Abstract
Voluminous quantity of phosphogypsum waste is generated by phosphoric acid manufacturing industry. Due to limited technologies available to treat the waste and render it useful, this waste is either landfilled or discharged into the sea in a form of slurry. It is critical that the focus shifts from landfilling or disposal into the sea as this result into environment contamination. This study was carried out to determine applications for raw and treated waste phosphogypsum in building and construction and determine the best conditions to produce the final product. Two significant, readily available waste materials namely phosphogypsum and fly ash were used and blended with hydrated lime. Conditions that yielded best strength from a mixture of phosphogypsum-lime-fly ash specimens were at elevated temperatures. The strengths obtained at the temperature of 80 0C were above the permissible strength for building masonry bricks of 3.5 MPa with unconfined compressive strength up to 4.8 MPa. At lower temperature of 40 0C the optimum strength obtained was at the minimal phosphogypsum content of 30%. The optimum strength was achieved at the PG content of 50% for raw PG and 60% for treated phosphogypsum at elevated temperatures. The strengths obtained for the treated phosphogypsum were lower than the minimum permissible load bearing strength due to the non-uniform particles distribution and the presence of impurities and forces of adhesion between citric acid and phosphogypsum. Increasing the curing temperature also reduced the radionuclides initially present in the raw PG without any prior treatment.