Study On In-Situ Remediation Technology Of Chromium Contaminated Soil And Demonstration Project

Soil contaminated by chromium(Cr)has triggered numerous environmental issues and social contradictions in China in the past decades.Due to historical reasons,these contaminated soils are rare-protected and severely contaminated,which made it hard to be remediated and thus a significant threat to human health and economy development in China.In-situ chemical flushing of soil has aroused great intention for its great efficiency.Currently,the research on soil flushing in China are limited on batch experiment and feasibility study while a few applications has taken part abroad.In China,Cr contaminated soils are common,but the complicated situation of the contaminated sites has limited the research and application soil flushing,hence,it is urgent to start in-situ soil flushing research for typical Cr contaminated site and develop an efficient in-situ soil flushing technologyIn this paper,in-situ soil flushing was chosen for a typical Cr contaminated site Citrate acid(CA)was elected to be the prior chelent and its mechanism of removal of Cr has been studied by lab experiment.A technology for remediation of typical Cr contaminated soil based on in-situ soil flushing and hydrolic capture was developed and a demonstration project has been successfully carried out.The main outcome of this research are shown as follows:1.The site investigation revealed that the soil of research area was highly polluted and the plume went deep(>10m).The permeability of vadose and aquifer soil is adequate.The research area is a united hydro-geology unit with a constant and steady impermeable bed.The flow field is clear and controllable.In-situ soil flushing is suitable for this contaminated site.2.The comparison of several common chelants were carried out in lab.The results showed that CA is the prior chelant for this site due to its high efficiency for the removal of Cr from soil.More than 60%Cr in soil was removed by 0.1mol/L CA,with solid-to-liquid ratio of 1/20.3.The column study demonstrated that CA is efficient on Cr removal from different sized soil.Flushed by 0.5mol/L CA for 450 PVs,concentration of Cr in soil decreased from 1392.75mg/kg to 181.75mg/kg,removal rate is 86.95%,which is 33%higher than DI water.Intermittent flushing showed slight advantage than constant flushing.When the experiment ended,soil washed by CA is no longer a threat to environment according to Chinese relative standard4.The demonstration project went well as monitoring data showed,the eluent concentration has decreased to≈500mg/L from original peak 3458.43mg/L in the first 17 days.Meanwhile the pH of groundwater drop to 7-8 from 12.8.2 tons chelants has been ejected to site soil and 9.85 tons eluent has been pumped out as well.12.8kg Cr has been recycled,which contributed to 30%of Cr that the whole soil in site contained.