Effect of dry-wet cycles on leaching behavior of recovered soil collected from tsunami deposits containing geogenic arsenic

Abstract

Geogenic contaminants, such as arsenic, are often found in soil recovered from coastal areas. These contaminants may leach out when the soil is used as embankment material. Moreover, the leaching of such contaminants might be influenced by environmental changes, such as dry-wet cycles, and higher environmental risks due to a larger amount of leaching are anticipated in some cases. In this study, therefore, soil recovered from tsunami deposits was subjected to dry-wet cycles under three different drying conditions to investigate how environmental changes affect the leaching behavior. To evaluate the physical and chemical changes in the soil surface, microscopic/spectroscopic studies were conducted. Batch leaching tests revealed that dry-wet cycles slightly alter the leaching behavior of most elements, such as Fe, Si, Na, Ca, etc. Arsenic leaching was seen to increase in certain dry-wet cycles before decreasing, and microscopic/spectroscopic confirmed that this increase was likely due to pyrite oxidation. These dry-wet cycles can disintegrate pyrite morphology and cause pyrite oxidation, leading to a more acidic leaching condition that accelerates arsenic leaching. After a certain oxidation procedure, the resulting ferric hydroxide may prevent the pyrite surfaces from further oxidation. The Fe oxides and hydroxides can also act as arsenic adsorbents, preventing the increase in arsenic concentration.