Mercury flow via coal and coal utilization by-products: A global perspective

Mercury (Hg) has been known to society and used since ancient times. The metal has drawn considerable attention and concern due to its toxicity, persistence, bioaccumulation and long range transport in the atmosphere after emission from coal-fired utilities as well various other high temperature processes. Coal is an important fuel for the production of heat and electricity and in recent years annual hard coal production has approached a level of around 5000 million metric tonnes (Mt, t = 1000 kg). Global Hg flows via coal and coal utilization by-products (CUBs) are presented in this paper, which are important in light of the regulations to limit the global emissions of Hg and its cycling as well as its circulation via coal and the CUBs. There are no detailed statistics on the global production and consumption of coal fly ash (FA) and in this study, we have estimated the total global FA production for the year 2003 based on ash content in coals and typical flue gas control technology for pulverized coal combustion. The mode of occurrence and concentration of Hg in coal and coal FA for different countries have been evaluated and presented in this study. The total Hg amount in coals processed worldwide was found to be 1534 t in 2003 based on a global average concentration of 0.3 mg/kg in coal. In addition, "hidden" flows of Hg through export and import of coal assessed during this study, add up to about 149 t. In this study, the economic uses of the FA in different sectors such as cement industry, agriculture, land reclamation, filers for asphalt, plastic and many others have been discussed in details. However, there is not much information on uses of coal FA in the developing countries. In the final part of the paper, a short survey has been focused on a few coal producing countries including Australia, China, EU-states, India, Japan, Korea, Russia, South Africa and South American countries, addressing the status of coal and coal FA use and the fate of the Hg that is mobilized. (c) 2007 Elsevier B.V. All rights reserved.