[A-HW27] Water Environment and Geology in Urban Areas

[AHW27-P08] Evaluation of temperature dependance for adsorption of heavy metals onto soils and sediments

*Keigo Kurita¹, Takeshi Saito², Chiaki T. Oguchi¹, Yoshishige Kawabe² (1.Graduate School of Science and Engineering, Saitama University, 2.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology)

Keywords:temperature dependence, adsorption, arsenic, boron, soils, sediments

Underground temperature increases slightly with increasing the depth from the ground surface. Subsurface temperature increase due to global warming and urbanization has been,as well recently,observed in many areas all over the world. In addition to above these,it is also being concerned the rise in groundwater temperatrure by the ground source heat pump (GSHP) which is expected as a general-purpose heat utilization used as renewable energy in the near future. These phenomenon caused by the global warming and waste heat from artificial structures could induce changes in physical,chemical,and microbial processes in subsurface environment including soil and groundwater. However,the effect of temperature increase on subsurface environment has not been sufficiently investigated and clarified. Thus,the present study focuses to clarify temperature dependence for adsorption of hazardous elements onto soils and sediments based on laboratory batch adsorption experiment under several temperature conditions. Four representative soils and sediments (i.e.,volcanic ash soil,brown forest soil,alluvial clay sediments,and marine silt sediments) were selected as adsorbents. Experimental solutions of boron and arsenic as adsorbates were prepared for initial concentration of 100mg/L. There were no significant differences between adsorbed amounts of boron at 20 degrees Celsius and 40 degrees Celsius,which means that there was almost no temperature dependence observed. On the other hand,arsenic showed significant temperature dependence in the same condition of the experiment. The adsorbed amounts of arsenic at 40 degrees Celsius were generally higher than those at 20 degrees Celsius by up to 30%. Although the mechanism of adsorption is not clear at the moment,the characteristics of adsorption site are fairy different between boron and arsenic. These results indicate that at least arsenic will be trapped much if the subsurface temperature increase and if the adsorption sites in sediments are enough remained.