DETERMINATION OF ACID POTENTIAL BY INFRARED SPECTROMETRY IN NATURAL SOILS AND EXCAVATED MATERIALS

Abstract

The present invention is a rapid method for determining the acidifying potential of an excavated material for the purpose of its neutralization by determining the mass content of iron pyrite and carbonate in the excavated material from an infrared spectroscopy analysis.

Claims

1. Method for analyzing an excavation material comprising the following steps: a) analysis by infrared spectroscopy of a sample of an excavation material in a wave number range between 4000 cm-' and 350 cm-' to obtain an infrared spectrum, b) determination of the mass content of iron pyrite in said sample from the infrared spectrum obtained in step a).

2. Method according to claim 1 in which the excavation material has a dry matter content of 70% to 100%.

3. Method according to claim 1 or claim 2 in which step b) comprises the following sub-steps: b1) detection between 450 cm-' and 435 cm -1of a specific absorption band of iron pyrite in the infrared spectrum obtained in step a), b2) integration of the absorption band detected in step b1) to calculate an area, and b3) comparison of the area obtained in step b2) with a calibration curve to determine the mass content of iron pyrite in the excavation material.

4. Method according to any one of claims 1 to 3, further comprising the following step: c) determining the mass content of carbonate ion in said sample from the infrared spectrum obtained in step a).

5. Method according to claim 4 in which step c) comprises the following sub-steps: c1) detection between 1550 cm-' and 1180 cm -1of a specific absorption band of the carbonate ion in the infrared spectrum obtained in step a), c2) integration of the absorption band detected in step c1) to calculate an area, and c3) comparison of the area obtained in step c2) with a calibration curve to determine the mass content of carbonate ion in the excavation material.

6. A method for neutralizing an excavation material comprising the following step: d) adding an amount of weak base buffer to an excavation material to be neutralized to obtain a neutralized excavation material, wherein the mass content of iron pyrite in the excavation material to be neutralized has been determined by the analytical method as defined in any one of claims 1 to 5, the mass content of carbonate ion in the excavation material to be neutralized has been determined by the analytical method as defined in claim 4 or claim 5, and the amount of weak base buffer added to the excavation material to be neutralized is adjusted - relative to the mass content of iron pyrite in the excavation material to be neutralized, - relative to the mass content of carbonate ion in the excavation material to be neutralized, and - such that the neutralization potential ratio, NPR,of the neutralized excavation material is equal to a predetermined value., 7. Method according to claim 7 in which the predetermined value is equal to 4.

8. A method according to claim 6 or claim 7 wherein the weak base buffer added to the excavation material to be neutralized is a hydroxide, a carboxylate, a carbonate or mixtures thereof.

9. A method according to any one of claims 6 to 8 wherein the weak base buffer added to the excavation material to be neutralized is calcium carbonate.

10. Method for recovering a neutralized excavation material according to the neutralization method as defined in any one of claims 6 to 9 comprising a step of recovering said neutralized excavation material as a construction material.

11. A method according to claim 10 wherein the construction material is a fill or an aggregate.