The Cost Effective Sulfate Removal (CESR)
Many industrial wastewaters, particularly those associated with mining and mineral processing, contain high concentrations of sulfate. These concentrations typically exceed the secondary drinking water standard of 250 mg/L and may be subject to discharge limits between 250 and 2000 mg/L.
The Cost Effective Sulfate Removal (CESR) process was developed to address the shortcomings of other technologies used for sulfate removal. The advantages of the CESR process, which will be detailed later in this paper, are:
- Low concentrations of sulfate in treated water,
- No liquid waste,
- Additional removal of metals and other parameters, and
- A minimal volume of hazardous waste.
The most common method for removing high concentrations of sulfate from water is through addition of lime or calcium hydroxide (Ca(OH)2). This precipitates the sulfate as calcium sulfate (CaSO4):
Na2SO4 + Ca(OH)2 => CaSO4 + 2 NaOH
Calcium sulfate, which hydrates to become the common mineral gypsum, has a solubility of approximately 2000 mg/L as sulfate. Reuse of water with this sulfate concentration typically causes problems such as severe scaling in heat exchange systems, clogging of reverse osmosis or electrodialysis membranes, and precipitation in pipes. Discharge to surface water or to a publicly owned treatment works (POTW) may not be possible due to the water's high specific conductivity (SC) and total dissolved solids (TDS).
Sulfate reduction below 2000 mg/L has been possible in the past only through expensive technologies such as reverse osmosis (RO) or ion exchange (IX). Large volumes of liquid waste are generated with RO and IX, which typically create additional treatment and disposal costs. The CESR process can reduce the sulfate concentration in most wastewaters to less than 100 mg/L through use of a proprietary powdered reagent.
Hydrometrics, Inc., 2727 Airport Road, Helena, MT 59601. Tel: 406-443-4150; Fax: 406-443-0760.