Characterizing surface electrochemical properties of simulated bulk soil in situ by streaming potential measurements

Abstract

To evaluate the feasibility of using streaming potential to characterize the surface electrochemical properties of soil in situ, a quartz sand‐packed column was used to mimic the porous structure and architecture of bulk soil. A laboratory‐made apparatus was developed to measure in situ the streaming potential of quartz grains in the packed column under environmentally relevant physicochemical conditions (e.g. electrolyte pH, Fe oxide coating on sand grains, transport of goethite and amorphous Al hydroxide colloids, and the presence of humic acid). The results showed a significant positive relation between the measured streaming potentials and zeta potentials of the quartz grains examined. With decreasing electrolyte pH, the streaming potential of the quartz grains became less negative because of the greater protonation effect. Similarly, when Fe oxide was adsorbed on to the quartz surfaces, the streaming potential of Fe oxide‐coated quartz grains was less negative than that of uncoated quartz grains as a result of charge neutralization between positively charged Fe oxide and negatively charged sand grains. However, the streaming potential of Fe oxide‐coated quartz grains became more negative when humic acid was added to the electrolyte solution because of increased adsorption of negatively charged humic acid. Interestingly, an obvious change of streaming potential in the processes of colloidal goethite and amorphous Al hydroxide transport in the sand‐packed column grains occurred. Given that the overall positive charge of the colloidal amorphous Al was greater than that of goethite colloids, transport of amorphous Al colloids was found to exert a stronger effect on the variation in streaming potential of quartz sand. Taken altogether, the in situ streaming potential results showed that streaming potential can be used as a powerful index to characterize directly the surface electrochemical properties of quartz grains representing bulk soil. Highlights The variation in surface electrochemical properties of bulk soil needs investigation. We measured the streaming potential produced by simulated bulk soil using a laboratory‐made apparatus. The streaming potential of bulk soil varied with the change in environmentally relevant conditions. Streaming potential is a powerful index characterizing the surface electrochemical properties of bulk soil.

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