【作者】 冯雄汉；

【导师】 刘凡；

【作者基本信息】 华中农业大学 ， 土壤学， 2004， 博士

【摘要】 土壤氧化锰矿物是动植物锰素的重要来源，是土壤中的重要吸附载体、氧化还原主体、化学反应催化剂及环境信息载体，其资源属性和环境属性日益受到人们的关注。开展土壤氧化锰矿物的合成、转化及性质研究，对于深入了解和认识锰的地球化学行为、土壤演变、土壤质量与生态环境之间的关系，促进氧化锰矿物资源的开发与利用具有重要的理论和实践意义。 本文采用X-射线衍射（XRD）、透射电镜（TEM／ED／EDAX）、高分辨透射电镜（HRTEM）、傅里叶红外光谱（FTIR）、激光拉曼光谱（LR）、热重分析（TGA）、全量分析和表面酸性位点分析等技术，系统研究了水钠锰矿、钙锰矿、锰钾矿、黑锰矿和锂硬锰矿等土壤中常见氧化锰矿物的合成条件、生成途径、表面电荷性质，以及对重金属离子的吸附和Cr（Ⅲ）、As（Ⅲ）的氧化特性及其影响因素，探讨了不同氧化锰矿物的结构特征、形成机制以及与土壤环境条件的关系。取得的主要结果有： 1、系统地开展了土壤氧化锰矿物的合成、表征与性质研究。合成了水钠锰矿、锂硬锰矿、锰钾矿、钙锰矿和黑锰矿等土壤中常见氧化锰矿物，对其结构、形貌、组成和电荷性质进行了鉴定和表征，初步探明了不同合成条件的影响规律。 （1） 反应液流动速率和氧气流量是影响碱性介质中水钠锰矿生成的主要因素，反应受O₂的扩散控制。反应前对MnCl₂和NaOH溶液通N₂或O₂处理以及反应过程中温度对水钠锰矿的生成没有影响，且提高温度可以增加产物的结晶度。合成单相水钠锰矿的条件为：OH／Mn摩尔比为13.7，O₂的流量2L／min，在常温和机械搅拌（450r／min）下氧化5小时。 （2） 盐酸滴加速度、反应时间和老化处理是影响酸性介质中水钠锰矿合成的主要因素。对生成的水钠锰矿进行老化处理可以大大提高产物的结晶度。单相酸性水钠锰矿的合成条件为：HCl：KMnO₄=2：1，在沸腾和搅拌条件下以0.7mL／min的速度滴加盐酸，滴加完毕后再反应30min，产物在60℃下老化处理12h。合成的酸性水钠锰矿为含少量K的H型水钠锰矿，红外光谱表明它与碱性水钠锰矿具有类似的短程结构。 （3） 影响钙锰矿热液合成的主要因素是热液温度和处理时间，体系压力对钙锰矿的合成影响小。以Mg-水钠锰矿为前驱物，热液合成的钙锰矿呈纤维状，三个互交120°方向生长的晶体共同组成三连晶结构。 （4） 锰钾矿的结晶度随反应温度的提高而增加，老化处理对产物的结晶度略有增加，而延长反应时间对产物的影响较小。合成单相锰钾矿的条件为：MnO₄^-／Mn²⁺摩尔比为0.7，在100℃下反应20min，产物经50℃老化处理24h；以水钠锰矿为母几种常见氧化锰矿物的合成、转化及表面化学性质体，与LimAln（oH）x针轻基复合离子交换后，热液条件合成的铿硬锰矿为六方片状晶体，其中含有少量水钠锰矿杂质;在弱碱性介质中，以O:为氧化剂氧化Mn（OH）2合成黑锰矿，合成的单相黑锰矿为暗黄色假立方晶体。 （5）酸性水钠锰矿、碱性水钠锰矿、锰钾矿、钙锰矿的PZC较低，分别为1 .75、3.37、2.10和3.5，其表面可变负电荷量的大小顺序为:酸性水钠锰矿>碱性水钠锰矿>锰钾矿妻钙锰矿，黑锰矿的 PZC较高，表面可变负电荷量远低于其他四种氧化锰矿物。 2、首次在回流条件下一次合成了大量单相钙锰矿，填补了国内外在该领域的空白。回流sh和24h合成的钙锰矿的平均化学组成分别为Mgo.:郝no2.:，（H 20）1.15和Mgo.;7MnO2.10（H2O）088，随着回流时间的延长，钙锰矿结晶度进一步提高，且无其它矿相生成;回流条件合成的钙锰矿与天然钙锰矿及某些热液条件合成的钙锰矿具有相同的形貌特征和生长特点，其表面具有较强的L喇s酸性位点，而Bronsted酸性位点较弱;回流条件合成的钙锰矿保持热稳定性达400℃。提出了钙锰矿在热液条件和表生条件下可能具某些相似的形成机制，即在较高的热液温度下，钙锰矿的形成时间较短，在温度较低的表生环境中，钙锰矿的形成需要较长的时间。 3、结合快速x射线衍射（xRD）方法和相关氧化锰矿物的Eh一pH平衡关系分析，查明了碱性介质中02氧化Mn（OH）2合成水钠锰矿的反应过程和生成途径。反应过程可分为以下四个阶段:（l）黑锰矿（Mn3o4）和六方水锰矿（p一MnOOH）的形成阶段;（2）黑锰矿和六方锰矿转化为布塞尔矿阶段;（3）布塞尔矿生长阶段;（4）布塞尔矿转化成水钠锰矿阶段。生成途径可表示为:Mn（0H）:^六方水锰矿^布塞尔矿^水钠锰矿、尸黑锰矿 矿物的转化受矿物表面溶解O:浓度决定的Eh值控制。 4、初步探明了不同类型氧化锰矿物对重金属离子的吸附和Cr（lII）及As（m）的氧化特性。（l）酸性水钠锰矿对PbZ+、CuZ+、eoZ+、edZ+和znZ+等重金属的吸附能力最强，黑锰矿的吸附能力最弱，除黑锰矿吸附更多的c矿+外，供试氧化锰矿物对Pb2+的最大吸附量远大于其它重金属。并提出:①重金属的水解常数和矿物的表面负电荷量，都是通过改变氧化锰矿物表面诱导水解作用及吸附离子形态来影响氧化锰矿物对重金属的吸附;②酸性水钠锰矿吸附的重金属离子，尤其是Pb2+，主要为非水化离子形态，而锰钾矿、钙锰矿和黑锰矿则是水化离子形态为主。（2）氧化锰矿物对Cr（In）的最大氧化量大小顺序为(mmol服更多还原

【Abstract】 As essential source of Mn element for the nutrition of animals and plants, one of important adsorbents, redox agents, catalysts and carriers for environmental information in soils and aquatic system, Mn oxide minerals have been attracting more and more concerns of researchers on their resource and environmental properties. Investigations on the syntheses, transformations and properties of them could shed light on geochemistry behaviors of Mn, soil progress, and relations between soil quality and environments, they are also of great significance to promote exploration and utilization of Mn oxide minerals.Base on a review of research development on the common Mn oxide minerals in soils, this dissertation dealt with syntheses conditions, origination and transformation, and surface chemistry characteristics of them, using techniques of XRD, TEM/ED, HRTEM, IR, LR, TGA and surface acidity analysis. Structure identifications, formation mechanisms and their relations to the environments in soils and sediments were also discussed.1 .Fluxion velocity of reactive suspension and the rate of O2 flow significantly influenced the synthesis of birnessite. Vigorous stirring made the synthesis facile to produce pure birnessite. However the pretreatment of the reacting solutions by N2 and the reaction temperature had little effect on the synthesis. Increasing the reaction temperature led to a larger crystal size, better crystallinity and lower surface area. The adopted conditions for synthesis of pure birnessite were: NaOH to Mn molar ratio of 13.7, the O2 flow rate of 2 L/min, and oxidation for 5 h during vigorous stirring at normal temperature. The average composition of the synthesized pure birnessite was Nao 2sMnO2.o7’0.66H2O, and surface area of 38 m2/g.2. At 25 , the formation process of the birnessite by oxidation of Mn(OH)2 with 62 in alkali medium could be divided into four stages: 1) hausmannite and feitknechtite formation period, 2) transformation of hausmannite and feitknechtite into buserite period, 3) buserite crystal growing period, 4) transformation of buserite into birnessite period. The diffusion of O2 was the key step on the product during the course of the oxidation The pathways of the birnessite formation in this study might be:3 x Hydrothermal temperature and treatment time significantly influenced the synthesis of todorokite. Variation of system pressure caused by changing filling ratio of the autoclave had little effect on the synthesis. The crystal of the synthetic todorokite consisted of fibers, grew at 120?angles to form trilling patterns, which morphology and growth characteristics were the same to those of naturally occurring todorokite. Its average composition was Mgo i6MnC>2.o7’0.82H2O, and surface area of 35.5 m2/g. The formation mechanisms of todorikite may be similar under hydrothermal and surficial conditions, it takes longer time to form todorokite in surficial environment than that at a relative high temperature in hydrothermal environment.4> Single phase and well-crystallized todorokite was synthesized by heating and refluxing process from birnessite as a precursor. The average chemical composition of the synthesized todorokites by refluxing for 8 h and for 24 h was Mgo.i9MnO2.n(H2O)i 15 and MgonMnCh io(H2O)o88, respectively. Their surface area was 103.9 and 98.5 m2/g. The crystallinity of the todorokite increased and no other phase was produced with increasing refluxing period. The synthesized todorokites had the same morphologies and the similar structural characteristics with the natural todorokites and hydrothermally synthesized samples. The chemical compositions of the synthetic tordorokites by refluxing process were close to those of todorokites synthesized by hydrothermal process, except a higher average oxidation state of Mn for the former. The synthetic todorokite had strong surface Lewis acidity and weak Bronsted acidity. It could keep thermally stable up to 400 癈, above the temperature, it would gradually decompose, release O2 and transformed to spine phase eventually.5 > D更多还原