Study of nickel leaching using sulfuric acid and phosphoric acid on the selectivity of low-grade laterite nickel ore under atmospheric conditions has been successfully carried out. In this study, the laterite nickel leaching process was carried out by varying the solution concentration and operating time. The concentrations of sulfuric acid and phosphoric acid solutions were varied at 5 M and 6 M concentrations, while the operating time was varied at 4 hours and 6 hours. For other operating conditions, it is kept constant with an operating temperature of 90 ℃, pulp density 15% w / v, particle size ≤ 200 mesh. After that, the analysis stage was carried out using an atomic absorption spectroscopy (AAS) tool to determine the nickel content in the sample. The results showed that the highest nickel recovery was obtained at the concentration of 5 M sulfuric acid solution of 2.60% and 5 M phosphoric acid of 2.59% with the optimum operating time at 4 hours of operating time.

The use of inhibitors is one of the most effective ways to control corrosion. The study aims to determine and examine more deeply the effect of variations in the concentration of organic inhibitors from Moringa leaf extract on the corrosion rate of A36 steel material in seawater media. Moringa leaf extract's effectiveness in inhibiting the corrosion rate of A36 steel material in seawater media is also determined. This research was conducted by immersing specimens with inhibitor concentrations of 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm for seven days of immersion. The corrosion rate is calculated using the weight loss method. The results showed that the corrosion rate decreased with the inhibitor concentration in the corrosion media. The inhibitor concentration of 500 ppm Moringa leaf extract was able to inhibit the corrosion rate optimally. It is indicated by the smallest corrosion rate value of 1.07 mpy. On the other hand, the inhibitor efficiency increases with the inhibitor concentration in the corrosion media. The highest inhibitor efficiency was 78.71% at the addition of 500 ppm inhibitor to the solution.

Synthesis and immobilization of silver nanoparticles (AgNPs) to Whatman paper carried out using Cromolaena odorata extract irradiated by sunlight. The UV-Vis shows silver nanoparticles successfully formed from AgNO3 1 mM, 2 mM, and 3 mM with the absorption peaks at 455 nm, 452 nm, and 451 nm, respectively. The SEM shows AgNPs are spherical with an average particle size are 60.45 nm, 63.19 nm, and 68.42 nm, respectively. The EDX spectrum shows the composition of silver immobilized to Whatman paper increase with increasing concentration of 10.14Wt%, 64.48Wt%, and 70.48 Wt%, respectively. AgNPs/Whatman paper has a cubic crystal structure, space group Fm-3m, lattice parameter (a) 4.0862 Ǻ and crystal size of 42.94 nm. FTIR reach peaks at 520.78 cm-1 and 1,059 cm-1 explains the vibration of the Ag-O bonds indicated the formation of AgNPs. Furthermore, the photocatalyst ability for dye degradation was evaluated using methylene blue 10 ppm under sunlight for 6 hours. The result shows a changed colour to fade and decreases the absorbance ability of methylene blue. Therefore, it can be concluded that green synthesis and immobilization of AgNPs/Whatman paper have a potential to be applied as photocatalyst materials for dye degradation.