Solidification mechanism of heavy metal of red mud-based engineered cementitious composites

Abstract In this paper, the occurrence form and leaching characteristics of heavy metals in red mud were clarified, the solidification mechanism of heavy metals by the hydration products and solidification agents was explored. The results show that the contents of heavy metals in red mud from high to low are Cr, Pb, Ni, Cu, As and Cd, which are 754 mg/kg, 78.2 mg/kg, 41.8 mg/kg, 33.2 mg/kg, 15.0 mg/kg and 0.77 mg/kg respectively. The potential ecological hazard level is moderate. The occurrence form of heavy metals in red mud-based cementitious materials gradually changes from effective state to stable state with the increase of curing age. When the curing age is 120 days, the curing rate tends to be stable, and the curing rates of As, Cu, Ni, Cd, Cr, Pb reach 99.91%, 97.62%, 97.02%, 96.83%, 95.91%, 91.11% respectively. The lifting effect of three heavy metal curing agents is: 5A zeolite < fly ash < attapulgite. The optimum heavy metal curing agent is attapulgite with a content of 6%. When the curing period is 28 days, the curing rate of heavy metal element Pb reaches 99.74%, and the curing rate of Cr reaches 99.40%, increased by 8.86% and 4.28% respectively. The results can realize the green and safe application of red mud based cementitious materials.