燃煤电厂固体废弃物重金属渗滤特性研究

发布时间：2018-10-05 06:45

【摘要】：我国作为世界上最大的煤炭生产国和消费国,也是世界上唯一以煤炭资源为主的大国,并且这种能源结构在今后相当长的一段时间内不会发生改变。煤作为一种不清洁的能源,燃烧时所释放的重金属会长期存在于环境中,很难被降解,还会在生物体内不断蓄积。当前有关痕量重金属污染物排放问题已经成为燃烧污染中一个重要的研究方向,引发了越来越多的关注。因此,本文以燃煤电厂的固体废弃物(飞灰和脱硫石膏)为研究对象,首先测定了电厂固体废弃物(飞灰和脱硫石膏)中重金属的总量;然后在综合考虑了影响重金属渗滤特性因素后,研究了飞灰和脱硫石膏在不同pH值、液固比(L/S)和浸出时间这三个最为重要的因素下重金属的渗滤特性;最后利用场发射扫描电子显微镜(FESEM)、X射线衍射仪(XRD)、X光电子能谱(XPS)等先进仪器,研究了飞灰和脱硫石膏重金属渗滤机理。本文主要结论如下:(1) FA2、DG1、DG2 中的 As 以及 DG1 中的 Cd 的总量超过了 GB15618-1995的限定值,其中DG1中Cd的总量超过GB15618-1995限定值的3倍多,属于重度污染等级,并且飞灰和脱硫石膏中大部分重金属的含量都超过了国标中食品类的限定值,因此对于堆放电厂固体废弃物附近区域的土壤应当谨慎利用。(2)随着初始pH值的增加,飞灰和脱硫石膏中重金属的浸出量整体均呈现“U”型变化趋势。以FA1为例,在强酸环境初始pH=2时,FA1中As、Cr、Zn的浸出量达到最高,依次为0.72μg/g、1.39μg/g、0.51μg/g;而在强碱环境初始pH=12 时,FA1 中 As、Cr、Zn 的浸出量依次为 0.71μg/g、1.36μg/g、0.49μg/g,这说明样品中的重金属更容易在酸性环境下浸出;随着液固比的增加,飞灰和脱硫石膏中重金属的浸出量总体呈现上升的趋势。在液固比30时,样品中重金属的浸出率依然保持上升的趋势,这说明继续增加液固比,重金属的浸出量将进一步提高;利用Elovich方程对燃煤飞灰中As、Cr、Zn渗滤动力学数据进行拟合可以发现,FA1中Cr的渗滤速率最快,高达FA1中As、Zn渗滤速率的3倍之多,FA2中Cr的渗滤速率也表现出了类似的规律。(3)酸化飞灰的表面变得光滑,大量块状物质填充了其空隙,使空隙度明显减少且连通性降低,结构更为紧密,这样使重金属的浸出变得更加困难;酸洗飞灰中正长石(KAlSi3O8)比占要比原样飞灰高出9.1%,此外酸洗飞灰中还检测出了夕线石(Al2(SiO4)O),这可能是在酸性环境时飞灰中某种物质和H+发生了反应,因而夕线石的特征峰值变得更加明显;燃煤飞灰和脱硫石膏中的As3+在酸碱化过程中表现的比较稳定,As5+的相对含量在酸碱化过程中一直在减少,而以硫化物形态存在的相对含量总是呈现上升的趋势,因此可以推测酸碱化过程中以硫化物形态存在的As可能大部分由As5+转变而来。
[Abstract]:As the largest producer and consumer of coal in the world, China is also the only country with coal resources in the world, and this energy structure will not change for a long time in the future. As a kind of unclean energy, coal releases heavy metals in the environment for a long time, which is difficult to be degraded and accumulates in organisms. At present, the emission of trace heavy metal pollutants has become an important research direction in combustion pollution, which has attracted more and more attention. Therefore, taking the solid waste (fly ash and desulphurized gypsum) of coal-fired power plant as the research object, the total amount of heavy metals in the solid waste (fly ash and desulphurized gypsum) of power plant is first determined. After considering the factors affecting the percolation characteristics of heavy metals, the percolation characteristics of fly ash and desulphurized gypsum under different pH values, liquid-solid ratio (L / S) and leaching time were studied. Finally, the mechanism of heavy metal percolation in fly ash and desulphurized gypsum was studied by using advanced instruments such as field emission scanning electron microscope (FESEM) X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The main conclusions of this paper are as follows: (1) the total amount of As in FA2,DG1,DG2 and Cd in DG1 exceeds the limit value of GB15618-1995, and the total amount of Cd in DG1 is more than three times of the limit value of GB15618-1995, which belongs to the serious pollution grade. And most of the heavy metals in fly ash and desulphurized gypsum exceed the limited value of food in national standard, so the soil near the solid waste of power plant should be used carefully. (2) with the increase of initial pH value, The leaching amount of heavy metals in fly ash and desulphurized gypsum all showed a "U" type change trend. Taking FA1 as an example, the leaching amount of As,Cr,Zn in FA1 was the highest in the initial pH= _ 2 of strong acid environment, which was 0.72 渭 g / g ~ (1.39) 渭 g / g ~ (-1) 渭 g 路g ~ (-1) in turn, and 0.71 渭 g / g ~ (1.36) 渭 g / g ~ (0.49) 渭 g / g ~ (-1) of As,Cr,Zn in the initial pH=12 environment, which indicated that the heavy metals in the samples were easier to be leached in acidic environment. With the increase of liquid-solid ratio, the leaching amount of heavy metals in fly ash and desulphurized gypsum increased. When the liquid-solid ratio is 30, the leaching rate of heavy metals in the sample is still increasing, which indicates that the leaching rate of heavy metals will be further increased by increasing the liquid-solid ratio. Using Elovich equation to fit the data of As,Cr,Zn percolation kinetics in coal fly ash, it can be found that Cr in FA1 has the fastest percolation rate. The percolation rate of Cr in FA2 as much as three times that of As,Zn in FA1 showed a similar regularity. (3) the surface of acidified fly ash became smooth, and a large number of bulk materials filled its voids, which significantly reduced the porosity and decreased the connectivity. The structure is closer, which makes the leaching of heavy metals more difficult; The ratio of KAlSi3O8 in fly ash is 9.1 higher than that in the original fly ash. In addition, Al2 (SiO4) O),) has been detected in the fly ash. (Al2 (SiO4) O), which may be the reaction of some substance in fly ash and H in acid environment), Therefore, the characteristic peak value of sillimanite became more obvious, and the relative content of As3 in fly ash and desulphurized gypsum decreased in the process of acid-alkalification. However, the relative content of sulfides is always on the rise, so it can be inferred that the As that exists in the form of sulphide in the process of acid-alkalification may be transformed mostly by As5.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM621;X773

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