Acta Chim. Sinica ›› 2017, Vol. 75 ›› Issue (6): 637-644.DOI: 10.6023/A17020056 Previous Articles    

Special Issue: 铁环境化学



程鹏飞a,b, 王莹b, 程宽b, 李芳柏b, 秦好丽a, 刘同旭b   

  1. a 贵州师范大学 化学与材料科学学院 贵阳 550001;
    b 广东省生态环境技术研究所 广东省农业环境综合治理重点实验室 广州 510650
  • 收稿日期:2017-02-15 出版日期:2017-06-15 发布日期:2017-04-25
  • 通讯作者: 刘同旭
  • 基金资助:


The Acid-Base Buffer Capacity of Red Soil Variable Charge Minerals and Its Surface Complexation Model

Cheng Pengfeia,b, Wang Yingb, Cheng Kuanb, Li Fangbaib, Qin Haolia, Liu Tongxub   

  1. a School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China;
    b Guangdong Institute of Eco-environmental Science & Technology, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Guangzhou 510650, China
  • Received:2017-02-15 Online:2017-06-15 Published:2017-04-25
  • Contact: 10.6023/A17020056
  • Supported by:

    Project supported by the "973" Program (2014CB441002) and the National Natural Science Foundation of China (41571130052).

Iron oxides and kaolinite are the main sources of variable charges in the red soil. As a result of being protonated and deprotonated under different acid-base conditions, the surface hydroxyl groups can buffer the pH changes of red soil. In this study, iron oxide and kaolinite were titrated by the standard HCl and NaOH solution through the auto potentiometric titration under the controlled pH=2.9~9.5, to study the surface charge of soil minerals. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and N2 desorption/adsorption isotherms (BET) were used to characterize the crystal structures, surface groups and specific surface areas of soil minerals. Based on the characterization data and titration curves, the acid-base properties of the minerals were analyzed by using 1-site/2-pK surface complexation model. The Gran plot method, commonly used to determine the equivalence points, was applied to calculate the concentration (Hs) and density (Ds) of the surface active sites on the soil minerals. The acid-base equilibrium constants (pKaint) of soil minerals were obtained by extrapolation and the corresponding pHpzc were calculated by the following formula:pHpzc=1/2 (pKa1int+pKa2int). The result of calculated value of pHpzc was nearly equal with the experimental value, which showed that it is feasible to apply this model calculation method on the soil minerals. In addition, the above parameters can explain the acid-base buffer capacity of the minerals quantitatively. The results show that goethite and kaolinite have the higher surface active site concentration. According to the parameters, the surface chemical speciation of minerals at different pH were calculated by Visual Minteq software with the double layer model (DLM) to explain the mechanism of acid-base buffer behavior on the mineral surfaces. Finally, the acid-base titration method and model calculation approach were also used to analyze the acid-base buffer capacity of the natural red soil samples. The feasibility of this method on the red soil was further verified. Then, the surface chemical species (≡SOH2+, ≡SO- and ≡SOH) of the red soil were calculated by surface complex model to further explain their acid-base buffer mechanism.

Key words: iron oxide, kaolinite, red soil, acid-base buffer capacity, surface complexation model