Amendment Reclamation And Phytostabilization By Energy Crop On Copper Mine Tailings

Mine tailings resulted from ore mining activities not only occupy land but may also Cause secondary pollution of the surrounding environment.Revegetation of mine tailing reservoir is a common practice to stabilize mine railings,prevent secondary pollution and improve environmental amenity.Revegetation using tolerant energy crops can provide additional economic benefit.Miscanthus have strong root and big biomass and are called fuel-crops in European and American.In the present study,we try to demonstrate that after chemical stabilization, selected energy crops can be grown on a copper mine tailings reservoir in Tongling, AnHui Province,P.R.China.The amendments applied in mine tailing include cattle manure,lime,attapulgite,bentonite,zeolite and phosphate rock.Field investigation and laboratory analysis was fist carried out.By analyzing samples and barley root elongation test,this study work out the main limitation factors that inhibited plant growth in mine tailings.Basing on the result,the energy crop production demonstration was carried out.All study results are as follows:1) Stretching from southwest to northeast,the experimental site covers an area of 2880 m²(96m by 30m).The site is characterized by a sharp pH gradient along the SW-NE axis,being alkaline on the SW end(high latitude) and acidic on the NE end (low latitude).Acidification only occurred in the top 20 cm.In general,bioavailable heavy metals(0.1M NaNO₃ extractable fraction) increase with decreasing pH.On the far NE end,copper mine tailings were contaminated by As containing effluents from nearby gold mine. 2) The site was divided into 144 plots of 20 m²(5m by 4m).Acidic copper mine tailings from different field plots were mixed and used in laboratory barley root elongation test to screen the best soil additive(s).1.9%(w/w) of cattle manure was mixed with copper mine railings to improve nutritional status(increase organic matter by 1%) and structure of the mine tailings.Different application rates of lime,three clay minerals(attapulgite,bentonite,zeolite),phosphate rock were then added and tested in their efficacy in reducing phytotoxicity of heavy metals in the mine tailings.Results showed that simply liming to about pH 6(1%w/w lime) is most effective.Further increase of pH will further decrease bioavailable heavy metals,but phytotoxicity will increase.Chemical analysis indicated that increased phytotoxicity at pH above 6 was coupled with increase in NH₄H₂PO₄ extractable As.A combination of 1%lime and clay minerals or phosphate rock did not result in significant differences in barley root length compared with the addition of only 1%lime.In the field trial,cattle manure was applied in all plots at a rate of 0.127t/hm². Then the experimental site was split into four treatments:control,lime(1%w/w), phosphate rock(0.1%w/w),1%w/w lime+0.1%w/w phosphate,respectively.Each treatment includes 36 plots.3) The field experiment was run at 5.7^th 2008.The amendments decrease bioavailable heavy metals which lead to stabilization of heavy metal.Lime increase the pH value and phosphate rock increase the bioavailable heavy metals of mine tailing in acidification area.4) Four energy crops,Miscanthus sacchariflorus(Maxim.) Benth,Miscanthus floridulus(Labill.) Warb,Arundo donax L.and Phragmites australis(Cav.) Trin were transplanted in the field.Each plant was grown in 36 plots.Preliminary results showed that Miscanthus sacchariflorus are growing very well in all plots(survival rate 99.3%). Miscanthus floridulus and Phragmites australis can survive and grow well in most plots. Whereas,Arundo donax performed poorly in most plots.Lime and phosphate rock promote energy crops' growth in low pH area,but phosphate rock do reverse action in high pH area.Intrusion wild plants on demenstration base inclued Gramineae,Polygonceae, Compositae,Euphorbiaceae,Leguimnosae more than 17 families.Gramineae and Polygonceae occupies dominant position.