The link below may help:

https://www.suezwaterhandbook.com/water-and-generalities/fundamental-physical-chemical-engineering-processes-applicable-to-water-treatment/chemical-precipitations/removing-hardness-calcium-and-magnesium

Ionosmosis could be a simple way to treat the very hard water directly. You find a paper about here in Research Gate. Best regards

Matthias

Sodium Acetate as a Replacement for Sodium Bicarbonate!

Please kindly read the following article

Article Sodium Acetate as a Replacement for Sodium Bicarbonate in Me...

Dinesh Gudadhe

You wrote "... is then treated with calcium carbonate to reduce the hardness ...".

I assume that the "calcium carbonate CaCO3" should be read as "sodium bicarbonate NaHCO3", right?

I understand that you use lime Ca(OH)2 to neutralize the acid wastewater as to precipitate the heavy metals. In that case, I would recommend to dose sodium hydroxide NaOH (with automatic pH control) and add a dose of sodium sulfide Na2S to precipitate the heavy metals.

As to reduce hardness without adding any chemicals incl. sodium bicarbonate NaHCO3, I would recommend to use a pellet reactor with grounded calcite (100% CaCO3).

Thanks for your suggestion and input. We are looking for alternative to existing treatment which must be economical than existing.

Dinesh Gudadhe

Your current lime based treatment is indeed not really sustainable and economic.

It requires massive quantities of lime (cost 1) to precipitate the metals in the acid (low pH) effluent as hydroxides at high pH, producing a lot of calcium carbonate + metal hydroxides sludge (cost 2) and increasing hardness considerably. Then this hard effluent is neutralized by adding a lot of acid (cost 3) and the 5000 ppm hardness is reduced by adding a lot of sodium bicarbonate NaHCO3 (cost 4). Both steps increase salinity and TDS a lot which needs to be removed for ZLD (cost 5).

That's exactly why I proposed our proven efficient treatment that does not increase hardness and that removes metals very selectively.

If still in doubt, then I would recommend to do a comparative lab test of both methods and calculate all your quantities of chemicals, sludge and TDS with their costs 1 to 5.