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.

Synthesis of silica-coated ferromagnetic fine powder by heterocoagulation

In this paper, the synthesis of core-shell particles (i.e. temperature-sensitive ferrite (TSF) covered with silica) has been investigated. At first, TSF (mean diameter of 10 nm) was prepared by the coprecipitation method in an alkaline solution. Then, silica coating on the TSF surface was carried out by the controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The core-shell particles were formed by a surface precipitation procedure using TSF nanoparticles as a core material. The particles of silica were formed and these particles were then absorbed on the TSF nanoparticles. The coating procedure was described and explained by calculating the potential energies of interaction between the TSF and SiO(2) nanoparticles, according to the Derjarguin-Landau-Verwey-Overbeck (DLVO) theory. The coating process was found to be influenced by the pH and concentration of the TEOS precursor. The thickness of the silica layer on TSF cores was observed by means of transmission electron microscopy (TEM). The results showed that the optimum thickness of the SiO(2) layer on TSF core particles was obtained at pH 7.5, while the TEOS concentration was kept at 9 mM.