Green liquor dregs for injection, follow-up

Important results from the project

Aim with this project was to verify injection of green liquor dregs in larger scale. Apart from some minor practical/technical issues the project was running smoothly without any problems. The injection of green liquor dreg slurry increased pH in the leachates from around 3.8 to around 7.5. Concentrations of cobalt and copper were reduced with 87 and 92 %, respectively. The appearance of the pile did not change, which means that the piles “Eriks hög” are still accessible for mineral hunters and geoscientific research.

Expected long term effects

Follow-up measurements of leachates indicate a clear increase in pH, and with markedly decreased levels of cadmium, cobalt, copper, nickel, lead, and zinc. Increased concentrations have been noticed mainly for iron and sulphate, which probably has to do with acidic secondary minerals being dissolved as pH increased. When iron start to precipitate these levels will decrease. At the second sampling after injection levels of iron had significantly decerased. To summarize, the remediation worked very well and concentrations of main problematic elements decreased considerably.

Approach and implementation

As a whole the remediation was performed as planned without any major problems. Injection was done at 99 points evenly spread over the area. Green liquor dreg was transported from Mönsterås and was tipped close to Eriks hög. Slurry mixing was done using a pan mixer and pumping was performed using a slurry pump. A total of 63 tonnes of dry green liquor dreg was injected. The initial plan was that 120 tonnes were to be injected. The reason why less green liquor dreg was injected was that voids in the piles were too large to keep the slurry. This was due to the rocks being rather newly tipped on the area.