By-Products from the Wet Process

Wet process acid contains most of the uranium present in the original rock, and when the acid is concentrated to a typical value of about 54% P2O5, it can contain 100 ppm or more of the uranium heavy element. This compares well with seawater (-0.003 ppm) and conventional uranium ores (350-5000 ppm). 

Solvent extraction of wet process uranium is now commercially feasible - most of the available processes use phosphate esters, for example, tri-octylphosphine oxide and di-2-ethylhexyl phosphate in kerosene (Chapter 12.11). Significant quantities of rare earth elements such as La and Th are also present, but commercial extraction of these is not yet economic [10,11]. 

FIGURE 5.2 Commercial utilisation of phosphate rock - towards the end of the twentieth century. 

The fluorine is a potentially valuable by-product and most of it can be recovered as Sip4 or H2SiFg. Present recovery processes do not, however, seriously compete with mined fluorite as a source of the element. 

Examples are friction compounds (for brakes), based on phosphogypsum and butadiene rubber [12], sound-proofing panels based on phosphogypsum and mineral wool [13] and wood products modified with phosphogypsum and urea formaldehyde resins [14]. Use in supersulphate cements and as a paper filler has also been considered. There has also been limited use as a soil conditioner. 

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