Experimental Investigation of Soapstone and Granite Rocks as Energy-Storage Materials for Concentrated Solar Power Generation and Solar Drying Technology.

The intermittence of solar energy resource in concentrated solar power (CSP) generation and solar drying applications can be mitigated by employing thermal energy storage materials. Natural rocks are well recommended thermal energy storage materials as they are efficient for CSP generation. This study explores the potential of soapstone rock and also the influence of the sites' geo-tectonic setting to soapstone and granite rocks as thermal energy storage materials. Experimental characterization was done to investigate the thermo-chemical properties (thermal stability (TGA), crystalline phases (XRD), petrographic imaging and chemical composition (XRF), and high temperature test); the thermo-physical properties (density, porosity, specific and thermal capacity (DSC), thermal diffusivity, and conductivities (LFA)); and the thermo-mechanical properties (Young's modulus) of the rocks. Consequently, the rock with the most desired properties for thermal energy storage was the soapstone rock from the Craton geo-tectonic setting and it had a Young's modulus of 135 GPa at room temperature. At solar drying and CSP temperatures it had thermal capacities of 3.28 MJ/(m3·K) and 4.65 MJ/(m3·K); densities of 2.785 g/cm3 and 2.77 g/cm3; and conductivities of 2.56 W/(m·K) and 2.43 W/(m·K) respectively, and had weight loss of 0.75% at 900 °C. At high temperatures, only granite from Craton had visible cracks while the other 3 rocks did not show visible signs of fracture. Conclusively, soapstone and granite from Craton in the Dodoma region and Usagaran in the Iringa geo-tectonic settings exhibit significant differences in most thermo-properties.

Removal of fluoride from water using activated carbon fibres modified with zirconium by a drop-coating method.

Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO32-, HCO3- and Cl- had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO42- decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal.

Effect of Elevated Temperature on Compressive Strength and Physical Properties of Neem Seed Husk Ash Concrete.

High temperature rise mostly caused by a fire outbreak is currently becoming a threat that endangers concrete's structural performance for buildings and the safety of occupants. The behavior of concrete after fire subjection has been of much interest for the structural materials design purposes. This study investigated the physical properties and the compressive strength of M25 concrete incorporating Neem Seed Husk Ash (NSHA), exposed to and through targeted different levels of temperature (200 °C to 800 °C) for a period of three hours in an electric furnace. The NSHA was produced by calcining neem seed husks at 800 °C for six hours and then sieved through the 125 µm sieve. Different amounts of NSHA were investigated while considering the plain concrete as the control sample. 150 concrete cubes of 150 mm sizes were cast and properly cured for 7 and 28 days. The experimental results show that the compressive strength of the 5% NSHA concrete exposed to temperatures up to 400 °C is 21.3% and 23.8% better than the normal concrete at 7 and 28 curing days, respectively. Surface cracks and spalling are noticeable at 600 °C and 800 °C for all samples considered in this study.

Crustacean derived calcium phosphate systems: Application in defluoridation of drinking water in East African rift valley.

Calcium phosphate adsorbents, derived from prawns and crabs shell biomass wastes have been developed using wet chemistry and low temperature treatment. The adsorbents were characterized by X-ray diffractometry and Fourier transform infrared spectroscopy. Batch adsorption test were carried out to investigate their effectiveness in adsorption of fluoride from ground and surface waters. Adsorption capacities were compared with bone char and synthetic hydroxyapatite (CCHA). Results indicate that prawns derived adsorbent (PHA) formed hexagonal structure with phases identifiable with hydroxyapatite while crabs based adsorbent (CHA) formed predominantly monoclinic structure with crystalline phase characteristic of brushite. Vibrational analysis and kinetic studies predicted defluoridation occurred mainly by ion exchange and ion adsorption mechanisms. Defluoridation capacity of the adsorbents was found to be superior compared to bone char and CCHA. CHA was the most effective with efficiencies above 92% and highest capacity of 13.6 mg/g in field water with fluoride concentration of 5-70 mg/L. PHA had highest capacity of 8.5 mg/g which was still better than 2.6 mg/g recorded by CCHA and bone char. Adsorption was best described by pseudo 2nd order kinetics. The findings indicate that crustacean derived calcium phosphate systems have better potential for defluoridation than traditional bone char and synthetic systems.