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One of the techniques used in extracting gold in small-scale gold mining is mercury amalgamation. However, the use of mercury presents significant health and environmental hazards, as well as suboptimal efficiency in gold extraction. This study explores the possibility of the use of rice husk as a prototype adsorbent for mercury removal from its leaching in mining environments. To support the analysis, the rice husk adsorbent was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, electron dispersive X-ray spectroscopy, atomic absorption spectrophotometers and Brunauer − Emmett − Teller analysis. To investigate the removal of Hg from aqueous solutions, batch adsorption experiments were conducted, and the efficiency was optimized under various parameters such as contact time, rice husk dosage, and initial concentration of mercury. Kinetic and isotherm investigations were also carried out to gain a better understanding of the adsorption properties. The kinetic adsorption was analyzed using the pseudo-first-order and pseudo-second-order. Furthermore, the isotherm adsorption was analyzed using ten adsorption isotherm models (i.e., Langmuir, Freundlich, Temkin, Dubinin – Radushkevich, Flory – Huggins, Fowler – Guggenheim, Hill – de Boer, Jovanovic, Harkin – Jura, and Halsey). The amount of mercury absorption increased with increasing contact time, adsorbent mass, and initial concentration of mercury. The pseudo-second-order kinetic model is the best model that can be applied to describe the adsorption process. Analysis of the adsorption results obtained shows that the adsorption pattern is explained through the formation of a monolayer without any lateral interaction between the adsorbate and adsorbent. In addition, the formation of multilayers due to inhomogeneous pore distribution also occurs which causes a pore filling mechanism. We found that the isotherm phenomena are near the Jovanovic models with the maximum adsorption capacity) of rice husk found to be 107.299 mg/g. As a result, rice husk could be a promising option for wastewater treatment due to its fast and efficient removal capacity, as well as its affordability and eco-friendliness. The predicted thermodynamic studies using the Flory – Huggins isotherm model show that the adsorption process is endothermic, spontaneous, and physisorption. The impact shows that the utilization of rice husk can be used and fit for the current issues in the sustainable development goals (SDGs).

Heat exchangers are used to transferring energy (heat), using fluids or gases, both hot and cold, from one area to another due to temperature differences. Almost all agricultural wastes serve as carbon products which are essential to produce graphene oxide, it is very possible to get graphene oxide by synthesizing it from agricultural waste which is expected to reduce the amount of waste on the earth. After carrying out the synthesis, it is necessary to test the characterization of the resulting product. The characterization stage requires a sintering process (20oC to 98oC) until the product is completely solidified. This research aims to design a heat exchanger that is highly effective in assisting the sintering process. For the design to be well-directed, several things must be done, such as calculating the main components (shell and tube) and designing a heat exchanger. Based on the TEMA standard and the use of simple calculations that refer to the attached calculation formula using Ms. Excel, hot and cold fluids used in this heat exchanger design are ethylene glycol and water. The length of the shell and tube as a whole is 5 m, the inner and outer shell diameters are 254 mm and 279.4 mm; the inner and outer tube diameters are respectively 22.09 mm and 25.40 mm. The calculation results show an excellent design effectiveness value of 86.14%. Continuous innovation in the design and materials of the heat exchanger can increase the effectiveness value to close to 100% so that it can help the graphene oxide synthesis process to make it cheaper and more efficient.

The objective of this study is to develop a new environmentally-friendly brake pad made from eggshells (Es) and banana peels (BPs) as reinforcement agents. E and BP particles as dual reinforcement with various compositions were combined. The E/BP mixture was then embedded on a polymer matrix composing a resin/hardener mixture in a 1:1 ratio. As a standard, brake pads using a single reinforcement of E and BP particles were also fabricated. Physical properties (i.e. particle size, surface roughness, morphology, and density), as well as mechanical properties (i.e. hardness, wear rate, and friction coefficient properties) were investigated. It was observed that using dual reinforcements was preferable (compared to using single reinforcements) because they had a synergistic effect on the mechanical properties of the brake pad. The best mechanical properties were found in dual reinforcements of brake pad specimens using E/BP particles with a higher BP ratio in which the value of the stiffness test, puncture test, wear rate, and coefficient of friction were 4.5 MPa, 86.80, 0.093×10-4 g/s.mm2, and 1.67×10-4, respectively. A high BP particle ratio played a dominant role in dual reinforcements, increasing the resin's bonding ability and resulting in good adhesion between the reinforcement and matrix. When compared to commercial brake pads, the brake pad specimens fabricated in this study met the standards. The techno-economic analysis also confirmed the prospective production of brake pads from E and BP particles (compared to commercial brake pads). From this research, it is expected that environmentally friendly and low-cost brake pads can be used to replace the dangerous friction materials.

The purpose of this study was to analyze the effect of a resin composition on the performance of brake pads with durian seeds (BDs) as the base material. Experiments were done by attaching saw-milled BD particles to a polymer matrix. Various resin compositions were used for preparing the brake pad, which was then tested (press test, puncture test, and friction test). Physical properties (i.e., particle size, surface roughness, morphology, and density), as well as mechanical properties (ie: hardness, wear rate, and friction coefficient properties), were investigated. Based on observations, the best mechanical properties were found in the highest resin mixture, reaching a compressive strength value of 2.4 MPa. The impact of the homogeneity of the brake pad filler particles is the main reason. The high resin composition causes more cross-links to be formed. This research demonstrates the prospective environmentally friendly and inexpensive brake pads used to replace current products that use hazardous materials.

This study aims to demonstrate the preparation of carbon microparticles obtained from red dragon fruit peel waste and their adsorption isotherm characteristics. The carbon microparticles were prepared by combining carbonization (at 250°C) and saw-milling process, and to get carbon microparticles with a specific size, sieve analysis was used. The adsorption isotherm was done by testing the adsorption ability of carbon microparticles with a specific size into curcumin solution in the batch-type reactor. The adsorption results were then compared to several standard isotherm models (i.e., Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models) for understanding what phenomena happen during the adsorption process. The adsorption analysis was also confirmed by testing several sizes of the carbon microparticles to predict the proposal mechanism in the adsorption process. The analysis results showed that the multilayer adsorption process occurs for all sizes in the micrometer range, and the process involves physical interactions between adsorbate and surface of adsorbent. The existence of multilayers is due to the possibility in the existence of porous structure in the carbon microparticles. This study is important for giving an alternative solution for reusable organic waste as well as supporting the fundamental researches in the further applications of carbon particles as catalyst and adsorbent.

The objective of this study was to investigate isotherm adsorption of carbon microparticles from pineapple peel waste. Carbon microparticles were prepared by carbonizing pineapple peel waste at 215-250°C and grinding using a saw-milling process. To investigate adsorption properties of carbon microparticles, experiments were done by evaluating adsorption of curcumin (as a model of adsorbate) in the ambient temperature and pressure under constant pH condition. To confirm the adsorption characteristics, carbon particles with different sizes (i.e., 100, 125, and 200 ?m) were tested, and the adsorption results were compared with several standard isotherm adsorption models: Langmuir, Freundlich, Temkin, and Dubinin- Radushkevich. To support the adsorption analysis, several characterizations (i.e., optical microscope, sieve test, and Fourier transform infrared analysis) were conducted. The adsorption test showed that the adsorption profile is fit to the Freundlich model for all variations, indicating the multilayer adsorption process on heterogeneous surfaces and interactions between adsorbate molecules. The results from other isotherm models also confirmed that the adsorption process occurs physically via Van der Waals force in binding adsorbate on the surface of adsorbent.