The Wet Acid Process
The WAP process was first patented in 1842 and represents >90% of all phosphoric acid production today.
- The core of the WAP process is breaking the strong bonds in fluorapatite (phosphate rock)—between calcium and phosphate ions.
- WAP produces phosphoric acid—the desired product—but at low concentrations and containing dissolved impurities; for high-value phosphate products, the impurities must be removed and the acid concentrated using steam energy.
- WAP also produces phosphogypsum (as calcium phosphate) , now contaminated with phosphoric acid and other impurities; phosphogypsumdisposal must comply with environmental regulations, adding capital, operating and closure costs to the WAP cost structure.
- WAP requires relatively high concentration phosphate rock (>28% P2O5) with low impurities; otherwise the reaction does not work effectively; this forces miners to produce higher quality rock, which both leads to inefficient exploitation of the limited natural resource and higher mining costs.
- Almost all WAP producers buy sulfur and make sulfuric acid in a dedicated sulfuric acid plant; the sulfuric acid plant usually provides all the energy needs of the facility but requires construction and operation of an additional process unit.
Wet Acid Process – Environmental Footprint
WAP byproduct. Phosphogypsum
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- Wet process operations result in the generation and perpetual storage of large quantities of phosphogypsum in stack systems (4.5–5.0 ton generated per ton of phosphoric acid produced)
- Phosphogypsum is an acidic and mildly radioactive precipitate that is deposited and maintained in large stacks and monitored over the lifetime of a phosphoric acid plant
- Phosphate companies must ultimately incur large site remediation and closure costs associated with the decommissioning and closure of phosphogypsum stack systems
- According to the Florida Industrial and Phosphate Research Institute (FIPR Institute) there are currently about 1 billion tons of phosphogypsum stacked in 24 stacks in Florida and about 30 million new tons are generated each year. These stacks are up to 200’ high and cover several hundred acres. Storing phosphogypsum and acidic water has risk and accidents have occurred.