Table 2, mostly taken from Reference [1], shows the advantages and disadvantages of the different processes.
Table 2 ADVANTAGES Dihydrate Process Single stage filtration. Simple design. Flexibility of rock source. Proven process. Ease of operation/shut-down. Requires lower grades of materials of construction. Wet rock grinding possible. Low maintenance cost and high operating factors. Easy transport of gypsum slurry. Hemihydrate Process Single-stage filtration. Produces strong acid directly 40-48% P2O5. No intermediate storage if acid is produced at user's strength. Uses coarse rock. Ease of operation.
HRC Process Single stage filtration. Proven process with sedimentary rock. Produces a pure gypsum. Higher P2O5 efficiency (97%). Slightly higher acid strength (30-32% P2O5). Lower sulphuric acid consumption. Lower filter area.
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DISADVANTAGES
Produces acid at 26-32% P2O5. Normally requires steam for evaporation. Acid has high levels of F and Al. P2O5 efficiency 94-96%. May require rock grinding. Requires weak acid storage and evaporation.
Limited number of rocks processed industrially. Large filter area required for 48% P2O5 acid. High lattice loss, low P2O5 efficiency (90-94%). Produces impure hemihydrate. Tight water balance. Requires higher grade alloys. Care required in design and shut-down. Requires a fine rock grind. Requires sulphuric acid dilution. Large recrystallisation volume required. May dissolve more partially soluble impurities. Requires 32% acid storage and evaporation. Post-precipitation before and after evaporation. Requires sophisticated materials of construction.