Abstract
In this study, the flocculation performance and kinetics of magnetic cationic polyacrylamide (MCPAM) microspheres, compared with cationic polyacrylamide (CPAM), were systematically investigated under different magnetic field strengths. Flocculation performance was observed by jar test experiment. The density of flocs was estimated by the determination of floc settlement velocity and image analysis. The frequency distribution of floc size was measured with a Malvern Mastersizer instrument. When the diatomite suspension was treated by MCPAM and CPAM, the residual diatomite turbidity was 16.28 NTU and 244.13 NTU, respectively. The maximum turbidity removal efficiency of MCPAM was about 99.65% under 1000 Gauss magnetic field, which was higher than that (94.75%) of CPAM. The synergy of gravitational and magnetic fields for MCPAM promoted the formation of larger flocs with higher growth rates compared with CPAM. The effective density range of flocs in the MCPAM flocculation was increased to 10–252 kg m−3. The kinetic constants were calculated by monitoring the frequency of floc collisions. The increase of kinetic constant (k) to 25.81 × 10−11 s−1 suggested that interaction of contact and collision between magnetic flocs was sufficient. According to the evolution of the size and density of flocs under the synergy of gravitational and magnetic fields, the magnetic flocculation rate equation dN/dt=−1/9μρ−ρlg+ρkmHdH/dXai2−aj2−ai2e9μt/2ai2ρ+aj2e9μt/2aj2ρai+aj2 was derived. The study of magnetic flocculation kinetics can provide theoretical support for magnetic flocculation and is critical for the analysis of solid-liquid separation processes.
Highlights
Flocculation is an important process in the water treatment system
The performance and flocculation kinetics of magnetic cationic polyacrylamide (MCPAM) under different magnetic field strengths were investigated and compared with cationic polyacrylamide (CPAM). e density of flocs was estimated by the determination of floc settlement velocity and image analysis. e frequency distribution of floc size was measured by the Malvern Mastersizer instrument. e kinetic constants for particle collisions and aggregation were calculated based on the bimolecular reaction model
Under a 1000 Gauss of magnetic field, the transmittance of supernatant increased to 98.96% at 40 s after adding MCPAM and stabilized at 99.65% after 100 s. e transmittance of supernatant was improved by 8.64% at 40 s as the applied magnetic field was from 0 to 1000. e results indicated that the efficiency of magnetic flocculants in high magnetic field intensity was higher than that in low magnetic field intensity. e strength of the magnetic field can affect the movement of magnetic flocs
Summary
Flocculation is an important process in the water treatment system. And flocculants are a key in achieving high flocculation efficiency in the aggregation process. More attention has been paid to the improvement of flocculation performance of flocculants and development of water treatment technology. Conventional organic flocculants, such as cationic polyacrylamide (CPAM), exhibit excellent flocculation performance in water treatment due to favorable adsorption and bridging. Magnetic flocculants have been widely applied in microalgae harvesting, heavy metal removal, enhancing emulsification of water media, and tailings disposal, etc. Magnetic flocculants can remove heavy metal ions with low economic cost [8,9,10,11]. Magnetic nanoparticle-supported layered double hydroxide nanocomposites (MLDO) could be an economical option for the removal system of As(V) and Sb(V) in water treatments
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