Acid Mine Drainage Neutralisation Estimator
Estimate the alkaline reagent (limestone, hydrated lime, quicklime or caustic soda) needed each day to neutralise acidic mine water, from the water flow and its acidity. A quick stoichiometric first-pass for planning treatment of acid mine drainage (AMD).
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the water flow in megalitres per day (ML/day) and the acidity in mg/L expressed as CaCO₃ (from a laboratory titration).
- Choose the reagent stoichiometric factor: 1.0 limestone (CaCO₃), 0.74 hydrated lime (Ca(OH)₂), 0.56 quicklime (CaO) or 0.80 caustic soda (NaOH). Leave blank for limestone.
- Optionally set the reagent purity (%); the tool returns the acidity load and the reagent required in kg/day and t/day.
How it works
The acidity load is the mass of acidity to be neutralised each day, expressed as calcium carbonate: load (kg/day) = acidity (mg/L as CaCO₃) × flow (ML/day). The units line up because one milligram per litre carried in one megalitre is exactly one kilogram. Each neutralising agent supplies a different amount of acid-neutralising capacity per kilogram, captured by a stoichiometric factor relative to CaCO₃ (100 g/mol, one equivalent): limestone 1.0, hydrated lime 0.74, quicklime 0.56, caustic soda 0.80. The reagent mass is then load × factor, divided by the purity fraction to account for inert content: reagent (kg/day) = load × factor ÷ (purity/100).
Worked example
Worked example. A pit-dewatering discharge of 2 ML/day has an acidity of 500 mg/L as CaCO₃, to be treated with hydrated lime (factor 0.74) at 90% purity. Acidity load = 500 × 2 = 1,000 kg/day as CaCO₃. Reagent = 1,000 × 0.74 ÷ 0.90 = 822.22 kg/day, or about 0.822 t/day of hydrated lime.
Common mistakes
- Entering acidity as pH instead of a titrated acidity in mg/L as CaCO₃ — pH alone cannot give the acid load.
- Using the wrong stoichiometric factor for the reagent, which directly scales the mass required.
- Treating the result as a final dose — it ignores reaction efficiency, mixing and a safety margin, so real dosing runs higher.
Frequently asked questions
Why is the acidity expressed 'as CaCO₃'?
Acidity and alkalinity in water chemistry are conventionally reported as an equivalent mass of calcium carbonate so that acid and neutralising agents can be compared on one scale. The stoichiometric factors here are all relative to CaCO₃.
Does a lower factor mean a cheaper reagent?
Not necessarily. A lower factor (e.g. 0.56 for quicklime) means less mass is needed for the same neutralising power, but cost, handling, safety, sludge volume and dissolution rate all differ between reagents and must be weighed alongside mass.
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