Effects Of Different Freezing Rates On Progressive Freezing Purification Efficiency Of Sandy Soil Contaminated By Heavy Metal Copper

Soil,which is the basis of human survival,has been a hot topic of environmental and soil science researchers.In recent years,there are large amounts of land polluted by heavy metal pollutants during the process of industrialization.The heavy metal pollutants accumulate in the human body through the food chain and endanger people’s health.To reduce the total contaminant mass in soil,many researches are working for developing the heavy metal remediation and a number of remediation methods have been practiced,including soil replacement,soil leaching,electric remediation,soil solidification remediation,phytoremediation and microbial remediation.However,these methods have high cost and tend to cause secondary pollution during the treatment process.According to the above drawbacks,a new soil remediation technology – progressive freezing method is raised in the paper.In this paper,the stand sand is the object and the copper is the specific pollutant.Progressive freezing is a traditional freezing concentration technique,which has been widely used in seawater purification and freezing concentration.During the freezing process,the aqueous solution in the soil solidifies into ice and the freezing process is similar to that of aqueous solution.The water-soluble contamination is purified when the soil is freezing.The frozen soil is purified and the concentration of heavy metal copper increases observably in unfrozen region.Therefore,the efficiency will be improved while avoiding secondary pollution in the environment.In this paper,a series of freezing purification tests on sandy soil saturated with heavy metal copper were conducted by employing a testing apparatus equipped with a programmable refrigerating circulation.And the distributions of temperature field,water content and heavy metal copper are studied.The experimental results show that the freezing rate is an important factor affecting the freezing purification efficiency for heavy metal copper and the purification rate decreases rapidly with increasing freezing rate.When the soil freezing rate is 0.3 ℃/h,the purification rate of heavy copper is only 27% and it is far less than 85% when the soil freezing rate is 0.05 ℃/h.Finally,the change rule of purification rate and its mechanism are investigated and analyzed.A strong correlation between the purification rate of heavy metal copper and the soil freezing rates is established,indicating that the purification rate can be expressed as a cubic of soil freezing rate.Therefore,it will be useful to establish the theoretical model of heavy metal pollutants when the soil is freezing.This paper has 39 figures,5 tables and 104 references.