Solidification of chromium-containing sludge with attapulgite combined alkali slag.

To solve the harm caused by hazardous chromium-containing sludge (CCS, chromium-containing sludge) waste to humans and the environment, this study used attapulgite to strengthen alkali slag to prepare cementitious materials to solidify/stabilize CCS. Single-factor and orthogonal experiments were used to optimize the preparation parameters of alkali slag cementitious materials. The compressive strength, heavy metal leaching toxicity, and microscopic characterization of a CCS solidified body were tested to investigate the solidification effect and mechanism of CCS formation. The best attapulgite content was 4%; the solidified body after the treatment of chromium-containing sludge had a good performance of heavy metal leaching and mechanical properties. The addition of attapulgite enhanced the compressive strength. Compared with the original CCS, the leaching concentration of heavy metals in the solidified body was significantly reduced. Among them, the solidified efficiency of chromium is stable above 90%. The changes in the results of XRD and FTIR for each component were studied. It indicated that the solidified body may solidify/stabilize heavy metals through physical encapsulation of the amorphous form and chemical immobilization. This research recognized the use of waste to treat waste, realized the combined effect of solidification/adsorption, and indicated the possibility of application of attapulgite and its solidified products in construction.