Study On The Remediation Of Passivating Lead-contaminated Soil By Modified Blast Furnace Slag

Lead is one of the main pollutants in national soil pollution.And the remediation of the lead-contaminated soil cannot be delayed.Compared with other technologies,in-situ passivation is a low-cost and low-energy consumption technology in which the choice of amendents is the key to remediation.After screening and modification,potassium dihydrogen phosphate modified blast furnace slag(PDP-BFS)is produced,an economical green and multi-effect lead-contaminated soil amendent.Its effects and the mechanism are also explored.The main findings are as follows:(1)The passivation experiment of lead-contaminated soil was carried out with blast furnace slag,fly ash,phosphate fertilizer and corncob biochar.It was found that blast furnace slag could exert the best passivation effect.In order to further improve the passivation effects of blast furnace slag,chitosan,humic acid,potassium dihydrogen phosphate and dipotassium hydrogen phosphate were selected to modify the blast furnace slag respectively.The results showed that there was a minimum soil available lead content in PDP-BFS treatment.Therefore,the best soil lead amendent in this study is PDP-BFS.(2)PDP-BFS played a positive role on the growth of ryegrass in lead-contaminated soil.It was found that with the increase of PDP-BFS amount,the content of available potassium and available phosphorus in soil increased,and the raygrass biomass increased significantly while the soil pH with a slightly dynamic.The results indicated that PDP-BFS could improve soil fertility,and promote the growth of ryegrass.Meanwhile,the effect was enhanced with the increase of the addition ratio.(3)There was a significant passivation effect on soil lead by PDP-BFS.It was found that,with the increase of time and PDP-BFS amount,the lead leaching toxicity in the 1%,2%,and 5% treatments reduced by 18.36%,61.97%,and 94.38% compared with that in 0%,respectively.Lead would be transformed from acid-soluble and reducible fractions to oxidizable and residual at 1% and 2%.After the dosage was increased to 5%,lead was transformed from acid-soluble,reducible,and oxidizable to residual.The lead in ryegrass in PDP-BFS treatments reduced significantly compared with that in 0%.Under the experimental conditions,the passivation effect of 5% treatment is the best.(4)The mechanism of passivationon mainly included adsorption and precipitation reactions.The porous porosity of the PDP-BFS and its unique lattice structure provided conditions for the adsorption of lead.And the electrostatic adsorption also existed.Phosphorus and silicon carried by PDP-BFS probably lead to the production of lead phosphate and lead silicate precipitates,thus achieving the passivation on lead.The research results indicated that PDP-BFS can effectively reduce the bioavailability of lead,inhibit lead leaching toxicity,and passivate soil lead.Meanwhile,it improves soil fertility,and provides plants with nutrient element like phosphorus,potassium,and silicon.In this way,blast furnace slag can be reused.