有机碳和无机碳对改性天然菱铁矿除砷的影响及机理

发布时间：2018-03-22 10:45

  本文选题：除砷　切入点：间歇性处理　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：地下水中的砷(As)污染是全球关注的热点问题,高砷地下水中通常伴随有高浓度的有机碳和无机碳。改性粒状天然菱铁矿(MGNS)是一种特殊的Fe(II)/Fe(III)的混合体系,并且对于As(III)比As(V)具有更高的吸附能力。因此,研究有机碳和无机碳对MGNS的除砷影响及机理具有重要的理论和实际意义。利用三元系统(NOM-MGNS)-As和(NOM-As(V))-MGNS研究吸附态和溶解态NOM的对MGNS去除As的影响,结果发现吸附态和溶解态NOM对As(III)去除均无显著影响。对As(V)的去除抑制作用的顺序为(HA-MGNS)-As(V)(FA-MGNS)-As(V)(FA-As(V))-MGNS(HA-As(V))-MGNS,吸附态NOM比溶解态NOM对As(V)的抑制作用更强。使用阻排色谱法(SEC-HPLC)和电感耦合等离子体质谱(ICP-MS)与HPSEC-UV连用(SEC-UV-ICP-MS)探究NOM对MGNS去除As(V)的抑制机理。在(NOM-As(V))-MGNS体系中,溶解态FA和HA对于As(V)的去除抑制作用主要是通过竞争吸附,尽管形成大分子络合物会使得吸附速率变慢,但其聚沉对吸附量的影响并不大。而FA与As(V)之间的静电排斥作用更强,使得溶解态FA对As(V)吸附的抑制作用要强于溶解态HA。在(NOM-MGNS)-As(V)系统中,吸附在MGNS上的HA比FA更多,尽管FA与As(V)之间的静电排斥作用较强,但分子量更大的HA会占据更多的吸附点位,从而表现为吸附态HA对As(V)吸附有较强的抑制作用。其次,利用柱实验研究了pH、HCO_3~-以及间歇性处理对As(III)去除的影响,结果显示As(III)吸附量随着pH值的增加而降低,HCO_3~-会抑制MGNS对As(III)的吸附且抑制作用强于同等条件下pH的影响,间歇性处理会增强As(III)的去除率。通过对柱实验使用之后的MGNS进行As、Fe不同形态的提取,SEM和XRD的分析,发现pH、HCO_3~-以及间歇性处理均影响在除砷过程中铁矿物之间的转化(从菱铁矿转变为针铁矿),抑制转化过程会大大降低As(III)吸附,尤其是HCO_3~-通过抑制菱铁矿的溶解对这一矿物转化过程产生影响。此外,出水溶液中只发现As(V),在提取了柱实验使用之后的MGNS样品As形态分析,发现As(V)是固体上主要的As形态,并且在间歇性处理中可以观察到更多的As(III)被氧化成As(V),说明As(III)的氧化过程也是影响其去除的一个重要因素。通过对MGNS产生羟基自由基的监测,结果发现改性天然菱铁矿产生羟基自由基的量比天然菱铁矿明显增加,Cl~-、NO_3~-和SO_4~(2-)的存在对MGNS产生羟基自由基的影响非常微弱。而HCO_3~-明显抑制了MGNS产羟基自由基,当溶液中HCO_3~-的含量在大于50 mM时,MGNS产生羟基自由基的量已低于检出限。SiO_3~(2-)与PO_4~(3-)均对MGNS产生羟基自由基有影响,但相对于HCO_3~-来说较弱。Ca~(2+)/Mg~(2+)的存在会轻微促进MGNS产羟基自由基。综上,在MGNS吸附As(III)的过程中,HCO_3~-抑制菱铁矿的溶解,进而影响Fe(II)在水溶液中产生羟基自由基的过程,并且不利于菱铁矿转变为针铁矿。
[Abstract]:Arsenic As) pollution in groundwater is a hot issue of global concern. High arsenic groundwater is usually accompanied by high concentrations of organic and inorganic carbon. Modified granular natural siderite (MGNS) is a special mixed system of Feo II / FeIII. And it has higher adsorption capacity for ASN III than ASV). It is of great theoretical and practical significance to study the effect and mechanism of organic and inorganic carbon on the removal of arsenic from MGNS. The effects of adsorbed and dissolved NOM on the removal of as from MGNS are studied by using the ternary systems of NOM-MGNSI-As and NOM-As-VGNS. The results show that the adsorption state and the dissolved state NOM have no significant effect on the removal of AsN II, and the order of the inhibitory effect of the adsorption state and the dissolved state NOM on the ASV removal is as follows: (1) the order of the inhibitory effect of the adsorption state and the dissolved state NOM on the ASV removal is as follows: the order of the inhibitory effects of the adsorption state and the dissolved state NOM is FA-MGNSU, FA-AsVN, HA-AGNSU, and the adsorption state of NOM is stronger than that of the dissolved NOM on the inhibition of AsHV. The SEC-HPLCand inductance coupling of the adsorbed NOM have been used in this paper. The inhibition mechanism of NOM on MGNS removal by MGNS was investigated by ICP-MS and HPSEC-UV. The inhibitory effect of dissolved FA and HA on the removal of ASV was mainly through competitive adsorption. Although the adsorption rate was slowed down by the formation of macromolecular complexes, the effect of the accumulation of FA and HA on the adsorption capacity was not significant, but the electrostatic repulsion between FA and ASV) was stronger. In the system of NOM-MGNSS-As-V), there are more HA adsorbed on MGNS than on FA. Although the electrostatic repulsion between FA and AsV) is stronger, HA with larger molecular weight will occupy more adsorption sites. The results showed that the adsorbed HA had a strong inhibitory effect on the adsorption of ASV. Secondly, the effects of pH ~ (+) HCO3- and intermittent treatment on the removal of AS-III were studied by column experiments. The results showed that the adsorption capacity of AsHCO3- decreased with the increase of pH value, which inhibited the adsorption of AsHCO3- by MGNS and was stronger than that of pH under the same conditions. Intermittent treatment can enhance the removal rate of As-II I). The different forms of As-Fe extracted from MGNS were analyzed by SEM and XRD after the column was used in the experiment. It was found that pH = HCO3- and intermittent treatment both affected the transformation of iron minerals (from siderite to goethite) in the process of arsenic removal. In particular, HCO _ 3C _ (-) has an effect on the process of mineral transformation by inhibiting the dissolution of siderite. In addition, only Aso _ (V) is found in aqueous solution. After extracting the MGNS sample after the column experiment, it is found that as _ (()) is the main form of as on the solid. It is also observed that more ASI) are oxidized to ASV ~ (2 +) during intermittent treatment, which indicates that the oxidation process of AsHIII) is also an important factor affecting its removal. The hydroxyl radicals produced by MGNS are monitored. The results showed that the amount of hydroxyl radical produced by modified natural siderite was significantly higher than that of natural siderite. The effect of the existence of MGNS on the production of hydroxyl radical in MGNS was very weak. When the content of HCO3- in solution is more than 50 mm, the amount of hydroxyl radical produced by MGNS is lower than the detection limit. However, compared with HCO3-, the presence of weak 路Caan2 / Mg2) can slightly promote the production of hydroxyl radicals in MGNS. In summary, during the process of MGNS adsorption, HCO _ 3 inhibits the dissolution of siderite and thus affects the process of producing hydroxyl radicals in aqueous solution. It is not conducive to the conversion of siderite to goethite.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X523
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本文编号：1648312