Preparation and performance evaluation of high-strength phosphogypsum aggregates by compaction and hydration

The preparation of high-strength phosphogypsum aggregates (HPA) was explored in this study by the compaction-fragmentation-grinding-hydration process from mixture of PG GGBS OPC dry powders. The dry powder blocks were first produced by compaction using the programed pressure and then was crushed into small pieces with angular shapes. The small pieces were grinded and then sprayed with saturated lime water. Hydration occurs in water-sprayed pieces, and the high-strength phosphogypsum aggregates (HPA) was produced after 28 days curing. The apparent density and cylinder compression strength of the HPA in drying state were up to 2010 kg/m(3 )and 23.58 MPa, respectively. These results indicated that the rehydration process after compaction can make the prepared HPA obtain high density and strength, solving the shortcoming of the high-doped phosphogypsum products with low strength. Investigating phosphorus and fluoride pollutants in HPA showed that they met the requirements of water with Class I. Finally, the microscopic analysis of XRD and SEM identified that the phase type of the HPA were CaSO4 and ettringite. The changes in the internal pores of the HPA in the curing process were explored by mercury intrusion porosimetry and the results further verified the HPA is well compacted.