An Improved Apparatus Driven by Gravity for Streaming Potential Measurement of Simulated Soil
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S153.2

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China Postdoctoral Science Foundation

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    Abstract:

    【Objective】Theoretically, surface electrochemical properties of bulk soil can be well characterized by streaming potential measurement. Since the streaming potential measurement is usually adopted to measure the zeta potential of charged solid with large size (e.g. bulk soil) . Nevertheless, commercial streaming potential apparatus is cumbersome to operate and expensive. This limits the application and development of streaming potential measurement in soil research.【Method】In this study, a laboratory-made streaming potential apparatus was developed to measure the zeta potential of simulated bulk soil. Packed quartz grains and Fe oxide-coated quartz grains column were used to mimic the porous structure and surface electrochemical characteristics of bulk soil. The zeta potentials of quartz grains in NaCl electrolytes with different ionic strength (0.01, 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 mmol·L–1) were measured by the streaming potential measurement. Also, using this self-made streaming potential apparatus, we measured the zeta potentials of quartz grains and Fe oxide-coated quartz grains in electrolytes with same ionic strength (20 μS·cm–1) but different pHs (4.4, 5.2, 6.1, 6.6, 6.9, 7.7, and 8.0) . In addition, the zeta potentials of colloidal quartz in different pH’s electrolytes measured by traditional electrophoresis measurement was used to verify the accuracy of the streaming potential measurement.【Result】The results show that, with increasing ionic strength, the zeta potential of quartz grains measured by steaming potential measurement became less negative due to compression of the diffusion layer of the electric double layers on charged solid surfaces at higher electrolyte concentrations. Similarly, with increasing electrolyte pH, the zeta potentials of both quartz and Fe oxide-coated quartz grains measured by steaming potential measurement decreased because of the greater deprotonation effect of functional groups on the surface of quartz and Fe oxide-coated quartz grains. When Fe oxide was adsorbed on the quartz surface, the zeta potential of Fe oxide-coated quartz grains was higher than that of uncoated quartz grains. This was because of charge neutralization between positively charged Fe oxide and negatively charged quartz grains. The measured IEP (isoelectric point) of the Fe oxide-coated quartz grains was between the IEPs of quartz grains and Fe hydroxide. There was a good consistency between the zeta potentials of quartz grains measured by streaming potential and the zeta potentials of quartz colloids measured by electrophoresis measurement.【Conclusion】The results obtained by using the laboratory-made streaming potential measurement apparatus are consistent with the theoretical prediction and electrophoresis measurement. Also, the structure of the laboratory-made streaming potential apparatus is simple, its operation is convenient, and the cost to build this apparatus is low compared to commercial apparatus. Thus, the streaming potential measuring apparatus used in this study can be used as a powerful tool to conduct studies in the field of soil electrochemistry.

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LI Zhongyi, LIU Fangming, WU Jinwen, XU Renkou, XIE Deti. An Improved Apparatus Driven by Gravity for Streaming Potential Measurement of Simulated Soil[J]. Acta Pedologica Sinica,2022,59(3):746-756.

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History
  • Received:January 13,2021
  • Revised:April 30,2021
  • Adopted:July 15,2021
  • Online: July 19,2021
  • Published: