Mine water pH adjustment
November 2010
System Integration & Control Systems Design
Mine underground water, process run-off and underground clarifiers and settling ponds suffer from pH difficulties. These arise from the different water uses and the characteristics of the different mining types. pH outside of the standard or ‘balanced’ range does not bode well for some flocculants and biocides and renders them ineffective. One mine in particular, outside of South African borders, was struggling with very low pH and control was limited to ‘throwing bags of lime into the clarifiers’. The problems arising from this were:
* Unstable pH complicated by pH bounce.
* Settling of the lime inside the clarifiers and hence not being distributed efficiently.
* Biocides are ineffective outside of their active pH range.
* Wastage of chemicals.
What was needed was on-line monitoring and controlled proportional dosing of a pH adjuster. Lime (alkali) being most effective for large-scale pH adjustment (to bring up the pH) would be the obvious choice. The solution sounds straightforward in principle; however, ProMinent discovered underground applications are more complex.
The pH measurement would have to be done three floors below the area for the lime dosing and make up. The make up system would have to be within the lime storage area, and the final lime dosing point would be in excess of 300 metres away. To further complicate the matter, there was no off the shelf lime make up system within the company’s range of products.
The solution, having assessed the system and complexities: a make up system based on the ProMinent flocculent make up system. The Ultromat type system makes up a solution proportional to flow and maintains the lime in a suspended solution. The pH measurement was achieved using 4-20 mA transducers to overcome the 300 m distances. The dosing was simplified using the ProMinent range of peristaltic with integrated VSD drives.
The result: a fully automated pH measurement, pH control, automated lime make up system and accurate reliable dosing all from a single source. The immediate benefits realised, were automated and accurate pH control, lower chemical costs and reliable disinfection from stable pH.
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