The Survey On The Distribution Of Heavy Metals In Mining Area Sediments And Its Compound Effects With Industrial Wastewater

Due to mining and the steel smelting, heavy metal pollution events which include Cd, Tl,Pb and so on, have happened multiple times in the upper reaches of Beijiang River. Especially,mining in Dabaoshan mine area all the year round resulted in a large number of heavy metalsdraining into the lower reaches of Hengshi River Basin, which did serious harm to nearbyresidents’ health. Therefore, it is necessary to make a comprehensive distribution investigationon heavy metals in the Hengshi River Basin and observe the heavy metal pollution conditioncaused by mining. Effects of wastewater from coke plant of Songshan Group in the north ofDabaoshan mine area on the migration and transformation of heavy metals in sediments atwater-sediment interface were also analyzed.The overlying water on each cross section and surface sediments were collected fromHengshi River Basin in Dabaoshan mine area. The methods for extracting chemical speciationof sediments by BCR (European Communities Bureau of Reference) extraction procedure andmeasuring heavy metals by GFAAS (graphite furnace atomic absorption spectrometry) wereestablished. The risks of the heavy metals in the sediments were discussed with the method ofpotential ecological risk index, following analyzing heavy metals in water body andsediments of Hengshi River. Furthermore, the experiments on sediments from differentoverlying water such as Beijiang River, Maba River and coking wastewater, were finished byblending and mixing. The results were as followed:Firstly, as far as the establishment of analytical methods, BCR extraction procedure wasused to extract heavy metals speciation in sediments, HNO3-HF mixed acid system ofmicrowave digestion was applied to extract the total amount of heavy metals, and GFAASwas introduced to measure chemical speciation and total amount of each heavy metals. Thesemethods were adopted to the detection analysis of As、Cd、Cr、Pb、Cu、Tl in water body andsediments of Hengshi River Basin. The concentrations of Cd、Pb、Tl、Cu、Cr all exceededsurface water standard. The As、Pb、Cu、Tl element contents in sediments were respectively4.8、3.9、8.6and9.0times as much as the mean value of sediments in the Beijiang River Basin.Analysis showed that six heavy metals in water body and sediments were significantlycorrelated.Secondly, Six heavy metals in the sediments existed mainly in the form of residue. Thecontents of residual fractions reduced with the decreasing of total amount along the river.During the process, residual states were gradually translated into the bioavailability such asacid-soluble states, reducible states and oxidizable states. Among heavy metals in sediments of Hengshi River, Tl had higher potential ecological risk, while Cu had the highest potentialecological risk. The ecological risk of Cu and Pb were at intermediate level. Because of lowmigration, the ecological risk of As and Cr were at the lowest level.Thirdly, comparing water body in the Beijiang River with Maba River, cokingwastewater was rich in aromatic organic matter, soluble microbial by-products and highconcentrations of inorganic salt. The dynamics of interaction between organic componentsand heavy metals kept heavy metals in sediments from moving to the overlying water andhigh concentrations of Cl-ion made heavy metals deposition by coordination. In addition,coking wastewater restrained the dissolution of heavy metals. The chelation and complexionof organic colloid in coking wastewater had effect on heavy metals speciation that Cd、Pb、Cu and Tl in acid-soluble states moved to reducible states which had lower mobility.Results showed that sediment samples could digest completely by HNO3-HF mixed acidsystem of microwave digestion while the speciation and total amount of heavy metals couldbe analyzed accurately by GFAAS. The leached acid wastewater of mine tailings caused bymining in Dabaoshan mine area had made the environment seriously polluted by a variety ofheavy metals which could be observed that concentrations exceeded in water body and metalsdeposited in sediments. What’s more, the speciation distribution characteristics of six heavymetals were obviously different. Coking wastewater restrained the migration activity of heavymetals in sediments and overlying water.