Surface characteristics and wettability enhancement of respirable sintering dust by nonionic surfactant

Plenty of respirable sintering dust are generated in ironmaking process and part of this hazardous particle easily escaped from electrostatic precipitators, becoming Particulate Matter 10. Previous studies are usually focused on the comprehensive recovery of this dust, however, its wetting, which was an essential procedure in many industrial processes, has long been a challenge due to its strongly hydrophobic property. The current study investigated the origin of its hydrophobicity through wettability tests, dynamic contact angle analysis, Fourier transform infrared spectrophotometer and X-ray photoelectron spectroscopy, with the goal of enhancing its wettability. The results revealed for the first time that the hydrophobicity of respirable sintering dust was attributed to a hydrophobic shell consisting of organics with n-alkyl chains and/or aromatic groups and bonding by hydrophilic functional groups. Further, results of response surface methodology with central composite design and dynamic contact angle analysis demonstrated that increasing agitation strength, such as stirring speed and time, can improve the wettability of respirable sintering dust, while the largest wettable ratio of 95.3% was obtained by stirring with 0.2% Triton X-100. Eventually, a possible wetting mechanism was mainly concluded as nonionic surfactants adsorbing with the hydrophobic shell on respirable sintering dust surface via its hydrophobic tail and leaving its hydrophilic head groups exposed to water, achieving sufficiently and efficiently wetting. The adsorption experiments and surface analysis results implied that the adsorption process for Triton X-100 onto respirable sintering dust is favorable and governed by physisorption. This study provides an effective method on the wetting of respirable sintering dust, which is essential for its treatment such as dust control and hydrometallurgy.