An innovative approach to the synthesis of sorbent materials for metal fixation

摘要

A new approach has been developed for the synthesis of wastewater treatment materials from calcareous substrates via the process of accelerated carbonation. This paper presents results from an investigation of the characterization and performance testing of carbonated ordinary Portland cement (CASM) as a sorbent for metal removal. CASM was synthesized by exposing cement to carbon dioxide gas, at a pressure of 2 bar, in the presence of moisture. The resulting product had funnel-shaped pores of 30-40Angstrom and a specific surface area of 49m(2) g(-1). The main phases of CASM were crystalline polymorphs of calcium carbonate, amorphous silica/alumina and unreacted mineral phases. In a sessile kinetic sorption study CASM demonstrated the following trend in metal uptake (in mg/g): Pb(185) > Cd(180) > Cr(175) > Mo(106) > Co(69) > Ni(65) > Cu(59) > Cs(37). The fate and speciation of the immobilized metals were determined by the analysis of metal-bearing CASM specimens. Cadmium, lead and copper formed carbonate-based species, whereas molybdenum and chromium formed scheelite CaMoO4 and the amorphous analogue of bracewellite CrO(OH), respectively. Sorption, ion-exchange and (co-)precipitation were suggested to be the mechanisms of nickel and cobalt fixation, whereas cesium was exclusively associated with anhydrous silica. The results indicate that accelerated carbonated may be used to produce new sorbent materials.