The Effect And Mechanism Of Soil Flushing On Arsenic Contaminated Irrigation Soils

Undeservedly mining in the mining area lead to downstream soil contaminatedby As(the content of arsenic can be up to19400mg/kg). As a rapid and effectivemeans of repair for various types of heavy metal polluted soil, Soil washing has beenextensive laboratory studied in recent years. That three kinds of natural chelatingagent (citric acid, Trisodium (S,S)-ethylenediamine-N,N′-disuccinate, Nitilotriaceticacid) were experimented to study the flushing efficiency, and removal efficiency ofchemical speciation, loss of nutrient, washing kinetics, stability constant of Chelatereaction were studied to explore the mechanism of soil washing process, the followingmain conclusions:1. The results show that best flushing condition of citric acid, NTA and EDDSare: liquid/soil ratio are30,30,15mL/g respectively; flushing fluid concentration are0.2,0.05and0.1mol·L-1respectively; pH are2.67,13and13respectively; flushingtime are6、3and2h respectively. Considering cleaning removal rate and cleaningagent dosage, NTA is the suitable cleaning agent for soil sample.2.Three cleaning agent all have different levels of removal rate for five chemicalspeciation of arsenic. The reason why NTA’s cleaning removal rate is higher thancitric acid and EDDS is that NTA’s removal rate of four chemical speciation exceptexchangeable are significantly higher than citric acid and EDDS or there is nosignificant difference between them.3. The adsorption kinetics equation are employed to describe the dynamicprocess. The results show that the first-order kinetics model is well fit theexperimental data of citric acid that R2is0.98657, while pseudo-second-orderequation is well fit the experimental data of NTA and EDDS that the two-stage R2are0.99905and0.95053,0.99307and0.88161respectively.4.The selected soil content of organic matter, total nitrogen and ammoniumnitrogen are low, the content of total phosphorus, total potassium, available phosphorus and available potassium are at a high level. The turnover rate of totalphosphorus, available phosphorus and available potassium are at a high level afterwashing, the turnover rate of total potassium are all at a low level, the turnover rate oforganic matter, total nitrogen and ammonium nitrogen are further reduced so that thecontent of ammonium nitrogen is zero.5. Citric acid, Trisodium (S,S)-ethylenediamine-N,N′-disuccinate andNitilotriacetic acid reacted with As in a molar ratio of2:1, the stability of citricacid-As, NTA-As and EDDS-As are3.43×1010,2.73×1010and3.14×105.