A further study on adsorption interaction of humic acid on natural magnetite, hematite and quartz in iron ore pelletizing process: Effect of the solution pH value

• The sorption amount of HA onto magnetite, hematite and quartz decreased with increasing pH value.
• The sorption amount of HA onto the three oxides was in the order: magnetite > hematite > quartz.
• HA was adsorbed onto magnetite and hematite via electrostatic interaction and ligand exchange.
• The small amount of HA onto quartz was attributed to the hydrogen binding.
• The most suitable structure and viscosity for the MHA binder were obtained at pH ~ 7 for pelletizing.

Humic acid (HA) was the predominant component of the MHA (modified humic acid) binder invented by the authors. This work aims to study the effect of the solution pH value on the HA adsorption onto natural magnetite/hematite/quartz particles and the strength of green pellets with the MHA binder. The SEM images for HA indicated that HA had distinct morphology at different pH values. The adsorption density of HA on the three oxide minerals was significantly pH-dependent and decreased with increasing pH value. The zeta potential values of the magnetite, hematite and quartz particles coated by HA became negative and the isoelectric point of the three natural oxide minerals disappeared in the tested pH value range. The electrostatic interaction and the ligand exchange were the two leading interactions for the HA sorption onto the magnetite/hematite particles, while the small adsorption amount of HA onto the quartz was attributed to the hydrogen-bond interaction. The pH value of the MHA binder solution affects markedly the strength of green pellets from magnetite and hematite concentrates. At pH ~ 7.0, the HA molecule was expanded and dispersed well and the relatively strong bonding bridges were formed among the iron ore particles. The optimal pH value was founded to be around 7.0 for preparing high-quality iron ore green pellets.

Fig. 1 diagram of the magnetite coated by the MHA binder at different pH.(a) pH = 3.0, (b) pH = 7.0, (c) pH = 12.0At low pH, HA is adsorbed and stacked on the iron ore particle surface. When the green pellets with MHA binder are dropped, the aggregates of MHA binder are difficult to expand, disperse or slip, and broken up under shear force. When the pH value is increasing to 7.0, HA has a relatively smooth surface and moderate viscosity. When the shear force is implemented, the MHA binder micelles are easy to disperse among the particles and slip on the surface of particles, and so that keep binding the particles together. At higher pH, HA molecules present a fibrous structure and the strength of bonding bridge of the MHA binder is much weaker, so the green pellets are easy to break up under shear force.Figure optionsDownload as PowerPoint slide