Application of Screw Press Filtration to Tailings Dewatering

A pilot scale screw press filter was tested at an operating mine site where it filtered coal tailings containing high levels of kaolin clays. Its performance is compared to that of a recess plate pressure filter that was used to filter the same tailings materials at the same time. During the pilot scale site filtration program, various flocculant types, dosing rates, concentrations, addition points and mixing regimes were trialled. The following performance characteristics were measured:

· Hydraulic drainage capacity;

· Solids throughput capacity;

· Filter cake solids concentration;

· Filtrate clarity and solids loading;

· Performance when fed with a range of clay rich tailings;

· Flocculant consumption;

· Operating process stability;

· Equipment wear rates.

The filter feed materials were characterized using XRD to determine mineral content, geochemically to determine exchangeable and soluble cations content and geophysically to determine size distribution and particle density.

The filter feed materials were also analysed in a series of laboratory tests to determine the optimum flocculant dosing regime for maximum floc size and strength. The processes investigated were:

· Turbulence (intensity of mixing);

· Mixing time;

· Staged addition of anionic polyelectrolyte flocculant;

· Flocculant concentration;

· Final addition of cationic polyelectrolyte flocculant; and

· Anionic and cationic polyelectrolyte flocculant type.