I have achieved significant success in reducing my sulphates in the effluent by dosing calculated quantities of lime Ca(OH)2. I found that I reduce the most sulphates out the optimum ph range is 9-13. I want to try and see if I cannot reduce my sulphates even more by forming sodium sulphate Sludge as well Na2SO. This I would achieve by using my expired stock of the following powders: Na2CO3, NaHCO3 CaCO3. I know I might be forming a lot of carbon dioxide. Please any advice or Experience on this.
I knew that I cannot achieve great success on that route, what I'd do rather is to consider forming a barium salt (BaSO4) rather. High pH proved to achieve great success in the lab (1L), pilot plant (1000L) and also large scale (9000 L).
The solubility of sodium sulfate (Na2SO4) in water is 9500.0 mg/L.
The solubility equilibrium is given by:
Na₂SO₄(s) ←→ 2Na⁺(aq) + 2SO₄²⁻(aq)
The process must have the following characteristics:
· Low concentrations of sulfate in treated water,
· Additional removal of metals and other parameters,
· No liquid waste, and
· A minimal volume of hazardous solid waste.
The most common method for removing high concentrations of sulfate from water is through addition of hydrated lime (Ca(OH)2), which precipitates calcium sulfate:
Na2SO4 + Ca(OH) 2 => CaSO4 + 2 NaOH.
Calcium sulfate has a solubility of approximately 2000 mg/L as sulfate. 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.
Lime is inexpensive, readily available and produces stable products which can be reused or disposed in landfills. The sludge produced is dewatered separately in a filter press to prevent contamination of the pure gypsum.
For further precipitation another step of treatment is needed for Formation of Insoluble Complex [ETTRINGITE, Reduction of Sulfate to < 50 mg/L).
Thank you Elisavet for the valuable information. Using Sodium sulphate will obviously be not a good idea. I'm currently using hydrated lime my sulphate concentration is usually between 1500-10000 mg/l. and my well designed process is able to reduce the sulphates to even below 500mg/l-200mg/l, which is far below my municipal limit (< 1500 mg/l).