【作者】 廖岳华；

【导师】 周立祥；

【作者基本信息】 南京农业大学 ， 生态学， 2008， 博士

【摘要】 近十多年来,起源于生物湿法冶金的生物沥浸（Bioleaching）技术被成功应用于城市污泥中有毒重金属的脱除。氧化亚铁硫杆菌（Acidithiobacillus ferrooxidans）和氧化硫硫杆菌（Acidithiobacillus thiooxidans）是生物沥浸中最为重要的两个微生物菌种。但在有氧化亚铁硫杆菌参与的污泥生物沥浸处理中,很多学者观察到铬溶出效率较低,铜的溶出与平均水力停留时间也并不呈显著相关关系。还有一些研究者发现污泥中铬和铁的生物沥浸远远不及化学浸提法的效率高,城市污泥中生物沥浸出来的铜还有随沥浸时间延长而再次减少的现象。有学者猜测该体系中形成了次生铁矿物—氢氧化铁和黄铁矾,并推测是由于这些次生铁矿物的吸附作用,导致了上述重金属生物沥浸效率不高。最近几年来,本课题组对制革污泥生物沥浸及溶出铬的回收开展了一系列卓有成效的研究。在利用以氧化亚铁硫杆菌菌株Acidithiobacillus ferrooxidans LX5和氧化硫硫杆菌Acidithiobacillus thiooxidans TS6为主的复合菌群进行制革污泥生物沥浸中试规模实验中,本文首次从制革污泥生物沥浸体系分离出次生铁矿物,并鉴定出这些铁矿物并非由以往许多学者所猜测的氢氧化铁和黄铁矾所组成,而是单一的次生羟基硫酸高铁矿物—施氏矿物（schwertmannite）。受污泥生物沥浸过程生成大量施氏矿物现象的启发,本研究模拟污泥生物沥浸反应条件,利用分离纯化的Acidithiobacillus ferrooxidans LX5菌株氧化FeSO₄溶液进行了施氏矿物的生物合成实验,优化了合成反应条件。并对生物成因施氏矿物的稳定性或相变规律进行了探讨。最后,本文重点研究了生物合成的施氏矿物对模拟地下水环境中As（Ⅲ）的去除效果及去除机理。主要研究结果如下:将pH约为3的制革污泥生物沥浸滤液(富含水溶性有机物和Fe²⁺、Cr³⁺、SO₄^2-及氧化亚铁硫杆菌)置于28℃、180rpm摇床中培养40 h,即有大量赭黄色沉淀生成。沉淀物经X-射线衍射（XRD）和傅立叶转换红外光谱（FT-IR）技术鉴定为纯施氏矿物。扫描电镜（SEM）及X—射线能谱（EDS）分析表明该施氏矿物为直径1μm的球形颗粒,其化学组成可表示为Fe₈O₈（OH）_4.60（SO₄）_1.70,且矿物从污泥沥浸液中吸持了含量高达2.43%、已从污泥中沥浸溶出的三价铬。与氧化亚铁硫杆菌促进形成的矿山酸性废水及其影响下的水体或沉积物环境中多形成施氏矿物-黄铁矾-针铁矿-水铁矿等次生矿物共生体不同的是,污泥生物沥浸体系中仅仅形成唯一一种次生铁矿物—施氏矿物,其中原因应归结于污泥中高浓度的水溶性有机物（＞300mg C/L）、较短的反应时间（～40 h）及低pH、高含量SO₄^2-的存在。利用氧化亚铁硫杆菌氧化FeSO₄溶液可简便、大量地合成纯施氏矿物。最优化的反应条件是:加入的细菌密度为1×10⁷cells/mL,起始Fe²⁺（以FeSO₄·7H₂O为铁源）浓度为8-12g/L,起始pH 3.2左右（不滴加任何酸碱溶液）,在28℃、180rpm摇床中反应48-60 h。合成产物为直径约2μm、表面无明显毛刺的球状施氏矿物,其化学组成为Fe₈O₈（OH）_4.42（SO₄）_1.79。合成反应中铁的沉淀率为37.43%。将生物成因施氏矿物及吸附了As（Ⅲ）的施氏矿物按质量浓度为1g/L加入到去离子水中,以稀氢氧化钠调节矿物悬浮液pH为6.0或8.5,置于恒温恒湿培养箱中并定期振荡考察了矿物的稳定性或矿相变化情况。结果表明,生物成因施氏矿物及吸附了As（Ⅲ）的施氏矿物较文献报道的利用化学方法合成施氏矿物或矿山环境中自然形成的施氏矿物更为稳定,在pH 6和pH 8.5的环境中90天内其矿相均未发生任何变化。采用序批式吸附试验研究了施氏矿物对As（Ⅲ）的去除效果及去除机理。结果表明:施氏矿物对As（Ⅲ）有很强的吸附能力,且吸附速度快,在60min内即可达到平衡吸附容量的95%,施氏矿物对As（Ⅲ）的吸附去除过程符合Lagergren拟二级速率方程。在pH 7-10时,施氏矿物对As（Ⅲ）有最大吸附;溶液离子强度和竞争阴离子如Cl^-、NO₃^-及一定浓度的SO₄^2-（＜0.01M）和PO₄^3-（＜0.001M）对除砷效果基本无影响。采用Langmuir吸附等温线能很好地描述施氏矿物吸附As（Ⅲ）的过程（R²＞0.99）,室温下饱和吸附容量达113.9mg/g;As（Ⅲ）在施氏矿物上的吸附能自发进行,该过程吸热,但温度变化对吸附容量影响并不显著。吸附As（Ⅲ）后,施氏矿物的PH_pzc由5.4下降为4.3。红外光谱分析结果表明As（Ⅲ）与施氏矿物表面的羟基发生了直接的表面络合。As（Ⅲ）在施氏矿物上的吸附属于专性吸附,形成内层络合物,吸附机理包括As（Ⅲ）与矿物表面金属羟基的表面络合、As（Ⅲ）与矿物表面及隧道结构内SO₄^2-的配位体交换作用。全文研究表明,污泥生物沥浸过程仅形成矿相单一的次生矿物—施氏矿物。模拟污泥生物沥浸反应条件,利用氧化氧化亚铁硫杆菌和硫酸亚铁能大量、简易地合成施氏矿物。该生物成因施氏矿物稳定性高,对As（Ⅲ）的专性吸附是通过表面络合和配位体交换作用实现的。作为一种优质吸附材料,施氏矿物在砷污染地下水的深度净化上可发挥重要作用。更多还原

【Abstract】 During the last decade,the bioleaching technique,originated from biohydrometallurgy industry for extracting rare metals from sulfide minerals,has been successfully applied in municipal sludge treatment for removal of toxic heavy metals and proved to be an efficient and cost-effective alternative to physical or chemical technologies.Acidithiobacillus ferrooxidans（A.ferrooxidans） and Acidithiobacillus thiooxidans（A.thiooxidans） have been employed as the most significant microorganisms involved in bioleaching processes. However,it was observed that Cr could not be effectively solubilized and Cu solubilization was weakly correlated to mean hydraulic residence time in sewage sludge bioleaching experiments with inoculation of Acidithiobacillus ferrooxidans.Some researchers also reported that the bioleaching efficiencies of Cr and/or Fe were much lower than corresponding values in the chemical leaching process,and even that the solubilized Cu from sludge decreased again if the bioleaching time prolonged in the medium with pH ranged from 2 to 3.Some researchers hypothesized that secondary iron minerals including iron hydroxide and jarosite likely formed in sludge during bioleaching process,and that the adsorption of heavy metals on these secondary iron minerals resulted in the above-mentioned lower solubilization efficiencies.In recent years,the application of bioleaching approach in tannery sludge treatment in terms of the removal or recovery of Cr, a dominant toxic metal in tannery sludge,has been studied extensively by our research group.In the present work,the secondary iron mineral was separated for the first time from bioleached tannery sludge when sludge bioleaching experiments were performed in an air-lift bioreactor mainly by Acidithiobacillus ferrooxidans LX5 and Acidithiobacillus thiooxidans TS6 at pilot scale.The secondary iron mineral was identified to be a sole secondary hydroxyl iron sulfate mineral—schwertmannite,but not a mixture of ferric hydroxide and jarosite as hypothesized in earlier studies.Enlightened by the formation of schwertmannite in sludge during bioleaching in the bioreactor,synthesis of schwertmannite through oxidation of FeSO₄ by Acidithiobacillus ferrooxidans strains（i.e.A.ferrooxidans LX5） was studied systematically and the synthesis conditions were optimized.Furthermore, the stability or phase transformation of the biogenic schwertmannite was investigated. Moreover,the removal of As（Ⅲ） in aqueous medium by schwertmannite was studied extensively.The main results were presented as follows:The bioleached tannery sludge filtrate with pH～3 was rich in dissolved organic matter （DOM）,Fe²⁺,Cr³⁺,SO₄^2- and A.ferrooxidans LX5.A large amount of ocherous precipitate was formed in the filtrate within 40 h during the sludge filtrate was incubated in a gyratory shaker at 28℃and 180rpm.The ocherous precipitate was identified as pure schwertmannite by X-ray diffraction（XRD） and Fourier transform infrared（FT-IR） spectroscopy.Results of scanning electron microscopy（SEM） and energy-dispersive X-ray spectroscopy（EDS） analysis showed that the schwertmannite particles were spheroids of uniform size with a diameter of approximately 1μm and their chemical composition could be expressed as Fe₈O₈（OH）_4.60（SO₄）_1.70,but Cr（Ⅲ） that had already solubilized from sludge by bioleaching incorporated into schwertmannite was about 2.43% by weight.It has well been accepted that the generation of acid mine drainage（AMD） is closely linked to the effects of Acidithiobacillus ferrooxidans and a schwertmannite-jarosite-goethite mineral paragenesis always occurs in AMD and waters or sediments impacted by AMD.However,there is only a sole secondary iron mineral（i.e. schwertmannite） formed in sludge bioleaching system.The presence of schwertmannite as monominerallic phase in sludge bioleaching environment should be predominantly attributed to extremely high content of DOM（＞300 mg C/L）,short reaction time（＜40 h）, high sulfate concentration（～9000 mg/L） and low pH value in this system.Biosynthesis of pure schwertmannite with a large quantity could be easily achieved through oxidation of FeSO₄ solution mediated by A.ferrooxidans LX5 resting cells.The yield of schwertmannite was affected mainly by bacterial density,the starting pH of reaction solution and reaction time,etc.The optimized reaction conditions were:1×10⁷cells/mL of bacterial density,8-12 g/L of the initial concentration of Fe²⁺（added as FeSO₄·7H₂O）,about 3.2 of the starting pH（without addition of any acid or base solution） was incubated in gyratory shaker at 28℃and 180rpm for 48-60 hours.The biosynthesized product was spherical schwertmannite of uniform size with a diameter of about 2μm, having no obvious characteristic pin-cushion morphology,and its chemical composition could be expressed as Fe₈O₈（OH）_4.42（SO₄）_1.79.The precipitation rate of iron in the course of synthesis reaction was 37.43%. The stability and phase transformation of the biogenic schwertmannite and As（Ⅲ）-containing schwertmannite were investigated in the present work.The synthetic schwertmannite suspension（1 g/L of mass concentration） was allowed to stand at 25℃in a incubator with occasional shaking.The solids sampled from the schwertmannite suspension were analyzed for mineralogical composition.Experimental results showed that the biogenic schwertmannite and As（Ⅲ）-containing schwertmannite were more stable than those synthesized by chemical method or naturally formed in acid mine drainage,as indicating that no any phase transformation occurred at pH 6 and pH 8.5 environments over a period of 90 days.Batch adsorption experiments were conducted to explore the adsorption process and related mechanism of As（Ⅲ） from aqueous solution on synthetic biogenic schwertmannite. Results indicated that biogenic schwertmannite has a strong adsorption for As（Ⅲ） and the adsorption capacity attained to almost 95%of equilibrium capacity within the first 60 minutes.The adsorption kinetic data could be described by the Lagergren pseudo-second order rate equation.Arsenite elimination was favored at pH=7-10.The changes of solution ionic strength（0.0001-0.1M） and the normally presented anions in natural environment had no obvious side effect on arsenite removal efficiency by schwertmannite except for phosphate（＞0.001M） and sulfate with a concentration of above 0.01M.Adsorption isotherm data for As（Ⅲ） was found to fit well to Langmuir isotherm equation（R²＞0.99） with a maximum adsorption capacities of 114 mg/g at room temperature.The adsorption of arsenite on schwertmannite could be achieved spontaneously and it was a endothermic process,but temperature changes within experiment range had no significant impact on the adsorption capacity.The pH_pzc（pH of the point of zero charge） for schwertmannite was found to be initially 5.4,but when As（Ⅲ） was adsorbed,it decreased from this value to about 4.3.Moreover,FT-IR analysis results suggested that direct surface complexation between surface OH groups and As（Ⅲ） occurred.It was concluded that As（Ⅲ） was specially adsorbed onto schwertmannite by an inner-sphere mechanism through surface complexing action between surface hydroxyl and As（Ⅲ） and by ligand exchange between SO₄^2- and As（Ⅲ）.It was concluded that synthesis biogenic schwertmannite with large quantity could be easily achieved through oxidation of FeSO₄ by A.ferrooxidans LX5 simulating the sludge bioleaching reaction conditions.Arsenite in aqueous solution can be specifically adsorbed onto the biogenic schwertmannite.It was indicated that biogenic schwertmannite,as a potentially excellent adsorbent,would play an important role in treatment of arsenic-contaminated groundwater in terms of arsenite removal.更多还原