Washing Technology For Lead-contaminated Soil And The Effect Of Plant Growth And Development After Washing

Lead is a non-essential elements of the human body, and the body absorb excessivelevels of lead can cause serious organ and nerve damage. With the rapid development ofChina’s industrialization and urbanization construction continues to accelerate, originallylocated in the urban area of industrial enterprises mostly relocated to the outskirts ofcontaminated sites left by these enterprises become huge hidden dangers of environmentalhazards. Lead-related enterprises especially the lead-acid battery manufacturing andrecycling industry is the "12th Five-Year Plan" as a key remediation industry, so a largenumber of lead-acid battery factories shut down relocation, a large number oflead-contaminated soils stay in the relocation sites. How to fix this single leadcontaminated sites quickly and completely and retain the use value of the soil is theproblems to be solved.Soil washing method use the soil washing equipments, washing fluid recycling, use ofequipment and washing soil dewatering filter press equipment consisting of sets ofremovable soil washing equipment, added to the formulation washing agents conditioningtechnology parameters thereby washing contaminated soil repair technology. Thistechnique used frequently in the treatment of contaminated sites abroad, such as PortugalAlmada shipyard heavy metal contaminated site restoration and restoration of the LondonOlympic Games venue. This engineering practice in our country are fewer, due to thedifferent sources of pollution and soil conditions, the mature experience of foreigncountries can not be directly applied to the restoration of our venues, the experimentalstudy and verify the actual contaminated sites to find the application specific types ofwashing agents to specific sites, the dose and the best conditions parameter.This study in order to experiment much closer to the actual washing process, productionworkshop near soil of a lead battery plant in southwest China as the research object, anduse the experimental studies screened seven previous washing agents for site remediationeffect better, respectively EDTA-Na2, EDDS-Na3, hydrochloric acid, citric acid,rhamnolipid, SDS and saponins, using different concentrations of the cleaning agentrespectively, on the different loads of lead-contaminated soil oscillating cleaning experiments the kind and concentration of the washing agents to filter contaminated soilwashing process parameters selected by adjusting the pH of the washing liquid temperatureand the washing time, and lead in Soil morphological changes before and after the washing,not only from the perspective of the maximum amount of total lead removal to select themost appropriate washing conditions from further optimization to minimize environmentalrisk point of view of the cleaning conditions. In order to verify the availability of soilwashing effect,using washing soil contrast of clean soil cultivation of maize seedlingsdetermination of the concentration of lead in some physiological indices and judgment theeffection of growth.The experimental results showed that:1. The most suitable concentration of seven washing agents were: EDTA-Na2:0.05mol.L^-1, of EDDS-Na3:0.05mol.L^-1, citric acid:0.1mol.L^-1, SDS:0.02mol.L^-1, hydrochloricacid: of1mol.L^-1，rhamnolipid:2%, saponin:20mg.L^-1. Recommended washingremediation of lead contaminated soil using EDTA-Na2, EDDS-Na3, hydrochloric acid, andcitric acid as the main washing agent, Rhamnolipid available as an auxiliary washingagents. EDTA-Na2, EDDS-Na3highly lead-contaminated soil washing has an obviousadvantage, citric citric advantage is not obvious.2. Using EDTA-Na2under the different pH condition of4points location washing datashow that the soil under the condition of weak acid soil all can achieve the best leadremoval, washing fluid and optimum pH range is associated with the degree of acid andalkali of soil pollution itself; Analysis before and after wash lead morphology change trendand its bonding strength coefficient and the redistribution of coefficient, relative to thewashing before the original soil lead form, different pH can effectively reduce the soil leadactive state （in addition to the residual state in the form）, but under acid condition （pH=2or4） residue in the soil after washing state of lead to the maximum, that acid environment notonly in terms of lead extraction efficiency advantage, at the same time for the reduction inenvironmental risk and appropriate conditions; Through the washing fluid temperaturecontrol experiment of the washing fluid temperature in30⁴0℃, can exert the bestwashing effect.3. Through contaminated soil screening particle size respectively, after cleaning, found thatthree kinds of cleaning for the difficulty of clay powder particle size of contaminated soil>coarse sand grains> fine sand, with the increase of cleaning time, increasing the removal rate of lead, when the cleaning time of240min,4points can achieve a better removal ofcontaminated soil, the cleaning time continue to increase, removal rate growth is slow, sothe cleaning time is240min is more appropriate.4. Through soil grow corn seedlings after cleaning experiment:300mg.kg-1leadconcentrations had no obvious effect on maize seed germination, but600mg.kg–1the leadconcentration of maize seed germination rate and growth condition has obvious inhibitoryeffect; Lead concentration is the main factor of cytoplasm membrane permeability change,citric acid can reduce the effects of lead on the cytoplasmic membrane and EDTA-Na2effect is not obvious, Antioxidant enzymes system have certain effect for lead and washingagents to resistance stress, SOD is the most sensitive response to lead in enzyme system, itcan be as indicated on the impact of lead pollution on maize growth indicators. Along withthe increase of Pb concentration effects of maize seedlings increased, but the addition ofcitric acid can effectively alleviate the phenomenon, EDTA-Na2was increased maizeseedling to lead absorption, from the seedling root leaf lead accumulation of three parts,the citric acid and EDTA-Na2can promote the corn seedling to lead absorption, the rootscan effectively lead absorption and fixation, effective hindrance to lead to the ground part,to a certain extent to protect the growth of stems and leaves.