Multidimensional Separation by Magnetic Seeded Filtration: Experimental Studies

Abstract

The current state of separation technology often neglects the multidimensional nature of real particle systems, which are distributed not only in terms of size, but also in terms of other properties, such as surface charge. Therefore, the aim of this study is to experimentally investigate the applicability of magnetic seeded filtration as a multidimensional separation process. Magnetic seed particles are added to a multisubstance suspension, and a selective heteroagglomeration with the nonmagnetic target particles is induced, allowing for an easy subsequent magnetic separation. The results show that high separation efficiencies can be achieved and that the parameters pH and ionic strength govern the agglomeration process. Selective separation based on surface charge was observed, but undesirable heteroagglomeration processes between the target particles lead to a loss of selectivity. Particle size was clearly identified as a second relevant separation feature, and its partially opposite influence on collision frequency and collision efficiency was discussed. Finally, experimental data of multidimensional separation are presented, in which a size-distributed two-substance suspension is separated into defined size and material fractions in a single process step. This study highlights the need for multidimensional evaluation in general and the potential of magnetic seeded filtration as a promising separation technique.

Multidimensional Separation by Magnetic Seeded Filtration: Theoretical Study

“…However, the selectivity in a charge-based system is limited, as all materials undergo some degree of separation. This agrees well with the previous experimental study [9], where hetero-agglomeration phenomena between nonmagnetic target particles were shown to result in the formation of multimaterial agglomerates that are separated. Specifically, negatively charged nonmagnetic particles, generally not attracted to the magnetic particles (see Figure 4a), agglomerate to positively charged nonmagnetic particles.…”

“…Multidimensional separation with MSF is studied theoretically for two different cases of varying surface property φ. Simple model functions for the collision efficiency matrix α m are used which capture the underlying affinities discussed in the previous publication [9]. A "charge-based" separation is modeled for case 1 by 4a.…”

“…A previous study [9] proposed magnetic seeded filtration (MSF) as a multidimensional process that separates both by particle size and surface properties. Here, magnetic seed particles are added to a suspension containing the nonmagnetic target particles, and a selective hetero-agglomeration is induced.…”

“…These hetero-agglomerates are then removed from the suspension by a simple magnetic separation. During the previous experimental investigations [9], a polydisperse suspension with two nonmagnetic materials of different zeta potential was separated into two fractions of more or less defined particle size and material. Thus, in general, MSF is able to achieve a selective and multidimensional separation.…”

“…Experimental work investigating a multidimensional separation currently faces several downsides and limitations. As discussed in [9], analytical methods are intricate, even in suspensions with only two nonmagnetic materials, necessitating the combination of multiple offline analyses to obtain material-specific information. Thus far, separation was quantified continuously with respect to size and discretely, i.e., material-wise with respect to surface charge.…”