河北保定典型污灌区土壤Cu吸附特性研究

Adsorption Characteristics of Cu onto Typical Sewage Irrigated-Soils from Baoding, Hebei Province

我国部分地区土壤污染形势严峻,主要表现为Cu等重金属元素严重超标。污水灌溉以及含Cu饲料过量使用等不合理的农业生产方式是导致Cu在耕地中富集的主要因素,严重威胁粮食安全和人类健康。以河北保定典型污灌区为研究区,通过静态吸附批量实验探究土壤吸附Cu的动力学和热力学特性。吸附动力学模型和等温吸附经验模型中得到的参数一致表明,表层土壤S1对Cu的吸附能力强于底部土壤S2。S1的有机质含量高于S2,提供了更多的表面吸附点位,这可能是导致土壤S1对Cu的吸附能力更强的原因之一。离子强度对土壤Cu吸附率的影响较小。溶液pH和溶解性有机物(DOM)含量对土壤Cu吸附率的影响明显,pH值与吸附量呈正相关,DOM浓度与吸附量呈负相关。由于土壤对pH有很强的缓冲能力,短时间的酸雨可能不会导致Cu的迁移。施用有机肥时,有机肥浸出液中高浓度的DOM可能会与Cu形成水溶性Cu-DOM络合物,促进Cu在土壤中的迁移,导致浅层地下水污染。

As one of the most toxic inorganic pollutants in soil, heavy metal Cu can readily accumulate in organic farmland soil. Its accumulation in soil would both cause harm to plants and threaten local economic development, human health and ecological stability. Sewage irrigation results in pollutant accumulation(including Cu) in soils. In this study, the dynamic/thermodynamic characteristics of Cu adsorption on two typical sewage irrigated-soils from Baoding, Hebei were investigated by batch adsorption experiment. The parameters obtained from the kinetic adsorption model and isothermal adsorption empirical model show that the Cu adsorption capacity on soil S1 surface is stronger than that on the deeper soil S2. The organic matter content of S1 is higher than that of S2, which provides more surface adsorption interface, which may account for the stronger Cu adsorption capacity of soil S1. Ionic strength has little effect on soil Cu adsorption rate. The effects of solution pH and DOM content on Cu adsorption are significant. Adsorbed Cu content is positively and negatively correlated to pH and DOM content, respectively. Our results also suggest that soils are strong pH buffer, and thus short periods of acid rain would not cause significant Cu transport. However, the application of organic fertilizer may form water-soluble Cu-DOM complex with Cu, which accelerates the Cu transport in soil and pollutes shallow groundwater.