Electrochemical purification of kaolinitic for removing Fe and Ti oxides applying an ultrasonic pre-treatment

A study to determine the mechanisms of electrochemical purification and the effect of ultrasonic pre-treatment to remove impurities of Fe and Ti oxides was presented with the intention of optimizing the purification process of kaolinitic clays and increasing their use in different industrial applications. Cyclic voltammetry and chronoamperometry studies as well as SEM/EDS, ICP and whiteness index (WI) were conducted to evaluate the electrochemical purification of four different kaolinitic clays (ACE, CFL, ASC and AAM), with and without ultrasonic pre-treatment. The results show that the purification of kaolinitic clays was initially carried out by the chemical dissolution of Fe and Ti oxides, with oxalic acid added and pH < 1.5, while the electrochemically progressive deposition to Fe and Ti occurs on the silver electrode. Studies indicated that there is a higher removal of the impurities of Fe and Ti (82–92% Fe y 35–79% Ti) for CFL, ASC and AAM kaolinitic clays when an ultrasonic pre-treatment was applied; whereas ACE kaolinitic clay it was indifferent to ultrasound treatment. The results can be attributed to the fact that ACE kaolin clay contains low contents of magnetite and anatase, as well as, a high quantity of kaolinite. Finally, some kaolinitic (ACE and CFL) obtained a whiteness index >90, when ultrasonic pre-treatment was applied, thus increasing their use in different applications.