The application of multi-scale magnetic matrix materials in high-gradient magnetic separation: From micro- and nano- to millimeter-scale

Abstract

Micro- and nano- to millimeter-scale magnetic matrix materials have gained widespread application due to their exceptional magnetic properties and favorable cost-effectiveness. With the rapid progress in condensed matter physics, materials science, and mineral separation technologies, these materials are now poised for new opportunities in theoretical research and development. This review provides a comprehensive analysis of these matrices, encompassing their structure, size, shape, composition, properties, and multifaceted applications. These materials, primarily composed of alloys of transition metals such as iron (Fe), cobalt (Co), titanium (Ti), and nickel (Ni), exhibit unique attributes like high magnetization rates, low elastic modulus, and high saturation magnetic field strengths. Furthermore, the studies also delve into the complex mechanical interactions involved in the separation of magnetic particles using magnetic separator matrices, including magnetic, gravitational, centrifugal, and van der Waals forces. The review outlines how size and shape effects influence the magnetic behavior of matrices, offering new perspectives for innovative applications of magnetic matrices in various domains of materials science and magnetic separation.

1. Introduction

Magnetic matrix materials have garnered significant attention in the fields of materials science and engineering due to their unique physical and chemical properties. These magnetic matrices, primarily composed of alloys of transition metals such as Fe, Co, Ti, and Ni, are the focus of research due to the ease of processing, high purity, and good biocompatibility of transition metals, resulting in alloys with high magnetization rates, low elastic modulus, and high saturation magnetic field strengths [1−3]. The distinct magnetic properties of spinel ferrites arise primarily from the spin asymmetry of iron ions (Fe²⁺ and Fe³⁺), which play a critical role in shaping magnetic domains by contributing to key characteristics such as low coercivity and the facile processes of magnetization and demagnetization [4−6]. Therefore, these unique properties position soft magnetic alloys as optimal candidates for next-generation magnetic materials, particularly in applications involving millimeter and micro- and nano-scale matrix materials.

The demand for these materials has steadily increased with the advent of magnetic nano- to millimeter-scale particles, commonly known as "magnetic beads". These nanomaterials, which can be precisely manipulated by external magnetic field gradients, present new avenues for exploring magnetic matrices with sizes ranging from 1 µm to 500 µm, enabling a wide array of advanced applications [7, 8]. These magnetic matrices, which are micro- and nanostructured, have high surface area-to-volume ratios and size-dependent physical-chemical characteristics. By comparison with macroscopic material, they exhibit lower hysteresis lines, stronger magnetic saturation, and higher reactivity [8, 9]. Micro- and nanostructured magnetic matrices are widely used in many different fields because of their fantastic mechanical and thermal stability, high surface area, unique physical, chemical, and electrical capabilities, and high optical and magnetic qualities [8, 9]. They are being used in many different applications, such as mineral processing studies [10], the delivery of drugs [11, 12], the storage of data [13], magnetic fluid management [13−15], cell sorting [16] and environmental remediation [17]. The applications for micro- and nanostructured magnetic matrices in mineral processing are developing quickly. These include their use as dispersants in the magnetic flotation process, as sensors for mineral detection in superconducting quantum interferometric devices (SQUID) and magnetic force microscopes (MFM) [18], as magnetically conductive media in high gradient-based magnetic separators (MGMS) and slurry magnetic separators (WHIMS) [19−21], and in the purification of magnetic ore [21, 22]