Study Of Nano-hydroxyapatite Combined Ryegrass Phytoextraction Of Pb-contaminated Soil

Heavy metal pollution in soil attached great importance to the whole society on impact of national ecological safety and people’s health. Based on the increasingly serious soil pollution situation and harmful consequences, contaminated sites remediation and soil protection were put forward higher requirements. And the nation enacted the soil pollution prevention action plan. This study selected heavy metals lead(Pb) to conduct a number of experiments on the base of field survey. A remediation technology was proposed by explorated translocation of Pb between solution, soil, vegetation, soil enzymes, and nano-materials. This study made the following conclusions:1: To study on adsorption characteristics of nano-materials on Pb by comparing adsorption isotherms of Pb in aqueous solutions. The absorption efficiency of Pb was nano-hydroxyapatite > nano-Fe > nano carbon black ≈ carbon nano tube. Nanohydroxyapatite could obviously improve soil adsorption capacity and strength of Pb, repair effect of Pb-contaminated soil.2: Research in ultra-pure water continuously leached in Pb-contaminated soils to figer out the characteristic of mobilty under nano-hydroxyapatite or not. Results showed that the Pb-leaching occured mainly in the early, but leaching rates were all below 1%. Pb in soils had trend to mobile down while leaching, and Pb mainly concentrated in the 11-15 cm. The addition of nano-hydroxyapatite reduced above 90% of the content of Pb in leachate, and reduced the trend of downward migration effectively.3: The observation experiment of ryegrass seed germination and root growth with the combined effects of nano-hydroxyapatite and Pb was by hydroponic experiments. The results indicated that ryegrass seed germination rate and germination index were inhibited obvious,while seedlings shoot length was promoted. Ryegrass seedling root length showed low Pb concentrations for promotion but high Pb concentration for inhibition. When concentration of Pb solution was less than 100 mg/L, the content in seed increased. After added 10 mg nano-hydroxyapatite, ryegrass had higher physiological indicators, but Pb content in the seedlings decreased.4: The combined application of nano-hydroxyapatite and phytoextraction by ryegrass to Pb-contaminated soil was evaluated by conducting pot and field experiment. The results showed that, 0.2% of nano hydroxyapatite combined ryegrass can fix high concentrations oflead in the soil in actual environment. Combined effects of nanomaterials and ryegrass remediation efficiency can be achieved more than 40% in two months, which nano-hydroxyapatite can be reached 35% in one month. After added nano-hydroxyapatite,Translocation Factors of ryegrass increased significantly as time goes on. Most of Pb removal from plant roots to aerial parts to achieve the effect of removing Pb pollution in soil.5: Applied nano-hydroxyapatite in Pb-contaminated soil increased urease, catalase and dehydrogenase activity in soils. Nano-hydroxylapatite could also raise the p H of Pbcontaminated soils, effectively transform Pb of high mobilization into immobilization, that was reducing the biological activity of Pb to achieve effective passivation in soil.