PHYSICO-MECHANICAL PROPERTIES OF BAUXITE RESIDUE-CLAY BRICKS

ABSTRACT This study is focused on consolidating knowledge on the application of Bauxite residue in the building industry. X-Ray fluorescence (XRF) reports of the bauxite and bauxite residue are given. Physico-mechanical properties of red mud (RM)-Clay (AC) bricks are also presented. The RM-AC bricks have compositions; 90%-10%, 80%-20%, 70%-30%, 60%-40%, 50%-50%, 40%-60% prepared and fired at sintering temperatures 800 o C, 900 o C and 1100 o C. The experimental results obtained showed that at each of the three stated sintering temperatures, bulk density increases as apparent porosity and water of absorption reduces. Bulk densities computed were within the range (1.3-1.8)g/cm 3 at 1100 o C sintering temperature. Maximum flexural strength was found to be associated with 50%-50% (Red mud-clay) composition at 1100 o C. And the compressive strength (3.2-12.5) MPa range found for all batches at 1100 o C sintering temperature. Generally, flexural and compressive strengths were increased with higher sintering temperature. The results obtained for various characterization analysis compares well with literature and hold potential in bauxite residue eco-friendly application as fired brick

Managing Excess Lead Iodide with Functionalized Oxo‐Graphene Nanosheets for Stable Perovskite Solar Cells

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI2) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI2. Dec-oxoG NSs provide anchoring sites to bind the excess PbI2 and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7 % in inverted (p-i-n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination and exhibit high stability under thermal and ambient conditions

Nonmetallic Inclusions in Solar Cell Silicon: Focusing on Recycling of Scraps

The solar grade silicon ingot produced from directional solidification process usually pushes the impurities to the top and finally cut off and discarded, which leads to material loss. The hard inclusions lead to wire breakages during the cutting of the ingot in wafers. The main kinds of inclusions found in solar grade silicon have been investigated using vacuum filtration: needle-like Si3N4 and lumpy SiC inclusions. Clusters of SiC inclusions and Si3N4 are also found. Surface observations of the scraps before polishing reveals that Si 3 N 4 inclusions are usually bigger and in some cases can be about a few millimeters. SiC inclusions are usually smaller, ~200mum but can be ~500mum in some cases. Inclusions observed after filtration are mainly SiC with diameters ~10mum. Through the vacuum filtration, 99% inclusions can be removed 99%. The possible mechanisms of filtration are cake filtration for the larger sized Si 3 N 4 and SiC inclusions and deep-bed filtration the SiC inclusions. For the directional solidified silicon ingot, an approximate distance of ~10mm gave an encouraging cutoff thickness. The inclusions sizes were below 10 m

Awaso bauxite red mud-cement based composites: Characterisation for pavement applications

This paper presents the development of Bauxite residue (red mud) based cement composite mortar blocks for applications in pavement construction. The experimental techniques considered include the structural, thermal, morphological and microscopy analysis of the raw bauxite and red mud samples calcined at 800 °C. Composite mortar blocks of different batch formulations were produced and their physicochemical properties were investigated. The results show that the compressive strength of the as-prepared composite mortar blocks increased by ∼40% compared to the type M mortar strength of ∼2500 N/mm2. The load bearing applications of the composites are discussed to influence the adoption of the calcined red mud as supplement in the production of low-cost Portland cement based composite mortar blocks for the construction industry

Effect of Magnesium and Sodium Salts on the Interfacial Characteristics of Soybean Lecithin Dispersants

One of the most widely accepted oil spill response strategies is chemical dispersant application. However, since the surfactant used in their formulation may be ionic, its interfacial characteristics may be influenced by ions present in the sea. In this work, we have examined the effect of magnesium salts (MgSO₄ and MgCl₂) and sodium salts (NaCl, Na₂SO₄, and sodium benzoate) on the interfacial characteristics of hydroxylated soybean lecithin dispersant (H–PI). The oil-in-water emulsions formed with magnesium salts were more stable than those formed with sodium salts. Magnesium salts recorded the highest interfacial tension reduction and the highest dispersion effectiveness values when compared with sodium salts. These observations were attributed to (i) the Mg²⁺ ions interconnecting the negatively charged headgroups of H–PI at the oil-droplet–water interface, thus increasing the surface elasticity and viscosity, and (ii) the smaller ionic size of Mg²⁺ allowing for easy packing between the charged head groups of H–PI

Activated cashew carbon-manganese oxide based electrodes for supercapacitor applications

The current global energy challenge which affects most developing countries in particular, is of major source of concern today. The availability of less expensive techniques of storing excess generated energy is critical to the success of the renewable energy roadmaps implementation. In this study, hydrothermal and chemical leaching methods have been used to synthesize MnO2 nanoparticles using KMnO4 and MnSO4 as precursors at 140 °C and from natural local manganese ore. Activated Carbon (ACF) have also been produced from agricultural Cashew biomass waste, through a physical carbonization and KOH activation process using temperatures of 700 °C – 900 °C for periods between 1 and 2 h. The as-prepared materials have been characterized via XRD, Raman, FTIR, SEM. Electrochemical performance measurements (CV, EIS and GCD) were carried out on the prepared electrodes. The specific capacitance values obtained were in the range of 2.8 F/g - 6.5 F/g at different scan rates of 20 mV -50 mV respectively in a potential range of -0.4 to +0.4 V and -0.4 to +0.6 V for the various types of electrodes

Corrosion behavior of 5-hydroxytryptophan (HTP)/epoxy and clay particle-reinforced epoxy composite steel coatings

The corrosion behavior of 5-hydroxytryptophan (HTP), and clay particulate reinforced epoxy coatings is studied on a steel substrate that is used widely in pipelines and tanks. The corrosion behavior was studied in sodium chloride (3.5 wt. % NaCl) solutions that simulate potential seawater exposure at pH 3 and 7. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were used for microstructural characterization of the samples. The thermal stability was characterized using Thermogravimetric Analysis (TGA). The underlying corrosion reactions and reaction products were also elucidated via Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical impedance spectroscopy (EIS) and in-situ observations of interfacial blisters were used to study the underlying degradation mechanisms. Electrochemical impedance spectroscopy revealed that for prolonged exposure of about 90 days and above, the composite materials exhibited better corrosion resistance at a pH of 3 as seen by the higher diameter of the Nyquist plot. Fewer corrosion products were observed on the scribed areas of the HTP samples in the scribe test in pH of 3 corroding environment. This signifies improved adhesion of the coatings in that environment for the HTP/epoxy coatings. The results obtained also show that a 1 mm blister size was observed in the pristine epoxy sample while no blisters were observed in the clay/epoxy and HTP/epoxy samples exposed at pH of 3. In the pH 7 environment, the EIS experiment revealed the presence of blisters with diameters in the range of 1–4 mm, after exposure for 90 days. The implications of the results are discussed for the corrosion protection of steel surfaces with composite coatings

Application of clay ceramics and nanotechnology in water treatment: A review

The increasing demand to provide clean water for drinking has brought to the fore the importance of seeking other materials with the ability or combined effect with other materials to purify water. Clay ceramics are known to be natural and also easily engineered porous-structured materials. Review papers on water filtration over the last decade have been on specific mechanisms or technologies. This review paper presents a single platform which provides information encapsulating all these technologies. This paper highlights water contaminants, and their various treatment technologies. The effectiveness of these technologies are evaluated via scholarly documented peer-reviewed papers. Moreover, the discussions are interspersed with the World Health Organization’s (WHO) standard for various contaminants along with the exploration of the efficiency of clay minerals as potent water filtration material. Finally, current trends in application of nanotechnology in water purification systems are also highlighted. These technologies include adsorption, microbial disinfection, and photocatalysis

Synthesis and Characterization of Modified Kaolin-Bentonite Composites for Enhanced Fluoride Removal from Drinking Water

Fluoride-contaminated drinking waters are known to cause severe health hazards such as fluorosis and arthritis. This paper presents the encapsulation of iron oxide nanoparticles in kaolin-bentonite composites adsorbents (KBNPs) for the removal of fluoride from drinking water by adsorption compared with kaolin-bentonite composite (KB). Adsorbents with an average weight of ∼200 mg and ∼7 mm diameter (granules) were prepared in the ratio of 10 : 10 : 0.1 for kaolinite, bentonite, and magnetite nanoparticles, respectively. The granules were air-dried and calcined at 750°C and contacted with 2 mg/L sodium fluoride solution at varying time periods. The adsorbents were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) formulation, and Brunauer–Emmett–Teller (BET), whereas the adsorption mechanism and the kinetics were explained using the Langmuir isotherm, Freundlich models, and pseudo-first-order and pseudo-second-order models. The results showed that the BET surface areas for the granules were 10 m2/g and 3 m2/g for KBNPs and KB, respectively. The SEM images for the adsorbents before and after adsorption confirm the plate-like morphology of kaolin and bentonite. The FTIR analyses of bentonite (3550 cm−1–4000 cm−1) and kaolin (400–1200 cm−1) correspond to the structural hydroxyl groups and water molecules in the interlayer space of bentonites and the vibrational modes of SiO4 tetrahedron of kaolin, respectively. The KBNPs composites also recorded a fluoride removal efficiency of ∼91% after 120 minutes compared with 64% for KB composites without Fe3O4 nanoparticles. The adsorptions of fluoride by the KBNPs and KB granules were found to agree with the Freundlich isotherm and a pseudo-second-order kinetic model, respectively. The results clearly show that the impregnation of clays with magnetite nanoparticles has significant effect in the removal of fluoride, and the implication of the results has been discussed to show the impact of clay-magnetite nanoparticles composites in the removal of fluoride from contaminated water