可溶性有机碳在典型土壤上的吸附行为及机理

定量分析可溶性有机碳(DOC)在不同土壤上的吸附行为可为DOC在不同地区土壤中的去向及污染风险评估提供理论基础。本研究以河南潮土(包括砂质、壤质和黏质3种质地)、江苏黄泥土、江西红黏土和海南砖红壤等典型土壤为吸附介质,采用一次平衡法比较了DOC在不同土壤中的吸附容量及平衡液中DOC的结构变化。结果表明,供试土壤对DOC的吸附可用修正的Langmuir模型拟合。最大吸附量(Q_(max))从高到低依次为红黏土(2 892.67 mg/kg)、砖红壤(1 969.77 mg/kg)、黏质潮土(1 803.03 mg/kg)、黄泥土(1 003.84 mg/kg)、壤质潮土(989.31 mg/kg)和砂质潮土(441.18 mg/kg)。黄泥土的亲和系数(k)最大(2.53×10~(–3)),其次为砖红壤、红黏土和3种潮土。吸附后,除砂质潮土和壤质潮土外,其他土壤平衡液的芳香性均降低。相关性分析表明无定形氧化铝显著影响了Q_(max),而氧化铁的形态(无定形、络合态和低结晶态)决定了k值大小。红黏土、砖红壤和黄泥土更容易吸附DOC中的芳香族成分,主要吸附机制可能为配位体交换;砂质潮土和壤质潮土主要为阳离子架桥,而黏质潮土同时存在这两种吸附机制。

Mechanisms of Dissolved Organic Carbon Adsorption on Different Typical Soils in China

Six representative soils with contrasting physico-chemical properties including Usti-Alluvic Primosols in Henan, China (Fluvo-aquic soil, including sandy, loamy and clayey texture), Hapli-Stagnic Anthrosols in Jiangsu (Huangni soil), Argi-Udic Ferrosols in Jiangxi (Red clay soil), and Rhodi-Udic Ferralosols in Hainan (Latosol) were collected to determine dissolved organic carbon (DOC) adsorption characteristics with batch equilibrium technique. The equilibrium solution after adsorption was characterized by SUVA254 to estimate the aromatic carbon content. The results showed that adsorption of DOC to soils was well-described using a modified Langmuir equation. The maximum adsorption capacity (Qmax) followed an order of Red clay soil > Latosol > Clayey fluvo-aquic soil > Huangni soil > Loamy fluvo-aquic soil > Sandy fluvo-aquic soil. The binding affinity (k) followed the decreasing order of Huangni soil, Latosol, Red clay soil, Clayey fluvo-aquic soil, Sandy fluvo-aquic soil and Loamy fluvo-aquic soil. Among all the soil properties, oxalate-extractable aluminum (Alo) had significant influence on Qmax, and k was best correlated with oxalate-extractable iron (Feo), pyrophosphate-extractable iron (Fep) and crystalline iron (Fecry). After adsorbed on Red clay soil, Latosol, Huangni soil and Clayey fluvo-aquic soil, the SUVA254 values of DOC in the equilibrium solutions were lower than in the initial DOC solution, indicating the aromatic carbon was preferentially adsorbed on these soils from the solutions. Our studies suggest that the predominant mechanism of DOC retention by Red clay soil, Latosol and Huangni soil was ligand exchange, whereas, cation bridging contributed to DOC adsorption on Sandy fluvo-aquic soil and Loamy fluvo-aquic soil. And both ligand exchange and cation bridging were likely to play an important role in DOC adsorption on Clayey fluvo-aquic soil. These results have important implications for soil carbon cycle as well as soil environmental pollution.