Slurry pH Research Articles

Release and mobilization of Ni, Co, and Cr under dynamic redox changes in a geogenic contaminated soil: Assessing the potential risk in serpentine paddy environments

The release dynamics and mobilization of geogenic Ni, Co, and Cr in serpentine paddy soils under fluctuating redox conditions have not yet been well studied. Here we investigated the release dynamics of Cr, Co, and Ni and controlling factors (e.g., Fe, Mn, Mg, Cl−, PO43−, SO42−, and dissolved organic carbon (DOC)) in a geogenic-contaminated serpentine soil under wide range of redox potential (EH) changes. The effects of re-oxidation process have been also investigated. The soil was incubated for 28 days and EH was controlled from oxidation (+200 mV) to reduction (−200 mV) and re-oxidation (+240 mV) using a microcosm setup in duplicates. The slurry pH increased, along with decreasing EH. The average concentration of dissolved Co (17.1–23.6 μg L−1) decreased under low EH/high pH and vice versa. The average concentration of dissolved Cr decreased sharply from 624 μg L−1 to 54.4 μg L−1 with decreasing EH from +200 mV to 0 mV and the associated increase of pH from 7.8 to 8.5; then, it was constant around 24.5 μg L−1. Concentration of dissolved Ni was lower (73.5–84.6 μg L−1) under high EH at the first week of incubation; then, increased to 108.5 μg L−1 under low EH (−200 mV); thereafter, increased more at the end up to 124.5 μg L−1 at high EH (+240 mV), because of the pH decrease. A factor analysis identified that Cr and Co formed one group with Mn and Mg, while Ni was clustered together with Cl−, DOC, and SO42−. This indicates that the redox-induced release dynamic of Cr and Co was mainly governed by MnMg compounds, while the release of Ni was mainly affected by the aliphatic compounds of DOC and the redox chemistry of chlorides and sulfur in this soil. The re-oxidation increased the mobilization of Ni and Co and did not affect the release of Cr. These findings suggest that the redox-induced mobilization of geogenic Co, Ni, and Cr from soil to water in serpentine rice soils should be considered due to the high solubility and thus the associated bioavailability and potential environmental and human health risks, when such metal-enriched soils will be used for agricultural flood-dry cycle systems.

Effect of phosphoric acid as slurry additive on Li4Ti5O12 lithium-ion anodes

The aqueous processing of lithium-containing electrode materials is challenged by the reactivity of such materials towards water, resulting in lithium leaching, slurry pH increase, and consequent corrosion of the aluminum current collector. The addition of (mild) acids to the aqueous electrode slurry has been reported as a viable method to suppress the corrosion issue. Herein, we present a comprehensive investigation of the addition of phosphoric acid (PA) to an aqueous electrode slurry containing Li4Ti5O12 as the active material. Following an initial evaluation of the slurry pH evolution as a function of the PA content, a comparative investigation of the PA-free electrodes and the “corrosion-free” electrodes was performed. The latter clearly outperform the PA-free electrodes in terms of their electrochemical performance. Interestingly, this is not only resulting from the buffered pH, but the phosphate anion also plays a decisive role.

Surface Planarization of CdZnTe Wafers: Effect of Slurry Formulation and CMP Processing Parameters on Surface Planarity

This study investigates the effect of chemical mechanical planarization (CMP) processing parameters such as platen velocity, the concentration of the oxidizer and abrasive nanoparticle, slurry pH and surfactant types on the surface roughness of cadmium zinc telluride (CdZnTe) substrate. It was found that these parameters have a significant effect on the quality of the polished surfaces. It was found that lower platen velocity, lesser concentration of abrasive particles, basic slurry pH, and addition of anionic surfactant (SDS) into the CMP slurry solution showed improved surface planarity. Optical Surface Profiler and atomic force microscopy (AFM) techniques were used to monitor the surface topography before and after polishing. A notable root-mean-square surface roughness, (Rq), ∼0.9 nm, has been obtained on the polished CdZnTe (CZT) surface over a scan area of 481 × 361 μm2 under the optimized conditions of 60 rpm relative velocity, slurry pH of 9, 3.75 vol% of oxidizer (H2O2) and 1.25 wt% of abrasive (SiO2 nanoparticle). A probable mechanism of the present CMP surface planarization of CZT substrate has been proposed. Unlike the conventional surface planarization processes, which involve two-step lapping followed by CMP for the CZT surfaces, we have developed a single step CMP process to obtain good surface planarity.

Utilization of Livestock Dung as A Biogas Starter from Water Hyacinth to Suppress Water Weeds

Animal manure and water hyacinth will become waste in the environment if not utilized. One form of utilization of both is to make it as raw material for biogas. The aims of this study were: to determine the effect of the type of manure on the process of forming biogas from water hyacinth, which is related to: 1) the speed of biogas formation, 2) the temperature of the slurry , 3) the pH of the slurry , and 4) the volume of biogas produced. This study was designed with a completely randomized design (CRD), consisting of five (5) treatments, namely Treatment 1 (P 1 ) cow dung + water hyacinth + water, (P 2 ) buffalo dung + water hyacinth + water, (P 3 ) manure goat + water hyacinth + water, (P 4 ) horse manure + water hyacinth + water, and (P 5 ) broiler chicken manure + water hyacinth + water. Each treatment was repeated 4 times to obtain 20 experimental units. In this study, the composition of the mixture of raw materials was used as follows: 8 kg of chopped water hyacinth (2 cm) + 3 kg of animal dung + 2 liters of water. This is based on the results of research by Sari et al. (2014) which showed that the composition was good enough to produce biogas made from water hyacinth. The composition of the raw material mixture is as follows: 8 kg of chopped water hyacinth (2 cm) + 3 kg of animal dung + 2 liters of water. The variables observed in this study were: the rate of gas formation, slurry pH, slurry temperature, and the volume of gas produced. The research was conducted at the Biology Science Education Laboratory, Faculty of Tarbiyah and Teacher Training, UIN Mataram. The time of research was carried out from March to October 2018. The results showed that the type of manure only had a significant effect on the amount of biogas formed, but did not significantly affect the time of gas formation, slurry pH, and slurry temperature. Thus, the five types of manure can be used as a starter in the manufacture of biogas made from water hyacinth.

Hydration of alumina (Al2O3) toward advancing aluminum particles for energy generation applications

Transforming metal particle combustion may require alteration of the metal oxide passivation shell surrounding the metal core. One approach for aluminum (Al) relies on the hydrated form of the metal oxide to incite surface reactions. This study explores the conditions required for hydrating alumina (Al2O3) particles and then extends those conditions toward hydration of the Al2O3 passivation layer surrounding an Al core particle. By raising the pH of the water slurry to 11 and controlling temperature and time in slurry (i.e., aging), aluminum hydroxide Al(OH)3 formation from Al2O3 particles was optimized. The procedure was then extended to Al nanoparticles (nAl). Even though heating and extended aging time in slurry proved advantageous for Al2O3 particles, these conditions were discarded for nAl particles because they favored formation of AlOOH, a less desirable hydrate. Through microscopy, spectroscopy, X-ray diffraction, and thermal analyses, results indicate that for a pH range of 11.26–11.56, the original Al2O3 shell on Al particles transformed into Al(OH)3. Results indicate a feasible path forward towards producing new shell chemistries that may result in more directed energy from metal particle combustion.

Aqueous Processed Thick-Film Li(Ni0.6Mn0.2Co0.2)O2 Electrodes with 3D Architectures

The development of high areal energy density electrodes with layered metal oxide cathode materials is currently worldwide a main topic in research and industry. Water-based binders were applied in the presented work for the manufacturing of NMC 622 (Li(Ni0.6Mn0.2Co0.2)O2) cathodes in order to achieve environmental friendly and cost-reduced production, replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to over 12 due to the reaction between NMC 622 particles and water, which decreases the specific discharge capacity of the cells and on the other side results in the chemical corrosion of the current collector during casting. In order to avoid the damage of the current collector and protect the cathode material, different acids could be applied during mixing process to adjust the slurry pH value. In addition, the energy density at battery level can be increased with increasing electrode film thickness which corresponds to an enhanced areal capacity. However, capacity fading of thick-film electrodes at C-rates above C/2 is mainly due to a limited lithium-ion diffusion kinetics and crack formation in cathode particles. 3D electrode architectures produced by ultrafast laser ablation are proven to improve the capacity retention at high discharge rates and the electrolyte wettability of electrodes as reported in our previous works.In this work, NMC 622 electrodes with a film thickness of 150 µm (5.8 mAh/cm2) were manufactured with aqueous binders TRD 202A and CMC, and were subsequently laser structured. With increasing film thickness from 70 µm to 150 µm, the mass loading of cathodes increased from 17 mg/cm2 to 36 mg/cm2. The slurry pH values were adjusted between 9 - 10 with citric acid (CA), phosphoric acid (PA), and acetic acid (AC). The dried electrodes were characterized using XPS and SEM. The unstructured and structured electrodes with different thicknesses were afterwards assembled versus lithium in coin cells. Rate capability test and cyclic voltammetry (CV) were performed in order to investigate the electrochemical performance of the electrodes. Cells containing 70 µm cathodes with PA and CA+PA showed about 10 mAh/g higher capacity at C/20 to C/5 compared to cells with PA, while at 1C to 3C cells with CA showed the lowest capacities With increasing electrode film thickness, cells with PA and PA+CA retained 5-10 mAh/g more capacity than cells with CA at C/20 to C/5. The cells with PA maintained about 120 mAh/g discharge capacity at C/2, while cells with PA+CA and CA showed about 80 mAh/g and 45 mAh/g, respectively. In comparison to cells with unstructured electrodes, laser structuring increased the discharge capacity of cells with 70 µm electrodes from 1C to 3C, regardless of the type of added acid. As for cells with thick-film electrodes, the discharge capacity of cells containing structured electrodes with CA+PA increased to 120 mAh/g, which is about 40 mAh/g higher compared to cells with unstructured electrodes. Finally, CV proved that the addition of acids had no effect on the redox reaction of NMC 622.

Bio-acidification of animal slurry: Efficiency, stability and the mechanisms involved

Slurry acidification is effective for reducing gaseous emissions during slurry storage. However, an alternative to sulfuric acid traditionally used is needed. This study investigated the efficiency of slurry bio-acidification treatment by adding different types and amounts of fermentable substrates to initiate and sustain the fermentation process. The carbon pools in the slurry were quantified to understand the mechanisms involved during the bio-acidification. Substrate addition efficiently reduced slurry pH during storage via lactic acid production. Substrates with a low pH proved beneficial in initiating the fermentation process, but higher glucose dosage did not produce the highest lactic acid concentration. Once the treated slurries reached pH 4.2 during the fermentation process, the production of lactic acid was promoted and provided substrate was still available, the weaker volatile fatty acids were avoided, resulting in lower CH4 emissions. In conclusion, bio-acidification could replace the sulfuric acid to reduce gaseous emissions during slurry storage.

HIGH CAPABILITY OF THE BUFFERING AGENT IN PROVIDING CONSTANT pH TO IMPROVE THE BEHAVIOUR OF SYNTHESIZED HA/b-TCP CERAMIC

During the synthesis of different calcium phosphate phases, the pH variation of the slurry solution affects the purity, structure, and chemical composition of final products. High-capacity buffering agent solutions were used to keep the pH value constant during the synthesis procedure. Consequently, high purity and single-phase HA, b-TCP. Also, morphological evaluation of granules from plate-like to completely porous structure is another result of keeping the slurry pH constant during the synthesis step. Increasing the specific surface area of BCP granules from 10 to 38 m2/g affected the in vitro behaviour of the products. Precipitation of 20 nm hydroxyapatite phase after suspension of experimental samples for 30 days in simulation body fluid attributed to using Tris buffer solution during synthesis.

Highest Quality and Repeatability for Single Wafer 150mm SiC CMP Designed for High Volume Manufacturing

Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.

Rheological properties of halloysite soil slurry: a case study of weathered tephra involved in a shallow landslide triggered by the 2018 Eastern Iburi earthquake in Hokkaido, Japan

The 6.7 Mw Eastern Iburi earthquake of 6 September 2018 triggered destructive landslides in southern Hokkaido, Japan, many of which were characterized by the flow-like downslope movement of volcanic soils formed from weathered tephra containing halloysite. This study aims to elucidate the mechanism of landslide generation through rheological characterization of halloysite soil slurries. The examined slurries were prepared from either oven-dried or moist soil. Both slurries showed a power-law correlation between measured yield stress and moisture content. However, at a given water content, slurry made from dried soil showed stresses that are one-to-two orders of magnitude lower than those of slurry made from moist soil. Compared with the measurements for the slurry of dried soil, those for the slurry of moist soil are closer to prior numerical modeling of a specific landslide, indicating that the soils involved were moist. The yield stress also varied with slurry pH, generally increasing with decreasing pH, which is in part explained by the DLVO force model based on the electrical double layer and van der Waals forces between the colloidal particles. The pH dependence is more prominent in the slurry of moist soil, and thus the mechanical state of the slope appears to vary significantly with rainfall-induced changes in subsurface chemistry. Dynamic viscoelasticity measurement indicated that both initially solid-like slurries can become fluid under an applied oscillatory strain of 0.5 to 10 Hz: the susceptibility to fluidization depends greatly on water content and frequency. The ground motion during the earthquake easily fluidized the slurry, indicating this was a factor contributing to the observed flow-like landslides.Graphical

Effect of Particle Size Distribution, pH, and Na+ Concentration on the Chemical Mechanical Polishing of Sapphire and 4H-SiC (0001)

As two typical representatives of super-hard materials, sapphire and silicon carbide, their processing has always been a hot spot. Chemical mechanical polishing (CMP) technology is the only way to achieve global planarization, and it has also become one of the most important processes for precision machining of sapphire and silicon carbide. This paper introduced the relationship between the removal rate and surface roughness of sapphire and 4H-SiC (0001) and the size distribution and pH of alumina slurry. More importantly, this paper explored the negative effect of Na+ on the removal rate of alumina-based sapphire polishing slurry, and the more negative effect of Na+ on the removal rate of alumina-based silicon carbide polishing slurry and the surface state of SiC(0001). At the end of the article, the polishing mechanism of sapphire with alumina as a brasive was given.

Effect of Alkali Metal Ion on Chemical Mechanical Polishing of LiTaO3

Low material removal rate (MRR) and poor surface quality are the two main problems in ultra-precision machining of LiTaO3 wafer. In order to improve the MRR of LiTaO3 in chemical mechanical polishing (CMP), the effect of alkaline metal ion in slurry on the MRR of LiTaO3 was studied. The results show that adding an appropriate concentration of alkali metal ions to the slurry can increase the abrasive particle size and reduce the electrostatic repulsion between the abrasive and the wafer surface so as to enhance the mechanical effect. At mean time, Li+ replaced by K+ on the LiTaO3 wafer to produce easily removed KTaO3. Adding a certain amount of alkaline metal ion to the slurry improves the MRR of LiTaO3 wafer. Finally, when CMP was performed in slurry (pH 9) with a composition of 10 wt% SiO2 and 0.07 M KCl, the MRR of LiTaO3 is 111 nm min−1 and the surface roughness (Sq) is 0.3 nm.

Study on the effect of supercritical CFB boiler air preheater and flue gas treatment facilities on sulfur trioxide emission characteristics

The current situation of air pollution in China is very serious, and the control of non-conventional pollutants in addition to conventional air pollutants has received more and more attention. The emission of SO3 in flue gas has attracted widespread attention due to the environmental hazards and equipment problems caused by it, and the study of its emission characteristics and control strategies is the basis for national, local and industry to formulate relevant policies and implement emission control work. The SO3 monitoring and emission control study of a supercritical circulating fluidized bed boiler was carried out based on the controlled condensation method of on-site flue gas sampling, laboratory testing, and instrumental analysis of coal and ash samples, and the synergistic SO3 removal capability of the air preheater and flue gas treatment facilities was explored and summarized. The results showed that the SO3 co-removal rate of the four operating conditions of the test unit ranged from 74.34% to 88.51%, and the highest SO3 co-removal rate (88.51%) was achieved when the SNCR ammonia to nitrogen molar ratio was 1.2 and the slurry pH of the desulfurization system was 5.45 (primary tower) and 6.28 (secondary tower). During the test period, the differential pressure of the air preheater basically fluctuated between 1.245 kPa–1.326 kPa under the operating conditions of working condition 2, with no significant increase. For the same type of unit, the ammonia to nitrogen molar ratio and wet FGD slurry pH can be adjusted to reduce SO3 emissions.

Process development for recovering critical elements from acid mine drainage

The rapid development of advanced technologies has increased the demand for critical elements, such as Mn, Co, and Ni. A systematic study was conducted to develop a process for producing high-purity Mn, Co, and Ni products from an acid mine drainage (AMD). As major contaminants, Fe and Al in the solution were sequentially precipitated and eliminated by elevating the pH to around 4.00 and 6.50, respectively. After that, a pre-concentrated slurry containing 3,794 mg/L Mn, 59 mg/L Co, 127 mg/L Ni, and 300 mg/L Zn was obtained by collecting the precipitates formed in the pH range of 6.50 to 10.00. The pH of the pre-concentrated slurry was decreased to around 5.00 by adding HCl to re-dissolve Co, Ni, and Zn for further purification. At this pH, greater than 50% of Mn remained undissolved, and filtration of the undissolved material resulted in a product with around 30 wt.% Mn. Sodium sulfide was added into the re-dissolved solution to selectively precipitate Co, Ni, and Zn while remaining Mn in the solution. Almost 100% of Co, Ni, and Zn but only around 15% of Mn were precipitated using a sulfur to metal molar ratio of 1 at pH 4.00. The sulfide precipitate was calcined at 200 °C for 2 h and then completely dissolved in 1.2 M HCl. The critical elements existing in the dissolved solution were efficiently separated using a two-stage solvent extraction process. Ultimately, Co and Ni products with almost 94% and 100% purity were obtained by sulfide and alkaline precipitation, respectively.

Novel insights from lignocellulosic waste to biogas through regulated dry-wet combined anaerobic digestion: Focusing on mining key microbes

Dry-wet combined anaerobic digestion is a novel approach for treating lignocellulosic waste by increasing the organic load of reactor while accelerating the conversion of organic acids. Here, we investigated the effect of regulated substrate ratios and initial pH in the dry acidogenesis stage on the bioconversion efficiency of dry-wet combined anaerobic digestion. Our data revealed microbial interactions and further identified key microbes based on microbial co-occurrence network analysis. On day three of acidification, the kinetic hydrolysis rate and acidification yield reached 1.66 and 60.07%, respectively; this was attributed to enhancement of the synergistic effect between Clostridiales and Methanosaeta, which increased the proportion of corn straw in the substrate or lowered the initial spray slurry pH to 5.5–6.5. With increased acidification capacity, acetoclastic methanogens were enriched in the wet methanogenesis stage; the syntrophic effect of Syntrophomonadales, Syntrophobacterales and Methanospirillum, meanwhile, was enhanced, leading to an overall improvement in biogas production.

Effect of Particle Size and pH Value of Slurry on Chemical Mechanical Polishing of SiO2 Film

This study investigated the effects of particle size and pH of SiO2-based slurry on chemical mechanical polishing for SiO2 film. It was found that the removal rates and surface roughness of the material was highly dependent on the particle size and pH. As the particle size varied, the main polishing mechanism reasoned to provide activation energy to mechanical erasure. In addition, pH affected the particle size and Zeta potential, which had an important effect on the strength of the mechanical and chemical action of the chemical mechanical polishing. The change in mechanical action greatly influenced the removal rate. According to the experimental results, the best polishing of SiO2 film was achieved with 40 nm particle size SiO2 abrasives when the pH was 4.

The effect of slurry pH on the chemical mechanical planarization of a carbon-doped Ge2Sb2Te5 phase change material

The investigation of the chemical effect of slurry pH on the CMP process of a C-GST film through electrochemical means reveals a conversion of polishing behavior from the cycling to mechanical mechanism as the pH level varies.

Urea as a complexing agent for selective removal of Ta and Cu in sodium carbonate based alumina chemical–mechanical planarization slurry

This work reports urea as a promising complexing agent in sodium carbonate-based alumina slurry for chemical?mechanical planarization (CMP) of tantalum and copper. Ta and Cu were polished using Na2CO3 (1 wt. %) with alumina (2 wt. %) in the presence and absence of urea. The effect of slurry pH, urea concentration, applied downward pressure and platen rotational speed were deliberated and the outcomes conveyed. Prior to the addition of urea, the Ta removal rate (RR) was observed to increase with pH from acidic to alkaline, having a maximum RR at pH 11. However, Cu RR decreases with increasing pH with minimum RR at pH 11. With the addition of urea in the slurry, a Cu to Ta removal rate selectivity of nearly 1:1 was encountered at pH 11. The addition of urea simultaneous boosts the Ta RR and suppresses Cu RR at pH 11, as it adsorbs on the metal surface. Potentiodynamic polarization was conducted to determine the corrosion current (Icorr) and the corrosion potential (Ecorr). Electrochemical impedance spectroscopy of both metals was carried out in the proposed formulation and the obtained outcomes are elaborated.

Assessing the influence of pig slurry pH on the degradation of selected antibiotic compounds

Veterinary medicines are routinely used in animal husbandry and the environment may consequently be exposed to them via manure applications. This presents potential environmental and societal risks such as toxicological effects to aquatic/terrestrial organisms and the spread of antimicrobial resistance. Regulatory studies that assess the degradability of veterinary antibiotics during manure storage currently permit the use of just one manure per animal type although we speculate that heterogenic properties such as pH could be driving significant variability within degradation rates. To bridge this knowledge gap and assess degradation variability with pH, laboratory degradation studies were performed on a broad range of antibiotics (ceftiofur, florfenicol, oxytetracycline, sulfamethoxazole and tylosin) at three different environmentally relevant pH levels (5.5, 7, and 8.5). The effect of pig slurry pH on degradation rates was found to be significant and compound specific. Usually, acidic slurries were found to inhibit degradation when compared to neutral pH, for florfenicol, tylosin, and ceftiofur; the associated changes in DT50 (half-life) values were 2–209 h, 35.28–234 h, and 0.98–2.13 h, respectively. In some circumstances alkaline slurries were observed to enhance the degradation rate when compared to those for neutral pH, for tylosin, the respective changes in DT50 values were from 3.52 to 35.28 h. Comparatively, the degradation of sulfamethoxazole was enhanced by acidic conditions compared to neutral (DT50 20.6–31.6 h). Tentative identification of unknown transformation products (TPs) was achieved for sulfamethoxazole and florfenicol for the first time in pig slurries. These results reveal the importance of considering slurry pH when assessing the degradation of antibiotic compounds, which has implications for the acidification of manures and the environmental risk assessment for veterinary medicines.Environmental relevance and significance: Given the significant effect of pig slurry pH on degradation rates, manure degradation studies need to be harmonised and standardized, taking into account the influence of pH.

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.