Experimental Study On Heavy Metal Pollution Characteristics And Remediation Of A Chromium Salt Plant Site

With the development of China’s cities and the transformation of enterprises,some enterprises have closed down,and the heavy metal contaminated sites left by them make land safety problems increasingly prominent.Among them,there is a huge demand for chromium salt in China,and the hexavalent chromium produced in the production process poses a great threat to human health.A chromite plant which has been discontinued is selected as the research object.Through the investigation of the site,it is determined that the soil of the site is contaminated with a wide area and high chromium concentration.Through the comparison and selection of different soil remediation technologies,the solidification/stabilization technology,leaching treatment technology and electric remediation technology were selected for experimental research,and the chromium removal effect of different treatment technologies was compared,so as to screen the appropriate treatment technology for this contaminated site.The experimental results show that:(1)In the solidification/stabilization technology experiment,the contents of total chromium and hexavalent chromium in the soil leaching solution were 0.13mg/L and0.04 mg/L,respectively,24 hours after adding 7% ferrous sulfate to the soil.It reaches the minimum concentration of hexavalent chromium specified in the relevant standards for hazardous solid waste landfill and surface water Ⅲ class.(2)In the leaching technology experiment,EDTA and citric acid had better removal effect on heavy metal chromium,and the content of hexavalent chromium in the soil was 23.78mg/kg after EDTA was leaching with 0.05mol/L eluent twice.The content of hexavalent chromium in the soil was 10.96 mg/kg after 12 hours of treatment with 0.5mol/L citric acid solution.It is lower than 30 mg/kg of the control value of the first class land in the soil related standards of construction land.(3)In the experiment of electromechanical remediation technology,the content of hexavalent chromium in the soil near the anode of the electromechanical device was significantly reduced by saponin as an activator under the condition of 30 V voltage continuous energized for 7 d,and the content of hexavalent chromium in the leaching solution was 0.045 mg/L.However,the content of hexavalent chromium in the soil leaching solution increased with the increase of the cathode.According to the experimental results,compared the advantages and disadvantages of each technology,the leaching technology for the removal of chromium in the soil is the best,the treatment cost is higher.Fixation/stabilization technology has simple operation process and longer time than leaching technology,but the follow-up monitoring of soil should be strengthened.Electric repair technology is not recommended for this site at the moment.