Specific adsorption of chromium species on kaolinite surface.

The specific adsorption of hydrolysed Cr species on kaolinite surface was studied. Mexican kaolinite was purified first by using a high-intensity magnetic separator to remove Fe mineral particles and then by screening to remove coarse particles. The electrokinetic behaviour of kaolinite particles in aqueous sodium salt solutions (NaCl) in the presence of chromium chloride showed that kaolinite can reverse its charge. The zeta potential was negative in the range of pH 2-12 and no isoelectric point (IEP) appeared without CrCl3. The zeta potential increased as pH increased from 2.5 to approximately 6; it then decreased with pH and approached a value as though CrCl3 were not present. The adsorption of Cr on kaolinite reached a maximum value at a pH of approximately 6, which was the precipitation pH (ppt) of chromium hydroxide at the corresponding CrCl3 concentration and then kept a plateau to pH 6.3-6.5. This adsorption followed the Langmuir isotherm and was irreversible; and a chemical adsorption model between kaolinite surfaces and the hydrolysed multivalent metal species was proposed.
The specific adsorption of hydrolysed Cr species on kaolinite surface was studied. Mexican kaolinite was purified first by using a high-intensity magnetic separator to remove Fe mineral particles and then by screening to remove coarse particles. The electrokinetic behaviour of kaolinite particles in aqueous sodium salt solutions (NaCl) in the presence of chromium chloride showed that kaolinite can reverse its charge. The zeta potential was negative in the range of pH 2-12 and no isoelectric point (IEP) appeared without CrCl3. The zeta potential increased as pH increased from 2.5 to approximately 6; it then decreased with pH and approached a value as though CrCl3 were not present. The adsorption of Cr on kaolinite reached a maximum value at a pH of approximately 6, which was the precipitation pH (ppt) of chromium hydroxide at the corresponding CrCl3 concentration and then kept a plateau to pH 6.3-6.5. This adsorption followed the Langmuir isotherm and was irreversible; and a chemical adsorption model between kaolinite surfaces and the hydrolysed multivalent metal species was proposed.