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

[AHW27-P07] Applicability of alkaline waste and by-products for neutralization of acidic soils

*Takeshi Saito¹, Isiri Upeksha Nagasinghe², Takato Takemura², Naoki Watanabe³, Yoshishige Kawabe¹ (1.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 2.College of Humanities and Sciences, Nihon University, 3.Research Institute for Natural Hazards and Disaster Recovery, Niigata University)

Keywords:Acidic soils, Neutralization, Calcium carbonate, Alkaline waste and by-products, Steel slag

Acidic soils are widely distributed all over the world. These soils could induce serious negative impacts specially on agricultural field. Soil neutralization using calcium carbonate has been often performed practically in the field, however, calcium carbonate is a limited natural resource. The objective of this study was therefore to evaluate applicability of three alkaline waste and by-products expected as alternative neutralizers for acidic soils. Three representative acidic soils were selected to perform laboratory neutralization experiment. Autoclaved lightweight aerated concrete, recycled concrete, and steel slag were utilized as alternative neutralizers, while calcium carbonate was selected for a control and reference neutralizer. In the neutralization experiment, 5 g of each air-dried acidic soil and each neutralizer with 0 mg to 1200 mg were mixed with 12.5 mL of pure water and then kept at room temperature of 20^oC and relative humidity of 60% for 24 hours. Subsequently, each sample was shaken at a speed of 180 rpm for 5 hours and excess CO₂ was removed by aeration. pH values in all acidic soils clearly increased with increasing additive amount of each neutralizer as pH measurement was immediately carried out for the supernatant. In particular, the lowest additive amount required for the neutralization (i.e., the highest neutralization performance) was observed in steel slag among three tested alkaline waste and by-products. Steel slag was comparable to calcium carbonate in neutralization performance, suggesting that it is the most applicable alternative neutralizer.