Black tea adsorption on calcium carbonate: A new application to chalk powder for brown powder materials

Black tea adsorption on calcium carbonate has been studied for a new application to chalk powder as a method for surface modification. Black tea was used as a dyeing material for making brown powder materials. Chalk and pure calcium carbonate powders were reacted with the black tea aqueous solution from 30 min to 3 weeks at room temperature and the brown powders were obtained as the reaction products. The brown powders were characterised by X-ray diffraction, infrared spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, analysis of CHN and other elements and high performance liquid chromatography. Thermal study was also performed. The results indicate that the tea organic compounds are adsorbed on the surface of calcite crystals as a thin layer. They resembled tea scum-like materials transformed from at least two tea pigments such as theaflavins and thearubigins in the tea solution. In the adsorption process, the Ca(II) ions leached from calcite crystals mediated to form them. Possible tea adsorption mechanisms are also discussed in explaining the obtained results.