MINING-NITRIC ACID

Parsons Case Study:
Mining – Nitric Acid

Executive Summary

Parsons were asked by a major mining consortium, with a site in Zambia, to prepare a design study for the effective treatment of Nitrogen Oxides (NOx) on the gold refining process, at a copper mining facility. The study was taken up and the recommended solution followed.

Challenges

Concentrated Nitric Acid (HNO3) is used in the refining of gold ore remnants, which produces high concentration discharges to the treatment ventilation system, initialy estimated at 5000 and later found to be in excess of 50,000 parts per million (ppm).

The discharge from the treatment ventilation system had to comply to the National Mining Inspectorate requirements.

Solution

Parsons designed, manufactured, installed and commissioned a turn-key packed column absorption system.

This was complete with an extract fan, a stack, a chemical storage and dosing system manufactured from polypropylene GRP in accordance with BS 4994:1987  (BS EN 13923:2005, BS EN 13121-3:2008+A1: 2010).

Results

Due to the constraints of the available testing equipment the initial discharge concentrations were significantly underestimated. The absorption package was installed and commissioned. On testing the unit, the percentage removal efficiency was found to be greater than promised, however the discharge levels were still too high due to the exceptional inlet concentrations. The inlet was re-tested with more appropriate equipment giving a more accurate picture. With the revised data Parsons were able to apply their knowledge of scrubbing plant to  re-sequence the package with minimum disruption to the client and bring discharge levels down to a level acceptable to all parties.

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