Quantification of changes in zero valent iron morphology using X-ray computed tomography

• Published in: Journal of environmental sciences (China) 2013-11, Vol.25 (11), p.2344-2351
• Main Authors: Luo, Ping, Bailey, Elizabeth H., Mooney, Sacha J.
• Format: Article
• Language: English
• Subjects: acidic drainage; Groundwater - chemistry; Iron - chemistry; mass balance; permeable reactive barrier; pore-clogging; porosity change; PRBS; Tomography, X-Ray Computed; typical groundwater; Water Pollutants, Chemical - chemistry; X-ray computer tomography; X射线CT; zero valent iron; 实验室规模; 断层摄影术; 水化学处理; 计算机断层扫描; 量化; 铁形态
• ISSN: 1001-0742; 1878-7320
• DOI: 10.1016/S1001-0742(12)60237-X

Morphological changes within the porous architecture of laboratory scale zero valent iron （ZVI） permeable reactive barriers （PRBs）, after exposure to different groundwater conditions, have been quantified experimentally for different ZVI/sand ratios （10%, 50% and 100%, W/W） with the aim of inferring porosity changes in field barriers. Column studies were conducted to simulate interaction with different water chemistries, a synthetic groundwater, acidic drainage and deionised （DI） water as control. Morphological changes, in terms of pore size and distribution, were measured using X-ray computed tomography （CT）. CT image analysis revealed significant morphological changes in columns treated with different water chemistries. For example, 100% ZVI （W/W） columns had a higher frequency of small pores （0.6 mm） was observed in ZVI grains reacted with typical groundwater, resulting in a porosity of 27%, compared to 32% when exposed to DI water. In comparison, ZVI grains treated with the acidic drainage had higher porosity （44%） and larger average pore size （2.8 mm）. 10% ZVI PRB barrier material had the highest mean porosity （56%） after exposure to any water chemistry whilst 100% ZVI （W/W） columns always had the lowest （34%） with the 50% ZVI （W/W） in between （40%）. These results agree with previously published PRB field data and simultaneously conducted geochemical monitoring and mass balance calculation, indicating that both the geochemical and hydraulic environment of the PRB play an important role in determining barrier lifespan. This study suggests that X-ray CT image analysis is a powerful tool for studying the detailed inter pores between ZVI grains within PRBs.