| Arsenic pollution is becoming more serious and pollution area expands inceasingly, especially in the south of China. Planting crops on the polluted soils or irrigating farmlands with polluted water will probably increase the As(especially the arsenic) accumulation in plants, which will not only be toxic to crops by declining the yield and quality of crops, but also, eventually, get to humans through the food chain and do harm to human wellbeing and other organisms. We hope to provide a theoretical basis and data support for China’s food security. In this work we used corn straw as raw materials, and then load them into biochar(BC). Then manganese oxide-modified biochar(MBC) were produced by combining manganese oxides with biochar. To study the effects of manganese oxide-modified biochar on removal and oxidation of arsenic in the adsorption process and effects on arsenic species and content in rice, we finally added BC and MBC, respectively 0.5%, 1%, 2% of soil weight in soil polluted by arsenic in two level pollution(47.19mg·kg-1 and 73.04 mg·kg-1). Some main conclusions are listed below:(1) In this research we successfully made manganese oxide-modified biochar composites with different ratios(w/w)X ray spectrum analysis showed that manganese has been successfully embedded into the biochar in MBC. FTIR analysis showed that some surface functional groups of MBC changed and the number of hydroxyl, phenolic hydroxyl, carboxyl groups also significantly increased on the surface. The adsorption of arsenic(III) on manganese oxide-modified biochar and unmodified biochar were investigated on the basis of a set of batch adsorption experiments. The results showed that compared with unmodified biochar, the maximum adsorption capacity of the manganese oxide modified biochar for arsenic(III) was greatly improved from 11.41 to 20.08 mg·g-1, and the adsorption of arsenic onto the unmodified biochar and the biochar-manganese oxide composites were rapid when the adsorption equilibrium could be reached within 30 min, and the adsorption behavior could be described well with pseudo-second-order kinetic equation with a R2 values extract to 0.99.(2) Manganese oxide-biochar composite(MBC) prepared by pyrolysis of a mixture of potassium permanganate and biochar, was investigated for its influence on red soil as an absorbent of arsenicThough the impregnation of the manganese oxide decreased the biochar’s specific surface area, the arsenic in red soil-MBC mixtures exhibited lower mobility than in soils treated with pristine biochar and without biochar. As the biochar content increased, more arsenic was retained by the soil and the soil p H increased. Fourier-transform infrared spectrometry combined with X-ray photoelectron spectroscopy indicated that several functional groups, especially O–H, C=O, Mn–O, and Si–O, participated in the adsorption process and increased arsenic adsorption capacity 1.786 times, then manganese oxides played a significant role through the possible oxidation of arsenic. Consequently, MBC may be used as a material to re-mediate red soil contaminated by arsenic, decreasing the risks to human health.(3) MBC promoted the grain yield reduced the absorption of arsenic by rice grain and had an tendengcy to increase the proportion of essential amino acidIn the high concentration polluted soil, compared with the blank, the grain yield was increased by 61.4%-87.3% with the increase of MBC addition, and grain yield increased by 21.5%-42.7% compared to the BC added, the total arsenic in grain were decreased by 0%, 11.4% and 19.4% respectively, As(III) and methylarsenic, decreased by 5.63% and 11.2%, 17.4% and 60.3%, 21% and 49.7%, respectively.In low concentration polluted soil, after the addition of BC and MBC, the biomass of rice were not increased significantly. However, with the increase of the MBC amount, the weight of rice was increased by 5.60%-20.03% compared with the blank control, the arsenic content in grains decreased by 18.4%, 26.3% and 18.4% and arsenic(III) content were decreased by 25.4%, 14.7% and 19.6%. Compared to BC, arsenic contents in rice grains added 1% MBC decrease 11.5%.After adding MBC, whether high or low contaminated soil, the percent of essential amino acid in total amino acid in rice grain had a rising trend, which suggested that MBC did not reduced the quality of rice.(4)The effects on adsoption of arsenic by riceWhile MBC were added to polluted soils, arsenic was absorbed onto the material surface and internal particles and then reduced its effectiveness. At last reduced the accumulation of arsenic in rice and promote rice growth, reduced the toxicity. |
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