Geotechnical and Leaching Characteristics of the Indian Raw Phosphogypsum

Phosphogypsum (PG) is an industrial waste of the phosphoric acid industry and is mainly composed of calcium sulphate. PG has sufficient mechanical strength to be used for secondary road embankments and base material. However, due to the presence of toxic substances, the use of PG is limited in road construction and ground improvement projects. This paper presents geotechnical, microstructural, and leaching characteristics of raw PG obtained from the Odisha State of India. The microstructure and crystalline phases of raw PG were investigated by scanning microscope (SEM) and X-ray diffraction (XRD) analysis. The compaction characteristics were examined for both air-dried and oven-dried PG. The mechanical properties were investigated by performing unconfined compression strength (UCS) and California bearing ratio (CBR) tests. The water leach and toxicity characteristics leaching procedure (TCLP) tests were also performed to assess the environmental risks. The findings revealed that air-dried PG has a significantly lower maximum dry density than oven-dried PG. The air-dried UCS specimens were broken and damaged during demoulding, indicating poor strength, whereas oven-dried PG showed sufficient strength. The dry-cured UCS specimens showed significantly higher strength than water-cured UCS specimens. The leaching of primary trace metals was also found to be well within the permissible limits as per EU (Council decision 1993/31/EC) and USEPA 2003.