六價鉻在土壤中的吸附特性及風(fēng)險評價研究
發(fā)布時間：2018-09-11 15:00
【摘要】：隨著重金屬污染的日益加劇，其對人類與動植物造成了巨大的危害。鉻作為環(huán)境中常見的重金屬，其危害性較強。鉻在土壤的存在形式主要為Cr(III)與Cr(VI)，其中Cr(III)毒性較小，在土壤中的遷移能力較差，而Cr(VI)的毒性較大，其可通過食物鏈進(jìn)入到動植物體內(nèi)，在環(huán)境中的生物降解性較差，并且具有一定的致癌能力。六價鉻在土壤中的遷移能力較強，其容易通過包氣帶進(jìn)入到地下環(huán)境中。因此，研究土壤對六價鉻的吸附性，并對其進(jìn)入地下水的風(fēng)險進(jìn)行評估，具有重大的意義。 本文通過靜態(tài)吸附實驗，研究了pH，有機質(zhì)，鐵鋁氧化物，六價鉻濃度，介質(zhì)粒徑對六價鉻吸附的影響。通過動力學(xué)與熱力學(xué)分析，對土壤吸附六價鉻的特性進(jìn)行了研究，闡明了土壤對六價鉻的吸附機理。并利用多元回歸分析研究了六價鉻分配系數(shù)（Kd）與各影響因素之間的關(guān)系，提出了六價鉻污染地下水的風(fēng)險評估模型并進(jìn)行風(fēng)險評價。本文的研究內(nèi)容和結(jié)論主要有： （1）不同鐵氧化物（針鐵礦、赤鐵礦、水鐵礦和磁鐵礦）、氧化鋁和腐殖酸均可對六價鉻的吸附產(chǎn)生影響，且影響規(guī)律相似，即均隨著pH的升高，各自吸附六價鉻的能力降低。通過測定各自的電荷零點（PZC）后，發(fā)現(xiàn)在2pHPZC時，能夠吸附六價鉻，而當(dāng)pHPZC時，基本不吸附六價鉻。說明當(dāng)2pHPZC時，土壤中上述物質(zhì)含量越高，六價鉻污染地下水的風(fēng)險就越低；實驗研究了不同pH、初始六價鉻濃度和介質(zhì)粒徑對土壤吸附六價鉻的影響，發(fā)現(xiàn)當(dāng)2pH8時，隨pH增加土壤吸附六價鉻的能力降低，六價鉻污染地下水的風(fēng)險增強。初始六價鉻濃度在10~100mg/L時，土壤對六價鉻的吸附量隨六價鉻濃度的增大而增加，當(dāng)六價鉻濃度大于100mg/L時，隨六價鉻初始濃度的增大，土壤對六價鉻的吸附量不再增加，說明隨六價鉻濃度的升高，可能會增加其對地下水污染的風(fēng)險。隨介質(zhì)粒徑的增大，其對六價鉻的吸附能力減弱，導(dǎo)致六價鉻污染地下水的風(fēng)險升高；通過動力學(xué)與熱力學(xué)分析了土壤對六價鉻的吸附特性。由動力學(xué)分析結(jié)果可知，土壤對六價鉻的吸附滿足擬二級動力學(xué)方程，說明六價鉻吸附未達(dá)到平衡時，其Kd較小對地下水的污染風(fēng)險較高。由熱力學(xué)分析結(jié)果可知，，土壤對六價鉻的吸附能夠自發(fā)進(jìn)行（△G00），且為吸熱反應(yīng)（△H00），即溫度升高，土壤對六價鉻的吸附能力增加，六價鉻污染地下水的風(fēng)險降低；本文闡述了土壤吸附六價鉻陰離子的兩種機制，即專性吸附與非專性吸附，最終實驗確定了土壤對六價鉻的吸附主要為專性吸附（化學(xué)吸附），當(dāng)六價鉻存在形態(tài)為HCrO4-時，對地下水的污染風(fēng)險低。 （2）利用SPSS軟件進(jìn)行多元逐步回歸分析，以pH、六價鉻濃度、土壤有機質(zhì)含量、氧化鐵含量、氧化鋁含量、粘粒含量為自變量，六價鉻分配系數(shù)（Kd）為因變量，進(jìn)行回歸擬合后得到的回歸方程為Kd=2.082+0.007C-0.204pH，R2=0.927，說明六價鉻的吸附分配系數(shù)主要與六價鉻濃度和pH條件有關(guān)。建立了六價鉻對地下水污染風(fēng)險的評估模型并進(jìn)行風(fēng)險評價，將六價鉻對地下水的污染分為從輕微到極強的五種不同風(fēng)險程度。
[Abstract]:As a common heavy metal in the environment, chromium is more harmful. The main forms of chromium in the soil are Cr (III) and Cr (VI), of which Cr (III) is less toxic, its migration ability in the soil is poor, and Cr (VI) is more toxic, which can be passed through food. Hexavalent chromium has a strong migration ability in the soil, and it is easy to enter the underground environment through aeration. Therefore, it is of great significance to study the adsorption of hexavalent chromium in the soil and evaluate the risk of its entry into groundwater. Righteousness.
In this paper, the effects of pH, organic matter, Fe-Al oxides, hexavalent chromium concentration and medium size on the adsorption of hexavalent chromium were studied by static adsorption experiments. The adsorption characteristics of hexavalent chromium in soils were studied by kinetic and thermodynamic analysis, and the adsorption mechanism of hexavalent chromium in soils was clarified. In this paper, a risk assessment model for groundwater contaminated by hexavalent chromium is proposed and the risk assessment is carried out.
(1) Different iron oxides (goethite, hematite, hydrous iron and magnetite), alumina and humic acid all have similar effects on the adsorption of hexavalent chromium, that is, their ability to adsorb hexavalent chromium decreases with the increase of pH. HPZC does not absorb hexavalent chromium basically. It shows that the higher the above-mentioned substance content in soil is, the lower the risk of hexavalent chromium contamination in groundwater is. The effects of different pH, initial hexavalent chromium concentration and medium size on the adsorption of hexavalent chromium by soil are studied experimentally. The risk of groundwater contamination increases. When the initial hexavalent chromium concentration is 10-100mg/L, the adsorption capacity of hexavalent chromium increases with the increase of hexavalent chromium concentration. When the hexavalent chromium concentration is higher than 100mg/L, the adsorption capacity of hexavalent chromium does not increase with the increase of the initial hexavalent chromium concentration. The risk of hexavalent chromium contamination in groundwater is analyzed by kinetics and thermodynamics. The results show that the adsorption of hexavalent chromium satisfies the quasi-second-order kinetic equation. The results of thermodynamic analysis show that the adsorption of hexavalent chromium can be spontaneously carried out (G00), and is an endothermic reaction (H00), that is, the adsorption capacity of hexavalent chromium increases with the increase of temperature, and the risk of hexavalent chromium contaminating groundwater decreases. In this paper, two mechanisms of adsorption of hexavalent chromium anion by soils, i.e. specific adsorption and non-specific adsorption, are described. Finally, it is determined that the adsorption of hexavalent chromium by soils is mainly specific adsorption (chemical adsorption). When hexavalent chromium exists in HCrO4-form, the risk of groundwater pollution is low.
(2) Multiple stepwise regression analysis was carried out with SPSS software. pH, hexavalent chromium concentration, soil organic matter content, ferric oxide content, alumina content, clay content as independent variables, and hexavalent chromium partition coefficient (Kd) as dependent variables. The regression equation was Kd=2.082+0.007C-0.204pH, R2=0.927, indicating the adsorption and distribution of hexavalent chromium. The coefficient is mainly related to the concentration of hexavalent chromium and pH condition.The risk assessment model of hexavalent chromium to groundwater pollution is established and the risk assessment is carried out.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：X53;X825
本文編號：2237032
[Abstract]:As a common heavy metal in the environment, chromium is more harmful. The main forms of chromium in the soil are Cr (III) and Cr (VI), of which Cr (III) is less toxic, its migration ability in the soil is poor, and Cr (VI) is more toxic, which can be passed through food. Hexavalent chromium has a strong migration ability in the soil, and it is easy to enter the underground environment through aeration. Therefore, it is of great significance to study the adsorption of hexavalent chromium in the soil and evaluate the risk of its entry into groundwater. Righteousness.
In this paper, the effects of pH, organic matter, Fe-Al oxides, hexavalent chromium concentration and medium size on the adsorption of hexavalent chromium were studied by static adsorption experiments. The adsorption characteristics of hexavalent chromium in soils were studied by kinetic and thermodynamic analysis, and the adsorption mechanism of hexavalent chromium in soils was clarified. In this paper, a risk assessment model for groundwater contaminated by hexavalent chromium is proposed and the risk assessment is carried out.
(1) Different iron oxides (goethite, hematite, hydrous iron and magnetite), alumina and humic acid all have similar effects on the adsorption of hexavalent chromium, that is, their ability to adsorb hexavalent chromium decreases with the increase of pH. HPZC does not absorb hexavalent chromium basically. It shows that the higher the above-mentioned substance content in soil is, the lower the risk of hexavalent chromium contamination in groundwater is. The effects of different pH, initial hexavalent chromium concentration and medium size on the adsorption of hexavalent chromium by soil are studied experimentally. The risk of groundwater contamination increases. When the initial hexavalent chromium concentration is 10-100mg/L, the adsorption capacity of hexavalent chromium increases with the increase of hexavalent chromium concentration. When the hexavalent chromium concentration is higher than 100mg/L, the adsorption capacity of hexavalent chromium does not increase with the increase of the initial hexavalent chromium concentration. The risk of hexavalent chromium contamination in groundwater is analyzed by kinetics and thermodynamics. The results show that the adsorption of hexavalent chromium satisfies the quasi-second-order kinetic equation. The results of thermodynamic analysis show that the adsorption of hexavalent chromium can be spontaneously carried out (G00), and is an endothermic reaction (H00), that is, the adsorption capacity of hexavalent chromium increases with the increase of temperature, and the risk of hexavalent chromium contaminating groundwater decreases. In this paper, two mechanisms of adsorption of hexavalent chromium anion by soils, i.e. specific adsorption and non-specific adsorption, are described. Finally, it is determined that the adsorption of hexavalent chromium by soils is mainly specific adsorption (chemical adsorption). When hexavalent chromium exists in HCrO4-form, the risk of groundwater pollution is low.
(2) Multiple stepwise regression analysis was carried out with SPSS software. pH, hexavalent chromium concentration, soil organic matter content, ferric oxide content, alumina content, clay content as independent variables, and hexavalent chromium partition coefficient (Kd) as dependent variables. The regression equation was Kd=2.082+0.007C-0.204pH, R2=0.927, indicating the adsorption and distribution of hexavalent chromium. The coefficient is mainly related to the concentration of hexavalent chromium and pH condition.The risk assessment model of hexavalent chromium to groundwater pollution is established and the risk assessment is carried out.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：X53;X825
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