Treatment of Sulfurous Waters Using Activated Carbons

Abstract

Efficient catalysts in the oxidation of hydrogen sulfide oxygen species are activated carbons. Activated carbon research highlights the important role of surface functional groups as a source for free radicals and initiate steps in catalytic activation of oxygen on the surface of activated carbon. Studies show that with increasing oxygen content on the surface of carbon, the concentration of functional groups increases the adsorption capacity of sulfur (II) species and their oxidation to higher degrees of oxidation. Is noted the important role of acid–base properties of activated carbons and their surface pH in suspension, influencing dissociation and oxidation of hydrogen sulfide to different species of sulfur. Oxidized active carbon is rich in acidic functional groups on the surface, has a higher catalytic activity and is more efficient compared to commercial activated carbon BAU-A, which is poor in functional groups and has an alkaline surface pH. Oxidized active carbon produced from peach stones and impregnated with ions Fe3+ and Cu2+ shows increased catalytic activity in the oxidation of sulfur species in reduced form, compared to adsorbents before impregnation with metals. Oxidation products generated in the presence of catalysts obtained by impregnation with metals are thiosulfates, sulfites and sulfates, without the formation of colloidal sulfur. The state or form of immobilized metals on the surface of activated carbon influences significantly the selectivity of formation of sulfur species. Impregnated metals present on the surface of activated carbon in the form of ions, favor the formation of sulfur in high oxidation degree of S4+ and S6+, while impregnated metals present as oxides, favor the oxidation of ion sulfide to elementary sulfur. Comparative analysis of the catalytic activity of obtained catalysts shows that the most effective catalyst is obtained from oxidized activated carbon from peach stones and impregnated with Cu2+ions. The catalyst shows pronounced catalytic activity at higher pH values of the solutions, which is important from the practical point of view, ensuring efficient catalytic activity under to near natural groundwater alkaline pH. The catalyst can be re-used for a long time, keeping the pores unclogged and maintaining the porous structure at the characteristic parameters of this adsorbent, being recommended for practical purposes to remove hydrogen sulfide species from sulfurous groundwater.