Methods and systems for treating phosphogypsum-containing water
Methods for processing pretreated phosphogypsum wastewater are disclosed. Precipitation of select constituents may be promoted to control a hardness level of the pretreated wastewater. Ammonia may then be removed from the process stream via reverse osmosis. A membrane contactor and/or polishing unit(s) may optionally be used. Related systems are also disclosed.
1 . A method of treating phosphogypsum-containing water, comprising:
promoting precipitation of at least one target hardness species selected from one or both of a calcium species or a magnesium species from a pretreated supernatant to produce a process stream having a predetermined hardness level of about 100 ppm or less;
removing non-ionized ammonia from the process stream having the predetermined hardness level using a gas transfer membrane contactor to produce treated water meeting at least one predetermined discharge requirement selected from a conductivity limit or a level of ammonia, fluoride, or phosphorous; and
discharging the treated water.
2 . The method of claim 1 , wherein promoting precipitation of at least one target hardness species comprises precipitating calcium carbonate.
3 . The method of claim 2 , wherein soda ash is introduced to the pretreated supernatant to promote precipitation of calcium carbonate.
4 . The method of claim 1 , wherein removing non-ionized ammonia involves introducing the process stream to a reverse osmosis (RO) unit operation.
5 . The method of claim 4 , wherein the RO unit operation comprises a single-pass or a dual-pass RO unit operation.
6 . The method of claim 4 , wherein the non-ionized ammonia in the process stream is passed through the RO unit.
7 . The method of claim 6 , wherein a pH level of the process stream is adjusted to promote the passage of non-ionized ammonia.
8 . The method of claim 1 , further comprising producing ammonium sulfate.
9 . The method of claim 1 , further comprising introducing sulfuric acid to the gas transfer membrane contactor.
10 . The method of claim 8 , further comprising delivering the ammonium sulfate downstream for use as a fertilizer.
11 . The method of claim 1 , wherein the pretreated supernatant is sourced from a double lime treatment (DLT) operation.
12 . The method of claim 1 , further comprising polishing the treated water prior to discharge.
13 . The method of claim 12 , wherein the treated water is introduced to an ion exchange (IX) unit operation.
14 . The method of claim 13 , wherein the IX unit operation comprises cation exchange resin.
15 . The method of claim 4 , further comprising returning a RO concentrate stream to a source of the phosphogypsum wastewater.
16 . The method of claim 12 , further comprising returning a polishing rinse stream to a source of the phosphogypsum-containing water.