Phosphates containing two or more phosphorous atoms per molecule, being formed when orthophosphates are heated under controlled conditions. Pyrophosphates have two phosphorous atoms (for example, sodium acid pyrophosphate); tripolyphosphates having three phosphorous atoms (for example, sodium tripolyphosphate). Further heating polyphosphates and chilling forms a longer chain (for example, sodium hexametaphosphate). Functions include sequestering, buffering, and chelating. They are also termed condensed phosphates.
These reagents have a general formula Men＋2PnO3n+1 or MenPnO3n+1, where n can be between 1 and 106.
Polyphosphates have a number of functions in mineral flotation practice, some of which
include:
? Precipitation of heavy metal ions. Polyphosphates are used in the flotation of basemetal
ores where control of heavy metals is required.
? Depressing of iron sulfides and alkaline earth minerals during flotation of
copper–molybdenum ores. Some of the phosphate compounds are used as gangue
depressants during pyrochlore flotation and also during flotation of phenacite and
bertrandite.
