Insight into the occurrence relationships between Pb, As, Zn and Cr with minerals phases in the coal gangue: A novel quantitative dissociation method

Abstract

Establishing the quantitative relationships between heavy metals and mineral phases in coal gangue is essential for its comprehensive landfill and refined utilization. In this study, the Guandi coal gangue was subjected to a stepwise dissociation method using seven concentration gradients (0.1, 1.0, 4.0, 6.0, 8.0, 10.0, 12.0 ​mol/L) of aqua regia and hydrofluoric acid. Combined with the Rietveld refinement method, inverse matrix calculations of residual fractions of mineral phases and dissociation degrees of heavy metals after dissociation, the quantitative relationships between Pb, As, Zn, Cr and the mineral phases were determined. The results show that kaolinite, quartz, pyrite, and the amorphous phase are the primary host phases for Pb, As, Zn, and Cr, with their contents in crystalline phases ranging from 71.36% to 87.68%. Validation via the standard addition method demonstrates that the relative standard deviation of the stepwise dissociation for Pb, As, Zn, and Cr is ​≤7.23%, with spike recovery rates ranging from 85.43% to 112.85%, indicating favorable test results. Sequential chemical leaching demonstrates that heavy metals are mainly distributed in stable aluminosilicate-bound state and carbonate or oxide-bound state. The toxicity characteristic leaching procedure test indicated that Cr exhibited high toxicity and thus required long-term monitoring. The results of this study provide important theoretical guidance for the comprehensive landfilling and resource utilization of Guandi coal gangue, and the established analytical method can be extended to studies on quantitative relationships between heavy metals and mineral phases in other tailings.