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Defining the MgO Problem and Its Economic Impact on Phosphoric Acid Production


This report covers a series of phosphoric acid pilot plant tests performed to determine the major effects of treating phosphate rocks containing relatively high quantities of MgO, up to 1.8%.

Run Averages are given in Table 2. Average Analyses – USAGES & PRODUCTS, are given in Table 3. Rock analyses are summarized in Table 4.

The tests show, as expected, increased losses and reduced filtration rates as the MgO is increased. Figures 1, 2 and 3 plot total losses, filtration rates and water soluble losses as a function of reactor acid strength at parameters of 0.65%,1.23% and 1.80% MgO in the phosphate rock.

The higher MgO affects filtration rate, as summarized in Table 5 which is derived from the test data. It shows that for 1.23 MgO, the filtration rates are not appreciably dfferent to a base case of 100 for 0.65% MgO and 27% reactor acid. Probably the effect would not be noticed in terms of capacity but the water soluble losses are higher.

The plant would suffer substantially, however, in filter capacity if 1.8% MgO rock were treated. A significant increase in rate is experienced, dropping from 27% acid to 25% reactor acid. This would be about 24% P2O5 after dilution across the filter.