Salts-activated synthesis of Cu/Co co-doped biochar for efficient removal of elemental mercury from coal combustion flue gas

Abstract

Mercury immobilization from coal combustion flue gas remains challenging due to the shortage of cost-effective sorbents. In this study, Cu/Co co-doped biochar (CuxCoyBCT) was synthesized through one-step pyrolysis of wood loaded with Cu and Co salts, which was applied to remove elemental mercury (Hg0) from the simulated flue gas. The BET surface area and pore volume of CuxCoyBC650 were vastly higher compared with CuBC650 because of the catalytic effect of cobalt. The synergistic effects between Cu and Co facilitated the transformation of Cu2O into CuO during pyrolysis. The doping of Co resulted in a more uniform dispersion of CuOx and highly dispersed CoOx was also observed in CuxCoyBCT. For this reason, the Hg0 removal performance of CuxCoyBCT was obviously improved after Co doping. The optimal Cu/Co molar ratio and pyrolysis temperature were 1:1 and 650 °C, respectively. The sample of Cu1Co1BC650 showed satisfactory Hg0 removal efficiency (>88 %) over a broad temperature range (100 °C–180 °C). It was remarkable that SO2 facilitated Hg0 removal and H2O had negligible effect on Hg0 removal over CuxCoyBCT. The presence of O2 and NO was conductive to Hg0 removal. The mechanism of Hg0 removal over CuxCoyBCT was further revealed. The results indicated that the heterogeneous adsorption and catalytic oxidation of Hg0 occurred simultaneously, where chemisorbed oxygen, CuO, and Co3O4 served as active components.