Aminoclay-templated nanoscale zero-valent iron (nZVI) synthesis for efficient harvesting of oleaginous microalga, Chlorella sp. KR-1

Abstract

Synthesis of aminoclay-templated nanoscale zero-valent iron (nZVI) for efficient harvesting of oleaginous microalgae was demonstrated. According to various aminoclay loadings (0, 0.25, 0.5, 1.0, 2.5, 5.0, and 7.5 aminoclay–nZVI ratios), the stability of nZVI was investigated as a function of sedimentation rate. Aminoclay-coated nZVI (aminoclay–nZVI composites) showed optimal dispersibility at the 1.0 ratio, resulting in the smallest aggregated size and uniform coating of aminoclay nanoparticles onto nZVI due to electrostatic attraction between nZVI and aminoclay nanoparticles. This silica-coated nZVI composite (ratio 1.0) exhibited a highly positively charged surface (∼+40 mV) and a ferromagnetic property (∼30 emu g⁻¹). On the basis of these characteristics, oleaginous Chlorella sp. KR-1 was harvested within 3 min at a > 20 g L⁻¹ loading under a magnetic field. In a scaled-up (24 L) microalga harvesting process using magnetic rods, microalgae were successfully collected by attachment to the magnetic rods or by precipitation. It is believed that this approach, thanks to the recyclability of aminoclay–nZVI composites, can be applied in a continuous harvesting mode.