Challenge

Dofasco, Inc., Hamilton, Ontario, Canada, needed to solve a waste problem resulting from the reclamation of ammonium sulphate and sulphuric acid. The mill had been recovering valuable products from a coking waste stream for a number of years.

Solution

The plant installed a Zimpro® wet air oxidation system to process coke oven gas scrubbing liquors containing hydrogen cyanide (HCN).

The process was designed so that ammonium thiocyanate, thiosulphate, suspended sulphur and organic material in the feed solution are oxidized in the liquid state to yield a product solution of 35 percent ammonium sulphate and two percent sulphuric acid.

The system was sized to treat between 34 and 83 liters per minute of diluted HCN effluent, with a COD of approximately 85 grams per liter.

Result

The plant experienced COD reductions of 97 percent; ammonium thiocyanate reductions of 99.9 percent, and suspended solids reductions of 98.1 percent.