Enhancing shear strength and handleability of dewatered clay-rich coal tailings for dry-stacking.

Mineral tailings dams pose high pollution risks to the environment and catastrophic failures. Dry stacking has been identified as a promising alternative to mitigate these risks and offers various benefits to the mining industry but lacks systematic research outcomes. To facilitate dry stacking, coal tailings slurries were dewatered using either filtration or centrifugation methods, resulting in a semi-solid form (cake) that can be safely disposed of. The handleability and disposability of these cakes are greatly influenced by the selection of chemical aids (such as polymer flocculants) and the mechanical dewatering technique employed. The effects of polyacrylamide (PAM) flocculants with a range of molecular weight, charge, and charge density are presented. Coal tailings samples with differences in clay mineralogy were dewatered using press filtration, solid bowl centrifugation, and natural air drying. Handleability and disposability of the tailings were assessed by their rheological properties, including yield stress, adhesive and cohesive stresses, and stickiness. Residue moisture, type of polymer flocculants, and clay mineralogy were found to be crucial factors affecting the handleability and disposability of the dewatered cakes. The tailing yield stress (shear strength) increased as the solid concentration increased. In the semi-solid regime (above 60 wt% solids), the tailings displayed stiff exponential growth. Similar trends were observed for stickiness and adhesive/cohesive energy of the tailings with a steel (truck) surface. Adding polymer flocculants increased the shear strength of the dewatered tailings by 10-15%, thus favouring disposability. However, the polymer selection for coal tailing handling and processing is a trade-off between its disposability and handleability, which requires a multi-criteria decision-making process. The current results also suggested that cationic PAM could be most suitable for dewatering by press filtration, while anionic PAM should be selected for dewatering by solid bowl centrifugation.

Improvement of dewatering characteristics by co-digestion of rice straw with sewage sludge.

A continuous mesophilic co-digestion of sewage sludge and softened rice straw was conducted and the dewatering characteristics of digested sludge were evaluated by a dewatering experiment using a belt press. The digestion was operated with solid retention time (SRT) of 25 days, and the feeding ratio of sludge to rice straw was 1:0.5 (total solids base). After 129 days of stable operation, the properties of digested sludge were analysed; then five kinds of cationic coagulants were tested to select the optimal coagulants for dewatering, and two coagulants were selected and used in the dewatering experiment because of lower doses and lower moisture of sludge cakes. Sludge property analysis showed that by the addition of rice straw, the fibrous materials in the digested sludge increased remarkably and the normalized capillary suction time (CST) decreased significantly, indicating that the dewatering properties was improved. The results of dewatering experiment showed that by the addition of rice straw, specific filtration rate of digested sludge increased by 81.2% and 174.6%, respectively; water content of dewatered sludge cakes decreased by 8.2% and 13.4%, respectively. The dewaterability of digested sludge was suggested to be improved due to rice straw addition.

A comparative study between spiral-filter press and belt press implemented in a cloudy apple juice production process.

In this study, advantages and disadvantages of the innovative, low-oxygen spiral-filter press system were studied in comparison with the belt press, commonly applied in small and medium size enterprises for the production of cloudy apple juice. On the basis of equivalent throughput, a higher juice yield could be achieved with spiral-filter press. Also a more turbid juice with a higher content of suspended solids could be produced. The avoidance of enzymatic browning during juice extraction led to an attractive yellowish juice with an elevated phenolic content. Moreover, it was found that juice produced with spiral-filter press demonstrates a higher retention of phenolic compounds during the downstream processing steps and storage. The results demonstrates the advantage of the use of a spiral-filter press in comparison with belt press in the production of a high quality cloudy apple juice rich in phenolic compounds, without the use of oxidation inhibiting additives.