Study On Chemical Washing And Remediation Of Cadmium-contaminated Soil

From the reform and opening up to the 70th anniversary of the founding of the People's Republic of China,with the acceleration of China's urbanization process and the rapid development of modern industry and agriculture,the problem of soil heavy metal pollution has intensified,which has seriously hindered the construction of a harmonious and beautiful socialist modernization.In this paper,ectopic chemical washing was used as the main technical method to repair cadmium-contaminated soil.Low-cost Mg Cl₂ and Ca Cl₂ solutions were selected as detergents.The solution concentration,washing time,soil-liquid ratio,washing temperature,washing liquid p H and washing were studied.The effects of temperature,concentration of cadmium in soil and washing times on soil cadmium removal rate,precipitation of cadmium ions in solution after washing with Mg Cl₂ with ammonia water,adsorption of cadmium ions in solution after washing with Ca Cl₂ with nano-Mg O,and the recycling performance of Ca Cl₂ solution after treatment were studied.A new method of washing cadmium contaminated soil with weak electric-field assistance Ca Cl₂ solution was also explored.The main findings of the dissertation are as follows:?1?At room temperature??20°C?,when the concentration of Mg Cl₂ solution was 1mol/L,the ratio of soil to liquid was 1:20,and the elution time was 60 min,the elution rate of 100 mg/kg cadmium contaminated soil reached 69.54%,and the best rinsing effect was obtained with twice rinsing.The elution rate of Cd²⁺increased with the increase of temperature,and the elution rate of Cd²⁺reached 80.94%at 60°C;the low solution p H was more favorable for Cd²⁺elution;for different concentrations of cadmium contaminated soil?10-400 mg/kg?the elution rate was above 60%.After the eluent was precipitated by ammonia water,the Cd²⁺in the solution could be effectively removed.?2?When the concentration of Ca Cl₂ solution was 0.1 mol/L,the ratio of soil to liquid was 1:20,the washing time was 60 min,and the washing times was 3,the total elution rate of cadmium in the soil reached 58.90%,and the first elution efficiency was better?Up to40.60%?.After the eluate was treated with nano-Mg O,the cadmium ions were co-precipitated with Mg?OH?₂ in the form of Cd₄Cl₃?OH?₅;the concentration of Ca Cl₂solution was adjusted and used to wash the new cadmium-contaminated soil and eluted in three cycles.The rate is about 40%,which indicated that the Ca Cl₂ solution could be recycled and reused,which greatly reduced the washing cost.?3?Under the weak electric field of 0.5-3.5 V,100 mg/kg cadmium contaminated soil was repaired with 0.1 mol/L Ca Cl₂ solution.The total removal rate of cadmium reached65-93%within 30 min.Compared with the single Ca Cl₂ solution washing repair,the removal rate of cadmium was increased by about 25-53%,which indicatied that with the weak electric-field assistance Ca Cl₂ solution washing technique was a very effective method for repairing heavy metals contaminated soil.