This paper presents the effect of adding dihydrate phosphogypsum, which is a byproduct of the production of phosphate fertilizers, on the mechanical behaviour of a lateritic clay typical of Brazil�s Midwest region. Because of the distinction of the mechanical behaviours of both materials, laboratory experiments were conducted with soil, phosphogypsum and mixtures with 10%, 20% and 50% phosphogypsum content. One-dimensional consolidation, direct shear and scanning electron microscopy (SEM) tests were conducted on optimally compacted specimens to show the effect of the loading time on the mechanical parameters of the materials. Water percolated through the materials was chemically analysed to verify the groundwater level contamination potential due to cation lixiviation in phosphogypsum. The results show that the addition of phosphogypsum to the soil increases the compressibility without significant effect on the strength parameters, and the broken phosphogypsum particles make the mixture deformability depend on the loading time. With this study, one can conclude that the dihydrate phosphogypsum content in geotechnical works must be maintained below 20%, since higher ratios negatively affect the soil mechanical behaviour and ground water contamination potential. This study also presents an option to reuse and dispose of the most commonly produced phosphogypsum type in Brazil.