This work is an investigation of a relatively new process to upgrade carbonaceous phosphate rocks via direct carbonation with CO2-water solution. The process is mainly based on the reaction of the CaCO3 present in the phosphate ore with CO2-water solutions to convert the former to a water-soluble compound (i.e. calcium bicarbonate). The carbonation experiments were carried out in a 0.054 m inner diameter column and 1.7 m high. The parameters that may affect the dissolution of CaCO3 in the CO2-water solution such as column pressure and temperature, CO2-bubbler perforation diameter, CO2 flow rate, phosphate particles size, solid/liquid ratio in the slurry mixture, and the slurry height in the column were investigated. The effects of before-carbonation phosphate ore preheating as well as multiple carbonations were also examined. It was found out that the rate of dissolution of CaCO3 increased with the increase of pressure inside the column, CO2-bubbler perforation diameter, and CO2 flow rate. Furthermore, it increased with the decrease of phosphate ore particles size, slurry height in the column, and temperature. Low solid/liquid ratio of 30-50 g phosphate ore per liter of CO2-water solution were found to give better dissolution rates. The heating of the phosphate ore to 150degreesC for 15 min (before carbonation) gave better dissolution than other preheating temperatures and time intervals. By multiple carbonation, it was possible to remove about 90% of the CaCO3 present in the phosphate ore in 10 stages. The recovery of CO2 and production of CaCO3 precipitate is possible and can be easily handled by heating the calcium bicarbonate solution under vacuum. (C) 2003 Elsevier B.V. All rights reserved.