Not all gypsum products are alike and some can be downright ineffective and even hazardous so know what you are buying before you purchase and apply it.
Gypsum can be mined from deposits or derived as a by-product from industrial processing. Synthetic gypsum can come from citric and lactic acid processing plants, phosphoric acid processing plants, or water treatment plants. It can also come from commercial power plants when calcium carbonate is used to neutralize acid solutions or capture sulfuric oxides for exhaust gases. Some of these synthetic gypsum products are similar to mined gypsum in terms of their dihydrate equivalent however some sources can contain metal or radioactive contaminants and shouldn’t be land applied.
It’s worth noting there are particular risks with phosphogypsum. Phosphogypsum is created as a byproduct when rock phosphate is treated with sulfuric acid to make phosphoric acid. Phosphoric acid is a basic ingredient in phosphorus fertilizers and other industrial products. Unfortunately phosphogypsum can be radioactive due to the presence of naturally occurring uranium or radium in the rock phosphate ore and can’t be land applied for agricultural uses. For every ton of phosphoric acid produced by the wet process method, some four to five tons of phosphogypsum are also manufactured.
With that said, the presence and amount of radioactive material is very much dependent on the original source of ore. For example, rock phosphate mined and processed in Florida is contaminated, and there are enormous stockpiles of phosphogysum that currently have no use. However, in Brazil phosphogypsum does not pose the same risk since their igneous phosphate rock is low in such elements.
Like other mined and other synthetic gypsum, phosphogypsum can be used for soil amelioration. It all depends on the source of ore process.
Dr. Davidson posts articles on soil health and management related subjects. If you have suggestions for topics or questions, feel free to contact him at firstname.lastname@example.org or call 402-649-5919.