| Deposit exploitation and mining waste discharge have been bringing a series of far-reaching environmental problems to human living.All over the world,people are facing to an urgent task, that is,how to prevent and restore the environmental pollution and ecology recondition in the discarded area for the deposit exploitation.It is now becoming one of the important subjects of scientific research.Shilu mine is the biggest iron-enrich ore deposit in Asia.It has been mined for more than seventy years,and inevitably discharged a large of waste around this region.In 2007, the Copper-Cobalt ore deposit in this mine was begun to exploit formally in industrial scale,and subsequent processing and smelting for the Cu-Co ore were also carried out.Environmental pressure on this mining area is getting more and more serious.Moreover,Changjiang County just lies in this mining area,so it is very urgent to do the environmental prevention and ecology protection there.Based on the geochemical theory,and set the rocks(ores),tailings,soils,waters,stream sediments,plants and human activities as an associated system,the pollution history,actuality and evolution tendency and the primary influential factors of the environment in this mining area were studied in this paper.An integrated study method was accepted in this study,it includes geochemical,ecological,and field surveys,and also includes the experimental analysis,planting test,simulating test and comprehensive methods.Consequently,a planting and chemical recondition scheme on the environmental pollution in this mining area was studied and developed. This study includes the following eight correlative parts,and summarizes the following results and conclusions.1.Geochemical background of this mining area was surveyed and studied based on the rock geochemical characteristic.The results show that the contents of toxic elements,such as As,Cd, Cu,Hg,Cr,Pb and Zn,in the intrusive rocks of this mining area are generally higher than their whole background level in Hainan intrusive rocks.These toxic elements,except for Pb,of the mesoproterozoic granite gneiss were highest in this mining area.The abundance of these toxic elements of the sedimental- metamorphite rocks in this area has similar parting properties. Moreover,Shilu Group,the host rocks of the iron-ore and Copper-Cobalt ore bodies contains the highest contents of As,Co,Cr,Cu,Mn,Ni,and Fe in this mining area.For the main bodies,the iron-ore and Copper-Cobalt ore,exploited in this mine,many elements except for iron are generally low in the iron-ore,and however,the contents of Hg,Ni and so on are very high in its host rocks.Contrarily,the contents of toxic elements,such as As,Cd,Hg,Ni,Pb and Zn in the Copper-Cobalt ore,are high with ore-forming elements Cu and Co.Therefore,the exploitations of both iron and Copper-Cobalt ores are quite possibly to bring the environment pollution with ore-forming elements,such as Fe,Cu,Co and the accompanying elements,such as As,Cd,Hg, Ni,Pb,Zn and Mn,etc.2.Environment geochemistry study were also carried on several environmental media,such as soils,and tailings,waters,stream sediments and plants,etc.and summarized the following results.(1)From the whole soils in Hainan,to the regional soils in Shilu region,to the local soils closely affected by the exploitation in the mining area,and to the upriver and the downriver soils of the tailing dam,the contents of the forementioned toxic elements are getting higher and higher. Especially,the abundances ratios(enrichment)of these toxic elements in the two latter are far higher than one.It indicates that the tailings are the possible source of these toxic elements polluted the downriver soils.According to the explains for the geochemical abnormality of the toxic element enrichment factors in the regional surface soils,the cause of the pollution was possibly farther deduced to the human action,i.e.the mine exploitation.(2)The contents of these toxic elements are quite high in the tailings and waste rocks for every period of tailing dam and dumping sites.The toxic element contents in the Cu-Co tailings are higher than that in the Fe tailings.Chromium is the most stable element in the tailings,and the organic combination is a quite usual occurrence form for these toxic elements in the tailings. The organic combinations of these toxic elements are higher in the surface layers than that in the down layers.The contents of the organic combinations and the potential activities of these toxic elements in the Cu-Co tailings are much higher than that in the Fe tailings.(3)From a comparison study on the toxic elemental characteristic of the present and the last century's stream sediments in this mining area,it was found that the contents of the toxic elements in these stream sediments have an increasing tendency.Comparing the toxic elements contents of these two stages in this mining area,we found that for the stream sediments,there was a time delay on the alteration of the toxic elements by the tailing dam and the iron dumping sites.This delay is factually the geochemical evolution of the tailing dam.(4)During the surface water flowing along the river,it happen a series of physical,chemical and biological interactions and absorption with the rocks,soils and stream waters in the riverbed. By this way some toxic elements such as Fe,Mn and heavy metals were dissolved into the water, and their contents in river water increase.So the contents of Fe,Mn and other elements of the river water are general enriched in Shilu mining region,especially much higher in the distributaries of iron(Fe1)tailings dam and Copper-Cobalt(Cu-Co2)tailings dam.It is also related to the interchange process between the leach water from the iron tailing dam,sewage from the ironworks and the complex tectonic rocks.Affected by the infiltration of the tailings dam,the metal elements such as Fe,Mn and sulfides,etc.of the tailings were dissolved into the groundwater on the sections of the tailings dam in this mining area,therefore,the contents of heavy metal elements of the groundwater are rapidly increase as a whole in this mining area.(5)The absorption of the toxic elements in soils by Brassica Chinensis in different growing backgrounds shows that the adsorb ability decreases from roots to leaves and to stems.However, every part of the Brassica Chinensis is sensitive to the geochemical property of the soils.So the toxic elements have positive relations between their contents in Brassica Chinensis and in the soils.Some metal elements in soil such as Cd,Pb,Zn,and Hg,etc.are liable to be absorbed by Brassica Chinensis.3.The toxic elemental compositions of the soils,surface water,and groundwater were changed by the exploitation,tailings and waste rocks in the mining area.Consequently,the environmental quality of the soils and waters was also deteriorated in the mining area,and was quite distinctive from the soils outside this mine.Finally this environment deterioration is getting a dangerous effect to the crops planting.Most of contents of As,Cd,Cu,Hg and Zn,etc.from the soils in this mining area are beyond the 1stlevel of the national soil standard.The environment quality was much worse for the downriver soils of the tailings dam and the refuse dumps,and some elements were especially beyond the 3rdlevel of the national soil standard.According to NMR's index,in Shilu mining area,the surface water in the tailing dam reach of Shilu river is badly polluted;surface water of the downriver is secondarily polluted;and they are evidently different from the outside surface water;the groundwater around the tailing dams is also badly polluted.Brassica Chinensis planted in the downriver soils of the tailing dams were polluted,the contents of As,Cd,Hg and Pb in these Brassica Chinensis were beyond the national standard. Totally,the environment quality in this mining area is bad.The primary influential factors are the pollutions from the tailings in the tailing dams and waste rocks in the refuse dumps.4.The environmental quality evolution of the soil in the mining area was surveyed and evaluated.The result shows that the exploitation and tailing dams and so on have bad affected the environment in this mine,and the environmental quality has a worsen tendency in general.In the coming period of 30 to 35 years,the contents of Fe,Mn and other toxic elements and sulphate and nitrate compositions contained in the whole Shilu river will exceed the drinking water standard.The toxic element contents of stream water in this area will be continuously increasing. Anyway,the environmental qualities of different environmental media in this mining area will go along with a worsen evolution tendency.The environmental pressure is increasing with the industrial scale exploitation and smelting of cupper-Cobalt in Shilu mining area.5.In order to find out some effective plants to treat the pollutions in the tailings,a survey on the natural vegetation was done in the area of tailing dams.We found that there were more than forty of natural plants growing about this tailing dams;and fortunately that,one of Typhaceae angutifolia was first found in Hainan province;the dominant plants are Typhaceae angutifolia, Polygonum hydropiper,Phragrnites.Karka,Imperata cylindrica,Saccharum arundinaceum, etc.in this area of tailing dams.Polygonum hydropiper,Phragrnites.Karka and Typhaceae angutifolia have strong absorbing capacity and tolerance to the toxic elements,such as Fe,Mn, Cu,Pb,Zn,As and Hg,etc.The plant species,plant coverage,and variety are closely correlated with the storage time of tailings,and the nutrient contents of Nitrogen,Phosphorus,and Potassium,etc.The longer the storage time of railings,the higher the contents of these nutrients, and the more the plant species,coverage,and variety.6.A pilot study was gone on the planting of the natural dominant plants,such as Polygonum hydropiper,Typhaceae angutifolia,Phragmites.Karka are the tropic plants in Hainan.The planting study was focused on the absorption and tolerance of the toxic elements into these plants in the area of tailing dams.We have got the following important conclusions.(1)Polygonum hydropiper and Typha Orientalis have strong ability to decontaminate the toxic elements such as Cu,Pb,Zn,Mn,etc.from the tailings.Polygonum hydropiper has a very high capacity of absorption,enrichment,and tolerance to Manganese.Both transfer and cumulation coefficients of Mn in Polygonum hydropiper are higher than one.The contents of Mn in it's over ground parts can accumulate to 13681.5 mg/kg,moreover,during the absorption of Mn,it has no antagonistic action;so it is totally the strongest super-accumulating plant for Mn absorption.(2)Typhaceae angutifolia has strong absorption and tolerance capacities to the toxic elements,such as Cu,Pb,Zn,etc.The max tolerant capacity to these toxic elements is 2000 mg/kg,350 mg/kg and 10000 mg/kg,respectively,which is far higher than that in the soil.(3)Agave Sisalana has strong tolerance and accumulation ability to the toxic elements such as Pb and Cd.It can stand up and tolerate high levels of these toxic elements,although the contents of Pb and Cd are as high as 15900 mg/kg,400 mg/kg,4000 mg/kg,and 1000 mg/kg, respectively.The contents of these toxic elements in its over ground parts are respectively 2220.26 mg/kg,321.87 mg/kg,2702.6 mg/kg,and 2348.08 mg/kg,while the contents in its underground parts are respectively 2544.78 mg/kg,4324.75 mg/kg,19399.08 mg/kg,and 16620.52 mg/kg.Both parts contain high contents of Pb and Cd.Although the transfer coefficients of these toxic elements in Agave Sisalana are less than one,its biomass is much large in this area,so it has an effective function to decontaminate the toxic elements of Pb and Cd. During the planting test of Agave Sisalana in the tailing dams,we found that one variety of Agave Sisalana,H.11648,has a stronger absorptive ability to these toxic elements,and can decrease their organic combinations,so it is a better variety to treat the tailings.7.To search out a possible chemical method for treating the railings,simulating test was carried.The eluting of the tailings using EDTA,and hydrochloric acid shows that,in acid or complex condition,the toxic metal elements are unstable in the tailings,especially,in the fresh railings.These toxic metal elements were easily to leach out from the tailings.The simulating results indicate that usage of lime,organic manure,and biological fertilizer is ineffective to improve the stale tailings,although it has effect to the fresh tailings to some extent.A mixture of lime of 0.1%and organic manure of 1%is possible the most effective to improve the fresh tailings.8.Main pollution sources in this mining area are from tailings filled in the tailing dams and from waste rocks in the refuse dumps.The important effective measure for the recondition of this mine is planting plants,and associated with chemical disposal method.The selection principle of plants for environmental recondition should follow the natural law,"the survival of the fittest". The dominant plants naturally growing in this area are the primary and effective selection.The treating project for different pollution sources should be different for different sections in the mining area.An innovative project was developed in this study;and it is effective to the tropic environmental recondition of Fe-Cu-Co mine.For the environmental recondition of dry sections in the tailing dams,a combined and synergistic project should be effectively taken.Planting of Agave Sisalana is the primary measure, and the chemical treat,with lime and organic manure,is an accessorial measure.The proportion of lime used to treat the new tailing dams is 0.1%,and organic manure used to plant Agave Sisalana is 1%.The planting distance of 3.6×1.2 m in girding is efficient enough to the environmental recondition.By the 2ndlevel of the national soil standard,the rehabilitating terms of Cd in the old tailing dams are 2 years,respectively,and the terms of Cd in the Cu-Co2 tailing dams are respectively 2 years,while the terms of Cd in the new tailing dams is 4 years. The planting and processing of Agave Sisalana in the tailing dams has notable economical benefit,it can get an annual production value of 72.9 thousands Yuan per hectare of tailing dam.For the environmental recondition of the mars with wastewater in the tailing dams,a primary project is planting plants.In the wastewater sections,Orientalis Presl should be planted; Polygonum hydropiper and Phragmites Karka should be planted in the intermediate zones,while let the other plants grow naturally;and then the phytobiocoenose was forming by the planting and naturally growing plants.The toxic elements absorbed into Typhaceae angutifolia and Phragmites Karka can't transfer to human and other bodies by food chain.These two of plants can be also used to make art ware and produce economic values.For the environmental recondition of the refuse dump,an engineering measure should be first taken to prevent the landslide and mud-rock flow;and secondly,basing on the tree planting and re-cultivating,the interplant of Agave Sisalana should be a helpful measure. |
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