Physical properties, strength, and impurities stability of phosphogypsum-based cold-bonded aggregates

While traditional disposal of phosphogypsum either occupies excessive amounts of land or causes serious pollution, novel recycling of phosphogypsum is desirable. Making phosphogypsum-based cold-bonded aggregates (PCBAs) through granulation technology is a potential recycling strategy. In this study, the quality of the recycled PCBAs is assessed, considering physical properties, mechanical strength, impurity stabilization ability, and microstructure. With the increase of phosphogypsum content from 60% to 90%, 28-day bulk density of the PCBAs decreased from 1080 to 950 kg/m(3), cylinder compressive strength in over dry (OD) condition decreased from 16.5 MPa to 3.9 MPa, and water absorption increased from 5.9% to 13.6%. SEM, XRD, and MIP analyses showed that as the phosphogypsum content increased, hydration products in the aggregates diminished and proportion of harmful pores (greater than200 nm) increased. Leaching test on 28-day PCBAs showed a reduced concentration of phosphorus and heavy metals in the leachate compared to the leaching of the original phosphogypsum. The study concluded that the PCBAs with the phosphogypsum content up to 80 % are qualified lightweight aggregates (LWAs) for concrete.