| Coal mine subsided land is an important mothball land in our country. Reclaiming for subsided land can reduce the contradiction between man and land. At present, the main method to reclaim the subside land which is widely used is covering soil after filling, but the area of subsided land is too large, there is not enough soil for subsided land. Some related studies have made on substrates which were composed of fly ash and distillers'grains, sewage sludge and furfural residue. But there are some heavy metals in fly ash and sewage sludge. A long-term measuration showed that the content of Cd in substrates were beyond Soil Environment Quality Standards (â…¡). In order to plant edible crops in substrates, there must remove Cd in substrates.This study chose crucifer and grass which have potential rehab ability for Cd as experimentation plants. Analyzed speciation of Cd in substrates and measured the growing condition, biomass and Cd of each position of plants, compared absorption and enrichment ability of plants, analyzed removing effect of plants which had remove Cd in substrates.The results showed that: (1) the physical and chemical character of substrates could meet the growth demonds of plants. The bulk density of substrates were below the average of soil, which was benefit for the growth of plants and transformation of nutrient; Field water-holding capacity were beyond 70%, which could provide enough water for the growth of plants; The content of salt in substrates were high at the beginning, and after eluviation of rain and planting of one year, which could satisfy the growth of common plants. Available nitrogen, available phosphorus, available potassium and organic matter kept in the natural level.(2) The content of Cu, Zn and Pb were low, and the content of Cd in substrates were beyond Soil Environment Quality Standards (â…¡), but which can't restrain the growth of plants. Species analysis showed that availability of Cd were bigger and the correlation of chemical species of Cd were remarkable. So it was feasible to remove the Cd in stubstrates by phytoremediation.(3)With the increase of the number of planting, the emergence ratio and growth of plants got better, and plant height and biomass increased greatly. Accumulation character analysis showed that, the transfer coefficients were more than 1. The system clustering analysis showed that the enrichment ability of cabbage and pakchoi belong to the first kind (middle), the enrichment ability of rape, clover and perennial ryegrass belong to the second kind (low). (4) Defined the removing rate of one year and relatively removing fixed number of year, which were used as indexes to estimate the removing effect of plants for the Cd in substrates. The results showed that the removing effect of pakchoi and cabbage were better than rape, clover, perennial ryegrass and bluegrass. Pakchoi can be used as the latency rehab plant of substrate 1and substrate3, pakchoi's largest removing rate is 2.45% per year and pakchoi's least relatively removing fixed number of year is 27.7. But at the action of phytoremediation and eluviation of rain, the content of Cd in substrates reduced 0.4~1.2mg/kg, eluviation made Cd transfered from root soil layer to sediment layer, but the Cd couldn't transfer to deep soil layer continue. So the Cd which was eluviated from surface soil layer couldn't pollute groundwater. By anlysis and forecast, the content of Cd in substrates can reduce to Soil Environment Quality Standards (â…¡) in 5~10 years around.(5) Phytoremediation can bring not only economy benefit but also society and zoology benefits for diggings, which can promote region economy development, improve habitation of inhabitant, and stabilize the order of society. The discussion on material of phytoremediation can provide theory direction for substrates phytoremediation of big area subside land. |
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