Preparation of Hardened Inorganic Materials for Prevention of Heavy Metal Leaching and the Effect of Grinding

• Project/Area Number: 15510079
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Environmental technology/Environmental materials
• Research Institution: Ichinoseki National College of Technology
• Principal Investigator: NIKAIDO Mitsuru Ichinoseki National College of Technology, Chemical Engineering, Associate Professor, 物質化学工学科, 助教授 (30218094)
• Project Period (FY): 2003 – 2004
• Project Status: Completed (Fiscal Year 2004)
• Budget Amount: ¥3,900,000 (Direct Cost: ¥3,900,000); Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000); Fiscal Year 2003: ¥3,400,000 (Direct Cost: ¥3,400,000)
• Keywords: Mechanochemical effect / Dry Grinding / Solid hardening / Ettringite / Heavy metal stabilization

Research Abstract

Soil (Okinawa red clay or dredged soil) and blast-furnace slag (contains CaO), which are industrial byproducts, were used as the primary raw ingredients for the preparation of hardened materials. To these raw materials were added reagents such as gypsum, quicklime, and aluminum sulfate. The hardened materials were obtained by dry grinding (mechanochemical treatment) of the mixture with a planetary ball mill, followed by compacting and water curing. Our study focused on ettringite formed in the hardened materials. Thus, we studied the effect of grinding on the strength of the hardened materials (compressive strength) and on the degree of alkali release. In addition, we studied the effect of grinding on heavy metal leaching by adding traces of cadmium and lead to the raw materials.
(Dredged soil materials)
1) The grinding (mechanochemical treatment) of the raw materials was effective in obtaining high-strength hardened materials.
2) The strength of the hardened materials was not improved by calcination of the raw materials. Therefore, it is important to obtain high-strength hardened materials by mechanochemical treatment, but calcination of the raw materials is not necessary.
(Okinawa red clay materials)
1) It was possible to change the degree of alkali release (pH) from the hardened materials by changing the quantity of aluminum sulfate added.
2) The formation rate of ettringite was high under high alkalinity. As a result, the strength of the hardened materials was increased, and leaching of the heavy metal cadmium was suppressed. On the other hand, cadmium was easily leached under neutral pH. Leaching of cadmium was suppressed, however, when the hardened materials were prepared after grinding of the raw materials.
3) Lead was not easily leached under neutral pH. Under high alkalinity it was easily leached. However, the leaching of lead from the hardened materials was suppressed when they were prepared after grinding of the raw materials.