Phosphogypsum: A Review of the Florida Institute of Phosphate Research Programs to Develop Uses for Phosphogypsum
Phosphogypsum disposal was a very simple matter in the early days of the industry. If at all possible, you located your plant near the ocean or on a river and dumped the phosphogypsum into the sea or the river. If you were foolish enough to locate where water disposal was not possible, you suffered the economic penalty of having to stack the phosphogypsum on dry land. The industry developed first in Europe and due to a number of circumstances, phosphogypsum disposal of any type did not create a problem because:
(1) Plants had very low capacities, often producing only 25 tons per day of P2O5 (typical plant today is rated at 1000 tons per day) with no more than 120 tons per day of gypsum for disposal.
(2) Since gypsum is slightly soluble in water, river dumping did not create problems for river traffic because there was no accumulation of material to block the channel.
(3) Ocean disposal was ideal since gypsum is more soluble in salt water than it is in fresh water. While ocean disposal has now been restricted, this disposal method has been demonstrated to have minimum adverse environmental effects when done properly.
(4) Land disposal was not a major problem due to the small quantities of material to be handled.
While some of the earlier plants in this country practiced water disposal, most of the phosphogypsum produced here has been piled on land. Again, it must be remembered that plant size (capacity) was a big factor in determining if there was a phosphogypsum problem. With the advent of 300, 500, 1000 and even 4000-5000 tons per day P2O5 plants, the phosphogypsum disposal problem took on new aspects. While most of the rest of the world looked at phosphogypsum as a valuable raw material and developed processes to utilize it in chemical manufacture and building products, this country – blessed with abundant low-cost natural gypsum – piled the phosphogypsum up rather than bear the additional expense of utilizing it as a raw material. It should be noted that during most of this time period the primary reason phosphogypsum was not used for construction products in this country was because it contained small quantities of fluorine and P2O5 as impurities and fuel was required to dry it before it could be processed. It has only been in recent years that the question of radioactivity has been raised and this question now influences every decision relative to potential use in building products in this country.
Phosphogypsum utilization has evolved along three broad use groupings:
(1) Chemical raw material
(2) Agricultural applications
(3) Construction materials
Each of these uses will be considered in more detail, but it should be pointed out that for years Florida has not been in the forefront of the efforts to utilize phosphogypsum. The impetus to develop uses for this material has come from countries where land area for phosphogypsum storage is in very short supply and/or very expensive, or where the cost to utilize natural gypsum exceeded the cost of utilizing the phosphogypsum. In most of this country, and specifically Florida, economic incentives to develop uses for phosphogypsum have not existed. A common theme can be found in the worldwide history of the development, adoption and abandonment of phosphogypsum utilization schemes – economic incentive. This critical influence of economic incentives will be obvious in the following discussions.