The green tuff from Hinai town, Akita is popular for architectural materials because of its beautiful pale green color and thermal and moisture retaining properties. When this stone is quarried and grinded for making products, approximately 60% of all quarried stone becomes the waste stone and it is required to be utilized effectively. Hinai-Green tuff is a porous media and it has abilities to neutralize acids and elute some minerals. These abilities may be effective for growth of microbes and our research group carries out the development of effective utilizations of Hinai-Green tuff as microbial activator. In this paper, the effects of Hinai-Green tuff on pH adjustment and microbial activities are described.
Hinai-Green tuff had an ability to neutralize both acid and alkaline water and especially neutralized acids effectivelly. For example, acid water of initial pH3 was neutralized to pH7 by adding 10(w/v)% Hinai-Green tuff into the acid water. Therefore, Hinai-Green tuff can neutralize acid soil and water and adjust acid environments to adaptable environments for microbes. Moreover, Hinai-Green tuff could buffer decrease in pH. The pH of water containing Hinai-Green tuff did not decrease rapidly with adding drops of 0.1M HCl, and especially the buffer action was strongly observed at pH 7 to 8. Hinai-Green tuff is very helpful to maintain pH appropriate for microbes for long time against decrease in pH caused by acid rain and/or acid metabolites of microbes. And pH adjustment effects of Hinai-Green tuff were caused by the ion exchange between Ca²⁺ leached from the stone and H⁺.
Consequently, microbes grew actively in a medium containing Hinai-Green tuff because of its pH adjustment effects. However, microbes did not grow in a medium containing natural zeolite from Futatsui town, Akita. The effects of Futatsui-Zeolite on pH adjustment for acid were low compared with Hinai-Green tuff.