Research On Adsorption Separation Processes Of Arsenic And Several Heavy Metal Ions In Slight-polluted Drinking Water Sources

Aiming at the recent development trend of remediation technologies for water sources contaminated with slight pollution of heavy metals, this dissertation has put forward three remediation schemes based on the situation of Shanghai water resource. These three schemes include Weak base anion exchange resin remediation technique, iron & manganese mineral remediation technique, and loaded adsorbent remediation technique. Adopting modern analytical and test technologies, that included FTIR、 SEM、XRD and so on, the optimized conditions and possible mechanisms of the separation processes of heavy metals were investigated for these technologies. Under the support of Key Project of Ministry of Science and Technology, the purpose of this paper is to provide technical and theoretical suggestions and support for the efficient remediation of water sources with slight heavy metals pollution, it will also be benefit for dealing with the emergency affairs of heavy metal pollution in water sources.This paper consists of four parts. （ I） Mobility and release of several heavy metals and arsenic between the sediment and the water （II） Study on the separation of several heavy metals and arsenic in the slight-polluted water by Weak base anion exchange resin （III） Study on the adsorption of several heavy metals and arsenic by mineral material such as α -FeO（OH）、β -FeO（OH） and δ -MnO₂ （IV） Study on the adsorption of several heavy metals and arsenic by loaded adsorbents such as R-MnC>2 and RFM.（ I ） In the first part of the dissertation, the background investigation was carried out to know the content of heavy metals in the overlaying water and surface layer sediments from Shanghai drinking water sources. Then BCR sequential extraction method was employed to analyze the distribution characteristics of heavy metals including Cr, Cu, Pb, Zn, Cd, Co and Ni in the sediments. The obtained experimental results showed :① The contents of heavy metals from overlaying water were not beyond the domestic drinking water standard, they can meet the second class water quality for surface water.② According to the data of heavy metals in sediments: The heavy metals pollution at the discharge location and their adjacent areas were more serious than other locations. The heavy metals pollution at the port area was very serious. The heavy metals pollution at the downriver area was more serious than that of upriver area. ③The distribution state of heavy metals in Huangpu river made it clear that the Huangpu river was contaminated by heavy metals when it flows from upriver area Dianfeng to downriver area Wusongkou, and the increased concentration of heavy metals was mainly caused by acid soluble fraction, which may endanger the total environment.Subsequently, the Huangpu river was selected for further study, the adsorption dynamics of heavy metals and Arsenic release between the sediment and the surface water was investigated. The following conclusions were given out from the experimental results.The surface sediments have strong affinity capacity for heavy metals such as Cu, Pb, Zn, Cd, and As. The affinitiy sequence was Pb＞Cu＞Zn≈Cd＞As（Ⅴ）. The affinity capacity was increasing with the extension of reaction time. The extent of heterogeneous of sorption sites was high.The increase of the vibration and the temperature could facilitate the discharge of As（Ⅴ） from the sediment. With the increase or the decrease of pH, the discharge amount of As（Ⅴ） will increase, and at the range of pH 5, the discharge amount was the lowest. The presence of PO₄^3- HCO₃^- could affect the discharge process greatly, and the discharge amount of As（Ⅴ） increased with the increment of PO₄^3- or HCO₃^- concentrations.（Ⅱ） In the second part of this paper, through the comparative investigation among the styrene resin, acrylic acid resin and epoxide resin, we selected Weak base anion exchange resin 331 as adsorbent to study the adsorption behaviors of Cu（Ⅱ）, Cd（Ⅱ）, and Cr（Ⅵ） on it respectively. Furthermore, with weak base anion exchange resin 331, batch systems were investigated through simulating the actual polluted water in which Cu²⁺, Cd²⁺, Cr（Ⅵ） were co-existed in aqueous solution. At last, elementary study on the adsorption of the Arsenic（Ⅴ） were also carried out. The experimental results showed:①Weak base anion-exchange resin is capable of selectively removing heavy metals from high concentrations of co-existed alkaline and alkaline earth metals through complexing action.②The maximum amounts of metals adsorbed by weak base anion exchange resin 331were 44.58, 84.03 and 77.52 mg/g for Cd²⁺, Cu²⁺, and Cr（Ⅵ） respectively. For the removal process of Cu² and Cd²⁺, it based on the complexing action. For Cr（Ⅵ）, the removal was associated with the ion-exchange and compexing action, and the rate for ion exchange was faster than that for complexing action.③The adsorption behaviors of heavy metals onto 331 weak base anion-exchange resin were strongly influenced by the presence of competing ions in the solution. When Cr（Ⅵ） is co-existing with other heavy metals, the weak base anion-exchange resin had a preferred adsorption of Cr（Ⅵ）, which led to the fewer adsorption for other heavy metal ions. Hence, if the weak base anion-exchange resin is applied to treat the heavy metals like Cu²⁺, Ni²⁺, Co²⁺, Pb²⁺, Mn²⁺, Cd²⁺ and so on, the competitive adsorption of Cr（Ⅵ） (CrO₄^2- and HCrO₄^-) must be considered.④the presence of SO₄^2- caused the interference in the removal of As（Ⅴ） by weak base anion-exchange resin 331.（Ⅲ） In the third part of this paper,α-FeOOH,β-FeOOH （goethite and lepidocrote） andδ-MnO₂ were synthesized for the further research. Batch experiments of adsorption were conducted to study the removal efficiency of heavy metals and arsenic from aqueous solutions. The behaviors and the possible mechanisms for As（Ⅴ） removal were discussed. The results showed:①Cr（Ⅵ） can be efficiently removed byα- FeO（OH） andβ- FeO（OH） within the natural water source pH range. The adsorption process follows Langmuir and Freundlich isotherm models, the maximal capacity were 50.25mg/g and 42.02mg/g, respectively. The adsorption capacity of Cr（Ⅵ） decreased with the increment of ion strength, the existence of HCO₃^- or H₂PO₄^- decreased the adsorption capacity by about 20%.②As（Ⅴ） can be efficiently removed byα- FeO（OH） andβ- FeO（OH）, the optimal pH range were pH 5～6.5 and pH 3.5～7, respectively. The maximal adsorption capacities were 5.05 mg/g and 23.42 mg/g respectively.③δ-MnO₂ synthesized by four different methods had the capacity to reduce the contents of Zn, Pb, Cd, Ni, Cu, Co in water solution to meet the drinking water quality standard when the initial heavy metal concentration was 1mg/L. Four types ofδ-MnO₂ had the different adsorption kinetics and capacities, which might result from the different micro-surface structures.④The sequence of adsorption capacity wasδ-MnO₂ （KMnO₄+MnSO₄）＞δ-MnO2 （KMnO₄+MnCl₂）＞δ-MnO₂ （KMnO₄+ HCl）＞δ-MnO₂ ( KMnO₄ +Mn（NO₃）₂. The adsorption kinetics for As（Ⅴ） were similar, the results meant that chemical reaction might be the principal control procedure and the it could be described by pseudo-second order rate equation. （Ⅳ） In the last part, loaded absorbent R-MnO₂ and RFM was synthesized by loading manganese （hydr）oxides and/or iron （hydr）oxides on weak basic anion exchange resin D301. Batch experiments of adsorption were conducted to study the removal of heavy metals and Arsenic from aqueous solutions.①The loaded adsorbent R-MnO₂ showed a high capacity for the removal of trace amount of heavy metals such as Cu²⁺, Co²⁺ Zn²⁺ and Ni²⁺ with the coexistence of high concentration of alkali and alkaline-earth metal ions at the wide range of pH 3-8. The maximum removal capacity was 78.13, 63.69, 129.87, 67.11 and 54.64mg/g for Zn²⁺, Cd²⁺, Cu²⁺, Co²⁺ and Ni²⁺ respectively. The sequence of adsorption capacity was Cu²⁺＞Zn²⁺, Cd²⁺, Co²⁺＞Ni²⁺. With 0.05mol/L HNO₃, R-MnO₂ could be regenerated to the efficiency of 80%. The IR and XRD analysis results indicated that the metal oxide loaded on the D301 resin was the mixture ofδ-MnO₂ and MnO（OH）. The high removal efficiency of heavy metals on R-MnO₂ was mainly due to the specific adsorption via surface hydroxide complexation reaction.②The loaded adsorbent R-MnO₂ can be used as an efficient adsorbent for the removal of As（Ⅴ） from aqueous solution at pH=2. In the case of water samples contaminated by low As（Ⅴ） concentration, the removal rate can reach almost 100%. Arsenic adsorption by R-MnO₂ decreased with the increase of ion strength, the presence of PO₄^3- or HCO₃^- inhibited the arsenic adsorption. The adsorption process followed pseudo second-order kinetics. The arsenic removal was supposed as the common results of specified adsorption, non-specified adsorption, precipitation and co-precipitation.③The loaded adsorbent RFM can be used as an efficient absorbent for the removal of As（Ⅴ） from aqueous solution in a wide pH range 4-9. In the case of water solution contaminated with low As（Ⅴ） concentration, the removal rate can reach almost 100%. Arsenic adsorption by RFM decreased with the increment of ion strength, the presence of PO₄^3-, HCO₃^- inhibited the arsenic adsorption process. The IR analysis results indicate that the surface of RFM has rich hydroxyl groups. The arsenic removal was supposed as the common results of electrostatic adsorption and ligand exchange reactions, and the ligand exchange reactions are the main sorption mode.