【作者】 赵玲；

【导师】 朱南文；

【作者基本信息】 上海交通大学 ， 环境工程， 2008， 博士

【摘要】 人类对于干电池的大量使用带来了严重的环境污染与资源浪费问题,尽管目前无毒害环保型电池代替旧的含有危险重金属电池的条件日趋成熟,但已经回收的和尚在使用中的各种危险电池如含汞电池、镍镉电池等仍未得到妥善处理。而现有的火法冶金、湿法冶金等回收处理技术又存在能耗高、潜在污染较大等缺陷。为寻求一种高效、经济、环境友好的废旧干电池处理方法,本论文基于生物湿法冶金原理,提出了生物沥滤法处理废旧干电池,即利用污泥中的土著硫杆菌为菌种来源和培养基的主要组成,添加基质,进行生物制酸,制酸产物用于沥滤电池中的重金属。该方法能同时使污泥中含有的重金属得到高效去除,污泥达到农用标准。生物法处理废旧干电池是近年来提出的新思路,目前相关研究很少,利用污泥沥滤作用处理废旧干电池则未见报道。论文以废旧镍镉电池作为研究对象,首先通过XRD、热重分析、ICP-MS等手段对其化学和物理特性进行研究。结果表明,废旧镍镉电池中存在的相有金属Ni0、Ni(OH)2、γ-NiOOH、Cd与Cd(OH)2以及电解液KOH成分。阴极材料中Ni元素含量为41.7%,Co元素含量为5.1%,阳极粉末Cd元素含量为64.8%。阳极材料Cd(OH)2含量约为62.2%,阴极材料Ni(OH)2(包括少部分Co(OH)2)的含量约为57.7%。采用城市污水厂污泥制取酸化培养物,同时其自身重金属得到滤出。在20～25g L-1污泥固体浓度范围内,金属Cd、Mn、Cu、Zn、Mg和Al的滤除效率高达98～100%,Ca和Cr也分别达到90%和76.36%。Pb的去除率最低,20～50%。所制得的生物酸液与0.2mol L-1的硫酸(化学酸)在同条件下浸取电池阴阳极材料。结果表明对于易溶态物质金属Cd,生物酸与硫酸沥滤效果相当。对于难溶态金属相,则生物酸效果较好。且小试试验同时发现电池电极材料中含有一部分不溶于强酸的残留物。为实现连续制酸和废旧镍镉电池的连续生物沥滤,本研究建立了一套连续运行二阶段批处理工艺。即污泥连续进入酸化池中,制酸产物经过沉淀处理后,上清液流入沥滤池,电池电极材料中含有的重金属在沥滤池中被沥滤溶出。工艺运行参数优化试验表明:酸化池污泥停留时间SRT为4d最适,酸化池pH可稳定在1.86以下,硫杆菌数量为2.8×107 cfu mL-1;沥滤池水力停留时间HRT则选择1～3d较为合适;沥滤池中pH从初始的5.0可在30～40d的沥滤过程中降至与入流液相同;HRT为1d时,Ni、Cd、Co三种金属的完全滤出需要的时间分别为25, 18和30d;三种金属的沥滤行为不同,Cd与Co在开始6、7d内pH为3.0～4.5时即大部分被滤出,而金属Ni的沥滤分为2个阶段,在第6d与第15d时分别达到沥滤高峰,对应pH值分别为3.0～4.0和2.5左右,前者为Ni的氢氧化物的溶解,后者为金属态Ni的溶出;硫酸亚铁(FeSO4?7H2O)作为基质时,终pH(2.0～2.3)不如单质硫(S0)作为基质(<1.0)低,但所产酸液具有一定的抗碱性冲击能力;对于电极材料的处理负荷,在进酸液量1L d-1的条件下完全滤出8节电池中的Ni、Cd、Co需30～40d。本工艺中,微生物的生长活性和酸化效率是提高电池沥滤效率的关键因素。为探讨微生物生长制酸的最佳工艺条件,论文通过摇床试验对污泥酸化的影响因子进行了研究。结果表明:嗜酸性硫杆菌具有广泛的环境适应性,初沉泥、二沉泥和混合浓缩污泥三种污泥在适当条件下均可达到良好的酸化效果,在12d内pH降至1.0左右;基质的添加量应与污泥固体浓度结合考虑,通常污泥生物沥滤较适合浓度为20～25g L-1,相应S0添加量选取1～1.5%(w/v),FeSO4?7H2O添加量选择4～6g L-1。论文同时对污泥混合物与纯培养硫杆菌在不同条件下的酸化效果进行了对比。结果表明:初始pH高达10.0时,污泥中硫杆菌仍可经历7d的停滞期后开始生长,而硫杆菌在纯培养基中的生长则被完全抑制;高温(50℃)、低温(10、20℃)条件下,污泥均比纯培养基有更高的pH降低和SO42-产生速率;提高硫颗粒的分散程度以及生物细胞附着程度可大大缩短纯培养基中硫杆菌生长停滞期;有机碳源葡萄糖添加使pH在前2d内由中性下降至3.0～3.5,但此过程中无硫被氧化;葡萄糖添加量为300mmol L-1以上时,污泥酸化完全停止,几乎无SO42-的产生,添加量100mmol L-1以下时,污泥酸化不受影响,纯培养基中则受到50%的抑制;对于小分子酸和氯化物及硝酸盐,硫杆菌在污泥中耐受浓度比纯培养基中高2倍左右。对酸化池与沥滤池中所涉及到的化学、生物机理进行分析。GC-MS方法从酸化污泥中只检测到个别长链和带苯环结构的有机酸,未检测到短链的有机酸。沥滤池中尽管重金属浓度较高,但仍有大量活性硫杆菌。其中HRT为6d时硫杆菌数量最高,达6.2×106 cfu mL-1。从中分离了一株可使pH快速下降的硫杆菌株,经16S rDNA系统发育分析,自分离的菌株与Acidithiobacillus ferrooxidans strain Tf-49在系统发育地位上几乎相同,相似性达到100.0%,判断其为一株氧化亚铁硫杆菌。重金属沥滤液的回收采用沉淀法制取复合铁氧体。通过优化工艺条件,经沉淀后的上清液金属离子浓度完全可以达标排放,形成的铁氧体粗制品具有一定的磁性。本研究中经优化后条件如下:最适pH范围为11～11.5,Fe与Cd投料比为Fe/Cd=16(摩尔比),30%H2O2加入量为0.3%(v/v),温度常温或略微加热即可。更多还原

【Abstract】 The vast use of batteries by human now leads to severe environmental problems and resource waste. Although people are trying to find nontoxic substitute to replace the batteries containing hazardous heavy metals, the already reclaimed batteries and many still in use ones such as Hg-containing batteries and Ni-Cd batteries have not been well disposed. The existing treatment methods are mainly pyrometallurgical and hydrometallurgical processes which have some limitations including high energy-consuming and secondary pollution, etc. In order to seek an effective, economical and environmentally friendly method to treat spent batteries, this paper introduced a biohydrometallurgical method which combined the sludge metal bioleaching and batteries treatment. The indigenous acidophilic thiobacilli in sewage sludge can grow and produce bio-sulphuric acid through the addition of energy source and the acid was used to leach the heavy metals in spent batteries. The metals in sludge were removed simultaneously to satisfy land application.The paper studied the chemical and physical characterization of spent Ni-Cd batteries through XRD, TGA and ICP-MS, etc. The results showed that the presence of diffraction lines corresponding to metallic nickel (Nio), Ni(OH)2 andγ-NiOOH in the cathode, and metallic cadmium (Cdo), Cd(OH)2 in the anode as well as some KOH. The content of Ni and Co in cathode was 41.7% and 5.1% respectively. The content of Cd in anode was 64.8%. The estimated Cd(OH)2 accounted for 62.2% in anode and Ni(OH)2 binding with minor Co(OH)2 accounted for 57.7% in cathode.The biological acid culture was obtained through the acidification of sewage sludge. The metals in sludge were leached simultaneously with microbial production of sulphuric acid. At the sludge solid concentration of 20～25g L-1, the solubilization efficiency of Cd, Mn, Cu, Zn, Mg, and Al was highest at 98～100%, and that of Ca was higher at about 90%, Cr 76.36%. As for Pb, the solubilization efficiency was lowest at 20～50%.The battery electrode materials were leached using the biological acid and ordinary 0.2mol L-1 H2SO4 respectively under the same conditions. The results showed that as for the dissoluble metal Cd, the leaching efficiency by biological acid and chemical acid was similar. But for the acid-insoluble materials, the biological acid seems better. Moreover, the flasks test showed that there are some residues are very difficult to dissolve even in strong acid.A continuous flow two-step batch leaching system consisting of an acidifying reactor and a leaching reactor was set up to achieve the continuous acid production and bioleaching of batteries. The acid supernatant produced in the acidifying reactor by the microorganisms was conducted into the leaching reactor to dissolve electrode materials.The optimizing test of process parameters showed that the optimum sludge retention time (SRT) in acidifying reactor was 4d and hydraulic retention time (HRT) in leaching reactor was 1～3d. The pH in acidifying reactor was below 1.86 and the population of thiobacilli was 2.8×10-7cfu mL-1. The pH in leaching reactor decreased from the initial 5.0 to equal to influent during the 30～40d leaching. The complete leaching of Ni, Cd and Co cost about 25, 18 and 30d respectively with HRT=1d. The leaching behavior of the metals Ni, Cd and Co was different. Cd and Co can be leached mostly in the begin 6 or 7d with pH 3.0～4.5. The leaching of Ni showed two stages. The maximum dissolution of Ni reached at the 6th day and the 15th day with the pH 3.0～4.0 and 2.5 respectively. The former was the dissolution of Ni(OH)2 and the latter was the dissolution of metallic Ni. When FeSO4·7H2O was the substrate, it was difficult to decrease the final pH to lower than 2.2, while with substrate S0 the final pH was below 1.0. But the iron-oxidizing system has a stronger buffering capacity of pH than the sulphur-oxidizing system. As for the process load, the complete leaching of metals Ni, Cd and Co in 8 spent Ni-Cd batteries required 30～40d with 1L d-1 acid.In this process, the activity of microorganisms and acidification rate were the key to increase metals leaching efficiency. Factors affecting the sludge acidification rate were studied through flasks experiments and the results showed that acidophilic thiobacilli have wide adaptability of environment and the favourable acidification can be obtained under appropriate conditions in each kind of sludge including primary settling tank sludge, secondary sedimentation tank sludge and mixed sludge. The amount of substrate addition depended on the sludge solid concentration. In general, the moderate sludge solid concentration for bioleaching was 20～25g L-1 and the corresponding S0 or FeSO4·7H2O addition was 1～1.5% (w/v) or 4～6g L-1 respectively. The growth lag phase was affected by surface area of sulfur particles and attachment of microorganisms.Comparison of acid production by sulfur-oxidizing bacteria in sewage sludge and pure culture was conducted. The results showed that sludge has a better ability to acclimatize itself to the change of ambient environment than a pure culture. The more disadvantageous the ambient environment is to the sulfur-oxidizing bacteria, the more obvious advantage of the sludge than pure culture. Even though the initial pH was 10.0, the sulfur-oxidizing bacteria began to grow after 7d lag phase while in pure culture it was inhibited completely. At low (10, 20℃) and high (50℃) temperature, the rate of pH decrease and SO42- production was higher in sludge than in pure culture. The addition of glucose made pH reduce from neutral pH to pH 3.0～3.5 in the first 2d but no sulfur was oxidized. The sludge acidification stopped and almost no SO42- produced when glucose addition was 300mmol L-1. But when it was 100mmol L-1, there was no effect on sludge and 50% inhibition on pure culture. The tolerance concentration of small molecules acids, chloride and nitrate was double in sludge than pure culture.The chemical and biological mechanisms involved in the acidifying reactor and the leaching reactor were analyzed. Only some benzene ring containing and long chain organic acids are found and short carbon chain ones can not be found from acidified sludge by GC-MS. It can be observed from the scaning electron microscopy of acidified sludge that the thiobacillus in it attached on the impurities. In the leaching reactor, there are great populations of live thiobacillus although the heavy metals concentration was high. When the HRT was 6d, the amount of thiobacillus was 6.2×106 cfu mL-1. Meanwhile, a strain accounting for the fast reduction of pH in the leaching reactor was isolated and sequenced. It was identified to be 100% similar to Acidithiobacillus ferrooxidans strain Tf-49 based on 16S rDNA sequence analysis. The relevant phylogenetic tree constructed indicates that the strain should be classified into genus Acidithiobacillus ferrooxidans.The recovery of heavy metals solution was achieved by producing ferrite through coprecipitation. The conditions were optimized and the results showed that under the conditions of normal or little higher temperature, pH=11～11.5, Fe/Cd (mol/mol)=16, 0.3% (v/v) of H2O2 (30%) added, the ferrite product had a preferable magnetism and the heavy metals concentration in effluent could be decreased to below the drainage standard.更多还原