Original Paper(Vol.61 No.1 pp.25-30)

Fluoride Leaching Control of Waste Plasterboard Powder Using Light Burned Magnesite and Its Applicability to the Stabilization/Solidification of Clay

Mikio YAMADA, Hiroaki SANO and Shigeru TSUBOKAWA

Abstract:The reuse of waste plasterboard must be promoted more to maintain the residual capacity of the controlled type landfill sites because it is predicted that the amount of plasterboard retrieved with demolition works of building continues increasing for the time being. However, mixing the board comminuted while separating base paper namely the powdery dihydrate gypsum into ground, the leaching concentration of fluoride which has been contained in plasterboard since inception by coming from raw materials might exceed the environmental quality standards for soil pollution.The light burned magnesite has been early used for not only the improvement of soft ground but also the insoluble treatment of heavy metal pollution soil. Referring to such on-site achievements, we have made the samples which consist of powdery dihydrate gypsum, light burned magnesite and distilled water. Having added magnesite of 10% and water of 50% for the mass of gypsum, fluoride leaching concentration satisfied a target level (hereafter referred to as ginsolubilization treated powderh). Moreover, regarding clay and sand mixed the insolubilization treated powder of which content was up to 30%, it was guessed that those might not re-leach fluoride under the stirring with an acid or alkaline water solution. Successively we performed the CBR test, box shear test and unconfined compression test to clarify a stabilization effect brought by mixing the insolubilization treated powder into clay. According to the results obtained from these tests, clay stabilized with the insolubilization treated powder surely indicated a tendency to increase bearing capacity and to develop strength as compared with clay in which only lime or cement was added.Judging from the novel findings mentioned above, it is possible to utilize the insolubilization treated powder as part of the soil materials.

Key Words:Waste plasterboard, Fluoride, Light burned magnesite, Leaching test, California bearing ratio, Constant pressure shear strength, Unconfined compressive strength