| Today,heavy metal pollution in soil is serious,and the damage it causes to the soil is irreversible.It has become a worldwide topic to find an efficient and environmental friendly technology for soil heavy metal pollution control.Based on the idea of expelling solute heavy metal pollutants by artificially frozen soils,this paper deeply explores the migration mechanism of solute heavy metal pollutants in frozen soils.Using a self-designed freezing test system,using glass beads to replace sand,using heavy metal zinc ions as the research object,and using a one-dimensional freezing method,a zinc ion migration test in saturated soil was carried out.By setting different test conditions,the variation law of soil temperature field,concentration field and water content during freezing process was obtained.The main conclusions are as follows:(1)Based on atomic absorption spectrometry,adsorption test of the molten glass beads was performed,and the molten glass beads were found to have a certain adsorption.The three factors,particle size,p H,and dosage,will affect the zinc ion adsorption rate and adsorption amount of glass beads,while the adsorption time has a small effect on zinc ion adsorption by glass beads.When the adsorption time is within 180 min,the adsorption rate will be affected by the adsorption time,and when the adsorption equilibrium is reached,its adsorption rate will not change.(2)During the one-dimensional freezing process from top to bottom,the temperature at the top of the sample decreases rapidly,while the temperature at the bottom decreases more slowly.The temperature field of the sample in the later period of freezing remains almost constant and stable.The final temperature of the top layer of the sample is closest to the set freezing temperature;The larger the freezing time,the lower the final temperature of the sample;the larger the particle size,the longer it takes for the sample temperature to reach 0℃;the moisture content at the top(the cold plate)of the sample is higher than the middle and lower portions of the sample;the increase in freezing time results in moisture migration As time increases,the amount of migration toward the cold end increases;the lower freezing temperature,the less the amount of water migration;the smaller the particle size,the less the water will migrate to the top.(3)During one-dimensional freezing,heavy metal pollutants continue to migrate to the bottom along with the freezing front,forming a small area with a high concentration at the bottom(layers 6-7),and a large area(layers 1-5)of soil are purified effectively.At the same time,some pollutant ions are adsorbed by the glass microbeads,and the adsorption amount of the bottom layer is the largest.The lower the freezing temperature,the worse the redistribution of zinc ion in the soil,and zinc ion has basically migrated to the bottom area of the soil.Increasing the freezing time will help drive zinc ion to the bottom of the soil.The initial concentration increases,and zinc ion moves to the bottom.The less complete the migration,and the more zinc ion will be adsorbed on the molten glass beads;the smaller the particle size,it is not conducive to the migration of zinc ion to the bottom layer of the sample,The adsorption quantity of glass beads will increase;decreasing the p H value will increase the zinc ion concentration in the pore water of the sample;Among them,the purification rate of the first to fifth layers of saturated soil can reach 70.3%. |
PDF Full Text Request