Supplying Fe from Molten Coal Ash to Revive Kelp Community

Abstract

The phenomenon of a kelp-dominated community changing to a crust-dominated community, which is called “barren-ground”, is progressing in the world, and causing serious social problems in coastal areas. Among several suggested causes of “barren-ground”, we focused on the lack of Fe in seawater. Kelp needs more than 200 nM of Fe to keep its community. However there are the areas where the concentration of Fe is less than 1 nM, and the lack of Fe leads to the “barren-ground.” Coal ash is one of the appropriate materials to compensate the lack of Fe for the kelp growth, because the coal ash is a waste from the coal combustion process and contains more than 5 wt% of Fe. The rate of Fe elution from coal fly ash to water can be increased by 20 times after melting in Ar atmosphere, because 39 wt% of the Fe(III) of coal fly ash was reduced to Fe(II). Additionally molten ash from the IGCC (integrated coal gasification combined cycle) furnace in a reducing atmosphere and one from a melting furnace pilot plant in an oxidizing atmosphere were examined. Each molten ash was classified into two groups; cooled rapidly with water and cooled slowly without water. The flux of Fe elution from rapidly cooled IGCC molten ash was the highest; 9.4 × 10^–6 g m^–2 d^–1. It was noted that the coal ash melted in a reducing atmosphere could elute Fe effectively, and the dissolution of the molten ash itself controlled the rate of Fe elution in the case of rapidly cooled molten ash.