Overview of fine coal filtration. Part II: Filtration aiding treatments and reagents

Filtration is the most common dewatering practice for solid–liquid separation because of its low cost and relatively high efficiency. However, the filtration of fine particles (e.g., flotation products, tailings) presents challenges due to the formation of low porosity cakes, which limit the flowrate and reduce filtration efficiency. This study provides a comprehensive review of various treatments for improving filtration performance. It discusses the mechanisms and effects of the mainstream treatments, such as flocculation and coagulation, on filtration performance and cake moisture. Additionally, novel techniques are reviewed, including the use of bio-degradable flocculants as a replacement for conventional polymeric flocculants, oil agglomeration in the filtration of ultrafine coal particles, and cake washing to mitigate soluble impurities in filter cakes. The review highlights that floc formation and surface hydrophobicity modification are influenced by slurry conditions and particle properties. Variations in slurry pH, conductivity, particle size, and particle surface charge can affect treatment performance, with optimal dosages for flocculating or hydrophobising reagents largely depending on these parameters. While natural flocculants may offer advantages in moisture removal due to their smaller structure, pH dependency remains a challenge, and there is a lack of knowledge regarding their application in coal flocculation. Preliminary work by the authors indicates that cake washing can mitigate inorganic salt residues and improve product quality, however, its feasibility and advantages in large-scale operations and dewatering efficiency are still debated.