In-situ Phytostabilization Of Reclaimed Farmland From Mine Tailings In Gejiu City

The soil heavy metal pollution is one of serious environment problems and has received a worldwide attention. As an agricultural country mainly to production and export of agricultural products, China has its crop production lost by13million tons every year due to heavy metal pollution.12million tons of polluted grains are produced in China each year, which not only lost its direct interest form agricultural product export of foreign exchange earning, but also caused a direct threat to human health. There are a lot of researches on phytoremediation all over the world in recent years, but most of them are still on the theory or the pot experiments, which still lacks of engineering experience.The research relied on the project named "Gejiu multi-metal mining area around polluted farmland eco-restoration techniques demonstration project", based on soil heavy metal in-situ phytostabilization technology, investigated the5heavy metals (As, Pb, Cd, Pb, Zn) both in soil and different varieties of sugarcane in the reclaimed farmland of Jiajie mountain tailings pond in Datun, Gejiu City, and determined its pollution degree. Through establishing96experimental plots, the effects of soil ameliorators (lime, superphosphate and slag were used both singlely and composited) on reducing sugarcane absorping heavy metals were tested. And the costs and benefits of the restoration were assessed. The main findings are as follows:(1) Through the sampling survey, the5heavy metals in the regional soil show a trend of higher in south but lower in north, with the extent of As:258-4566mg/kg, Pb content387-22516mg/kg, Cd1.47-183mg/kg, Cu102-2276mg/kg, and Zn24-20018mg/kg. The heavy metal pollution single factor indexes are:As:30.49±18.61, Cu4.28±2.68, Cd52.62±65.86, Pb10.79±5.93, Zn6.89±7.57. Pollution degree from high to low is in the order:As>Cd>Pb>Zn>Cu. Nemerow comprehensive pollution index is431.15, so the soil belongs to heavy pollution. Heavy metals comprehensive potential ecological risk index (RI) ranges from630.00to15358.45, and from its frequency distribution to see,100%of them are in strong potential ecological risk level.(2) In the surveyed eight sugarcane varieties from17sample points, in addition to the content of Cu in bagasse not exceed bid, other elements Pb and Cd, Zn, As in the sugarcane juice and bagasse are all beyond the food safety standards. The most serious is As, with a exceed bid rate of100%; next is Cd and Pb, of97%and93%respectively; Zn is34%. The heavy metal exceed bid more serious in bagasse than in sugarcane juice. Preliminary sure the variety "388" for heavy metal low absorption variety, but need further validation because of the sample is limited.(3) By adding ameliorators, the heavy metal contents in the sugarcane were reduced in some extent. The ameliorator combination lime+superphosphate+steel slag made a important role in reducing sugarcane absorption of all the five heavy metals such as Pb Zn, Cu, Cd, As; Ameliorator combination lime+superphosphate did the best effect on Cd reduce. At the same time, by adding ameliorator, and, to some extent, the heavy metals effective states in the soil were reduced. Effect of120days amelioration is better than that of60days. The longer the ameliorators affect, the heavy metal contents reduce more in the sugar cane. Especially,as a example, As content in sugarcane was beyond the food safety standard after60days soil amelioration, but after120days of amelioration, has already fallen to the food safety standards, which is less than0.3mg/kg.(4)After soil amelioration, sugar in sugarcane does not cut down than the control; individual ameliorator combination can even increase the cane sugar content within a narrow range(for example, the ameliorator lime with low concentration and the ameliorator lime+superphosphate+steel slag with high concentration can improve the sugar content in the sugarcane "Guitang No.5" to18%). It proved that the ameliorators don’t have bad effects on sugarcane yield.(5)Through the soil amelioration, especially with the effect of lime ameliorator, soil pH changed from partial acid to neutral, and this helps to reduce the effective states of soil heavy metal, so as to reduce the absorption of sugar cane to heavy metal. At the same time, though adding the phosphorus ameliorator, nitrogen and phosphorus content of the soil are improved, and, to some extent, enhanced the soil fertility.1.22×10yuan of economy loss by stacking with tailings can be avoided after the tailings are repaired, and,9151yuan of nutrient loss can be avoided at the same time. Benefits both in economy and environment will be improved after soil remediation.