| Biochar (BC) is a carbonaceous and porous product generated from the incomplete combustion of biomass and has been recognized as an efficient adsorbent. This study evaluated the ability of BC to sorb atrazine pesticide in soils, including laterite, red soil and dry red soil, and explored potential environmental values of BC on mitigating organic micro-pollutants. BC was produced from cassava waste via pyrolyzation under oxygen-limiting conditions at350,550, and750?(MS350, MS550, and MS750, respectively). Three biochars were characterized by applying TGA, EA, FTIR, SEM and so on and investigated as sorbents for the removal atrazine from tropica soil. The objective of the study was to obtain a wide and deep understanding of the influence of BC on pesticides and research sorption-desorption mechanism, and also provide a basis for biochar application to agriculture as bio-fertilizers and treatment pollution of organic compounds as an efficient sorbent. Main achievements are shown as follows.(1) Three BC samples were generated from cassava waste at different pyrolysis temperatures, and their characteristics were compared. As the charring temperature increased, the pH values and the ash content of BC also increase. The decrease in the O/C and (N+O)/C ratios indicated an increase in aromaticity and a reduction in polarity. The surface structure of cassava waste was complete and smooth before heating. However, after pyrolysis, its structure became rough, and multiple holes were formed, which increased the surface area of the BC with430.37m2/g for MS750and micropores of the BC with0.144cm3/g for MS750.(2) There was an obvious difference for sorption affinity of atrazine pesticide among3soils. The kinetics of AT in soils was completed in two steps:a fast step and a slow step, and the pseudo-second-order model perfectly simulated the sorption kinetics for AT with the coefficients R2more than0.993. Sorption isotherms of AT were nonlinear and there was a hysteresis effect. The Freundlich and the Langmuir were found to give relatively higher values of coefficients for AT sorption in soil. The sorption process in laterite and red soil was spontaneous and thermodynamically favorable.(3) Biochars added into soils chould improve sorption ability for AT. The kinetics of AT in soils was also completed in two steps:a fast step and a slow step, and the pseudo-second-order model perfectly fitted the sorption kinetics for AT. The properties and contents of BC have a positive effect on sorption strength and capacity for AT, showing in an order of MS750> MS550> MS7350and5%>3%>1%>0.5%/0.1%. Temkin model was the best fitting for AT isothermals in soil added-biochars. An apparent negative hysteresis effect haapened in the sorption-desorption process, which attributed to micropore structure of BC. A thermodynamic study indicated that the sorption of atrazine in BC-added soil was an endothermic process and was primarily controlled by physisorption with H-bonding.(4) The effect of pH value, solid-liquid ratio, contents of BC and coexist of heavy metals on AT sorption ability was investgated. The result showed:pH value was less conducive to the sorption of atrazine in BC-added soil; solid-liquid ratio was positive with AT sorption; more BC contents were beneficial to improve AT sorption affinity; however, the impact of coexist of heavy metals on AT sorption had been small.(5) The long-term sorption for AT in soil added-biochars showed that sorption amount increased with react time increasing, and was tend to be in equilibrium utimatly. Additionly, The effect of pH value, solid-liquid ratio, ionic strength and disturbance on AT release was investgated. With the increase of pH value and solid-liquid ratio, the release amount falled down. The effect of ionic strength and disturbance on AT release had no regularity. At the same time, there were no significanct changes for AT release in5%BC because of the variation of pH value, solid-liquid ratio, ionic strength and disturbance. |
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