Performance and Heavy Metal Analysis of Graphite Tailings Cured Using Cementitious Materials

Abstract

The massive accumulation of graphite tailings causes serious environmental pollution, mainly from heavy metal pollution. Therefore, this article introduces a method of using graphite tailings as a high-content main material, cement as a small component of the auxiliary cementitious material, and clay as a substitute for cement. The compressive strength and permeability of graphite tailing–solidified material (GT, GT–Clay) were tested, and the effect of clay partially replacing cement as an auxiliary cementitious agent on GT–Clay performance was compared. In addition, inductively coupled plasma mass spectrometry (ICP) was used to analyze the effect of the graphite tailing placement time on the heavy metal content, as well as the changes in the GT heavy metal leaching concentration and its heavy metal content under outdoor freeze–thaw conditions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to elucidate the microstructural changes in the GT–Clay. The experimental results show that, as the substitution of clay for cement increased from 0 to 50%, the compressive strength of the 90% GT–Clay gradually decreased, and the permeability also increased. The compressive strength of 95% GT–Clay did not show significant changes, but the permeability increased, and when mixed with quicklime, gypsum, and silica fume, the permeability decreased. The Ni and As in graphite tailings fluctuated significantly with the placement time. The heavy metal leaching concentrations of the 90% GT and 95% GT were below the standard limit, and Cd, As, and Ni in GT were potential sources of pollution. The analysis of the microscopic test results showed that the hydration products of the GT–Clay included ettringite, Ca(OH)2, and calcium silicate hydrates. The hydration product stabilized and filled the gaps between the tailing particles, thereby cementing them together. Not only did it improve the mechanical strength of GT, it also reduced the permeability and heavy metal leaching rate. This study provides a new analytical approach to applying graphite tailings for environmental treatment.