[Effects of solid adsorbents on the emission of heavy metals during coal combustion]

Experiments were carried out on laboratory-scale pulverized coal combustion with different adsorbents. Three solid adsorbents (calcium sulfate, limestone and bauxite) were used to control the emission of heavy metals (Pb, Cd, Cu, Co, Ni) during coal combustion. Sequential extraction procedure was developed for partitioning of metals species in coal ash into five fractions: absorbable metals, exchangeable metals, metals bound to carbonate, metals bound to sulfate, residual metals. The adsorbents showed a certain adsorptive ability to heavy metals, and different adsorbent had different ability. It can be proved from the distribution of heavy metals between coarse ash residues and fine particles and also from the increment of stable speciation of heavy metals in fine particles. Calcium sulfate was effective sorbent for removal of Pb, Cd and Cu, limestone for removal of Pb, Cd, Cu, Ni, and bauxite for removal of these five heavy metals. Fine adsorbents have higher adsorptive ability than coarse adsorbents.