镉污染土壤原位修复剂及其机理研究

【作者】 王立群；

【导师】 华珞； 马义兵；

【作者基本信息】 首都师范大学 ， 自然地理学， 2009， 博士

【摘要】 随着农药和化肥施用量的不断增加,工矿废弃污染物排放的日益加剧,含重金属的污染物通过各种途径进入土壤,造成土壤严重污染,导致农作物产量和质量的下降,并通过食物链危害人类的健康。目前,我国Cd污染农田目前已超过1.3×104 hm2,涉及11个省市的25个地区,因此对土壤Cd污染治理已成为当务之急。本文以富含巯基的新鲜植物残体、变性粘土、矿渣、工业废渣(纳米级)、有机物料(巯基化)等为基质对21种重金属钝化制剂进行了研究筛选,利用室内模拟培养和植物盆栽试验研究重金属钝化剂的效果和作用机制,并比较了不同生产工艺赤泥对土壤Cd的钝化效果。利用元素的拮抗原理,研究ZnSO4叶面喷施和拌种处理对土壤中Cd的单一及复合阻抗钝化效果。通过钝化剂作用下土壤性质的变化、土壤中各形态Cd转化以及对溶液Cd离子中Cd离子吸附解吸特性的研究,进一步探讨了钝化剂的作用机制。本论文得到的主要结论如下:以土壤中可交换态Cd含量为指标,研究了羟基磷灰石(HA)、磷矿粉(PRX和PRH)、沸石、赤泥、新鲜植物残体、玉米秸秆粉末以及相应的处理共21种钝化剂的作用效果,结果表明:与空白相比,纳米化赤泥、羟基磷灰石、纳米化酸洗赤泥可使土中可交换态Cd减少比例达35%~55%,赤泥、酸洗赤泥、沸石可达15%~25%。富含巯基植物残体在土壤中可有效的与Cd离子螯合,降低可交换态Cd的含量。新鲜蒜苗、油菜、大葱植物残体效果相近,可达20%~25%。PRX、PRH、大葱粉末、相对较差。秸秆和巯基化秸秆钝化效果在8周以上时间段表现较好。通过温室盆栽试验研究了钝化剂作用的生物效应,结果表明:与空白相比,赤泥、沸石、玉米秸秆和鲜蒜苗残体的加入对黄瓜生物量也有明显提高。赤泥类物质可使黄瓜植株内Cd的含量降低20.4%～60.2%,赤泥的纳米化处理明显提高了赤泥的钝化效果。沸石分别使植株内Cd的含量减少11.7%～48.0%,新鲜蒜苗残体钝化效果达到20.1%～59.4%。添加玉米秸秆可使黄瓜植株内Cd的含量减少20.3%～36.0%,巯基化秸秆使植株内Cd的含量减低20%～50%。随着各种钝化剂施入量的不断增加,黄瓜对Cd的富集系数呈明显减少的趋势。通过钝化剂对土壤性质与土壤中各形态Cd含量的变化分析研究,结果表明:与空白相比,钝化剂的添加都显著减小了土壤可交换态Cd的含量;赤泥类钝化剂主要作用机制为升高pH值,增大易还原锰结合态、EDTA可提取态、碳酸盐结合态和Fe、Al氧化态Cd含量;沸石的添加主要是增大土壤CEC值和EDTA可提取态、碳酸盐结合态以及残渣态Cd含量;添加玉米秸秆、巯基化玉米秸秆和新鲜蒜苗残体后的栽培土壤中,有机质含量和CEC值增大, EDTA可提取态、有机结合态和残渣态Cd的含量增大是其钝化作用的主要机制。通过第二季盆栽试验,比较了钝化剂效果的时间效应,其结果表明:第二季盆栽黄瓜植株的干重均高于第一季盆栽试验,添加钝化剂对植株干重的增大作用明显。在第二季盆栽中,各钝化剂作用下黄瓜植株中Cd的含量与空白相比显著减小。赤泥类物质的钝化效果好于第一季栽培,不同添加量秸秆类物质钝化效果的时间效应存在差异,沸石钝化效果的时间效应不明显,新鲜蒜苗残体表现为第二季好于第一季,且添加量变化对其影响较小。利用元素间拮抗作用原理,研究了ZnSO4阻抗剂对土壤Cd的钝化效应,结果表明:与空白相比,叶面喷施ZnSO4溶液阻抗剂可使植株中Cd的含量减小20.7%～32.5%;ZnSO4溶液拌种处理的钝化效果为20.3%～37.2%。在钝化、阻抗复合试验中,叶面喷施也对Cd吸收表现出了一定的抑制效果,但作用率小于土壤钝化剂施加,为10%左右。ZnSO4叶面喷施,增大了植物对Zn的吸收,而ZnSO4溶液拌种处理,植株中的Zn含量并未明显增大。利用盆栽试验,比较了不同生产工艺产生赤泥的钝化效果,其结果表明:各种施用量处理下,拜耳法工艺产生的赤泥其钝化效果要明显好于烧结法赤泥;其主要原因为拜耳法赤泥颗粒粒径小、表面积大以及氧化铁、铝含量高。通过钝化剂对溶液中Cd离子的吸附解吸试验表明:赤泥、沸石对Cd离子具有很大的吸附容量和较强的吸附亲和力;只有不到25%的吸附镉为水溶态和可交换态,而绝大部分吸附的镉(50%以上)为与赤泥结合稳定的、不易为生物利用的形态。纳米粉碎能显著提高赤泥对镉的吸附能力,并提高吸附产物的稳定性,焙烧处理也提高了沸石对镉的吸附容量。玉米秸秆粉末、巯基化处理秸秆粉末以及新鲜蒜苗残体都显示出对Cd2+较高的吸附容量,都高于土壤对镉的吸附容量,其中蒜苗残体最大,巯基秸秆次之。与土壤相比,沸石、焙烧沸石和新鲜蒜苗残体吸附的镉中,被解吸为水溶态和可交换态吸收态组分比例显著减小,但其对Cd的吸附固定结合效果均小于赤泥类物质。赤泥类物质、沸石、秸秆和蒜苗残体对Cd的吸附符合Langmuir和Freundlich模式方程,Langmuir方程拟合相关性好于Freundlich方程。赤泥对Cd的吸附等温线受背景K+离子浓度变化明显,表明吸附可能存在外层和专性两种作用。利用吸附动力学试验,研究了不同钝化剂对Cd离子吸附随时间变化的规律,其结果表明:不同钝化剂、不同的初始溶液浓度下对Cd离子的吸附过程基本上可分为两个阶段,即快速反应阶段和慢速反应阶段。赤泥类物质吸附速率较大,达到平衡时间较短,纳米化处理明显提高了赤泥的吸附速率,缩短平衡时间;沸石吸附Cd2+达到平衡时间较长,可能与其内部通道作用有关。对钝化剂吸附Cd离子的动力学曲线拟合较好的为准二级动力学方程和指数Ⅱ型方程,拟合参数基本上反映了不同的钝化剂的吸附动力学特征;从抛物线型拟合方程可以看出吸附作用可能存在两个扩散过程。通过以上研究可以看出,赤泥类物质,特别是纳米化处理赤泥对土壤中Cd有很好的钝化效果,但对土壤pH升高作用较大;新鲜蒜苗残体、沸石和玉米秸秆的钝化效果较好,这些物质的施加也可以对土壤起到增肥、保水等改良作用;巯基化处理增强了玉米秸秆的钝化效果,表明了巯基物质对Cd螯合作用的增加,但其处理成本较高且在初期施用对植物生物量略有降低。因此,在Cd污染土壤原位修复剂的推广应用上,应针对不同区域的土壤类型,结合当地资源综合评估,进行科学选择。本文系统的比较了21种不同种类钝化剂的作用效果,在富含巯基的植物残体、纳米化赤泥和巯基化玉米秸秆制剂的钝化效果的研究,与阻抗剂ZnSO4叶面喷施单一阻抗及与添加剂复合效果的研究上有所创新,为Cd污染土壤钝化剂的推广应用提供了科学指导。更多还原

【Abstract】 With the increase of agricultural pesticide , chemical fertilizer consumption and industrial and mining waste, contaminations containing heavy metals have entered into the soil through various sources which cause serious pollution, decreased agricultural product quality and yield, and produce adverse effects on human health through the biological chain, Over 1.3×104 hm2 farmlands in China have been contaminated with Cd, involving 25 regions of 11 provinces, so treatment of the pollution is very important and urgent. Some sulphydryl (-SH) containing plant offal, modification of clays、mineral slag、industry residue(nanoparticles)、organic material(sulfhydrylation)as amendments were applied in this research, the effects and influencing factors of heavy metal amendments were studied by laboratory incubation and pot culture experiment. According to the antagonism between different metal ions in absorption by plant, the effect of seed soaking and foliage spray were studied in pot experiments. The adsorption and desorption of solution Cd to different amendments was studied by the experiment of thermodynamic and kinetic aproaches. The results were given as follows:The hydroxyapatite (HA), phosphate rock powder (PRH and PRX), zeolite, red mud, plant offal, and their modified products were applied to the Cd-contaminated soils to assess the efficiency of these materials in immobilization of soil Cd. After incubation for different times, the concentration of exchangeable Cd was determined. The results showed that the concentration of exchangeable Cd in soils was decreased using red mud nanoparticles and HA by 35%~55%, using red mud, acid-treated red mud, and zeolite by 15%~25%, and using the sulphydryl (-SH) containing materials including garlic leaf, scallion, rape offal by 20%~25%. The immobilization by PRX, PRH, scallion powder, maize straw and sulfhydrylated maize straw were less effective compared with the above materials. The immobilizing effects of HA, ammonium saturated zeolite, red mud nanoparticles, and acid-treated red mud were stable at different incubation times, while the immobilizing effects of red mud, scallion offal, maize straw and its sulfhydrylation dispose increased along with the incubation times, especially for maize straw and its sulfhydrylated materials after eight weeks or longer incubation time. The results in the present study might be of practical importance in screening of amendments for remediation of soils contaminated with cadmium.The biomasses of cucumber aboveground increased by adding red mud into soils, but it decreased gradually along with the increase of the amount of application, it increased effectively with concentration of zeolite and maize straw increasing, the application of sulfhydrylated maize straw showed little effect on biomasses of cucumber. The application of garlic leaf offal also increased biomasses but no distinct change was appeared as the concentration of amendment increasing. The application of red mud decreased the concentration of Cd in cucumber plant by 20.4%～60.2%, and red mud nanoparticles increased the immobilizing effects significantly, saturated zeolite by 11.7%～48.0%, garlic leaf offal by 20.1%～59.4%, maize straw by 20.3%～36.0%, and sulfhydrylated maize straw by about 20%, but the concentration of Cd can be decreased by nearly 50% in 5 mg kg-1 Cd contaminated soils. With the application of different amendments, the enrichment factor of Cd in cucumber appears to decreaseThe pH values of soil increased by the application of red mud, while decreased by maize straw, sulfhydrylated maize straw and garlic leaf offal. The correlation between Cd concentration in cucumber and pH values was not significant. With the application of red mud, the cation exchange capacity decreased, while the cation exchange capacity increased with the zeolite, maize straw and garlic leaf offal applied. The correlation between Cd concentration in cucumber and CEC values was not significant. The application of maize straw, sulfhydrylated maize straw and garlic leaf offal increased organic matter in soils. The negative correlation between organic matter in soil and Cd concentration in plant was significant. The concentration of EDTA and EXC-Cd was the highest, then were FeOx-Cd, and ERMn, CA and OM-Cd were much lower, WS-Cd was the lowest. The EXC and OM-Cd decreased, but ERMn, EDTA, CA-Cd increased under the application of red mud. With zeolite application, the content of EDTA, CA and RES-Cd increased, while WS, EXC, ERMn and OM-Cd decreased. The concentration of EXC, ERMn, CA and FeOx-Cd in soils decreased continuously, while EDTA, WS, OM and RES-Cd increased with the application of maize straw, sulfhydrylated maize straw and garlic leaf offal. The variation of different forms of Cd, pH values, OM and CEC composed the immobilization mechanism of different amendments。During the second crop experiment,the biomasses of cucumber was higher than that in first pot culture experiment. With the application of amendments,Cd concentration in plant was much lower than CK. The effects of immobilizing on red mud in the second crop experiment were better than in the first time. The immobilization effect of maize straw was different in two pot experiments, while zeolite was stable. The garlic leaf offal was better than the first time, and showed no distinct change on effects of different concentration of amendment. The Cd concentration in cucumber plants was significantly decreased under antagonistic effect of foliar application of 300 mg kg-1 ZnSO4. In the complex immobilization experiment, foliage can also decreased uptake of Cd by the plants, but was not so effective as application of amendments. The uptake of Zn by the plants increased significantly under antagonistic effect of foliar spray application, Zn content in plants was not increased obviously under seeds marinated by ZnSO4. The immobilizing effects of red mud by bayer process is much better than by sintering process under different concentration of application, because of the smaller particle size, larger surface area, higher content of Fe2O3 and Al2O3。The adsorption capacity of red mud and zeolite to Cd was very large. The proportion of water soluble or exchangeable Cd was less than 25% in absorbed by red mud, and most absorbed Cd (more than 50%) was stable and nonbioavailable. Red mud nanoparticles and roasting zeolite increased adsorption capacity. The maize straw, sulfhydrylated maize straw powder and garlic leaf offal showed high adsorption capacity of Cd2+ higher than soils, garlic leaf offal appeared more efficient than the sulfhydrylated and maize straw, but the combination stability was lower than soils. In contrast with soil, the proportion of water soluble and exchangeable Cd in absorbed by zeolite, roasting zeolite and garlic leaf offal decreased obviously, but was less effective than red mud. The Cd2+ adsorbing capacity of red mud, zeolite, maize straw, and garlic leaf offal accord with Freundlich and Langmuir adsorption equation model, the parameter of the result showed adsorption character of different amendments. The adsorption isotherms of red mud were affected by the concentration of background ions obviously, and there may be two styles: external layer and special adsorption.The processes of Cd2+ adsorption can be divided into two stages, fast and slow reactions. Adsorptive rate of red mud was higher and the equilibrium time was shorter, red mud nanoparticles increased adsorptive rate obviously and shorten the equilibrium time. However the equilibrium time of zeolite was longer, it may be associated with inner tunnel structure。The pH value of solution under the application of red mud was much higher than zeolite. The adsorptions of red mud were well described by pseudo-second-order kinetics and model, zeolite, fluvo-aquic soil can be simulated better by pseudo-second-order kinetics model, indexⅡand Elovich equation. Fitting parameters of pseudo-second-order kinetics model and indexⅡmodel indicated kinetic different characteristics of amendments, the curve of parabola model indicated that the absorption may have two diffusion processes. Future research should focus on the immobilizing mechanisms at molecular level by advanced analysis technique, such as X-ray absorbance fine structure spectroscopy and Fourier transformed infrared spectroscopy.更多还原