Study On Release Law Of Heavy Metals From Sediments In Typical Lake Reservoirs Of Jiangxi Province And Its Stabilization Test

At present,domestic methods for remediation of contaminated sediments generally use sludge dredging?i.e.,ectopic repairation?.This method need a large amount of work hours,high investment,and large land occupation,and is not achievable for large rivers and lakes.It is easy to cause pollution on temporary storage areas.For in-situ remediation,it is generally done in the pollutation sensitive areas e.g.drinking water sources when the contents of heavy metal exceed the standard values.Emergency treatment is usually performed by adding chemical reagents to the polluted waterbody and adsorbing,complexing,flocculating and depositing heavy metal ions into the sediments?i.e.passivation&stabilization?.However,when external conditions?such as pH,Eh,hydraulic disturbances,etc.?change,heavy metals that have been passivated and fixed have a great risk of being dissolved and released into the water column to cause secondary pollution.This paper took a typical lake in Jiangxi Province as an example,and used the methods of field sampling and laboratory analysis to evaluate the eutrophication of the lake water and the evaluation of sediment nutrients and heavy metal pollution state.The concentration of Pb,Fe and Mn in the overlying water was measured as a function of time.The release flux was calculated and the release pattern was calculated.The effects of different treatments on the release characteristics of the sediment and the heavy metal removal rate were studied through the method of the static culture.The main conclusions were as follows:?1?The eutrophication index of surface water bodies and overlying water bodies at all sampling sites reached the eutrophication level.The Org-N contamination characteristics of the sediments at each site showed LW1>LW3>LW2>LW5>LW4,and the Org-Index contamination features showed LW1>LW5>LW3>LW4>LW2.The content of both heavy metals were far from the background values of 9.72 times and6.29 times,respectively.If only Pb and Cd as heavy metal pollution evaluation factor,the index of lake sediment pollution was much greater than 3?i.e.the standard value of the heavy pollution?.Correlation analysis showed that there was a significant positive correlation between sediment nutrient TN and TP,indicating that they were homologous;and there was a significant negative correlation between organic matter and TP,indicating that sediment P existed mainly in inorganic form,but there was a significant positive correlation with Fe.It was indicated that Fe exists mainly in organic state;the particle size was significantly negatively correlated with organic matter,TP and Fe,indicating that the smaller the particle size of the sediment,the easier it was to adsorb organic matter,TP and metallic Fe;meanwhile,Pb and Mn were significantly positively correlated,indicating Pb was homological with Mn.?2?There was a significant correlation between the release process of Fe and Mn at all sites.It showed that both of Fe and Mn had the same binding states.When the external environment changed,they could be simultaneously released by desorption or adsorption and sedimentation.The release process of Fe and Pb from LW1 and LW5 metals has significant correlation,while the content of Pb and Mn in sediments.There was significant correlation,indicating that although Pb and Mn are homologous,they may exist in the form of a more stable combination of non-water and iron-manganese binding states,leading to a significant correlation between Pb and Fe and Mn release processes.The release fluxes of heavy metal Pb from LW3and LW4 were-0.0292 mg?m²·d?^-1 and-0.0259 mg·?m²·d?^-1,respectively.The difference was very small,and there was a small fluctuation in release and adsorption.The release fluxes of Fe in the LW1-LW4 sediments were-3587.8 mg·?m²·d?^-1,-2569.2 mg·?m²·d?^-1,-9891.2 mg·?m²·d?^-1,and-5967.2,respectively.The difference in mg·?m²·d?^-1 is large,and the Fe content in sediments of LW3 is the lowest?29500mg/kg?compared with other sites,and the release flux is the largest,which may be easily eluted from Fe at the site.Morphologically,the LW4 sediment Fe has the same release characteristics.?3?If the sediment received hydrodynamic disturbance,the metal Fe and Mn ions would release a large amount of water to the body to cause some problems such as high salinity.The heavy metal Pb in the sediment was a stable chemical state,and needed to guard against environmental pH and Eh,etc.It changes to form an ion state and the upward floating body releases.For the heavy metal Cd,the fourth experiment group?covering 2cm biomass carbon+planted Vallisneria?had the best removal effect,followed by the third group of planted Vallisneria,and finally the second group?covering 2cm of biomass carbon?.The Pb removal efficiency from high to low was the fourth group>the second group>the third group.The effect of Vallisneria sp.on the enrichment of metallic Mn and Fe metal ions in interstitial water is much better than that of biomass carbon.