Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

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Milk of Lime Dosage (1 reply)

(unknown)
8 years ago
(unknown) 8 years ago

I am doing a correlation between the pH and the theoretical Ca(OH)2 requirement in mg per liter of acid drainage to reach to neutral Zone and precipitate Fe and Al.

The expression has the following form: mgCa(OH)2/L acid = k pH ^( -n). Where k is a constant and n is an exponent. This expression is supported by lab tests and titration simulations in PHREEQC.

I need to validate this expression to adjust the automatic feed. Does anyone know a better way to do that?

Bob Mathias
8 years ago
Bob Mathias 8 years ago
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Sounds like a pH stat titration may suit your requirements first on a closed system to determine optimum dosing rates then on a flow through system to demonstrate dynamic system control. By undertaking the flow through titration at a range of discharge rates I think you should be able to correlate the volumetric dispensing requirements of Ca(OH)2 with influent flow and initial pH. Obviously in the field if there is a lot of variability in Fe and Al flux you may get some over shoot or under dosing, but if the free Fe and Al concentrations correlate well with pH then I think you would probably achieve reasonable pH control. The H+-Fe-Al system will also be dependent on other major ion water chemistry which would dictate which phases precipitate as pH is increased and could influence the overall buffering capacity (H+ stoichiometry) so maybe validating the choice of phases used in your phreeqc model with some mineralogical characterisation of the precipitate could help. This may be particularly useful if you anticipate there are secondary mineralisation reactions occurring over time (i.e. assessing the geochemical stability of the initially precipitated phase).

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