【摘要】：近年來,我國區(qū)域性耕地土壤污染尤其是重金屬污染日趨嚴重。與輕度重金屬污染農(nóng)田相比,中重度污染土壤的面積雖小,但生態(tài)風(fēng)險和食物鏈風(fēng)險極大。一方面,將降低作物產(chǎn)量和品質(zhì),造成作物重金屬含量嚴重超標,影響人體健康;另一方面,通過各種途徑遷移至周邊土壤和地下水,污染周邊環(huán)境。因而,對中、重度土壤重金屬污染的有效控制和安全修復(fù)是當(dāng)前土壤污染防治工作的重點之一。因此,本文以鎘、鉛污染農(nóng)田土壤為研究對象,采用土柱淋洗法研究了復(fù)合淋洗劑對Cd、Pb污染土壤中重金屬的去除效率以及淋洗廢水的凈化處理方法和影響因素。(1)通過振蕩淋洗方法確定了 FeCl_3和有機酸(檸檬酸、蘋果酸、酒石酸)復(fù)合淋洗的最適宜的濃度配比和淋洗條件,采用土柱淋洗法研究了復(fù)合淋洗劑對湖南株洲和南京棲霞Cd、Pb污染土壤淋洗效率和淋洗條件對重金屬去除效率的影響,以及淋洗后土壤中重金屬結(jié)合形態(tài)變化。結(jié)果表明:FeCl_3和有機酸濃度分別為10mmol·L~(-1)和20mmol·L~(-1)進行復(fù)合比較適宜;對于湖南株洲土,FeCl_3-檸檬酸和FeCl_3-蘋果酸復(fù)合淋洗劑用量為750 mL,淋洗液分1次添加;FeCl_3-酒石酸復(fù)合淋洗劑用量為600 mL,淋洗液分3次添加,污染土壤中Cd、Pb的去除率最高。對于南京棲霞土,FeCl_3-檸檬酸復(fù)合淋洗劑用量為600mL,淋洗液分3次添加;FeCl_3-蘋果酸和FeCl_3-酒石酸復(fù)合淋洗劑用量為450mL,淋洗液分3次添加,污染土壤中Cd、Pb的去除率最高。重金屬形態(tài)分析實驗結(jié)果表明,污染土壤中Cd的主要存在形態(tài)是可交換態(tài)、碳酸鹽結(jié)合態(tài)和鐵(錳)氧化態(tài),而鉛的主要形態(tài)是有機態(tài)和殘渣態(tài)。淋洗后,可交換態(tài)的Cd含量大幅下降,同時化學(xué)淋洗能改變重金屬的存在形態(tài),土壤中Pb向著可遷移形態(tài)轉(zhuǎn)化。(2)研究了生物質(zhì)炭對溶液中Cd~(2+)、Pb~(2+)的吸附特性以及生物質(zhì)炭投入量、初始pH值、吸附時間和共存離子的影響。設(shè)置溶液中Cd~(2+)濃度為10 mmol-L~(-1)時,生物質(zhì)炭投入量80 mg,初始pH 6.0,25℃下振蕩15 min,生物質(zhì)炭的吸附率為95.5%。設(shè)置溶液中Pb~(2+)濃度為100 mmol·L~(-1)時,生物質(zhì)炭投入量150 mg,廢水初始pH 6.0,25℃下振蕩40 min,生物質(zhì)炭的吸附率為96.8%。有機酸存在下重金屬吸附率均有不同程度的降低,但Cl-的存在對吸附效率基本無影響。不同溫度(15℃、25℃、35℃)下生物質(zhì)炭對Cd~(2+)、Pb~(2+)的吸附等溫線用Langmuir模型能夠更好地描述,且對重金屬的吸附是一個吸熱反應(yīng)。(3)對土柱淋洗廢水,采用堿性沉淀結(jié)合生物質(zhì)炭吸附的凈化處理方法,比較適宜的處理方案:25℃條件下,添加2%的雙氧水,調(diào)節(jié)溶液pH至12.2,沉淀分離后上清液調(diào)節(jié)pH 6.0,生物質(zhì)炭添加量為3.75 g ·L~(-1),淋洗廢水處理后Cd~(2+)、Pb~(2+)濃度分別為0.07mg·L~(-1)、0.20mg·L~(-1),達到了國家污水綜合排放標準(Cd0.1 mg·L~(-1),Pb1.0mg·L~(-1))。淋洗廢水回用實驗表明,添加加FeCl_3至5 mol·L~(-1),檸檬酸為10 mol·L~(-1)時,對湖南株洲土 Cd的淋洗率達到了峰值,為72.09%,此時 Pb 為 28.09%。
[Abstract]:In recent years, the soil pollution of the regional cultivated land in China, especially the heavy metal pollution, has become more and more serious. Compared with the mild heavy metal polluted farmland, the area of moderately to severely polluted soil is small, but the ecological risk and the food chain risk are great. in one aspect, that crop yield and the quality are reduced, the heavy metal content of the crop is seriously exceed, and the health of the human body is influenced; and on the other hand, the surrounding soil and the ground water are migrated through various ways, and the surrounding environment is polluted. Therefore, the effective control and safety repair of heavy metal pollution in middle and severe soil is one of the key points for the prevention and control of soil pollution. In this paper, the removal efficiency of heavy metals in the contaminated soil of Cd and Pb, as well as the purification and treatment methods and influencing factors of the leaching wastewater were studied by soil column leaching. (1) The optimum concentration of FeCl _ 3 and organic acid (citric acid, malic acid and tartaric acid) and the leaching conditions were determined by the method of shaking and leaching. The leaching method of soil column was used to study the effect of the compound leaching agent on the Cd of the Zhuzhou and Nanjing Qixia, Hunan. The effect of the leaching efficiency and the leaching conditions of the Pb-contaminated soil on the removal efficiency of the heavy metals and the change of the combination of the heavy metals in the soil after the leaching. The results show that the concentration of FeCl _ 3 and the organic acid is 10mmol 路 L ~ (-1) and 20mmol 路 L ~ (-1), and the dosage of FeCl _ 3-citric acid and FeCl _ 3-malic acid is 750 mL, the leaching solution is added once, and the dosage of FeCl _ 3-tartaric acid is 600 mL. The removal rate of Cd and Pb in the contaminated soil was the highest. For Nanjing Qixia soil, the dosage of FeCl _ 3-citric acid composite eluent is 600mL, and the leaching solution is added for 3 times; the dosage of FeCl _ 3-malic acid and FeCl _ 3-tartaric acid composite eluent is 450mL; the leaching solution is added in three times; and the removal rate of Cd and Pb in the contaminated soil is the highest. The results of the heavy metal morphology analysis show that the main forms of Cd in the contaminated soil are exchangeable, carbonate bound and iron (manganese) oxidation state, and the main form of the lead is the organic state and the residue state. After the leaching, the Cd content in the exchangeable state is greatly reduced, while the chemical leaching can change the existence form of the heavy metal, and the Pb in the soil is transformed to the migration form. (2) The adsorption characteristics of Cd ~ (2 +), Pb ~ (2 +) and the influence of biomass carbon input, initial pH, adsorption time and coexistent ion of biomass carbon on the solution were studied. When the concentration of Cd ~ (2 +) in the solution is 10 mmol-L ~ (-1), the amount of biomass charcoal is 80 mg, the initial pH is 6.0, the oscillation is at 25 鈩，

本文編號：2329159