Elimination of Hexavalent Chromium Ions in Water Using a Manganese-Coated Pumice Adsorbent

A natural pumice stone stone coated with manganese (Mn) has been prepared and utilized to remove hexavalent chromium (Cr(VI)) ions in water via adsorption process. Prior to the application, the natural pumice was ground, sieved, and immerse in a dilute HCl solution. The coating of Mn on the acid-activated pumice was carried out by soaking the powder in 0.5 M Mn(NO3)2 solution for 72 h. The characterisation of the produced pumice adsorbent was performed with scanning electron microscopy and fourier-transform infrared spectroscopy instruments. The adsorption of Cr(VI) onto Mn-coated pumices was optimum at pH 3. Both the Langmuir and Freundlich isotherm models could be used to describe the adsorption process. The rate of adsorption followed the model for pseudo-second-order kinetics. The maximum adsorption capacity of Mn-coated pumice towards Cr(VI) ions was 1.94 mg/g.