Chemical properties of red bed soil from Mae Moh Mine for covering coal outcrop in final mine pit wall

Abstract

This research aims to find the chemical properties of the red bed soil in Mae Moh mine pit C for covering the coal outcrops occur in slope faces of the last pit slopes. To find the relationships of concentration values of major elements existing in red bed soil analyzed by Inductively Coupled Plasma (ICP) and Portable X-Ray Fluorescence (PXRF) analyzers, and to create the quality maps of each major element using geostatistical and geographic information system (GIS) techniques. Mae Moh Lignite Mine, Lampang needs to manage the final mine pit during the mine operation phase in the final mine pit area (pit C) for safety environment. Since the thick red bed soil occurs as overburden in mine pit area, so it will be used as covered material on some coal outcrops at the last pit slopes. Therefore, it is necessary to study the chemical properties of red bed soil and select the appropriate soil layers for covering. The samples of red bed soil are collected from three areas in mine pit using three types of sampling; The 108 samples are vertical collection from 4 bore holes, 75 samples from slope face along the road in mine pit area and 67 samples from surface area in mine pit. The samples from 4 bore holes are analyzed using ICP and PXRF techniques for chemical properties and the concentration values of identical major elements are determined to find the relationships. The best relationship with maximum coefficient of determination value (R-square value) of each element is selected to convert the PXRF values to ICP values. From the study, the equation for the best relationship of As is power, Cr is exponential, Pb is power, Mn is linear, Fe is exponential, Al is logarithm, Hg is logarithm and Ni is exponential. The concentration values of major elements resulted from conversion of PXRF analysis to ICP values of the samples from the slope face along the road and from the surface area in mine pit are used to create the quality maps. The distribution of each major element in the red bed soil can be created as quality maps using Kriging method and GIS techniques. The quality maps of each major element; As, Cr, Pb, Mn, Fe, Al, Cd, Hg, Ni and Se, contained in red bed soil located in the area between 4 drill holes are created from interpolation using Kriging method and GIS techniques. These quality maps show the concentrations of each element in 10 meters thick from the surface at elevation 225 m. (MSL) downward to elevation 85 m. (MSL). From the results, quality maps of the study areas show that only As concentration values exceed the soil quality standard value (27 mg/kg). The others area in soil quality standard limits and not harmful to the environment. According to the announcement of the National Environment Board Pollution Control Department, Thailand, No. 25, 2004. Subject: Determination of soil quality standards for other purposes than living and agriculture. The quality maps created can help to select the proper red bed soil for covering coal outcrops at the final pit slopes to prevent environmental problems and hazards after mine closure time. With the known conversion equations, the PXRF can be used as a tool to analyze or detect the major elements containing in the red bed soil in the mine site with convenience, quick and reliable.