Magnetic and magnetorheological characterization of biopolymer suspensions of nanoscale iron particles for ground water remediation

Nanoscale zerovalent iron (NZVI) particles are a potential remedial agent for chlorinated organic compounds and toxic metals. NZVI slurries can be injected in the subsurface to target the source of contamination with reducing times and costs of the remediation interventions. Unfortunately concentrated iron suspensions are agglomerated by colloidal instability leading to solid-liquid separation after short time. It limits the mobility and transport of the iron nanoparticles in porous media. In this study, a magnetic characterization was performed on some samples of nanoscale iron powder with and without the addition of biopolymer fluid which is used to reduce the aggregation and settling of the particles. Hysteresis loops have been measured on dry nano-powder and its biopolymer suspension using a vibrating sample magnetometer at room and low temperature. The magnetization processes do not follow a Langevin-type curve, typical of superparamagnetic systems. On the contrary it has been shown that the particles form large aggregates with a multi-domain magnetic behavior.Field cooled (FC) and zero field cooled (ZFC) curves have been measured on nanoscale iron samples. Together with the hysteresis loops obtained at different temperatures, they help studying the effect of magnetic dipolar interactions on agglomeration processes among the nanoparticles. Additionally, the freezing of the suspensions provides a mechanical blocking of the particles, which can be used to more effectively study the magnetization processes in the fluid. Magnetorheological properties have been measured by Anton Paar rheometer. The magnetorheological response of the biopolymer suspension of nanoscale iron particles results from the polarization of the suspended particles by application of an external field. The interaction between the induced dipoles causes the particles to form chain-like structures. It restricts the motion of the suspension fluid, thereby increasing the viscoelastic properties. In the flow process, biopolymer structure of the suspension fluid can also affect the interaction of particles. Under a small applied field, the steric effect of biopolymer among nanoparticles can be characterized through the rheological properties and magnetization variation of suspension. Magnetic and magnetorheological measurements have been compared to understand the magnetic interaction behavior of iron nanoparticles and its effects on the agglomeration in the biopolymer suspensions.