Effect Of Biochar On The Adsorption Behavior Of Sodium Pentachlorophenate And Carbofuran In Loess Soil

Biochar is pyrolysied by heating biomass in an oxygen-limited environment. Itsphysical and chemical properties are similar to charcoal, which typified by itsrelatively high carbon content and high surface area. Biochar can not only improvethe environment quality of soil, increase crop production, capture greenhouse gases,but also potentially contribute to control the environmental behavior of organiccontaminants.In this thesis, two types of biochars derived from wheat straw (at two differentpyrolysis temperatures,400℃and600℃, referred as BC-400and BC-600,respectively) were characterized by SEM, infrared spectroscopy (FTIR), and BETspecific surface area analyzer. Sodium pentachlorophenate (PCP-Na) and carbofuranare used as target pollutants to study their environmental behavior in loess soil innorthwest of China. In addition, the effects of biochar on the adsorption of sodiumpentachlorophenate and carbofuran in loess soil are discussed as well. Furthermore,some influential factors, such as pH, temperature and the size of soil particles, are alsoinvestigated. The aims of the work are (a) to reveal the adsorption of pesticidespollutants in loess soil,(b) to understand the forms and migration of pesticidespollutants in loess soil. The present work helps to reveal, effectively control andremove pesticides pollutants from loess soil.The results of this thesis are as follows:1. The adsorption and influential factors of PCP-Na and carbofuran in the loesssoilIn this thesis, batch experiments were performed to understand the adsorptionkinetics and thermodynamics of PCP-Na and carbofuran in loess soil. The resultsindicate that the adsorption kinetic of PCP-Na and carbofuran in the losses soil couldbe described by the pseudo-second-order model. The adsorption thermodynamics ofPCP-Na and carbofuran in the loess soil are nonlinear by nature, and fitted well withthe Freundlich isothermal model. The thermodynamic parameters of Gibbs freeenergy (ΔG), enthalpy (ΔH), and entropy (ΔS) tend to prove the spontaneous natureof the adsorption process, the exothermic nature of the adsorption, and the decreased randomness at the solid-solution interface due to the adsorption of PCP-Na andcarbofuran. The results also suggest that the pH value, the particle size and the initialconcentration of PCP-Na and carbofuran have significant effects on the adsorptivebehaviors of PCP-Na and carbofuran in the loess soil in the Northwestern China. Theresults indicate that the adsorption capacity of PCP-Na tends to decrease with theincrease of the pH value below6, while it increases when the pH value is bigger than6; on the other hand, the adsorption capacity of carbofuran tends to decrease with thepH value increase from4to10. When the particle size of loess soil decreased from0.425to0.075mm, the adsorption capacity of PCP-Na is likely to increase from0.006to0.046mg·g-1, and the adsorption capacity of carbofuran increase from0.009to0.049mg·g-1respectively. Besides, when the initial concentration of PCP-Naincreased from20to110mg·L-1, the adsorption capacity of PCP-Na would increasefrom0.076to0.200mg·g-1. When the initial concentration of carbofuran increasedfrom20to110mg·L-1, the adsorption capacity of carbofuran would increase from0.080to0.206mg·g-1.2. The adsorption behavior of PCP-Na and carbofuran to biomass-derivedbiochars at different temperatureIn this thesis, two types of biochars (BC-400and BC-600) derived from wheatstraw were characterized by SEM, infrared spectroscopy (FTIR) and BET specificsurface area analyzer. The results indicate that the adsorption kinetic of PCP-Na andcarbofuran by the biochars could be described by the pseudo-second-order model, andthe adsorption capacity of pesticides by the BC-600is much higher than that byBC-400. The adsorption thermodynamics of PCP-Na and carbofuran in the BC-400and BC-600are both nonlinear by nature and fitted well with the Freundlichisothermal model. The values of ΔGθare negative, which tend to prove thespontaneous nature of the adsorption process, and the values of ΔHθare positive,which suggest he endothermic nature of the adsorption. Furthermore, the values ofΔSθare positive, which resulted from the increased randomness at the solid-solutioninterface due to the adsorption of PCP-Na and carbofuran. The results also suggestthat the pH value has significant effects on the adsorption of PCP-Na and carbofuran in the biochars. That is, the adsorption capacity of PCP-Na tends to decrease with theincrease of the pH value below6, while it tends to increase when the pH value ishigher than6. The adsorption capacity of carbofuran tends to decrease with the pHvalue increasing from4to10.3. Effect of biochar on the adsorption behavior of PCP-Na and carbofuran inloess soilThe results showed that the adsorption kinetic of PCP-Na and carbofuran couldbe well described by the pseudo-second-order model in the presence/absence ofbiochar and the adsorption capacity showed the following inequation: soil+BC＞soil.The adsorption capacity of PCP-Na increases from0.173to0.987mg·g-1(about5.7times), and the adsorption capacity of carbofuran increases from0.449to1.063mg·g-1(about2.4times) respectively. The adsorption thermodynamics of PCP-Na andcarbofuran in the loess soil are nonlinear by nature, and fitted well with theFreundlich isothermal model in presence/absence of biochar. However, the KFvaluesin three temperatures (25、35、45℃) show the same trend: soil+BC＞soil, indicatingthat biochar helps to increase the adsorption capacity of PCP-Na and carbofuran inloess soil. On the other hand, the pH value has significant effects on the adsorptivebehaviors of PCP-Na and carbofuran in the biochar. The results indicate that theadsorption capacity of PCP-Na tends to decrease with the increase of the pH valuebelow6; while it tends to increase when the pH value is higher than6, whereas theadsorption capacity of carbofuran tends to decrease with the pH value increasing from4to10.