A Note on Neutralization Method by Pouring of Strong Acidic Water into Lava of Andesite

Abstract

Strong acidic water is flowing out from the old-Nishiazuma Mine Field and it is due to water pollution of the Matsukawa river whose water can't be used for irrigation.A disposition method of the strong acidic water was studied by field survey, with some laboratory tests and investigations for the acidification and neutralization of andesite rocks.As the results, PH value of the strong acidic water indicates from 1.4 to 3.4 and it's water flow is less than 0.273 m3/sec at the present condition. However, it will be possible to decrease less than 0.150 m3/sec in it's flow by means of protection of permeation of rain water under the ground surface near the old mine field.The old mine field is located near Ohgasayama Daichi plateau whose geological circumstance consists of tertiary tuff breccia which is covered unconformably by pyroxene andesite.On the part of this plateau, once there was a disposition area for the strong acidic water, the pyroxene andesite have got acidified up to about 50 m in depth under ground, where PH value indicates 4.0-5.0. But, rocks in deeper layer than the above and distant area from acidified area point out 7.0-8.0 in PH value.The result of infiltration test by two test wells in above mentioned area shows that the coefficient of permeability ‘K’ is 10-4-10-6 m/min and it is supposed that the boundary of strata is main water way of groundwater.The result of experiment in laboratory shows that the water changes to PH value 4.3 in the first 12 hours when the strong acidic water of PH value 1.4 touchs fresh rocks in this area and in 6-10 days it, which has been the most promoted in neutralization, become PH value 4.8.The disposition process of the stong acidic water is carried out as follows:1) a pipeline has been laid between the water's comeout point and the treatment site where a lot of wells are provided;2) the water in question transferred through a pipeline flours into the wells for permeation without any artificial pressure;3) the contaminated water injected into the wells is neutralized in the andesite and give off again;4) it flows into Yazawa river and Matsukawa river. The treatment water has no effect on the river, for it is almost neturalized.