INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, vol.34, no.5, pp.1914-1918, 1995 (SCI-Expanded)
For preparing reasonably pure MCP . H2O and DCP . 2H(2)O from wet-process phosphoric acid, a neutralization process consisting of four consecutive steps and using Ca(OH)(2) as the neutralization agent is suggested and the optimum conditions of the first step are examined. The first step of the suggested process consists of removing sulfate ions, heavy metal ions, and suspended organic impurities. Removal of sulfate and heavy metal ions is carried out by neutralizing the acid with Ca(OH)(2) and by reacting it with Na2S. Precipitated CaSO4 . 1/2H(2)O and heavy metal sulfides are removed from the acid by filtration. Removal of the suspended organic impurities takes place during the filtration since they are retained by the filter cake. It is found that sulfate removal of 98-99% and almost complete heavy metal and suspended organic impurity removals are performed when the weight ratios of Ca(OH)(2), Na2S, and H2O to wet-process phosphoric acid are 0.05, 0.02, and 0.2, respectively, at the neutralization temperature of 75-80 degrees C and with a reaction time of 2 h.