【作者】 赵巍；

【导师】 刘凡；

【作者基本信息】 华中农业大学 ， 土壤学， 2009， 博士

【摘要】 铅作为重金属污染元素,在环境中的行为和归趋一直是人们关注的重点。研究铅与土壤常见组分——水钠锰矿的作用机理,对于阐明铅在土壤、沉积物及水体中的形态与化学行为,以及对铅污染土壤的修复和水体的净化等有着重要意义。本论文以合成的酸性和碱性系列不同锰氧化度水钠锰矿为材料,采用X-射线衍射（XRD）、透射电镜（TEM）、高分辨透射电镜（HRTEM）、红外光谱（IR）、光电子能谱（XPS）、X射线吸收精细结构光谱（XAFS）等技术,通过研究不同锰氧化度水钠锰矿表面的Mn和O化学状态、（110）面网间距、Pb²⁺吸附量、吸附过程中释放的Mn²⁺、H⁺和K⁺的变化,以及水钠锰矿用Na₄P₂O₇、Zn²⁺或Mn²⁺溶液进行化学处理前后,其锰氧化度、（110）面网间距、Pb²⁺吸附量、吸附过程中阳离子释放量的变化,并结合Pb²⁺在不同锰氧化度水钠锰矿的微观吸附形态等,探讨了水钠锰矿亚结构变化对Pb²⁺吸附量的影响。取得的主要结果有:1、同系列的不同锰氧化度水钠锰矿具有相似的晶体形貌。它们的锰氧化度与其d₁₁₀面网间距呈极显著的负相关,与Pb²⁺的最大吸附量呈极显著的正相关,供试水钠锰矿锰氧化度的高低表观上反映了结构中八面体空位数量的多少,水钠锰矿随着锰氧化度的提高,导致其结构中的八面体空位数增多,对Pb²⁺的吸附容量增大,八面体空位数量对Pb²⁺吸附量的大小起着非常重要的作用。当八面体空位位点增多时,Pb²⁺吸附量增大,导致样品部分表面出现两个Pb²⁺离子同时配位吸附于一个空位单面位点区域的可能性增大。Pb²⁺的吸附量与吸附过程中Mn²⁺、H⁺和K⁺的释放量之和呈极显著的正相关,释放的Mn²⁺、H⁺和K⁺主要来自于水钠锰矿结构中八面体空位处吸附的相应阳离子。吸附前Mn^2+/3+与H⁺、K⁺占据水钠锰矿结构中八面体空位上下方位点的相对多少受水钠锰矿的锰氧化度高低的影响,锰氧化度低时,八面体空位上下方位点吸附Mn^2+/3+较多,吸附的H⁺、K⁺则较少,反之亦然。2、X-射线光电子能谱研究表明,在高真空测试环境下,不同锰氧化度水钠锰矿结构中,Mn存在饱和配位和不饱和配位两种化学状态,其相对含量分别为82.79%-91.69%和8.31%-17.21%,锰氧化度高的水钠锰矿,八面体空位上结合的-OH较多,由于晶粒间的团聚作用而导致不饱和配位Mn的含量相对减少。在不同锰氧化度水钠锰矿结构中,O以晶格氧、羟基氧和水分子中氧三种化学状态存在,其相对含量分别为50.44%-65.05%、24.90%-39.27%和8.07%-12.63%,锰氧化度高的水钠锰矿,八面体空位上结合的-OH较多,从而结构中羟基氧的相对含量增加。初步探讨了在沿（110）方向上含Mn³⁺的MnO₆八面体链中空位的分布,并建立水钠锰矿结构模型,为其亚结构的深入研究提供理论依据。3、红外光谱研究表明,水钠锰矿的899-920 cm^-1红外吸收带源于八面体空位处OH的弯曲振动,随着水钠锰矿锰氧化度的降低,空位处与OH配位的Mn⁴⁺被Mn³⁺替代的数量增多,OH弯曲振动频率向低频移动;1059-1070、1115-1124和1165-1171 cm^-1吸收带归属于层内Mn³⁺-OH的弯曲振动,并随着水钠锰矿锰氧化度的降低而逐渐增强。对于990和1023-1027 cm^-1两吸收带,归属于层间Mn³⁺ -OH的弯曲振动,当水钠锰矿吸附Pb²⁺后,部分层内Mn³⁺可迁移至层间,使得990 cm^-1吸收带增强并向高频移动;564-567 cm^-1吸收带源于空位处Mn-O的红外吸收,当空位上下方吸附重金属Pb²⁺或Mn³⁺后,由于振动耦合效应,该吸收带发生分裂;610-626和638-659 cm^-1吸收带的间距可反映水钠锰矿结构中Mn³⁺分布的对称性,当水钠锰矿吸附Pb²⁺后,由于Pb²⁺在结构中的不规则分布,降低了Mn³⁺分布的对称性,致使两吸收带的间距增大。4、锰平均氧化度为3.67的酸性水钠锰矿经不同pH焦磷酸钠溶液处理后,层结构边缘的Mn³⁺和部分层间Mn³⁺被络合出,处理后锰平均氧化度有所增加。处理前后水钠锰矿的晶体结构类型没有发生改变,但是处理后矿物结构中位于八面体空位上下方的Mn³⁺减少,H⁺增多,可吸附Pb²⁺的空位位点数量增加,对Pb²⁺的最大吸附量增大。处理前酸性水钠锰矿结构中的Mn³⁺可能约有1/6的Mn³⁺位于层结构边缘区,另外约5/6的Mn³⁺位于层间和层结构非边缘区。5、水钠锰矿经Zn²⁺和Mn²⁺分别处理后,矿物类型未改变,并具有相似的晶体形貌。Zn²⁺溶液处理水钠锰矿时,随着Zn²⁺浓度的增大,水钠锰矿的锰平均氧化度和d₁₁₀面网间距不变,结构中空位数量也未改变,Zn²⁺通过占据部分吸附点位,导致其对Pb²⁺的最大吸附量从3190 mmol/kg减少为2030 mmol/kg。而Mn²⁺溶液处理水钠锰矿时,大多数Mn²⁺被氧化为Mn³⁺,这些Mn³⁺部分位于八面体空位上下方的吸附位点,部分进入八面体空位中。随着加入的Mn²⁺浓度增大,Mn²⁺被氧化为Mn³⁺而进入八面体空位的数量增多,锰平均氧化度减小,d₁₁₀面网间距从0.1416 nm增大至0.14196 nm,结构中空位数量减少,对Pb²⁺的最大吸附量从3190 mmol/kg减少至1332 mmol/kg。研究结果进一步表明,水钠锰矿结构中的八面体空位数量对Pb²⁺的吸附量的大小起着非常重要的作用。6、X射线吸收精细结构光谱研究表明,在吸附Pb²⁺后的水钠锰矿中,Pb²⁺邻近存在两个Pb-O配位壳层和两个Pb-Mn配位壳层,对于相同锰氧化度的样品,当Pb²⁺吸附量低时,两个Pb-O配位壳层中,Pb²⁺的配位数分别为2.7、9.1,与Pb²⁺的距离分别为0.226、0.397 nm;两个Pb-Mn配位壳层中,Pb²⁺的配位数分别为2.8、6.6,与Pb²⁺的距离分别为0.356、0.375 nm;当Pb²⁺的吸附量增加时,其配位环境发生畸变,使得Pb-O配位壳层和Pb-Mn配位壳层中,Pb²⁺的配位数分别减少为1.5、3.4和1.2、3.6,与Pb²⁺的间距分别增大为0.227、0.398 nm和0.357、0.376 nm。Pb²⁺在不同锰氧化度水钠锰矿表面的吸附形态基本相同,均存在三种吸附形态,一是与水钠锰矿层结构a轴方向层边面形成单齿共角配合物,二是与结构b轴方向层边面形成双齿共角配合物,三是与八面体空位形成三齿共角配合物。随着水钠锰矿的锰氧化度增大,Pb²⁺吸附量增加,Pb²⁺在结构中的分布密集,导致其配位环境发生畸变,使得Pb-O配位壳层和Pb-Mn配位壳层中Pb²⁺的配位数减少,与Pb²⁺的间距增大。更多还原

【Abstract】 Lead is an environmental heavy metal that has always attracted extensive attention.An exploration of the mechanisms that determine lead and soil component interactions is crucial to understand the fate of lead in soils,sediments,and water.A greater understanding of Pb interaction mechanisms could also aid in water purification and lead-contaminated soil remediation efforts.In this study,two series of birnessites with ranges in Mn average oxidation state（AOS） were synthesized.The chemistry states of Mn and O on the surface of birnessites,the relation between d₁₁₀-spacing,maximum Pb²⁺ adsorption and the AOS in the birnessites before and after treatments with Na₄P₂O₇,Zn²⁺ or Mn²⁺ solution,characterization of Mn²⁺,H⁺ and K⁺ release from birnessites during Pb²⁺ adsorption,and complex configuration of Pb²⁺ adsorbed on the birnessites with different AOS were analyzed by XRD,TEM,HRTEM,IR,XPS,XAFS,BET.The effect of variance of birnessite substructure on the amount of Pb²⁺ adsorbed was discussed.1.One birnessite series was prepared in acidic media（49.6%to 53.6%Mn） and the other in alkaline media（50.0%to 56.2%Mn）.The correlations of synthetic birnessite Pb²⁺ adsorption capacity to d（110）-interplanar spacing,AOS by titration,and release of Mn²⁺, H⁺,and K⁺ during Pb²⁺ adsorption were investigated.Maximum Pb²⁺ adsorption to the birnessites synthesized in acidic media ranged from 1320 to 2457 mmol/kg with AOS values that ranged from 3.67 to 3.92.For birnessites synthesized in alkaline media, maximum Pb²⁺ adsorption ranged from 524 to 1814 mmol/kg and AOS values ranged from 3.49 to 3.89.Birnessite AOS values and Pb²⁺ adsorption increased as Mn content decreased.Maximum Pb²⁺ adsorption to the synthetic birnessites calculated from a Langmuir fit of the Pb adsorption data was linearly related to AOS.Birnessite AOS was positively correlated to Pb²⁺ adsorption,but negatively correlated to d（110） spacing. Vacant Mn structural sites in birnessite increased with AOS and resulted in greater Pb²⁺ adsorption,leading to the increase of the total amount of Mn²⁺,H⁺ and K⁺ released,and the increased likelihood for two Pb²⁺ adsorbed in the region of one side of a vacant site. Birnessite AOS values apparently reflect the quantity of vacant sites that largely account for Pb²⁺ adsorption.Therefore,birnessite Pb²⁺ adsorption capacity was largely determined by Mn site vacancies,from which Mn²⁺,H⁺,and K⁺ released during adsorption were mostly derived.2.The investigations on birnessites with different AOS by XPS indicated that there were two chemistry states of Mn,staturated and undersaturated coordinately Mn,whose relative contents were 83.79%-91.69%and 8.31%-17.21%in the structure,respectively. -OH located at vacant Mn octahedral site increased with the increase of AOS in birnessite accounting for the aggregation of crystal grains,which led to the decrease in relative content of undersaturated coordinately Mn.There were three chemistry states of oxygen, lattice oxygen,hydroxide and H₂O,whose relative contents were 50.44%-65.05%, 24.90%-39.27%and 8.07%-12.63%in the structure,respectively.-OH located at vacant Mn octahedral site increased with the increase of AOS in birnessite,which resulted in the increase in relative content of chemistry state of hydroxide in the structure.Structure models of birnessites were presumed,and the distribution of vacant sites in the Mn³⁺-rich MnO₆ rows was discussed,which provided fundamental for further study on the substructure of birnessite.3.The structural features of birnessites with different Mn average oxidation state（AOS） before and after Pb²⁺ adsorption were characterized by fourier transform infrared（FTIR）, and the adsorbent band centres of FTIR were determined by second derivatives of these spectra.The band at 899-920 cm^-1 was assigned to the bending vibration of -OH located at vacant Mn octahedral sites.The lower AOS in birnessite,the more Mn⁴⁺ coordinated to -OH located at vacant Mn octahedral sites displaced by Mn³⁺,which led to the position of -OH bending vibration shifting to a relative low wave number.The bands at 1059-1070, 1115-1124 and 1165-1171 cm^-1 were assigned to the vibration of Mn³⁺-OH located in the layer,and the intensity of these bands increased with the decrease of AOS in birnessite. The bands at 990 and 1023-1027 cm^-1 were assigned to the vibration of Mn³⁺-OH located in the interlayer.A partial of Mn³⁺ in the layer migrated to the interlayer during the Pb²⁺ adsorption inducing the intensity of the band at 990 cm^-1 to increase and its position shifting to a relative high wave number.The band at 564-567cm^-1 was assigned to the vibration of Mn-O located at vacant Mn octahedral sites,and would split due to the effect of coupling on vibration when Pb²⁺ or Mn³⁺ was adsorbed above or below vacant sites. The space between the bands at 610-626 and 638-659 cm^-1 reflected the symmetry of Mn³⁺ distribution in the birnessite,and increased after Pb²⁺ was adsorbed on the birnessite.4.Acid birnessite was treated with Na₄P₂O₇ at pH 2,4,5 respectively.After the treatments, the species and content of manganese ion in the complex solution,and the variation of average oxidation state（AOS） of Mn in birnessite,and the amount of Pb²⁺ adsorbed and Mn²⁺,H⁺ released during the Pb adsorption were investigated.The results indicated that after acid birnessite（AOS=3.67） was treated by Na₄P₂O₇ at different pH,Mn³⁺ located in the layer-structure-edge and partial of Mn³⁺ located in the interlayer were released to the solution through complexation with Na₄P₂O₇.The Mn AOS of birnessites after treatments were increased to 3.78（pH 2）,3.78（pH 4）,3.82（pH 5） respectively.While the crystal structure of birnessite didn’t change after treatments,the amount of Mn³⁺ located above or below vacant sites decreased,and the amount of H⁺ located above or below vacant sites went up in the structure.The amount of vacant sites responsible for Pb²⁺ adsorption increased,which led to the increase of the maximum amount of Pb²⁺ adsorbed. Additional,the distribution of Mn³⁺ in the strucuture of acid birnessite was deduced. About one sixths of Mn³⁺ located in layer-structure-edge,and five sixths of Mn³⁺ located in the interlayer and non-layer-structure-edge.5.The association of vacant Mn octahedral sites with Pb²⁺ adsorption was deeply elucidated from the variances of AOS,d（110）-interplanar spacing,maximum Pb²⁺ adsorption,maximum Zn²⁺ and Mn²⁺ release during the Pb²⁺ adsorption for the birnessites before and after treatments.The AOS and d（110）-interplanar spacing of the birnessites remained almost unchanged as the concentration of the treating Zn²⁺ increased,indicative of unchanged amount of vacant Mn octahedral sites.Whereas maximum Pb²⁺ adsorption decreased from 3190 to 2030 mmol/kg due to occupancy of the treating Zn²⁺ on adsorption sites.However,the AOS of the Mn²⁺-treated birnessites decreased,and most of the treating Mn²⁺ were oxidized to Mn³⁺ and located below or above vacant Mn octahedral sites or migrated into vacant Mn octahedral sites,when the concentration of the treating Mn²⁺ increased from 1 to 2.4 mM.The d（110）-interplanar spacings of the treated birnessites were found to increase from 0.14160 to 0.14196 nm,indicative of the decrease in the amount of vacant Mn octahedral sites,mainly due to the increase of the produced Mn³⁺ migrating into vacant Mn octahedral sites.Moreover,the maximum Pb²⁺ adsorption of the Mn²⁺-treated birnessites was observed to decrease from 3190 to 1332 mmol/kg.The results suggest that birnesstie Pb²⁺ adsorption capacity is largely determined by the number of Mn site vacancies.6.The investigations on birnessites with Pb²⁺ by XAFS indicated that two Pb-O and two Pb-Mn shells were found in the birnessites after Pb²⁺ adsorption.For the same birnessite, at low amount of adsorption,Pb²⁺ coordination numbers were 2.7 and 9.1,respectively,in the two Pb-O shells at distances of 0.226 and 0.397 nm,respectively,and Pb²⁺ coordination numbers were 2.8 and 6.6,respectively,in the two Pb-Mn shells at distances of 0.356 and 0.375 nm,respectively.At high amount of adsorption,in the two Pb-O shells, Pb²⁺ coordination numbers decreased to 1.5 and 3.4,respectively,the distances between Pb and O increased to 0.227 and 0.398 nm,respectively,and in the two Pb-Mn shells, Pb²⁺ coordination numbers decreased to 1.2 and 3.6,respectively,the distances between Pb and Mn increased to 0.357 and 0.376 nm,respectively on account of the distortion of the Pb²⁺ coordination environment.The same three bonding mechanisms in Pb²⁺ adsorption on the bimessites with different AOS:a single-corner-sharing complex on particle edges along a axis,a double-corner-sharing complex on particle edges along b axis,and a triple-corner-sharing complex in the interlayer above or below vacant sites. The amount of Pb²⁺ adsorbed increased with the increase in AOS of birnessite,which led to the decrease of Pb²⁺ coordination numbers and the increase of the distances between Pb and O in Pb-O and Pb-Mn shells due to the distortion of the Pb²⁺ coordination environment.更多还原