitted to the Gamma model to obtain estimates for the maximum recovery R∞ and the flotation rate distribution f(k). From reverse J-shaped distributions to normal probability density functions are representable from a Gamma f(k). Four size classes are studied: −20 μm, +20/−38 μm, +38/−75 μm and +75/−150 μm. The concave relationship between recovery and particle size is obtained up to a limiting flotation time; thereafter, a decreasing trend is observed for Pb and Cu. The finest (−20 μm) and coarsest (+75/−150 μm) classes present slower average rate constants. However, the different f(k) shapes (reverse J-shaped versus mound-shaped distributions) indicate that the use of average rate constants leads to limited conclusions in terms of mineral losses. Therefore, better kinetic interpretations can be obtained from the overall analysis of: the R∞ estimates, a location parameter of f(k) and the metal losses in a low f(k) percentile (e.g., 5%). From the proposed methodology, the poor performance of any erratic component can then be characterized as slow-rate-limited, R∞-limited or both together.

The use of enrichment ratios to support kinetic studies in flotation

This paper presents the use and evaluation of enrichment ratios (ER) from different batch flotation protocols. Two protocols under flotation time extensions (>20 min) are analysed, which favour steady recoveries to be obtained at the end of the process. Agar’s criterion is used to evaluate the consistency between the maximum recovery obtained by regression and the total measured recoveries. A good agreement is observed under critical flotation times (tcrit) lower than 40% of the total flotation time, where tcrit corresponds to the time at which the incremental concentrate grade equals the feed grade (grinding product).A discretized ER is used as an approximation of instantaneous ER to characterize the evolution of the enrichment along the process. This discrete ER is defined as the ratio between the incremental concentrate grade and the grade of the solid in the flotation cell prior to the respective flotation interval. Discrete ERs greater than 1 along with significant discrete recoveries are feasible, suggesting that further analyses are required to evaluate the process exhaustion. Four size-by-size tests are also studied to assess the distribution of the discrete ERs at long flotation times. Almost all the evaluated classes present discrete ERs greater than 1 in the last flotation intervals. Therefore, the non-selective mechanisms (i.e., entrainment, true flotation of gangue and gangue association) cannot be considered as the predominant contributions to the overall discrete recoveries. Exceptions may be laboratory tests under very fast kinetic responses, high mass recoveries, long flotation times and high content of non-floatable valuable minerals.

Malachite flotation using carbon black nanoparticles as collectors: Negative impact of suspended nanoparticle aggregates

In this study, the flotation behavior of malachite was investigated using carboxyl-functionalized carbon black nanoparticles (CB-NPs) as collectors in a hydrodynamically simplified Hallimond tube. We found that malachite floatability increased with increasing CB-NP concentration in the low range (0.5–2 kg/ton). To understand the mechanism of this higher floatability for low CB-NP concentrations, we examined the amounts of deposited CB-NPs on the malachite surface and hydrophobicity of the surface with deposited CB-NPs according to changes in the initial CB-NP concentration. The increase in malachite floatability was likely associated with increases in the amounts of deposited CB-NPs on the malachite surface, which enhanced malachite floatability by altering the hydrophobicity of its surface. Meanwhile, malachite floatability sharply decreased at CB-NP concentrations exceeding 2 kg/ton. To understand this unusual flotation behavior for high CB-NP concentrations, we also examined the amounts of CB-NPs deposited on the malachite surface and contact angles. However, the decreased malachite floatability could not be fully explained by these experiments, implying that at least one additional mechanism is involved. Therefore, additional flotation experiments including filtration processes and different flotation times were conducted, revealing that the unusual flotation behavior was likely due to the presence of suspended CB-NP aggregates, which reduced the kinetic rates of attachment between malachite and bubbles.

Evaluación de la recuperación de P2O5 a través de tres modelos de flotación espumante de roca fosfórica

El objetivo fundamental de la investigación es evaluar a través de 3 modelos de flotación espumante (directa, inversa y directa-inversa) la recuperación de P2O5 en roca fosfórica. Se tomaron muestras representativas del departamento del Tolima y se establecieron parámetros para cada una de las flotaciones con un tiempo de acondicionamiento de 5 minutos y tiempos de flotación entre 7-10 minutos. Se realizaron mediciones de ángulo de contacto, encontrándose para el caso del cuarzo un valor de 39° que refleja su hidrofilicidad. De acuerdo a las mediciones de Potencial Z, se determinó que existe una región de separación entre pH 2-5,8 usando colectores aniónicos para flotación directa y pH 5,8-10 usando colectores catiónicos para flotaciones inversas de Hidroxilapatito. Finalmente, se encontró que la flotación directa-inversa permitió una mayor recuperación de P2O5, utilizando como colectores el ácido oleico y el Aero® 845 Promoter en el proceso aniónico, y el colector Aeromine® 3030C y el depresante ácido fosfórico en el proceso catiónico.

Project Scheduling with Simultaneous Optimization, Time, Net Present Value, and Project Flexibility for Multimode Activities with Constrained Renewable Resources

Project success is assessed based on various criteria, every one of which enjoys a different level of importance for the beneficiaries and decision makers. Time and cost are the most important objectives and criteria for the project success. On the other hand, reducing the risk of finishing activities until the predetermined deadlines should be taken into account. Having formulated the problem as a multi-objective planning problem, the present study aims at minimizing the project completion time as well as maximizing the net present value and project flexibility by taking into account the resource constraints and precedence relations. Here the flexibility of project is calculated by considering a free float for each activity and maximizing the sum of these flotation times. Although most of the researches considered the resources as non-renewable resources, here the resources are considered as renewable ones. Moreover, performing each activity may be possible in various states of using resources (mode) which can change the project completion time and cost. Owing to the complexity of the problem, the Multi Objective Simulated Annealing Meta-heuristic Algorithm is used to solve the proposed model. In doing so, first a feasible answers is proposed and then, using the aforementioned algorithm, it was attempted to find Pareto answers. For accrediting the algorithm, four benchmark problems have been considered. Since the algorithm performed well in finding the optimal answers to the benchmark problems, it was used to find the optimal answer of large scale problems.

Effects of operating parameters on time-dependent ash entrainment behaviour of a sample coal flotation

It is well-known that entrainment of particles into the froth is a key factor in the selectivity and performance of the flotation process, especially for fine particle recovery. Since flotation is a continuous process, in this work, the effects of operating parameters on the entrainment of ash materials in a sample coal flotation is investigated from a time-sequence viewpoint. The effects of the pulp solid content, collector concentration, frother concentration, impeller speed, and particle size on the entrainment factor and water recovery at different flotation times are evaluated using a D-optimal response surface experimental design. The experimental work carried out shows that some parameters, especially particle size and pulp density, can yield completely different responses from those reported in the literature. The observed unusual behaviours can be attributed to the entrainment mechanisms and verified by the experimental results. It is also shown that the dominant entrainment mechanism can be varied by time. In addition, the statistical analyses of the experimental design show that the effects of some parameters change during time from the initial to the final stages of the flotation process. The results obtained indicate that the particle size and pulp density are the most important parameters influencing the entrainment rate and water recovery. The effects of the collector and frother concentrations are less on the entrainment and water recovery. In addition, the interaction between the solid percentage and particle size is the only significant mixed effect.

The response of diasporic-bauxite flotation to particle size based on flotation kinetic study and neural network simulation

This paper was to investigate the effect of particle size on diasporic-bauxite flotation. For this purpose, concentrate products of various size fractions were collected at different flotation times and forwarded to the testing of Al2O3 and SiO2 contents. Six flotation kinetic models were applied in the fitting of the experimental data in terms of Al2O3 and SiO2 recovery. Artificial neural network (ANN) model was also established to predict the effect of mean feed particle size on the recovery and separation efficiency of Al2O3. The results demonstrated that the classical first-order model was the most reasonable model to fit the diasporic-bauxite flotation process throughout this paper. Al2O3 and SiO2 were easier to be recovered from intermediate size fractions (−38+20μm and −54+38μm) than those from coarse size fractions (−74+54μm and −98+74μm) and/or extremely fine size fractions (−20μm). The separation efficiency of the intermediate size fraction was also greater than that of coarse or fine size fractions. The effective separation of coarse particles (+54μm) was only achieved at the initial stage of flotation process, whereas the effectual separation time of intermediate and fine particles is much longer compared with that of coarse size fractions. The prediction results using ANN model showed that the suitable mean feed size range of diasporic-bauxite flotation was from 21 to 41μm.

Effects of particle size on flotation parameters in the separation of diaspore and kaolinite

An attempt has been made in this paper to examine the effect of particle size on flotation parameters in the separation of diaspore and kaolinite. First of all, the basic properties such as zeta potential and contact angle and flotation behaviors of diaspore and kaolinite in sodium oleate (NaOL) and dodecylamine (DDA) solution were investigated. And then direct and reverse flotation experiments of mixed binary minerals at different size fractions were carried out. The classical first order flotation kinetics were used to fit the flotation data and first-order rate constant (k), ultimate recovery (R∞), modified rate constant (Km), selectivity index (SI) and separation efficiency (SE) were calculated and used as the flotation parameters to evaluate the separation effect of the two minerals. The results show that in the separation of diaspore and kaolinite, the particle size has a significant influence on the flotation parameters. The favorable particle size fractions for direct flotation were −38+20μm and −54+38μm and the adverse particle size fractions were −10μm and −20+10μm. While for reverse flotation, the favorable particle size fractions were −74+54μm and −10μm and the adverse particle size fractions were −38+20μm and −54+38μm. The optimal flotation times for the favorable size fractions were shorter than that for unfavorable size fractions. For the same size fractions, longer flotation times were required to reach the maximum separation efficiency in reverse flotation than those in direct flotation. Under the optimized condition (direct flotation, pH=10, NaOL dosage was 2×10−4mol/L, ore particle size was −38+20μm), concentrate products with diaspore recovery of 83.79% and A/S value of 7.96 can be obtained.

Development of a flotation model incorporating liberation characteristics

A liberation/flotation model has been developed to evaluate flotation performance, in which the grade distribution of composite particles is incorporated explicitly. The grade distribution of particles at a given size fraction was calculated using a predictive liberation model developed by the authors. Flotation behaviour of these particles in narrow size fractions were evaluated using batch flotation tests. The recovery of particles in narrow size/grade classes at various flotation times under a given flotation environment were obtained from SEM images of mounted specimens of feed, concentrate and tailings samples using image analysis techniques.By describing the size, grade and recovery data of particles in narrow size/grade classes by separate matrices, a transformation matrix technique has been developed that can predict the flotation performance of a composite sample of an ore comprising various size classes. It has been shown that the predicted results agree well with the observed results.This liberation/flotation model has wide applications in geometallurgical testing and design, where the downstream flotation performance is to be determined with limited availability of ore samples and their liberation characteristics. It also alleviates the deficiencies involved with flotation models that assumes first order behaviour.

Effects of Desliming and Hydroacoustic Cavitation Treatment on the Flotation of Ultrafine Bituminous Coal

ABSTRACTTesting was conducted to evaluate the effects of desliming in combination with hydroacoustic cavitation (HAC) treatment on flotation when processing nominal -150 μm Illinois-basin bituminous coal, which was obtained from a refuse stream at an operating coal-cleaning plant. Cavitation was produced either by flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic unit. Desliming was carried out using a 102 mm diameter hydrocyclone. Flotation tests were conducted using a laboratory flotation cell for different reagent amounts and flotation times. The results indicated that desliming improved flotation substantially. Moreover, in some cases, HAC treatment provided an additional benefit by liberating ultrafine inorganic material prior to desliming.

The Effect of Power Input on the Fine Coal Flotation Rate Constant

To explore the effect of the power input on the fine coal flotation rate constant, an energy consumption test system was established for the fine coal. In this investigation, the fine coal investigated was anthracite obtained from the flotation feed of the Xuehu Coal Preparation Plant of the Shenhuo mine in the Henan Province of China. A total of 65 sets of flotation rate tests were carried out with different power inputs at different flotation times. The relationship between the flotation rate constant and the power input at different flotation times was obtained. The result showed that the flotation rate displayed a constant increase, whereas the power input increased at any time during the flotation process. With the continuous increase of the power input, the increasing trend exhibited by the flotation rate constant decreases after reaching a maximum value. The calculation conjecture of the flotation rate constants and the power input were obtained by imitating the calculation method of the flotation kinetics model. Determining the value of the flotation power input and the flotation time during the flotation process of the different fine coal characteristics would therefore be helpful.

Flotation of pyrrhotite and pyrite in saturated CaCO3 solution using a quaternary amine collector

In the production of ground calcium carbonate (GCC) for the paper industry, any colouring contaminants must be removed during processing (usually flotation) to achieve sufficient GCC brightness. Flotation of GCC feedstock is characterised by the presence of both particulate and dissolved calcite (CaCO3), an alkaline pH and the use of amine collectors. This paper investigates the possibility of removing pyrrhotite and pyrite, under these conditions. Microflotation results show that the recoveries are highly dependent on pH. Pyrrhotite recovery decreases dramatically when going from pH 8 to pH 10. Pyrite display high recoveries at pH 8 and 9, and lower recoveries at higher pH. Recoveries were dependent on conditioning time. Pyrite floats considerably faster than pyrrhotite at all pH levels investigated, whereas pyrrhotite seems to be slow floating and could benefit from prolonged flotation times. Compared to the saturated CaCO3 system, flotation recoveries decreased when using deionised water or CaCl2 solution. The flotation results could not be fully explained by zeta potential. Bench scale flotation experiments on a sulphide bearing marble, confirmed the microflotation results at low collector concentrations (i.e. 200g/t). By increasing the amine concentration, the flotation performance became independent of pH.

Flotation of pyrrhotite to produce magnetite concentrates with a sulphur level below 0.05% w/w

Northland Resources is developing several magnetite mineral resources in northern Europe. The Tapuli, Sahavaara and Pellivuoma mineral resources are in Sweden and the Hannukainen resource is in Finland. Three of these resources (Sahavaara, Pellivuoma and Hannukainen) require flotation to remove more than 98% by mass of the sulphur in the feedstock to produce a saleable magnetite concentrate with a sulphur level below 0.05% w/w. The detrimental sulphur containing mineral is monoclinic pyrrhotite and its removal requires flotation. Previous published results related to pyrrhotite flotation from magnetite concentrate, e.g. on a magnetite deposit in Peru, only required the process to produce a final magnetite concentrate with a sulphur level below 0.4% w/w. There is currently no known published information on a process that floats pyrrhotite to achieve a magnetite concentrate with less than 0.05% w/w of sulphur.Extensive bench-scale tests were conducted on samples from Sahavaara, Pellivuoma and Hannukainen. Low-intensity magnetic separation (LIMS) tests showed that LIMS upgraded the magnetite and the sulphur in the pyrrhotite at the same ratio.The final flotation reagent regimes and conditions for each deposit were different being related to differences in mineralogy and grind size. The pH ranged from natural to pH of 4. Large dosage rates of xanthate collectors and long flotation times were needed. Flotation feed percent solids of between 45% and 50% w/w was required. Future work will modify these reagent regimes and flotation conditions in the full-scale plants to further optimise the flotation processes.

Performance enhancement of dissolved air flotation column in removing low concentrations of heavy fuel oil by adding powdered activated carbon

In this study, the effect of adding walnut shell-based powdered activated carbon (WS) to a bench-scale dissolved air flotation (DAF) column on oil removal was investigated. All experiments were conducted using synthetically prepared wastewater containing low but stable concentrations of heavy fuel oil. After comparing the effect of different WS doses from 0 (blank) to 40 mg/L at the saturator pressure of 5 bar and 10 min flotation time, 20 mg/L WS was chosen as the optimal concentration. In order to find the best flotation time for efficient use of WS capacity, experiments were repeated with and without 20 mg/L WS at longer flotation times. According to the obtained results, by adding WS, the removal efficiencies of oil and grease (O&G) and total petroleum hydrocarbons (TPH) after 60 min flotation time and without adding any coagulant, increased from 57.6 and 63.4% to 78.1 and 86.8%, respectively. By analyzing the samples taken at the flotation times of 10, 30, and 60 min, it was found that the most adsorbed TPH or nonpolar extractable hydrocarbons during the 60 min flotation time were removed during the first 10 min. Also, the TPH/O&G ratio was decreased, by increasing the flotation time.