Magnetic Flocculant Research Articles

Research Progress of Magnetic Flocculation in Water Treatment

As people’s material quality of life continues to improve, water resources become subjected to varying degrees of contamination. As one of the most commonly utilised agents in water treatment, a flocculant exhibits a diverse range of forms and a vast scope of applications. However, the application of flocculants gives rise to a series of issues, including the use of large doses, the formation of sludge, the difficulty of recycling flocculants, and other concerns. The development of new flocculation technology has become a crucial step in enhancing the purification of wastewater and reducing environmental pollution. Magnetic flocculation can be classified into two main categories: magnetic seeds flocculation and magnetic flocculation. This paper presents an overview of the factors influencing magnetic flocculation, including the type of magnetic seeds, magnetic seeds particle size, and other pertinent considerations. Furthermore, the classification of magnetic flocculants in the process of magnetic flocculation is discussed. This includes the types of magnetic flocculant, namely, inorganic composite magnetic flocculants, organic composite magnetic flocculants, and biological composite magnetic flocculants. Inorganic composite magnetic flocculants are inexpensive and simple to produce; however, their dosage is considerable, and the resulting floc is not tightly formed, which impairs the efficacy of flocculation. The use of organic composite magnetic flocculants requires a smaller dosage and exhibits a strong flocculating ability; however, it may possess toxic properties and potentially cause harm to the water body. The biological composite magnetic flocculant exhibits high efficiency and no pollution, yet it is subject to stringent environmental conditions, displays poor stability, and is applicable to a relatively limited range of treatment scenarios. Furthermore, the integration of magnetic flocculation technology with other techniques is classified and summarised in diverse contexts, and the prospective research focus and direction of magnetic flocculants are proposed.

Chitosan-Based Grafted Cationic Magnetic Material to Remove Emulsified Oil from Wastewater: Performance and Mechanism

In order to remove high-concentration emulsified oil from wastewater, a chitosan-based magnetic flocculant, denoted as FS@CTS-P(AM-DMC), was employed in this present study. The effects of factors including the magnetic flocculant dose, pH values, and coexisting ions were investigated. A comparative dosing mode with the assistance of polyacrylamide (PAM) was also included. The evolution of floc size was studied using microscopic observation to investigate the properties of flocs under different pH values and dosing modes. Particle image velocimetry (PIV) and extended Deryaguin–Landau–Verwey–Overbeek models were utilized to illustrate the distribution and velocity magnitude of the particle flow fields and to delve into the mechanism of magnetic flocculation. The results showed that FS@CTS-P(AM-DMC) achieved values of 96.4 and 74.5% for both turbidity and COD removal for 3000 mg/L of simulated emulsified oil. In the presence of PAM, the turbidity and COD removal reached 95.7 and 71.6%. In addition, FS@CTS-P(AM-DMC) demonstrated remarkable recycling and reusability performances, maintaining effective removal after eight cycles. The strength and recovery factors of magnetic flocs without PAM reached 69.3 and 76.8%, respectively. However, with the addition of PAM, they decreased to 46.73 and 51.47%, respectively. During the magnetophoretic processes, FS@CTS-P(AM-DMC) and oil droplets continuously collided and aggregated, forming three-dimensional network aggregates. Moreover, the magnetic floc generated a swirling motion, and the residual emulsified oil droplets could be further captured. Emulsified oil droplets were primarily removed through charge neutralization under acidic conditions. Under neutral and alkaline conditions, magnetic interactions played a major role in magnetic flocculation.

Using a New Fe3O4@CPAM Magnetic Flocculant and Microwave to Demulsify Heavy Oil-in-Water Emulsions.

In this study, cationic polyacrylamide (CPAM)-coated magnetic nanoparticles (MNPs) Fe3O4@CPAM were synthesized for treating heavy O/W emulsions. This Fe3O4@CPAM was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM) techniques, and its synergistic performances with microwaves were evaluated in detail with respect to the microwave radiation power, radiation time, and magnetic nanoparticle concentration. On this basis, the distribution of oil droplets and the wettability and chargeability of magnetic nanoparticles were measured without or with microwave radiation using biomicroscopy, contact angle measurement instrument, and a ζ-potential analyzer, thus revealing the synergistic demulsification mechanism between microwave and magnetic nanoparticles. The results showed that excessively high or low microwave radiation parameters had an inhibitory effect on the magnetic nanoparticle demulsification, and microwave promoted the magnetic nanoparticle demulsification only when the radiation parameters were in the optimal range. In addition, the water separation rate showed an increasing and then decreasing trend with the increase of magnetic nanoparticles concentration, with or without microwave action. As an example, the water separation rate of the emulsion for 1 h was 21.34% when the Fe3O4 concentration was 175 mg/L without microwave action, while it increased to 55.56% with microwave action. In contrast, when the concentration of Fe3O4@CPAM was 175 mg/L, the water separation rate was 42.86% without microwave radiation, while it was further increased to 77.38% under microwave radiation. These results indicate that magnetic nanoparticles and their complexes significantly affect the water separation process under different conditions. There is a more obvious coupling synergistic effect between Fe3O4@CPAM and microwave. This was due to the lower absolute potential of Fe3O4@CPAM and its higher hydrophobicity.

Magnetic coagulation and flocculation of kaolin suspension using Fe3O4 with plant polyphenol self-assembled flocculants

In this work, magnetic flocculant (Fe3O4@PP) was synthesized using plant polyphenol (PP) as a shaping ligand via in situ self-assembly. Characterization results revealed that Fe3O4@PP exhibited uniform particle size and excellent dispersibility with PP coating amount of 16.4 %. Experimental results suggested that Fe3O4@PP showed excellent turbidity removal efficiency in a wide pH range (3.0–10) and initial turbidity range (50–2000 NTU). Under the optimal conditions, Fe3O4@PP achieved 95.2 % of turbidity removal for simulated kaolin suspension and 96.9 % for actual wastewater. Fe3O4@PP exhibited excellent recycling and reusability properties, with high recycling efficiency of 93.3 % even after the fifth cycle. Microscopic observation revealed the formation process of magnetic flocs, involving particle aggregation, chain and cluster formation, and dense network aggregate formation. The structural characteristics and size of magnetic flocs were found to be significantly influenced by the combined effects of magnetic force, electric charge, van der Waals force, and functional groups on the surface of PP. The extended Deryaguin-Landau-Verwey-Overbeek models indicated that magnetic interactions were the primary mechanism for magnetic flocculation, accompanied by charge neutralization, adsorption bridging, sweeping, and net trapping.

SEDIMENTATION OF TITANIUM DIOXIDE SUSPENSION UNDER THE ACTION OF MAGNETIC FLOCCULANTS

Magnetic flocculants are synthesized from magnetite (Fe3O4) nanoparticles and ionic and nonionic acrylamide copolymers having different concentrations of ionic units and molecular weights. The synthesis is carried out in two steps: two magnetite samples having different size and surface characteristics are precipitated with ammonia from a mixed aqueous solution of Fe(II) and Fe(III) chlorides; then, the obtained samples are mixed with aqueous solutions of polyacrylamide flocculants. Individual particles of magnetite, copolymers, and magnetic flocculants based thereon are characterized by dynamic light scattering. Effect of the nature and flocculating ability of magnetic flocculants on the process of sedimentation of a titanium dioxide suspension is estimated. Varying the sizes of magnetic nanoparticles and the molecular parameters of acrylamide copolymers in the magnetic flocculant makes it possible to obtain a highly efficient multifunctional flocculant for the selective separation of multicomponent disperse systems.

Octopus tentacle-like molecular chains in magnetic flocculant enhances the removal of Cu(II) and malachite green in water

• A recyclable flocculant with strong adsorption configuration was prepared simply. • Flocculant can remove Cu(II) and malachite green efficiently and synchronously. • Adsorption by functional groups and sweep flocculation were the mechanism. • Flocculant was easily regenerated and separated. • Flocculant can remove multiple contaminants in single-stage water treatment. Conventional flocculants are difficult to effectively remove dissolved ions and organic matter from water. This work aims to develop an environmentally friendly and renewable core–shell type flocculant (MCHS-g-P(AM-IA)) with octopus tentacle-like strong adsorption structure. The organic shell hydrolyses into molecular chains like octopus tentacles and adsorb dissolved ions/organic macromolecules through suckers-like functional groups, while the magnetic core acts as the growth center of flocs. Configuration and physical/chemical properties of the flocculant were analyzed by a series of characterization methods. Set Cu(II) and malachite green (MG) as models of heavy metal and organic pollutants separately, the removal capacity of MCHS-g-P(AM-IA) for water contaminants was studied in single-contaminant system and binary-contaminant system. The flocculation behavior and mechanism of MCHS-g-P(AM-IA) were deeply investigated by analysis of pH-dependence, background cationic influence and flocculation kinetics and SEM-EDS/XPS analysis of flocs. Furthermore, the flocculation performance in actual water matrix and regeneration tests of MCHS-g-P(AM-IA) were carried out to evaluate the applicable feasibility of flocculants for purification of complex wastewater in single stage water treatment.

Using a New Fe3o4@Cpam Magnetic Flocculant and Microwave to Demulsify Heavy Oil/Water Emulsions

Using a New Fe3o4@Cpam Magnetic Flocculant and Microwave to Demulsify Heavy Oil/Water Emulsions

Biocompatible magnetic flocculant for efficient harvesting of microalgal cells: Isotherms, mechanisms and water recycling

• Harvesting efficiency of over 97% was achieved by using Fe 3 O 4 -chitosan composites. • The maximum adsorption capacity of Fe 3 O 4 -chitosan composites was 75.43 g/g. • Charge neutralization, double layer compression and bridging were the mechanisms. • The supernatant after harvesting could be reused to re-cultivate microalgal cells. As an environmentally friendly bioflocculant, chitosan has a great application potential for microalgae harvesting due to its biocompatibility. The rapid development of magnetic separation technology has attracted extensive attention because of its reusability, energy and time saving. In this work, Fe 3 O 4 -chitosan composites flocculant with high magnetic harvesting ability and fast separation was successfully prepared with sodium tripolyphosphate as crosslinking agent, and applied to the harvesting and separation of microalgae cells. The harvesting efficiency of 97.63% for Chlorella vulgaris was achieved within 3 min using chitosan/Fe 3 O 4 with the weight ratio of 3:1 and the dosage of 0.5 g/L under pH 3.0. Freundlich isotherm was more suitable for Fe 3 O 4 -chitosan to harvest microalgae, indicating the microalgae harvesting by Fe 3 O 4 -chitosan composites was a heterogeneous multilayer process. The highest adsorption ability of the Fe 3 O 4 -chitosan on Chlorella vulgaris could be reached 75.43 g/g. Double-layer compression, charge neutralization and adsorption bridging are primarily harvesting mechanisms between Fe 3 O 4 -chitosan composites and microalgae cells. The second-order polynomial model well simulates the experimental data, establishing the relationship between Fe 3 O 4 -chitosan and algae slurry pH, concentration of microalgae cells and settling time. The supernatant after Fe 3 O 4 -chitosan harvesting could be reused, saving water resources and cost, showing its biocompatibility. The Fe 3 O 4 -chitosan composites had excellent reusability, and the harvesting efficiency could reach 85.10% after four cycles, which improved the economic feasibility of magnetic harvesting. Fe 3 O 4 -chitosan has the advantages of high efficiency, fast separation, low economic cost, and low energy consumption. This work provides basic guidance and data analysis in the study of Fe 3 O 4 -chitosan for microalgae harvesting on a large scale.

Efficient separation performance of suspended soil and strontium from aqueous solution using magnetic flocculant

This study aimed at magnetically separating suspended soil and Sr2+ from a soil suspension using a magnetic flocculant (MNP/IF). MNP/IF was prepared using the electrostatic interaction between the magnetite particles and the inorganic flocculant (IF) based on CaCO3 and Na2SO4. By analyzing the physical properties of MNP/IF, it was confirmed that MNP/IF was successfully imparted with magnetism and had excellent adsorption capacity for Sr2+. The optimal MNP/IF dosage for the sedimentation of suspended soil was determined to be 0.3 g/g (mass ratio of flocculant to soil). Compared with raw IF, MNP/IF showed better flocculation performance to suspended soil for a shorter sedimentation time. The lower the pH, the more favorable the flocculation-sedimentation process of the suspended soil by MNP/IF, since Ca2+ and Mg2+, which are the most common strong flocculators, were further eluted from IF under acidic conditions. MNP/IF also showed excellent removal performance for Sr2+, exhibiting maximum Sr2+ adsorption capacities of 163.6 mg/g in the flocculation-sedimentation reaction of suspended soil. The Sr2+ adsorption process was consistent with the Langmuir model and followed the pseudo-second-order kinetics. These results provide that MNP/IF can be used for the simultaneous removal of suspended soil particles and Sr2+ from a radioactive soil suspension.

Removal of emulsified oil from water by using recyclable chitosan based covalently bonded composite magnetic flocculant: Performance and mechanism

In this work, a novel recyclable covalently bonded magnetic flocculant (FS-MC) was successfully prepared by combining chitosan-based modified polymers (MCS) with Fe3O4@SiO2 through a silane coupling agent. The covalent bond Fe–O–Si–O–C and the core–shell structure of FS-MC were confirmed through several characterization methods. The emulsified oily wastewater flocculation performance and mechanism by using FS-MC were evaluated and studied. Results showed that 94.47%, 93.95%, and 92.98% of emulsified oil could be removed by using FS-MC1, FS-MC2 and FS-MC3 at dosages of 2.0, 2.5, and 2.0 mg/L, respectively. Furthermore, FS-MC exhibited an excellent behavior on the removal of organic compounds with molecular weight > 10 kDa, including long chain alkanes, cycloalkanes, and aromatic hydrocarbon compounds. In addition, triple-phase separation of oil, water and flocculants was achieved by using magnetic FS-MC. Due to the introduction of cationic and hydrophobic groups in FS-MC, charge neutralization, compression double electric-layer action, hydrophobic interaction, interfacial adsorption bridging and sweep-flocculation synergistically contributed and enhanced the removal of emulsified oil. Recycling experiments also showed that no obvious decrease of oil removal rate was observed by using magnetic FS-MC flocculants in five cycles.

Treatment of water-based ink wastewater by a novel magnetic flocculant of boron-containing polysilicic acid ferric and zinc sulfate

Polysilicic acid ferric and zinc sulfate containing boron (PSBFZ) flocculants were prepared through reaction of sodium silicate, ferric trichloride, zinc sulfate and sodium tetraborate. A new type of magnetic flocculant PSBFZ-Fe3O4 was prepared through a simple method of solid state reaction at room temperature. The as-prepared PSBFZ and magnetic PSBFZ-Fe3O4 were used in treating water-based ink wastewater. The influence parameters (such as dosage, time, pH and temperature) on the removal rate of decolorization, turbidity and chemical oxygen demand (COD) were investigated. The results showed the products were suitable for neutral and basic water. When the dosage of PSBFZ-Fe3O4 was 0.3 g/L, the turbidity removal rate and the decolorization rate could reach 98.0 % and 98.5 % at room temperature, respectively. Through recycling by a magnet, the magnetic PSBFZ-Fe3O4 flocculants residues could be easily separated from the wastewater which makes the reusing of magnetic flocculants become possible.

Magnetic Template Anion Polyacrylamide-Polydopamine-Fe3O4 Combined with Ultraviolet/H2O2 for the Rapid Enrichment and Degradation of Diclofenac Sodium from Aqueous Environment.

In this study, a novel system was set up by preparing a magnetic flocculant combining with ultraviolet/H2O2 to realize the rapid enrichment and degradation of diclofenac sodium (DCFS). For the magnetic flocculant, template anion polyacrylamide (TAPAM) with anion micro-block structure was prepared. Thereafter, polydopamine was used to modify TAPAM, Fe3O4 nanoparticles was grafted to the modified TAPAM by chelation, named template anion polyacrylamide-polydopamine-Fe3O4 (TAPAM-PDA-Fe3O4). Furthermore, the TAPAM-PDA-Fe3O4 preparation protocol was optimized by the response surface method (RSM). In the DCFS enrichment section, the rapid separation of flocs from water was realized by an external magnetic field and it indicated that the π–π stacking effect was dominant in neutral/alkaline condition, whereas charge neutralization was favored in acidic conditions. Meanwhile, a DCFS enrichment kinetic curve was much fitted by the pseudo-second-order kinetic model and DCFS enrichment isothermal curve was close to the Freundlich isothermal model, indicating the dependence of DCFS quantity enriched by TAPAM-PDA-Fe3O4 and a multilayer heterogeneous enrichment process. The degradation experiment confirmed that DCFS was effectively degraded by ultraviolet/H2O2/TAPAM-PDA-Fe3O4 and the maximum value of DCFS degradation efficiency reached 98.1%. Furthermore, the regeneration experiment showed that the enrichment and degradation efficiency of DCFS could maintain a relatively high level in the initial three recycles.

Magnetic sedimentation of nonmagnetic TiO2 nanoparticles in water by heteroaggregation with Fe-based nanoparticles

A new approach to remove TiO2 nanoparticles from water is studied. Composite Fe3O4-SiO2 and Fe-C-SO3H nanoparticles with magnetic cores (5 nm) were designed to be used as flocculants for magnetic sedimentation of nonmagnetic TiO2 nanoparticles in water. The sedimentation dynamics of heterogeneous water suspensions (starting solid phase concentration of 100 mg/l) of (TiO2)1−x(Fe3O4-SiO2)x (x = 0.15–0.55) and (TiO2)1−x(Fe-C-SO3H)x (x = 0.01–0.17) was studied in a gradient magnetic field (B = 0.3 T, dB/dz < 0.16 T/m) for pH = 3–6. The NMR relaxometry and the UV - spectrophotometric methods were used to monitor the residual concentration of Fe3O4-SiO2, Fe-C-SO3H and TiO2 nanoparticles in water after magnetic sedimentation. The hydrodynamic sizes of the heteroaggregates (dh) depend on the pH value and on the mass content of the magnetic component, x. For the mixed (TiO2)1−x(Fe3O4-SiO2)x water suspensions the maximum of dh = 5 μm and the fastest sedimentation are reached for x = 0.35–0.5 at pH = 3, 4, and for x = 0.2 at pH = 5. At this regime, the highest efficiency of TiO2 particles removal from water, that is, 99.7% for 30 min, was observed. For the mixed (TiO2)1−x(Fe-C-SO3H)x water suspensions the largest heteroaggregates and the fastest sedimentation were observed for the smaller mass content of the magnetic flocculant, x = 0.03–0.05 at pH = 3, 4 and for x = 0.03 at pH = 5. However, by adding Fe-C-SO3H nanoparticles flocculant the achieved minimum residual concentration of TiO2 nanoparticles in water is two orders of magnitude higher. These results are discussed by assuming a specific distribution of Fe - based nanoparticles by heteroaggregation with TiO2 nanoparticles.

Magnetic flocculants synthesized by Fe3O4 coated with cationic polyacrylamide for high turbid water flocculation.

A novel magnetic flocculant (CPAMF) was synthesized by using Fe3O4 coated with cationic polyacrylamide (CPAM) for flocculation of high turbid water. The surface morphology and chemical structures of CPAMF were confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) was employed to verify the crystal structure of CPAMF. The magnetic property of CPAMF was compared with Fe3O4 in this study. The flocculation performance by using flocculants CPAMF was evaluated in high turbid water treatment. The maximum transmittance 92.4% of kaolin suspension was achieved at corresponding optimal flocculation conditions. The result indicated that CPAMF was efficient in high turbid water flocculation. Analysis of FTIR, XRD of flocs, and zeta potential (ZP) of supernatant were accomplished for flocculation mechanism investigation. Because of low recovery factor in reflocculation under the effect of shear force on flocs, the bridging effect was found to be dominant in both acidic and alkaline conditions. Sedimentation experiments under the role of permanent magnet indicated that nano-Fe3O4 could effectively improve the settling property of CPAM. Graphical abstract ᅟ.

Removal of Nickel from Plating Wastewater Using the Magnetic Flocculant PG-M

Removal of Nickel from Plating Wastewater Using the Magnetic Flocculant PG-M

Enhanced demulsification from aqueous media by using magnetic chitosan-based flocculant

A series of quaternized chitosan (QC)-grafted magnetic nanoparticles (MNPs) were successfully synthesized for demulsification from aqueous environments. Fe3O4 MNPs were synthesized by using a coprecipitation method, followed by surface coating with silica and aminopropyl to form a surface for further grafting of QC molecular chains. The synthetic magnetic flocculants were characterized by various technologies and their demulsification performances were evaluated in detail as a function of dosage, QC grafting ratio (Gq), pH and magnetic field. Results showed that pH did not significantly affect oil–water separation performance and MNPs with high Gq exhibited enhanced separation efficiency. The separation capacity was estimated to be >105 mg of diesel oil/mg of magnetic flocculant. Recycling experiment indicated the magnetic flocculant could be recycled up to at least 7 cycles at various pH levels. The grafted QC layer endowed the hybrid MNPs with permanent positive surface charges, thus allowing them to flocculate negatively charged oil droplets via electrostatic patching. The magnetic field could not only accelerate the separation of resulting flocs, but also remove the MNPs-coated dispersed oil droplets. In conclusion, QC-grafted MNPs provide a potentially new technique for developing environmentally friendly and highly efficient magnetic flocculant for practical demulsification applications.

Preparation and characterization of polymer-coated Fe3O4 magnetic flocculant

ABSTRACTThe ordinary flocculants rely on gravity settling for solid-liquid separation, it is difficult to meet the requirements of wastewater treatment in short flocculation settling time, few sludge production and low moisture content. A new type of flocculant is required to solve these difficulties. Magnetic materials are given more attention because of the magnetism in magnetic field. It is significant to prepare magnetic composite flocculant to realize solid-liquid separation with the combined effects of both gravity and external magnetic field. The gelatin-based magnetic flocculant consisted of poly (acrylamide-co-acryloyloxyethyl thimethylammonium chloride) grafted gelatin-coated Fe3O4 [magnetic poly (AM-co-DAC)-g-gelatin] was prepared in this article. A Box-Behnken design for determination of optimal plan with three-level and three-variable was designed. The best conditions of preparing magnetic poly (AM-co-DAC)-g-gelatin were determined. The structure of magnetic poly (AM-co-DAC)-g-gelatin was studied by infrared spectrum and its magnetic properties were characterized by magnetic hysteresis loop. The flocculation of magnetic poly (AM-co-DAC)-g-gelatin was compared with conventional flocculant. The flocculation experiment results showed that the magnetic poly (AM-co-DAC)-g-gelatin was effective for removal of turbidity and significantly reduced the settling time of flocs, compared to conventional flocculants.

Rapid and efficient removal of heavy metal and cationic dye by carboxylate-rich magnetic chitosan flocculants: Role of ionic groups

A multifunctional carboxylate-rich magnetic chitosan flocculant (Mag@PIA-g-CS) was prepared through surface graft copolymerization on magnetite particles. The effect of monomer molar ratio, initiator and pre-neutralized degree on polymerization rate was determined. Various analytical methods were applied to characterize Mag@PIA-g-CS, exhibiting the successful grafting of polymers, good magnetic feature and core-shell structure. The kinetic process of Ni(II) and malachite green (MG) flocculation by Mag@PIA-g-CS reached equilibrium within <60min with the optimal uptake rate of 98.3% and 87.4%, and exhibited satisfactory removal effect in wide pH range (4.0–8.0 for Ni(II), 5.0–10.0 for MG). Mag@PIA-g-CS exhibited superior flocculation performance over chitosan magnetic flocculant (Mag@CS). The pH-dependent behavior, rapid responsiveness and sensitivity to ionic strength in batch flocculation tests indicated the distinct effect of ionic groups. Moreover, sweeping action of linear molecular chains facilitated further flocculation. Mag@PIA-g-CS showed high stability in extreme environments, and can be easily regenerated and separated.

Long-chain poly-arginine functionalized porous Fe3O4 microspheres as magnetic flocculant for efficient harvesting of oleaginous microalgae

Considering the porous characteristics of magnetic porous Fe3O4 microspheres, this study aims to utilize long-chain poly-arginine (PA) to obtain PA-modified porous Fe3O4 microspheres (p-Fe3O4@PA). The microspheres possessed a loose porous structure on the surface, and the average pore size was 224.2Å. The harvesting efficiency for Chlorella sp. HQ improved markedly compared with that of p-Fe3O4 after modification with three PAs with different molecular weights. p-Fe3O4@PA-2 (PA molecular weight: 15,000–70,000) had the best performance with a decreasing dosage from 300mgL−1 to 10mgL−1. The results indicated that PA modification at a higher molecular weight could promote microalgae adsorption, whereas PA modification of an excessively high molecular weight (>70,000) was not conducive to microalgae harvesting. The modification percentage of p-Fe3O4@PA (57.9%) provided abundant adsorption media and active sites for Chlorella sp. HQ adsorption. Bridging flocculation and hydrogen bonding between Chlorella sp. HQ and p-Fe3O4@PA greatly enhanced harvesting efficiency. In addition, the p-Fe3O4@PA could maintain good cycling stability because of the relatively large size of the microspheres.

Functional graphene-based magnetic nanocomposites as magnetic flocculant for efficient harvesting of oleaginous microalgae

Magnetic graphene oxide (GO) nanocomposite was assigned to decorate with cationic polymer PDDA (diallyldimethylammonium chloride) to a sponge like nanocomposite GO-Fe3O4/PDDA, and employed in magnetic harvesting of oleaginous Chlorella sp. HQ. The results showed that huge surface area, light weight and stable dispersion of GO make contribution to the high harvesting efficiency of GO-Fe3O4 (80.14%), compared to Fe3O4 NPs (62.65%) with 70mg of nanomaterials/L of algal cells dose. In addition, graphene base provides more active sites to further decorate with PDDA, which imparts a positive zeta potential charge (21.94mV) to nanoflocculants, thereby achieving 95.35% harvesting efficiency within 5min. The adsorption followed Langmuir isotherm and pseudo-second-order kinetic model, with the maximum adsorption capacity of 14.06g dry-biomass/g. Moreover, the harvesting efficiency decreased dramatically when pH increased for Fe3O4 NPs, while GO-Fe3O4and GO-Fe3O4/PDDA could maintain in a wide pH range. Besides,GO-Fe3O4/PDDA can be effectively reactivated (88.68% harvesting efficiency after 5 times reactivation) with 70mgL−1 dose (add 30mgL−1 after every time). It can be expected that this novel graphene-based magnetic nanocomposite has great potential to be a promising magnetic flocculant applied to efficient harvesting of oleaginous microalgae.