Study on recycling and utilization of phosphogypsum and lithium slag in vertical barrier materials

Abstract

Traditional vertical barrier materials typically have a large carbon footprint and high cost. Phosphogypsum (PG) and lithium slag (LS), possess latent cementitious activity. This study investigated the potential use of PG and LS in vertical barrier materials. The basic characteristics of the system were studied for LS:PG (mass ratio) ranging from 1:1–1:9, with a bentonite content of 10 % and a water-to-solid ratio of 0.5. The PG-LS matrix was microscopically characterized using XRD, TG, FT-IR, and SEM analysis. Additionally, an economic and sustainability assessment was performed. The results indicated that when LS:PG was in the range of 1:3–1:1, the flowability and setting time ranged from 16.15 to 21.00 cm and 51–87 hours, respectively. The bleeding rate within 12 hours was consistently below 5 %. Furthermore, the compressive strength and permeability coefficient at 28 days were within the ranges of 1.81–7.99 MPa and 2.91×10−8 to 7.98×10−9 cm/s, respectively. Excessive addition of PG was found to be unfavorable for the formation of C-(A)-S-H gel, resulting in an increase in free alkali content in the system and promoting the carbonation-induced formation of Calcite, thereby reducing the compressive strength and increasing the permeability. Compared to traditional barrier materials, the PG-LS-based barrier material exhibited a 61 % reduction in CO2 emissions and a cost reduction of 75–82 %. Additionally, the leaching concentrations of Zn, Cr, Ni, Cu, Pb, Cd, and As were below the standard limits. Therefore, the utilization of PG and LS in vertical barrier systems demonstrated excellent performance, economic feasibility, and environmental benefits, indicating significant potential for widespread application.