Release and removal using sorbents of chromium from a high-Cr lignite in Shenbei coalfield, China

摘要

With the increasing use of coal, the growing impact on the environment of potentially hazardous trace elements including chromium has been attracted more concerns. Chromium is strongly enriched in the Shenbei lignite compared with average concentration in the Chinese coal. The occurrence of chromium in several high-chromium coals was determined and it mainly occurs as organic macromolecules. Combustion of a typical high-chromium coal from Shenbei coalfield and a high volatile bituminous coal (HN coal) adding chromate were tested in a bench-scale drop tube furnace (DTF) to understand the partition and emission of chromium in the combustion process. The emission concentration of chromium in PM_(10) during Shenbei high-chromium coal combustion is up to 0.331 mg/Nm~3. The retention of chromium from high-Cr coal combustion by 6 sorbents (Al_2O_3, CaO, Fe_2O_3, zeolite, bentonite, and bauxite) was investigated in a fixed bed reactor. Bauxite has the highest retention rate for high-Cr coal owing to its highest surface area. The retention rate of the six sorbents for high-Cr coal follows the order of bauxite ＞ zeolite ＞ CaO ＞ Fe_2O_3 ＞ bentonite ＞ Al_2O_3. The interaction mechanisms of chromium compounds and sorbents were discussed. Physical adsorption is the mainly mechanism for the capture of organic-bond chromium, whereas the formation of new chromium compounds Al_3CrO_6, FeCr_2O_4, and Ca_5Cr_3O_(13)H indicates the capture process of chromium contains chemical reaction.