Phosphogypsum

The patent literature contains numerous recipes for constructional materials which utilise phosphogypsum, the waste material from superphosphate manufacture. Plaster of Paris and anhydrite plaster can be made from phosphogypsum (Chapter 4.1) [58]. 

Industrially produced phosphogypsum usually has a P2O5 content of 0.5 3.0%, depending upon the source of the original phosphate ore and the particular manufacturing plant which produced it (Table 5.4). 

Although a universally successful commercial outlet for this waste product has yet to be developed, one success has been in Japan where it is used for the manufacture of plasterboard and other plaster-based building products. 

The largest quantity of byproduct gypsum arises in the production of phosphoric acid (so-called phosphogypsum ) by the reaction of natural phosphates with sulfuric acid (see Section 1.5.1)  

7 t gypsum/l raw phosphate produced in production of wet process phosphoric acid 

Direct use in the construction industry hindered by impurities such as organic or inorganic admixtures or substances incorporated into the gypsum crystal lattice 

Two-stage phosphoric acid manufacturing processes producing phosphogypsum with lower impurity levels  

7 t gypsum/t raw phosphate produced is so impure that it is unsuitable for direct use in the construction industry. These impurities are either admixtures of organic substances soluble alkali and magnesium salts poorly soluble salts (e.g. Na2SiFf,) or phosphates and fluorides incorporated isomorphously in the gypsum crystal lattice. 

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Phosphogypsum [13397-24-5] is the name given to the by-product gypsum residue when phosphate ore is acidulated to extract phosphoric acid. There are several processes commercially used. AH of them digest or acidulate tri-calcium phosphate. 

Miiller-Kiihne A process for recovering sulfuric acid from phosphogypsum, the waste product from the manufacture of phosphoric acid. The process is economic only if the lime co-product is converted to cement. Based on the work of W. S. Muller and H. H. Kiihne at Bayer, Leverkusen, from 1915 to 1918. Further developed in Germany in the 1950s and still in operation in Germany and Austria in 1989. 

Phosphodiesters, 17 625 Phosphoethyl methacrylate, 16 242 Phosphogypsum, 4 593 23 511 Phospholipids, 10 804, 822 24 53 in cosmetics, 24 159 Phospholipid surfactants, 24 161 Phosphomolybdic acid (PMA), 19 438 Phosphomycin calcium, registered for use in aquaculture in Japan, 3 22 It Phosphonate esters, 19 37 Phosphonate finishes, 11 498 Phosphonates... 

In a recent document [25] presenting techniques adopted by the French for pollution prevention, a new process modification for steam segregation and recycle in phosphoric acid production is described. As shown in Figure 9, raw water from the sludge/fluorine separation system is recycled to the heat-exchange system of the sulfuric acid dilution unit and the wastewater used in plaster manufacture. Furthermore, decanted supernatant from the phosphogypsum deposit pond is recycled for treatment in the water filtration unit. The claim was that this process modification permits an important reduction in pollution by... 

Figure 10 Phosphogypsum pond water seepage control (from Ref. 7).

With varying temperature and acid concentration either anhydrite (AH, x=0), hemihydrate (HH, x=l/2) or dihydrate (DH, x=2, also called gypsum) is crystallized from the acidic solution (see figure 1). As this so-called phosphogypsum is usually disposed, the (quality itself is not... 

EPA (1992b). U.S. Environmental Protection Agency. 40 CFR Part 61— National emission standards for hazardous air pollutants national emission standards for radon emissions from phosphogypsum stacks, Final rule, 57 FR 23305 (U.S. Government Printing Office, Washington). 

S.M. Luther, L. Poulsen, M.J. Dudas, P.M. Rutherford, Fluoride sorption and mineral stability in an Alberta soil interacting with phosphogypsum leachate, Can. J. Soil Sci. 

M.P. Motalane, C.A. Strydom, Potential groundwater contamination by fluoride from two South African phosphogypsums, Water SA 30 (4) (2004) 465-468. 

The Florida Institute of Phosphate Research (FIPR) has studied phosphogypsum utilization at length, but the U.S. Environmental Protection Agency has prohibited its movement from its stacks (piles) because of its low level radiation. The FIPR hopes to show that its use in road building subsurfaces and as an additive to enhance digestion of municipal waste in landfills can be accomplished without harm to the public now or in the future.25 26... 

Wissa, A. E. Z., and Fuleihan, N. F., Phosphogypsum Stacks and Ground Water Protection, Phosphorus Potassium May/June, 2000. 

Calcium sulfate may be decomposed to cement clinker and sulfur dioxide gas in a coke-fired rotary kiln at 900-1400°C (Miiller-Kiihne).28 However, the unfavorable economics of this process relegate it to countries that do not have other sources of sulfur. Phospho-gypsum (gypsum produced by the acidulation of phosphate rock) may be decomposed in this way as a means of recycling the sulfur values in the large waste phosphogypsum piles at fertilizer plants (OSW-Krupp and FIPR/Davy... 

Kazman,Z.,I. Shainberg, and M. Gal. 1983. Effect oflow levels of exchangeable Na and applied phosphogypsum on the infiltration rate of various soils. Soil Sci. 135 184-192. 

POSTER TITLE Extraction of rare earth elements from phosphogypsum... 

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