The use of zeolite-based additives for immobilising iron during pressure filtration of coal refuse slurry.

Pressure filtration of coal refuse slurry has the potential to provide a concentrated solids stream that can be stacked, thereby offering multiple environmental benefits. However, potential leachates from the solids stream can impact the environment. In that context, this study performed preliminary investigations of the application of zeolite-based additives to adsorb metals leaching from coal refuse slurry at low pH. Additives were added to the coal refuse slurry, which was filtered using bench- and lab-scale pressure filtration units. Results indicated that the overall filtrate flux and cake moisture characteristics were not significantly affected by the addition of additives up to 20% (by weight of solids). It was shown that adsorption as high as 80% was achieved by using the additives to capture iron. It was concluded that the finer additive with less silicon content was more effective in capturing iron. The results showed that the thickener feed stream leached out less iron than the thickener underflow stream. The adsorption process was not significantly affected by slight variations in initial iron concentration in the solution. The use of lower pH water on the filter cakes treated with the additive showed minimal release of iron and manganese into the aqueous phase.