Effect of chemical composition and crystal chemistry on the zeta potential of ilmenite

• Lattice substitution of Mn, Mg and V influences the zeta potential of ilmenite.
• Hematite exsolutions decrease the isoelectric point of ilmenite by releasing Fe3+.
• Sphene exsolutions containing Ca and Si affect the isoelectric point of ilmenite.
• Chemical composition can be used to predict the IEP of ilmenite.

The crystal structure, crystal chemistry and surface properties of three ilmenite samples including IL-F (purchased from the mineral dealership of A. and F. Krantz), IL-Q (Qara-aghaj hard rock deposit, northwest of Iran) and IL-K (placer deposit, south of Iran) were investigated. The microprobe analysis showed that different amounts of Mg, Mn and V have been substituted in the crystal structure of ilmenite. Using SEM, microprobe analysis and X-ray diffraction it was found that there are different amounts of exsolved fine lamellae of hematite inside ilmenite in the studied samples. Some fine lamellae of the sphene mineral were also observed inside the IL-K ilmenite. The isoelectric point (IEP) was determined as 6.25, 5.4 and 4.2 for IL-K, IL-Q and IL-F, respectively. Mn content has a good positive correlation with lattice constants (LC), unit cell volume, crystallinity index and IEP of ilmenite but the increase of Mg and V content in ilmenite was found to decrease them. The crystallinity index of ilmenite was not the major factor for determining IEP. A linear relationship with a correlation coefficient of r = 0.97 was found to exist between the measured isoelectric point and Ti content in the ilmenite crystal structure. Fe3+ ion sourced from hematite lamellae has a good negative correlation (r = −0.96) with the IEP value of ilmenite and it is one of the most important IEP determining ions. Si and Ca content come mainly from sphene exsolutions that tend to increase the IEP value of ilmenite.

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