铁盐混凝去除As（Ⅲ）和As（Ⅴ）及钛盐光催化氧化混凝去除As（Ⅲ）的机理研究

发布时间：2018-05-09 05:10

本文选题：砷 + 混凝　；参考：《西安建筑科技大学》2015年博士论文

【摘要】：世界上许多地区都存在地下水砷污染问题,长期使用砷含量超标的水会导致皮肤癌和各种内脏癌症,严重威胁人体健康。如何高效地去除污染水中的砷,是安全饮用水供给要解决的重要问题之一。天然水中的砷主要是无机的三价砷(As(Ⅲ))和五价砷(As(Ⅴ)),其中As(Ⅲ)比As(V)毒性更大,更难去除。本论文提出了一种新的以钛盐为混凝剂的紫外光催化氧化混凝方法。研究这种方法氧化及高效去除As(Ⅲ)的效能,并提出了硫酸钛紫外光催化混凝氧化As(Ⅲ)的机理。同时以铁盐为混凝剂,研究了铁盐水解初期沉淀物的粒径和Zeta电位对铁盐混凝-过滤去除As(Ⅲ)和As(V)的影响。研究结果表明,以硫酸钛为混凝剂的UVC (λ=254nm)紫外光催化氧化混凝(UVC/Ti(SO4)2混凝)可以在短时间内有效地将As(Ⅲ)氧化成As(V),并能在pH=4-6时高效地将其去除。As 3d XPS分析表明,pH=5时,在UVC/Ti(SO4)2混凝去除As(Ⅲ)时产生的沉淀物表面,84.7%的砷是以As(V)的形态存在的。UVC/Ti(SO4)2混凝过滤后,滤液中剩余的砷都是氧化态的As(V)。在pH=4-6, As(Ⅲ)初始浓度为200μg/L,混凝剂投量中等(10mg/L)时,UVC/Ti(SO4)2混凝-微滤几乎可以将As(Ⅲ)完全去除(99%)。由于As(Ⅲ)被氧化成As(Ⅴ), pH=5时,UVC/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率显著大于单独Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率,这种优势在混凝剂投量较低(2.5mg/L)时更明显。在As(Ⅲ)初始浓度为10～1000μg/L范围内,UVC/Ti(SO4)2混凝对As(Ⅲ)的去除率受As(Ⅲ)初始浓度的影响较小。pH=5时,硅酸盐对UVC/Ti(SO4)2混凝-微滤去除As(Ⅲ)的影响较小,磷酸盐对UVC/Ti(SO4)2混凝-微滤去除。As(Ⅲ)的影响较大,增加混凝剂投量可以减少硅酸盐和磷酸盐对As(Ⅲ)去除的影响。pH=7时,Ca2+和Mg2+通过压缩双电层作用明显降低了Ti(SO4)2水解沉淀物的负电位,从而减小了As(V)与Ti(SO4)2水解沉淀物之间的静电斥力,提高了UVC/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率。单独UVC紫外光对As(Ⅲ)的氧化效率较低(在反应21min后,仅为4.1%),由此表明UVC/Ti(SO4)2混凝对As(Ⅲ)的高效氧化不是由于紫外光的单独氧化作用。通过对UVC/Ti(SO4)2混凝去除As(Ⅲ)时产生的沉淀物的Ti 2p XPS能谱分析表明,As(Ⅲ)的氧化也不是由As(Ⅲ)不Ti(Ⅳ)之间的直接电子转移实现的。通过对羟基自由基捕获剂(TBA、MeOH)、空穴捕获剂(Ⅰ-)以及电子捕获剂(Cu2+)对UVC/Ti(SO4)2混凝氧化去除As(Ⅲ)的影响的研究,结果表明As(Ⅲ)的氧化机理主要包括羟基自由基(OH·)及过氧自由基(HO2·/O2·-)的作用。研究进一步表明,与UVC/Ti(SO4)2混凝类似,UVA/Ti(SO4)2混凝(λ=365nm)也是一种有效的As(Ⅲ)氧化去除方法。对UVA/Ti(SO4)2混凝去除As(Ⅲ)的研究结果表明,在pH=4-6, As(Ⅲ)初始浓度为200μg/L,混凝剂投量较低(5mg/L)时,UVA/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率大于96.1%,显著大于相同条件下单独Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率(68.7%)。pH=7～10时,UVA/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率下降。砷氧化态分析结果表明,UVA/Ti(SO4)2混凝-微滤后滤液中剩余的砷都是As(V)。在pH=8～10范围内,SO42-的存在降低了UVA/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率。F-的存在在pH=4～10范围内均使UVA/Ti(SO4)2混凝-微滤对As(Ⅲ)的去除率有所降低,降低程度在pH=4时最大。本论文同时也对铁盐水解初期沉淀物的粒径和Zeta电位对铁盐混凝-过滤去除As(Ⅲ)和As(V)的影响进行了系统的研究。结果表明,pH=5～10时,铁盐水解初期形成的沉淀物的颗粒粒径都在胶体范围内(4-755nm)opH小于7时,颗粒带正电,pH大于7时,颗粒带负电。由于在pH=5～10范围内As(Ⅲ)主要以不带电的中性分子形式存在,As(Ⅲ)与铁盐水解沉淀物之间不存在静电力的作用,铁盐水解沉淀物的Zeta电位对铁盐混凝-过滤去除As(Ⅲ)没有影响。而在pH=5～10范围内As(V)以带负电的氧化阴离子形式存在,As(V)与铁盐水解沉淀物之间的静电力作用对铁盐混凝-过滤去除As(V)影响较大。在铁盐水解沉淀物的Zeta电位为正(pH=5～7)时,As(V)与颗粒之间的静电引力促进As(V)在颗粒表面的吸附,As(V)的去除率达到最大。颗粒的负电位较大时(pH=8～10), As(Ⅴ)与颗粒之间的静电斥力阻碍As(V)的吸附,使As(V)的去除率明显下降。在本研究的pH范围内,含砷的铁盐水解沉淀物颗粒都可以被微滤和砂滤去除,颗粒粒径对铁盐混凝-过滤去除As(Ⅲ)和As(V)没有影响。pH=5～10时,增加一价电解质(NaCl)浓度或加入二价电解质(Ca(OH)2、 MgCl2)均会通过压缩双电层作用使FeCl3水解沉淀物的颗粒粒径显著增加。增加一价电解质浓度对FeCl3水解沉淀物的Zeta电位影响较小,而加入二价电解质显著减小了pH=8～10时FeCl3水解沉淀物的负电位。增加一价电解质浓度对FeCl3混凝-过滤去除As(Ⅲ)和As(Ⅴ)的影响较小。加入二价电解质对As(Ⅲ)的去除影响较小但明显增加了pH=8～10时As(Ⅴ)的去除率。加入HA时,FeCl3水解沉淀物的等电点由pH=7减小到pH=6。在pH=7～10时,HA的存在增加了FeCl3水解沉淀物的负电位。HA的存在使铁盐混凝-过滤去除As(Ⅲ)的效率在pH=5～10范围内均有所降低。在pH=5～8时,HA对As(Ⅴ)去除率的降低程度随着pH的升高而增大。混凝去除砷的两种机理-吸附和共沉淀-的相对重要性取决于溶液pH。
[Abstract]:In many parts of the world, there is a problem of arsenic pollution in groundwater. Long term use of water with excessive arsenic content can lead to skin cancer and various visceral cancers. It is a serious threat to human health. How to effectively remove arsenic in polluted water is one of the important problems to be solved in the supply of safe drinking water. The arsenic in natural water is mainly inorganic arsenic (As). (III)) and pentvalent arsenic (As (V)), of which As (III) is more toxic than As (V) and is more difficult to remove. A new method of UV photocatalytic oxidation with titanium salts as coagulant was proposed in this paper. The efficiency of oxidation and efficient removal of As (III) by this method was studied and the mechanism of coagulation oxidation of As (III) by UV photocatalytic oxidation of titanium sulfate was proposed. For coagulant, the effect of the particle size and Zeta potential on the removal of As (III) and As (V) by the coagulation filtration of iron salt at the initial stage of hydrolysis was studied. The results showed that the UVC (UVC/Ti (SO4) 2 coagulation) with titanium sulfate as the coagulant (UVC/Ti (SO4)) could effectively oxidize As (III) to As (V) in a short time and can be in pH=4. .As 3D XPS analysis at -6 showed that the precipitate surface produced by UVC/Ti (SO4) 2 coagulating As (III) when UVC/Ti (SO4) 2 was coagulated, and the arsenic in As (V) was filtered by As (V), and the remaining arsenic in the filtrate was oxidized. The initial concentration was 200 mu, and the dosage of coagulant was moderate (10). At mg/L), UVC/Ti (SO4) 2 coagulation microfiltration can almost completely remove As (99%). As As (III) is oxidized to As (V), pH=5, UVC/Ti (SO4) 2 coagulation microfiltration is significantly greater than single Ti (SO4) 2 coagulation microfiltration for the removal of (III). This advantage is more obvious when the coagulant dosage is low. In the range of 10~1000 mu g/L, when the removal rate of UVC/Ti (SO4) 2 coagulation on As (III) is less affected by the initial concentration of As (III), the effect of silicate on the removal of As (III) by UVC/Ti (SO4) 2 coagulation microfiltration is smaller, and the effect of phosphate on UVC/Ti (SO4) 2 coagulation microfiltration to remove.As (III) is greater, and the dosage of coagulant can be increased to reduce the silicate and to reduce the silicate. When phosphate affects the removal of As (III), Ca2+ and Mg2+ significantly reduce the negative potential of Ti (SO4) 2 hydrolysate by compressing the double layer effect, thus reducing the electrostatic repulsion between As (V) and Ti (SO4) 2 hydrolysate precipitates, and increasing the removal rate of UVC/Ti (SO4) 2 coagulation micro filtration. The rate is low (only 4.1% after reaction 21min), which indicates that the efficient oxidation of UVC/Ti (SO4) 2 coagulation to As (III) is not due to the separate oxidation of ultraviolet light. The Ti 2p XPS energy spectrum analysis of the precipitates produced by UVC/Ti (SO4) 2 coagulation removal of As (III) shows that the oxidation of As (III) is not a direct electron transfer between As (III)). The effect of hydroxyl radical trapping agent (TBA, MeOH), hole capture agent (I) and electron capture agent (Cu2+) on the removal of As (III) by UVC/Ti (SO4) 2 by coagulation oxidation of As (III) was studied. The results showed that the oxidation mechanism of As (III) was mainly composed of hydroxyl radical (OH) and peroxy free radicals (HO2 /O2.). C/Ti (SO4) 2 coagulation is similar, UVA/Ti (SO4) 2 coagulation ([lambda] =365nm) is also an effective As (III) oxidation removal method. The results of UVA/Ti (SO4) 2 coagulation removal of As (III) show that when pH=4-6, As (III) initial concentration is 200 micron, and when the dosage of coagulant is low, the removal rate of 2 coagulant microfiltration is greater than 96.1%, significantly greater than that of 96.1%. Under the same condition, the removal rate of As (III) by UVA/Ti (SO4) 2 coagulation microfiltration was reduced when the removal rate of As (SO4) 2 coagulation microfiltration (68.7%) was.PH=7 ~ 10, and the arsenic oxidation state analysis showed that the remaining arsenic in the filtrate after UVA/Ti (SO4) 2 coagulation and microfiltration was As (V). Within the range of pH=8 to 10, the existence of 2 coagulation micro (2) was reduced. The removal rate of the removal rate of As (III).F- in the range of pH=4 ~ 10 makes UVA/Ti (SO4) 2 coagulation microfiltration decrease the removal rate of As (III), and the degree of reduction is maximum in pH=4. This paper also systematically studies the effect of the particle size and Zeta potential on the removal of As (III) and As (V) by molten iron salt coagulation filtration at the initial stage of hydrolysis of iron salts. The results show that the particle size of the precipitate formed at the initial stage of hydrolysis of iron salt from pH=5 to 10 is all in the colloid range (4-755nm) opH less than 7, the particles are positive, and when pH is more than 7, the particle band is negative. Because As (III) is mainly in the neutral form in pH=5 to 10, there is no electrostatic between As (III) and the hydrolytic precipitate of iron salt. The Zeta potential of iron salt hydrolyzed precipitate has no effect on the removal of As (III) by iron salt coagulation filtration. In the range of pH=5 ~ 10, As (V) exists in the form of negative oxide anion, and the electrostatic force between As (V) and the hydrolyzed precipitate of iron salt has great influence on the removal of As (V) by iron salt coagulation filtration and removal of As (V) in the iron salt solution. When the potential is positive (pH=5 to 7), the electrostatic attraction between As (V) and particles promotes the adsorption of As (V) on the surface of particles, and the removal rate of As (V) is maximum. When the negative potential of the particles is larger (pH=8 to 10), the electrostatic repulsion between As (V) and particles hinders the absorption of As (V), and the removal rate of As is obviously decreased. Within the scope of this study, the iron containing arsenic is in the range of this study. The particles of saltwater precipitate can be removed by microfiltration and sand filtration. When the particle size is not affected by As (III) and As (V), the concentration of monovalent electrolyte (NaCl) or the addition of two valence electrolyte (Ca (OH) 2, MgCl2) will increase the particle size of the hydrolysate precipitate by pressing the double layer. The concentration of monovalent electrolyte has little effect on the Zeta potential of FeCl3 hydrolysate, while adding two valence electrolyte significantly reduces the negative potential of FeCl3 hydrolysate at pH=8 ~ 10. Increasing the concentration of monovalent electrolyte has little effect on the removal of As (III) and As (V) by FeCl3 coagulation filtration. The addition of two valence electrolytes has little effect on the removal of As (III). The removal rate of As (V) at pH=8 ~ 10 was obviously increased. When the isoelectric point of FeCl3 hydrolysate was reduced from pH=7 to pH=6. at pH=7 to 10, the existence of HA increased the existence of the negative potential.HA of the FeCl3 hydrolysate precipitate, which reduced the efficiency of the removal of As (III) in the range of pH=5 ~ 10. The removal rate decreases with the increase of pH. The two mechanism of arsenic removal by coagulation is the adsorption and co precipitation. The relative importance depends on the solution pH..

【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU991.2

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