Effect of co-pyrolysis of texting and dyeing sludge and modified kaolin on the fate of heavy metals and potential migration mechanisms

The existence of heavy metal in texting and dyeing sludge is one of the potential ecological pollutions. In this study, a series of modified kaolin was applied to co-pyrolysis with DS. The biochar characterization and heavy metal analysis reveal the effects of modified additives on the heavy metal behavior and potential mechanisms. Compared to raw texting and dyeing sludge, the total content of Cu, Zn, Cr, Mn, and Ni increased to a maximum value of 170.63, 451.85, 147.86, 731.69, and 57.91 mg/kg in biochar. The proportion of Cu, Zn, Mn, and Ni in stable fractions increased to 99.23 %, 88.71 %, 53.89 %, and 94.04 %, and the potential ecological risk index of biochar experienced a substantial reduction from 154.45 in DS to 11.18 in DAK. Co-pyrolysis and dilution effects synergistically reduced the leaching of heavy metals and promoted their enrichment in biochar. The Al/Si structural phase transition, pore structure, functional groups, and interactions between inorganic mineral components and heavy metals also were affected by acid-base modification. This resulted in the enhancement of heavy metal stabilization fractions and the reduction of environmental risks. This study aims to present an eco-friendly and efficient strategy to further mitigate the environmental risks associated with HMs in hazardous wastes. In addition, it also provides ideas for the application of modified mineral additives in the field of pollutant control.