Abstract
In China, coalmine wastes, such as gangues, are used for reclamation of mining subsided land. However, as waste rocks, gangues contain several trace metal elements, which could be released under natural weathering and hydrodynamic leaching effects and then migrate into the reclamed soil layer. However, it is very difficult to find adequate other backfill materials for substitution of gangues. In this paper, we present a novel method and case study to restrict the migration ability of trace metal elements in gangues by using another kind of coalmine solid waste—fly ashes from coal combustion. In this study, fly ashes were mixed with gangues in different mass proportions 1:0.2, 1:0.4, 1:0.6 and 1:0.8 as new designed backfill materials. Due to the help of fly ash, the occurrence states of studied trace metal elements were greatly changed, and their releasing and migration ability under hydrodynamic leaching effect were also significantly restricted. In this research seven trace metal elements in gangues Cu, Zn, Pb, Cd, Cr, Mn and Ni were studied by using soil column hydrodynamical leaching method and simulated precipitation for one year. The results show that under the driving of natural precipitation trace metal elements were generally transported deep inside the reconstructed land base, i.e., far away from soil layer and most of the trace metal elements were transformed into a bonded state, or combined in inert occurrence states, especially the residual state. With this method, the migration activities of tested trace metal elements were greatly restricted and the environmental potential risk could be significantly reduced.
Highlights
China is the biggest coal production and consumption country in the world
Unit: mg/kg. fly ash and four proportioned backfill materials are shown in Table 3 as follows
The results demonstrated that after leaching most Zn element exited in backfill material mainly as residual state, a little bit organic sulfide binding state, and few carbonate binding states
Summary
China is the biggest coal production and consumption country in the world. Coal occupies more than 70% domestic primary energy consumption in China, which covers about 75% primary fuels for industries and more than 90% primary fuels for civil use. In China, it is believed that coal will continued to be used as the main energy source for a long period in future [1,2,3,4]. Most coal is produced through underground mining in China, which makes use of a huge land area. There are more than 4.3 × 105 hm mining subsidence area in China currently. The annual increment of mining subsidence area is about 5 × 104 hm2 [2,3,4]. Coal mining has generated huge amount of solid wastes, mainly waste rocks (coal gangues). In China there are about 4.5 billion tons of
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