Abstract: The kinetic behavior and mechanism of the reaction between coal gangue and Cr(Ⅵ) were investigated. The study showed that the reduction process of Cr(Ⅵ) by coal gangue could be divided into two stages. During the initial stage, siderite and pyrite in coal gangue reacted with hydrogen ions to generate Fe(Ⅱ), S and H₂S. Since it was a solid-liquid reaction, the reaction rate was closely related to the mass transfer rate. The reaction rate constant obtained under stirring condition was 0.169 mg/(L·min), much higher than 0.048 mg/(L·min) got under static conditions. The second stage was the reduction of Cr(Ⅵ). The results got from elemental analysis, infrared and XRD characterization showed that the iron and sulfur elements in siderite and pyrite were oxidized to Fe(Ⅲ) and SO₄²⁻, and Cr(Ⅵ) was reduced to Cr(Ⅲ) which is low toxicity . Siderite and pyrite are common components in coal gangue. According to the above research and analysis, the use of coal gangue for treating wastewater containing Cr(Ⅵ) not only improves the utilization efficiency of coal gangue, but also provides a cost-effective and efficient method for the treatment of wastewater containing Cr(Ⅵ).