Influence of the Sorption of Iron and Manganese Ions on the Surface Properties of Activated Carbon Derived from Coconuts

Abstract

Active carbon proves very efficient in extracting organic and mineral contaminants from aqueous solutions. Sorbents derived from coconut shells are investigated in the present work, both in their initial state and after the sorption of iron and manganese ions from single-component solutions in kinetic, static, and dynamic conditions. The methods employed are infrared (IR) spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, thermal analysis, and nitrogen porosimetry. The absorption of iron and manganese ions from single-component solutions is found to be a purely physical process and does not lead to a strong bond with the coconut-based active carbon. IR spectroscopic data regarding the change in the relative content of oxygen groups at the surface of the sorbents containing iron and manganese ions correlate with the results of X-ray photoelectron spectroscopy (the relative atomic concentration of elements in the surface layers) and the thermogravimetric data (thermal decomposition and mass loss in different temperature ranges). The oxidation rate of the active coal increases after sorption of iron and manganese ions, probably because sorbed ions in the form of organometal complexes within the sorbent structure have a catalytic effect. Analysis of surface images of the samples obtained by scanning electron microscopy and porosimetric data shows that the iron and manganese ions are sorbed in micropores and mesopores. In addition, the sorbed manganese ions probably have a catalytic effect on oxidation of the carbon’s aromatic structure, with surface etching. Results regarding the extraction of iron and manganese ions in kinetic conditions establishes the limiting stage: external mass transfer for 100 min (iron) or 30 min (manganese). In dynamic conditions, the total extraction of iron from single-component solutions is 70.3%, as against 62.7% for manganese.