High pressure dewatering rolls: Comparison of a novel prototype to existing industrial technology

The Influence of Physical Activation of Portland Cement in the Electromagnetic Vortex Layer on the Structure Formation of Cement Stone: The Effect of Extended Storage Period and Carbon Nanotubes Modification

The article presents research of the influence of the electromagnetic vortex layer on the structure formation of cement stone during the activation of portland cement, both without additives and with carbon nanotubes modification. It has been shown that the storage of portland cement powders in open air for 60 days after activation in the electromagnetic mill leads to partial carbonization, wherein the role in absorption reducing of the super plasticizer additive is increased since there is more uniformly localization of the additive on the surface of the portland cement particles. The processing of portland cement in the electromagnetic mill leads to the physical activation of portland cement, which is accompanied by an increase in the amount of heat generated by the hydration of portland cement and the rate of hydration. Thus, the rate of hydration of compositions activated in the electromagnetic mill isincreased 1.615 times at the temperature of the thermostat 22 °C; 1.85 times at 40 °C; 2.71 times at 60 °C; 2.3 times at 80 °C. The modification of cement stonewith carbon nanotubes, which was obtained from portland cement activated in an electromagnetic mill, leads to a higher quantity of silicate phase of portland cement (by 12–39%), as confirmed by a decrease in the number of portlandite in these compositions by 8% in comparison with control composition.

Crystal Breakage Due to Combined Normal and Shear Loading

Combined normal and shear stress on particles occurs in many devices for solid–liquid separation. Protein crystals are much more fragile compared to conventional crystals because of their high water content. Therefore, unwanted crystal breakage is to be expected in the processing of such materials. The influence of pressure and shearing has been investigated individually in the past. To analyze the influence of combined shear and normal stress on protein crystals, a modified shear cell for a ring shear tester is used. This device allows one to accurately vary the normal and shear stress on moist crystals in a saturated particle bed. Analyzing the protein crystals in a moist state is important because the mechanical properties change significantly after drying. The results show a big influence of the applied normal stress on crystal breakage while shearing. Higher normal loading leads to a much bigger comminution. The shear velocity, however, has a comparatively negligible influence.

Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems

In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5-35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s^-1, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.

Consolidation of strong colloidal gels under arbitrary compressive loadings

Although highly successful, classical constitutive theories for the consolidation of strong colloidal gels are limited to one-dimensional (1D) uniaxial consolidation. Many consolidation applications are inherently multidimensional and there currently exists little understanding and no constitutive theory for how strong colloidal gels consolidate under arbitrary compressive loadings. In this study, we address this shortcoming by considering the consolidation mechanics of strong colloidal gels under arbitrary compressive loadings via 2D DEM biaxial simulations of assemblies of cohesive frictional particles. We show that although particle-scale consolidation differs significantly between uniaxial and isotropic consolidation, the maximum normal stress during consolidation is a unique function of the volumetric strain and hence the concentration of the solids phase. We use these insights to develop a generalised constitutive model for the macroscopic compressive rheology under arbitrary compressive loadings that is consistent with the classical constitutive model for uniaxial consolidation. Surprisingly, we find that this generalized constitutive model can predict multidimensional consolidation under arbitrary compressive loadings without need for further characterisation beyond uniaxial consolidation. These results provide significant insights into the consolidation of strong colloidal gels and facilitate prediction of multi-dimensional consolidation over a wide range of applications, and so represents an initial foray toward the development of a tensorial rheology of strong colloidal gels.

Pore Connectivity and Dewatering Mechanism of Tailings Bed in Raking Deep-Cone Thickener Process

Paste and thickened tailings (PTT) technology can improve the utilization and management of tailings from processing plants. The pore size distribution (PSD) and microstructure evolution affected by the rake shear in thickening tailings beds are essential to produce a high-density tailings underflow. Continuous thickening and computed tomography (CT) scanning tests were conducted to study the PSD with and without shear. The pore morphology was studied to reveal the shearing-dewatering performance of the tailings bed. The results show that at a flocculant solution concentration of 0.01 wt % and a feed slurry concentration of 10 wt%, the underflow concentration with and without shear can reach 58.5 wt %and 55.8 wt %, respectively. The CT image reconstruction models demonstrated that the porosity of the sheared tailings bed increased with the bed height. When the bed height increased from 2.5 to 10 cm, the porosity increased from 35.1% to 41.9%, the pore fractal dimension increased from the range 1.8–1.95 to the range 2.1–2.15, and the pore quantity decreased by 21.39%. The average pore volume increased with increasing height by 13.93%, 16.57% and 12.07%. The pore structure became more complex with the bed height, and the connectivity between pores increased to form water-flow channels, which were beneficial to the drainage of sealed water.