High-temperature removal of cadmium from a gasification flue gas using solid sorbents

In this work, the retention capacity of solid sorbents for cadmium species present in coal gasification flue gases at high temperature was investigated. The influence of HCl(g) on the gas atmosphere was also evaluated. The study was carried out in a laboratory scale reactor, using synthetic gas mixtures with the sorbent as fixed bed. The sorbents tested were kaolin, limestone, alumina and fly ashes. The results obtained were compared with data from the works of other authors, who used similar solid sorbents in typical coal combustion flue gases. Whereas in the combustion atmospheres described in the literature, kaolin, limestone and alumina showed high retention capacities for cadmium compounds (0.5-40 mg g−1), in the coal gasification atmospheres studied in the present work, the amount of cadmium captured by these solid sorbents was negligible. Fly ashes were found to be the most efficient for retaining cadmium in gasification atmospheres, their maximum retention capacity in the conditions studied being approx 0.75 mg g−1.