Study On Investigation And Remediation Of The Chromite Ore Processing Residue Contaminated Site

Chromite Ore Processing Residue (COPR) is the main pollution source of its disposal site. Interrelated investigations showed that the former disposal methods of COPR, which simply piled up of it, has resulted in severely pollution of ambient soil and groundwater. Although as pollution source, COPR were disposed or resource reused now and in the near future, the polluted soil still pose risks to the environment as a secondary pollution source. After the COPR disposed harmlessly, remediation of the polluted sites or soils is the first urgent work which should be done next.Used as succedaneum of Dolomite, the COPR in Qingdao Hongxing Chemical Plant were reused harmlessly in agglomeration and iron manufacture process at Qingdao Steelworks. The COPR-contaminated site in Qingdao Hongxing Chemical plant was selected as object of study. 27 sampling points were selected, one sample one meter, 185 samples were collected. Based on the pollution investigation of the contaminated site, three contents are studied as follow:(1) Polluted scope of the COPR contaminated siteBased on the analysis of leaching toxicity and contents of chromium in the samples, geographical statistics method was used to estimate the polluted scope of the COPR-contaminated site.(2) Speciation analysis of chromium in the contaminated soilsModified BCR squential extraction procedure was used to study the speciation distribution of hexavalent chromium and total chromium in the contaminated soils. The main objective of speciation analysis is to make clear the main form of hexavalent chromium and total chromium in the contaminated soil, so as to select feasible remediation technology.(3) Technical feasibility study of soil flushingContaminated silty clay was used as object of soil flushing, tapping water was used as eluent, the water-based soil washing technology was studied to inspect if the contaminated silty clay can be restored.The main results of the research summarized as follows:(1) The pollueted scope of Hongxing COPR-contaminated site is about 100×400m, which is limited to the extent of COPR stock dump located in west of Lousan River. (2) The main form of hexavalent chromium in the COPR-contaminated silty clay is weak-acid-extractive-state, the partition ratio exceed 80%. And the water soluble state hexavalent chromium is more, which proved that soil flushing would be feasible.(3) Soil flushing was used successfully to wash hexavalent chromium out from the contaminated soil. Aimed at the emission concentration limits of Integrated Wastewater Discharge Standard and the concentration limits of III of Ground Water Quality Standard, the extraction efficiency is higher than 89%. But, the water consumption is large.(4) 200mg/kg could be determined roughly as remediation target value of Cr (VI) in soil.