Studies were conducted in a laboratory pressure filter to evaluate and enhance the dewateringpotential of a thickener underflow sample from an operating coal mine in central Illinois. Thephysical properties of the sample such as, size distribution, zeta potential variation with pH (zetapotential and point of zero charge), microstructure and particle shape (via scanning electronmicroscopy), and ash content were evaluated. In addition cake microstructure data was obtainedthrough scanning electron microscopy (SEM).Experiments were conducted at a pressure of 42 psig. The initial solids content was maintainedat 15% in all the experiments. The baseline experiment yielded a cake with 33% moisturecontent. Intermittent breakup of the cake structure produced a thinner cake with moisturecontent that was 7% lower than the baseline case. The introduction of copper ions into the slurryresulted in enhanced filtration rates due to reduced specific resistance to filtrate flow andincreased porosity of the cake. Use of cationic and anionic surfactants reduced the total residualmoisture by over 4%. The combined effect of a surfactant and copper ion resulted in furtherreduction in cake moisture along with significant improvement in dewatering rates. Elevatingthe temperature of the slurry to 55 °C showed only a slight improvement in filtration rate butproduced the most compact cake with the lowest moisture content.Key implications of the findings of this study include the ability to achieve low moisture contentcakes at a high throughput for reduced capital expenditures on the filtration equipment.
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