Ricerc@Sapienza

Chitosan is very effective in removing metal ions through their adsorption. A preliminary investigation of the adsorption of chromium(III) by chitosan was carried out by means of batch tests as a function of contact time, pH, ion competition, and initial chromium(III) concentration. The rate of adsorption was rather rapid (t1/2 < 18 min) and influenced by the presence of other metal ions. The obtained data were tested using the Langmuir and Freundlich isotherm models and, based on R2 values, the former appeared better applicable than the latter.

Leather tanning processing and manufacturing industry uses high large amounts of water in the range of 40–45 L kg–1 during processing. As a result, tannery wastewater rises by the same amount, is characterized by a large inorganic load (chlorides, with concentration ranging from several hundred to over 10,000 mg L–1 Cl–; sulphate (VI), ammonium ions and sulphide ions, exhibiting concentration that ranges from tens to several hundred mg L–1) and together with organic pollution (the chemical oxygen demand value is usually several thousand mg L–1 O2).

Hexavalent Chromium species are classified as hazardous compounds due to their high toxic potential, considering also their remarkable solubility and redox potential. Various processes have been developed to remove/recover Cr(VI) species from polluted groundwater, such as membrane processes, ion-exchange and adsorption and chemical or biochemical reduction. Indeed, the reduction/removal process of Cr(VI) through iron-based materials usually leads to a pH increase of the reaction medium, allowing to facilitate the subsequent precipitation of the Cr(III) species.