COAL-MINE SPOIL-WATER INTERACTION .2. WEATHERING CONCENTRATED METALS IN SURFACE COAL-MINE SPOILS

Concentrations of metals are lower in coal shales collected from recen tly exposed surface mine wastes than in shales collected from spoils e xposed to surface weathering for 45 a, In this period, the character t er of the spoils changes dramatically as a result of the accelerated b reakdown of the freshly exposed minestones. Since the metals are held as unstable sulfides, it is suggested that enrichment may be caused by absorption of metals by colloid of iron or formation of organic compl ex compound with organic carbon existing in the remnant structure of c oal mine spoil. This process may contribute to the triggering of soil contamination thresholds on coal-lands already heavily loaded with met als.