Maier, M.V., Y. Wolter, D. Zentler, C. Scholz, C.N. Stirn, and M. Isenbeck-Schroter.
Water 11(11):2364(2019)

To accelerate ongoing but ineffective pump-and-treat efforts to remediate As in groundwater, the competitive effect of increasing phosphate doses contaminated aquifer material of different depths and under distinct geochemical conditions was examined. Columns with added phosphate showed significant amounts of As released rapidly under oxic and anoxic conditions, though levels were higher in anoxic columns. As(III) was the dominant species, in particular during the first release peaks and the anoxic tests. Higher amounts of phosphate did not trigger As release further and led to a shift of As species. The competitive surface complexation was the major process of As release especially when higher amounts of phosphate were used. While As release is commonly described at Fe-reducing conditions, observations suggested a change in redox potential towards Mn reducing conditions in the oxic tests. Fe reducing conditions in the anoxic column took place later and independently of As release. The reduction of As(V) to As(III) and a loss of sulfate in all columns with phosphate under both redox conditions was presumed to be an effect of microbial activity, which may play a significant role in the process of arsenic release. Preliminary tests with sediment material from a contaminated site showed that phosphate additions did not change the pH value significantly. Results indicated that in-situ application of phosphate amendments to As-contaminated sites could accelerate and enhance arsenic mobility to improve the efficiency of pump-and-treat remediation without negative side effects. This article is Open Access at https://www.mdpi.com/2073-4441/11/11/2364