| With the rapid development of economic society,in addition to the natural geochemical processes,arsenic?As?emissions caused by human activities such as industrial and mining wastes as well as continued increase in agricultural production processes,soil arsenic pollution and over-standard problems are becoming more and more prominent.It is increasingly urgent to develop technologies for soil remediation and safe utilization technologies.As one of the obvious advantages,soil passivation repair is becoming the primary measurement for mitigation of arsenic-contaminated soil;thus,research and development of more efficient passivation materials become the top priority.Based on the great advantages of biochar and modified material in the field of soil heavy metal pollution remediation,the metal oxide modified biochar material is becoming more important.In this study,a novel adsorbent by loading cerium and manganese onto wheat straw-modified biochar?Biochar,BC?was synthesized using high temperature pyrolysis at 600??Modified biochar,MBC?.Combining the macro and micro,soil micro-threshold experiments,biological simulation tests and indoor analysis methods were carried out to investigate the adsorption of cerium manganese modified biochar on water and its influencing factors,the passivation effect of modified biochar on soil As?arsenic?and its mechanism research,and the effects and mechanism of modified biochar on reducing crop absorption of As.The main results are as follows.?1?The Langmuir model and pseudo-second-order kinetic model offered an excellent description of As?V?adsorption in water by MBC.MBC exhibited good adsorption performance for As?V?in the pH range of 2.0?11.0.When pH=5,the maximum adsorption capacity is 142.80 mg·g-1.The adsorption process appears as a spontaneous endothermic reaction,?G is a negative value,and its absolute value increases with increasing temperature.Compared to the unmodified wheat straw biochar,the capacity of MBC was considerably improved and its equilibrium adsorption capacity is up to 114.88 mg·g-1(C0=200mg·L-1,pH=7.0,T=323 K).Moreover,the reaction temperature,ionic strength,and amount of material all have a certain effect on the amount of adsorption and removal efficiency.With the increase of temperature and ionic strength,the adsorption capacity of MBC to As?V?gradually increases.Increasing the amount of materials within a certain range is conducive to the removal of As?V?.The results of FTIR,XPS,XRD and other technical analysis showed that the high adsorption capacity of MBC for As?V?is closely related to the successful loading of cerium and manganese oxide.?2?The passivation effect of MBC on As in three different types of soil?red soil,yellow soil and purple soil?was discussed in this chapter.The results revealed that the application of modified biochar resulted in a significant decrease of water soluble arsenic content in three different kinds of soils.With the addition amount increasing,the stabilization efficiency of soil arsenic increased continuously.When the applied amount of MBC ranged from 1%to 10%,the stabilization efficiency of arsenic was in the range of 70%?99%.The corresponding stabilizing efficiency of the red,yellow and purple soils were70.59%?94.72%,75.24%?98.35%,and 76.53%?99.61%,respectively,after treated by MBC of1%?10%.At a higher addition of 10%MBC,the efficiency of stabilization reached 95%.On the contrary,the addition of unmodified biochar caused the activation and dissipation of As in soils.Comparatively speaking,according to the stabilization efficiency,the three soils ranked in this decreasing order:purple soil>yellow soil>red soil.It also illustrated that addition of MBC into soils led to the conversion of active arsenic to stable ones in soil,indicating the conversion from non-specifically sorbed?F1?,specifically sorbed?F2?to well-crystallized hydrous oxides of Fe and Al?F4?and residual phases?F5?,and reduced the mobility of arsenic in these soils.?3?The results of the rice seedling experiment showed that the application of biochar and cerium-manganese modified wheat straw biochar significantly increased the rice aboveground and root biomass in two different levels of arsenic contaminated soil with arsenic content of 68.99 and 158.52 mg·kg-1.At the same time,the modified biochar fixed the arsenic in the soil and mainly existed in pentavalent arsenic.The fixation efficiency of active arsenic in the two types of soil is as high as 35.46%and 27.11%respectively.In addition,the order of total arsenic content in various parts of rice is:root>stem>leaf,in arsenic contaminated soil with arsenic content of 68.99 mg·kg-1,the total arsenic content in rice roots,stems,and leaves decreased by 34.67%?77.17%,43.68%?66.90%,and 54.72%?64.65%,respectively.In high-concentration arsenic-contaminated soil(158.52 mg·kg-1),the total arsenic content in roots,stems and leaves decreased by 49.26%?79.03%,87.71%?94.88%and 75.77%?85.71%compared to the control.In general,the application of cerium-manganese modified wheat straw biochar promoted the transformation of arsenic in the soil from an active state to a stable state,and the mobility of As decreased,thereby reducing the bioavailability of soil As.It has realized the conversion of high-toxic trivalent arsenic to low-toxic pentavalent arsenic,which has the effect of reducing toxicity and reducing safety risks. |
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