Cd、Pb重度污染农田土壤化学淋洗及淋洗污水处理的研究

发布时间：2018-11-13 12:51

【摘要】：近年来,我国区域性耕地土壤污染尤其是重金属污染日趋严重。与轻度重金属污染农田相比,中重度污染土壤的面积虽小,但生态风险和食物链风险极大。一方面,将降低作物产量和品质,造成作物重金属含量严重超标,影响人体健康;另一方面,通过各种途径迁移至周边土壤和地下水,污染周边环境。因而,对中、重度土壤重金属污染的有效控制和安全修复是当前土壤污染防治工作的重点之一。因此,本文以镉、铅污染农田土壤为研究对象,采用土柱淋洗法研究了复合淋洗剂对Cd、Pb污染土壤中重金属的去除效率以及淋洗废水的净化处理方法和影响因素。(1)通过振荡淋洗方法确定了 FeCl_3和有机酸(柠檬酸、苹果酸、酒石酸)复合淋洗的最适宜的浓度配比和淋洗条件,采用土柱淋洗法研究了复合淋洗剂对湖南株洲和南京栖霞Cd、Pb污染土壤淋洗效率和淋洗条件对重金属去除效率的影响,以及淋洗后土壤中重金属结合形态变化。结果表明:FeCl_3和有机酸浓度分别为10mmol·L~(-1)和20mmol·L~(-1)进行复合比较适宜;对于湖南株洲土,FeCl_3-柠檬酸和FeCl_3-苹果酸复合淋洗剂用量为750 mL,淋洗液分1次添加;FeCl_3-酒石酸复合淋洗剂用量为600 mL,淋洗液分3次添加,污染土壤中Cd、Pb的去除率最高。对于南京栖霞土,FeCl_3-柠檬酸复合淋洗剂用量为600mL,淋洗液分3次添加;FeCl_3-苹果酸和FeCl_3-酒石酸复合淋洗剂用量为450mL,淋洗液分3次添加,污染土壤中Cd、Pb的去除率最高。重金属形态分析实验结果表明,污染土壤中Cd的主要存在形态是可交换态、碳酸盐结合态和铁(锰)氧化态,而铅的主要形态是有机态和残渣态。淋洗后,可交换态的Cd含量大幅下降,同时化学淋洗能改变重金属的存在形态,土壤中Pb向着可迁移形态转化。(2)研究了生物质炭对溶液中Cd~(2+)、Pb~(2+)的吸附特性以及生物质炭投入量、初始pH值、吸附时间和共存离子的影响。设置溶液中Cd~(2+)浓度为10 mmol-L~(-1)时,生物质炭投入量80 mg,初始pH 6.0,25℃下振荡15 min,生物质炭的吸附率为95.5%。设置溶液中Pb~(2+)浓度为100 mmol·L~(-1)时,生物质炭投入量150 mg,废水初始pH 6.0,25℃下振荡40 min,生物质炭的吸附率为96.8%。有机酸存在下重金属吸附率均有不同程度的降低,但Cl-的存在对吸附效率基本无影响。不同温度(15℃、25℃、35℃)下生物质炭对Cd~(2+)、Pb~(2+)的吸附等温线用Langmuir模型能够更好地描述,且对重金属的吸附是一个吸热反应。(3)对土柱淋洗废水,采用碱性沉淀结合生物质炭吸附的净化处理方法,比较适宜的处理方案:25℃条件下,添加2%的双氧水,调节溶液pH至12.2,沉淀分离后上清液调节pH 6.0,生物质炭添加量为3.75 g ·L~(-1),淋洗废水处理后Cd~(2+)、Pb~(2+)浓度分别为0.07mg·L~(-1)、0.20mg·L~(-1),达到了国家污水综合排放标准(Cd0.1 mg·L~(-1),Pb1.0mg·L~(-1))。淋洗废水回用实验表明,添加加FeCl_3至5 mol·L~(-1),柠檬酸为10 mol·L~(-1)时,对湖南株洲土 Cd的淋洗率达到了峰值,为72.09%,此时 Pb 为 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，

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