Three finely ground (−100 mesh) indigenous (Mussoorie, Udaipur and Purulia) and one exogenous (North Carolina, USA) phosphate rocks, acidulated with either sulphuric or phosphoric acid at three different levels (25, 50 and 75%) and cured at three temperatures (35, 45 and 55°C), showed that total phosphate content of acidulated products as compared to raw rock phosphate decreased with increasing degree of acidulation with H2SO4 but increased when acidulated with H2SO4. Both water soluble and citrate soluble P increased and insoluble P decreased with successive levels of acidulation, irrespective of the source of rock, acid and curing temperature. Mean available P (water soluble plus citrate soluble) content of partially acidulated phosphate rocks were in the order: North Carolina (9.27% + 4.39%) > Purulia (4.87% + 2.39%) > Mussoorie (1.71% + 4.15%) > Udaipur (3.04% + 2.34%). The water soluble as well as citrate soluble P decreased with increase in curing temperature from 35 to 55°C.
Partial acidulation, phosphate rocks, acids, water solubility, citrate solubility, curing temperature
