Effect of freeze-thaw process on the synchronous stabilization of cadmium and arsenic in soil by ferromag-netic biochar
Understanding the impacts of freeze-thaw processes on the long-term stabilization of heavy metals in pol-luted soil in cold regions of northern China is an important basis for screening remediation techniques.In this study,we examined the effects of freeze-thaw frequency and water content on the synchronous stabilization of cadmium and arsenic in soil by ferromagnetic biochar(F-MBC)in the freeze-thaw process,taking the soil contaminated by in-situ heavy metals for many years as the object.The results showed that as the frequency of freeze-thaw increased,soil pH and electrical conductivity showed a trend of first increasing and then decreasing,but both were higher than that before freeze-thaw.Under the same freeze-thaw frequency,the increase in initial water content did not have a significant impact on soil pH under F-MBC treatment,but soil electrical conductivity showed a downward trend.Compared with those before freeze-thaw,the contents of available Cd and As in soil experienced a pattern of first increasing and then decreasing during the freeze-thaw process,but both were significantly higher than those before freeze-thaw in the soil.With the increases of initial water content,soil available Cd content continued to decrease and was significantly lower than that in the control(non-freeze-thaw).Available As content first increased and then decreased,and was higher than that in the control(non-freeze-thaw).Our results demonstrate that F-MBC can still achieve synchronous and stable remediation of Cd and As contaminated soil after the freeze-thaw process,but the risk of As pollution would increase.These results provide theoretical support for optimizing the stabilization and remediation technology of cadmium and arsenic composite contaminated soil in cold regions.
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