Phosphogypsum waste can be turned into calcium carbonate for metalmaking

A chemical treatment produced a coarser calcium carbonate product from phosphogypsum while converting nearly all of the starting material.

Editorial illustration — not from the study.

The study tested how temperature, sodium carbonate concentration, the liquid-to-solid ratio and contact time affect the conversion of phosphogypsum into calcium carbonate, also called phosphochalk. Fine particles made by existing approaches can be difficult to filter and limit potential uses.

The researchers found that temperatures of 90–100 °C and a liquid-to-solid ratio of 10 encouraged calcium carbonate crystals to form larger agglomerates. With 250 grams per litre of sodium carbonate and contact lasting up to three hours, the process produced phosphochalk with a D90 of 45 micrometres and a conversion degree of 98.8%.

Making larger calcium carbonate particles

The experiments showed that increasing the conversion temperature to 90–100 °C and the liquid-to-solid ratio to 10 promoted the formation of larger calcium carbonate agglomerates. A sodium carbonate concentration of 250 grams per litre combined with a phase contact time of up to three hours produced phosphochalk with a D90 particle size of 45 micrometres and converted 98.8% of the calcium sulfate dihydrate in the feedstock. Based on its reported characteristics, the product was considered suitable as a raw material for flux production in the metallurgical industry.

A use for phosphogypsum waste

Phosphogypsum disposal sites can create complex environmental impacts, and the waste is produced in large quantities. Converting it into a calcium carbonate product with less fine-grained material could make filtration easier and expand its potential use as a secondary raw material. The study therefore provides process recommendations for a lower-waste route to phosphogypsum utilization, although it does not by itself establish how much waste could be processed commercially or how much environmental impact would be avoided.

What the experiments show

The findings come from a series of single-factor laboratory experiments examining reaction conditions. The abstract reports conversion and particle-size results under specified conditions, but it does not describe pilot-scale or industrial trials, long-term product performance, a life-cycle assessment, or an economic comparison with conventional flux materials. The claim of suitability for metallurgical flux production is based on the product’s reported characteristics rather than a reported test of its performance in an operating metallurgical process.

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