The Development of a Slurry Management Technique for Recirculating Weak Acidic Slurry Containing Natural Arsenic.

Abstract

Using a slurry shield tunneling method, the main leaching mechanisms of arsenic naturally contained in the ground are as follows: (1) the arsenic adsorbed on iron hydroxide elutes in an alkaline pH range, and (2) arsenic adsorbed on iron hydroxide is released into a reducing atmosphere as iron hydroxide decomposes. We use the slurry shield tunneling method to supply acid agents to the slurry regulation tank of a slurry treatment system to keep the pH of the slurry at the cutter face in a weakly acidic range of approximately pH 5. We use UltraFine Bubble (UFB, a bubble of less than 1 micrometer) technology with excellent gas-dissolution efficiency to increase dissolved oxygen and promote the oxidation of the slurry. As a result of laboratory and demonstration tests, by reducing arsenic elution, surplus soil (gravel, sand, and silt) and surplus slurry (silt and clay) recovered from the slurry treatment system meet the soil leachate standard.