Effects Of Different Biochars On Copper Bioavailable In Contaminated Red Soil

A series of natural and human activities including industrial solid sludge, waste agricultural, sewage irrigation, atmospheric pollution, and the containing use of copper pesticide have increased the soil heavy metal accumulation especially the copper pollution. In China, the whole agricultural soils copper content is abnormally excessive, a direct result is to reduce the crop yields, and accumulate into the food chain through the enrichment of harm to human health. Thus, finding a practical soil copper control technology has become the topic research of the field.Biochar is a kind of solid material rich in specific surface area, which is produced by the pyrolysis of biomass under hypoxia or anaerobic condition. Biochar has a good effect on the regulation of the remediation of heavy metals in water and soil due to its unique physical and chemical properties. Currently, the most commen use are crop straw biochar, bamboo biochar, and rice husk biochar etc., however, there is few use of Phytolaccae to make into biochar to research on remediation of soil heavy metal contamination. Therefore, this paper firing corn straw and Phytolaccae root and leaf into biochar, and discussing the adsorption mechanisms on the adsorption of Cu (Ⅱ) in water solution by adsorption experiment. On this basis, research the effects of corn biochar and Phytolacca biochar on soil available Cu and physiological characteristics of rape through aging experiment and pot experiment. The conclusions are as follows:(1) Compared with the corn straw biochar, Phytolacca root and leaf biochar has a larger adsorption capacity of Cu(Ⅱ)Compared with corn biochar, the Phytolacca root and leaf biochar have a better adsorption of Cu(Ⅱ). Kinetic experiments found that three kinds of biochar got their adsorption equilibrium within 90 minutes, and the adsorption process could be described well with pseudo second order kinetic equation (R2> 0.99), the maximum Cu(Ⅱ) adsorption of the Phytolacca root and leaf biochar were 103.43 mg·g-1 and 87.47 mg·g-1, which were higher than that in corn biochar (22.02 mg·g-1) about 4-5 times. During the pH range of 3-6, the adsorption capacity of the corn biochar and Phytolacca root and leaf biochar on the Cu(Ⅱ) increased with the increase of pH. The scanning electron microscope showed that the three kinds of biochars have a good adsorbtion of Cu(Ⅱ) in the solution. XPS photoelectron spectrum scan found that compared with the corn biochar, Phytolacca root biochar has a small amount of Mn atoms, which were formed into manganese oxide combined with O atoms.(2) The addition of Phytolacca root biochar can significantly reduce the Cu availablity in aging soilThe content of available Cu in red soil could be decreased significantly by adding corn biochar and Phytolacca root and leaf biochar under different aging time. Among them,4% addition of Phytolacca biochar in 400 ppm Cu contaminated soil aging for 25 days, soil available Cu content was decreased by 170.89 mg·kg-1, which was decreased 11.5% more than 4% addition of corn biochar; after 45 days aging,4% Phytolacca biochar treatment soil available Cu content was decreased 137.15 mg·kg-1 more than control, which has also decreased 12.5% more than 4% addition of corn biochar. Both of the two biochars can improve soil pH. And the effect is more obviously with the increase of the biochar content. After 45 days aging, in 400 ppm Cu contaminated soil, soil pH value was increased by 1.27 and 0.86 units respectively with 4% addition of Phytolacca biochar and corn biochar. Soil pH were increased by 0.77 and 1.38 units with 1% and 2% addition of Phytolacca biochar, about 1.5 and 1.59 times of corn biochar.(3) Corn biochar and Phytolacca root biochar could significantly increase the biomass of rape, and improve the photosynthesis and reduce the Cu accumulation of rapeIn high Cu contaminated soil, the addition of the two biochars, can not only increase the biomass and the chlorophyll content, decrease the activity of catalase in rape, but can also improve the rape photosynthesis, soil pH, and reduce rape Cu accumulation and the soil Cu availablity. The addition of 2% Phytolacca biochar does the best effect in increasing photosynthesis and decreased the activity of catalase of the rape. Adding 4% of Phytolacca biochar, the biomass of rape is 12.67 times than that with corn biochar; and the chlorophyll is 1.49 times than that with corn carbon. Compared with the control,4% corn carbon and Phytolacca carbon treatment in high Cu contaminated soil, Cu accumulation in the above part of rape were reduced by 19.9% and 66.8%; soil pH was increased 0.27 and 1.52 unit; soil available Cu content were decreased by 41.9% and 53.8%, respectively.In the low concentration of Cu contaminated soil, the two kinds of biochars were able to significantly increase the biomass of the rape, which is increaseds with the increase of the amount of biochar. Compared with the control, the biomass of the rape was increased by 21.2 times and 6.79 times with 4% addition of corn biochar and Phytolacca biochar. The addition of 2% Phytolacca biochar does best effect to the chlorophyll content and photosynthesis of the rape, which was 1.5 times and 3.3 times of corn biochar. In low Cu contaminated soil,4% addition of Phytolacca biochar can not only increased pH value of the soil but also reduce the rape Cu accumulatin significantly, however, the corn biochar has little effect. The two kinds of biochar can all reduce the content of soil available Cu, which could decrease by 21.9% and 45.2%. Based on the above results,2% and 4% Phytolacca biochar does the best effect in low and high Cu contaminated red soil respectively.