CAS OpenIR
臭氧氧化结合三价铁沉淀法除砷新技术研究
NASANTOGTOKH OTGON
Subtype博士
Thesis Advisor张广积
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword砷,臭氧,臭葱石,钠黄铁矾,水铁矿
Abstract

砷是一种剧毒元素,长期接触无机砷会导致癌症等严重疾病。砷天然存在于贱金属和贵金属矿物中,并且经常出现在固体或液体冶金工业废物中。由于砷的提取缺乏经济效益,将其转化为体量较小且性质稳定的固体废弃物进行填埋被认为是一个比较理想的处理方式。只有当砷以五价,砷才能被最有效地去除并形成稳定产物。因此需要将砷(III)氧化成砷(V)。由于铁对砷有很高的亲和力,所以通常用于除砷和固定。但在大多数情况下,砷铁共沉淀与石灰中和同时发生,形成的无定形氢氧化物污泥体积大、含水量高,不适于填埋。本博士研究的总体目标是设计一种去除和固定砷的工艺,形成一种容易处理的晶体沉淀产物。此方法包括在酸性溶液中使用臭氧将三价砷氧化为五价砷和一个两段提升pH形成沉淀的过程。 首先是在0.5-2的pH范围内,用臭氧将三价砷氧化成五价砷。间歇实验结果表明,在酸性溶液中,臭氧氧化可使三价砷迅速转化为五价砷。在pH 为0.5和20°C条件下,溶液中的三价砷浓度在120分钟内从5g/L降至0.0001 g/L以下。研究发现,臭氧活性在高温下被抑制,但会被Fe3+催化。在90°C时,在没有Fe3+的情况下,几乎没有三价砷As被氧化成五价。然而,在pH 为2时,在Fe3+的存在下,初始浓度为5 g/L的三价砷溶液中有97.2%的三价砷在2小时内被氧化为五价。 在两阶段砷沉淀过程中,实验结果表明,在pH值为2的条件下,用空气氧化亚铁,可以通过形成结晶态的臭葱石有效地从砷浓度为5g/L的溶液中去除砷。当pH值被进一步提高到3或4并使用铁砷摩尔比为2、3和4的溶液时, 由于形成的无定型水铁矿对砷的吸附作用,几乎所有残留的砷都被从溶液中去除。TCLP标准溶出毒性试验结果表明,在这些条件下产生的复合沉淀物(铁砷比为4,最终pH为3或4之间)非常稳定,使用乙酸缓冲液(pH4.93±0.05)在72小时的试验中,未检测到有砷被浸出。扫描电镜-能谱分析结果也表明,在pH 为2的第一阶段沉淀中,形成了结晶态的臭葱石,此后提高pH到 3或4,形成的无定型含砷水铁矿会沉积在臭葱石颗粒表面。实验结果表明高铁砷比是必要的,产生的过量的铁可以提升产物的稳定性。 在某些情况下,废水中含有砷和三价铁离子,这些三价铁离子会形成无定形的砷酸铁来干扰结晶。在本研究中,我们尝试使用我们先前提出的方法来处理含砷金矿生物氧化过程中产生的废水。废水中砷含量为1.6g/L,三价铁含量为25g/L。结果表明,在两段沉淀过程中,当pH值从2提高到3时,砷去除率为99.96%, 当pH值从2提高到4时, 砷去除率为99.99%。扫描电镜分析结果表明,沉淀物主要为晶体颗粒,但有部分无定型产物沉积在晶体颗粒上。XRD分析表明,晶体为黄钠铁矾,而不是臭葱石。用这些沉淀物进行TCLP试验,同样未检出有砷的浸出。;Arsenic (As) is an acutely toxic element and chronic exposure to inorganic arsenic causes severe illness such as cancer. It naturally occurs with base and precious metal minerals and is commonly encountered in the solid or aqueous metallurgical industrial wastes. For extraction of As is not profitable, it is thought that is an ideal process which converts this element into a compact and inert residue for landfill. Arsenic is most effectively removed and stabilized when it is present in the pentavalent arsenate form, so usually the oxidation of As(III) into As(V) is required.Normally iron is used for arsenic removal and fixation due to its high affinity to arsenic. But in most cases the As-Fe co-precipitation occurred together with the neutralization with lime and the formed As-bearing amorphous iron oxyhydroxides sludge has a large volume and high water content, which is unsuitable for landfill. Thus, the overall aim of this Ph.D. research was to devise a process for removal and fixation of arsenic by forming a crystal precipitate which can be disposed easily. This process consists of the oxidation of As(III) to As(V) using ozone in acidic solution and a two-stage enhancement of pH for precipitation. The oxidation of As(III) into As(V) with ozone was carried out at pH range of 0.5-2. The batch experiment results showed that the As(III) can be converted to As(V) by ozone oxidation in acidic solution rapidly. At pH 0.5 and 20 °C, the concentration of As(III) in the solution decreased from 5 g/L to less than 0.0001 g/L in 120 minutes. It was found that the ozone oxidation was inhibited at elevated temperature but catalyzed by Fe3+. However, in presence of Fe3+, 97.2% of 5 g/L As(III) was oxidized at pH 2 in 2 hours. During two-stage arsenic precipitation process, the experimental results showed that arsenic can be removed effectively from a solution with the arsenic concentration of 5 g/L by forming crystalline scorodite through oxidizing ferrous with air at a pH of 2. While the pH value improved to 3 or 4, it found that almost all the residual arsenic was removed from the solution due to the adsorption of the amorphous ferrihydrite when the molar ratio of Fe/As 2, 3 and 4 was applied respectively. The results of the TCLP tests showed that the complex precipitates generated under these conditions (Fe/As ratio of 4, final pH 3 or 5) were very stable, and no leached arsenic detected using acetic acid buffer solution (pH 4.93±0.05) in test period of 72 h. SEM-EDS results showed that the crystalline scorodite was formed at pH 2 in the first stage of 4 hours, and then the arsenical ferrihydrite (AsFH) deposited on the surface of scorodite particles when pH enhanced from 2 to 3 or 4. Experimental results suggest that a high Fe/As ratio was necessary, so that the excess iron promotes the formation a product of good stability.In some cases, the wastewater contained arsenic together with the ferric ions, which could interfere with the crystallization by forming amorphous ferric arsenate. In this research, we attempt to dispose the wastewater produced in biooxidation of arsenic-bearing gold ore using our proposed method earlier. In this wastewater, there was 1.6 g/L arsenic and 25 g/L ferric contained. It was found that in the two-stage precipitation process, 99.96% of arsenic was removed when pH was improved from 2 to 3 and 99.99% when the pH increased from 2 to 4. The SEM results showed that the majority of the precipitate was crystalline grains but there was some amorphous product deposited on these grains. XRD pattern showed that the crystalline grains were natrojarosite instead of crystalline scorodite. There was no leached arsenic detected in the TCLP tests with these precipitate. 

Language英语
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40680
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
NASANTOGTOKH OTGON. 臭氧氧化结合三价铁沉淀法除砷新技术研究[D]. 中国科学院大学,2019.
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