Geopolymer is the inorganic polymer commonly made from kaolin, clay, fly ash, or slag. Obsidian mineral is the new candidate material for geopolymer formation. Obsidian is a material that used in ancient eras, but nowadays, this function has been replaced by various metals. Obsidian consists of cristobalite and sodium aluminum silicate. Obsidian was reacted with disodium metasilicate (Na2SiO3) to form a mineral-based geopolymer. An analysis of the formation mechanism through X-ray diffraction and Fourier transform infrared spectroscopy showed that the geopolymer formation from obsidian takes place in two stages. The first stage is the formation of a geopolymer from a reaction among cristobalite, disodium metasilicate, and amorphous aluminum silicates, whereas the second stage is the incorporation of crystalline sodium aluminum silicate into the former geopolymer structure. Geopolymer is usually utilized to form brick or concrete for an infrastructure purpose, but in this research, the geopolymer is proposed to control the release rate of elements from fertilizer. The result of potassium release test shows that the geopolymer has a slow-release property.
Vibration characteristic of a structure is unique due to mainly its material and geometrical properties. Hence, a variation imposed on either one or both the parameters can cause a different vibration response. This fact can be used to develop an alternative approach in testing the purity of gold particularly when the gold bar (Au) is no longer isotropic material due to the presence of other metals. A fake gold bar is commonly made by filling inside of the bar with other material for example Tungsten or Wolfram (W) which has density nearly the same as gold but its price is cheaper. This can not be identified easily without performing a testing as it has the same appearance as the pure gold bar. The purpose of this research is to develop gold bar purity testing method by observing natural frequencies and Frequency Response Function (FRF) of vibration response. For early development, the vibration response of gold bar and fake one are investigated. For this, numerical calculations are used rather than measurements. The results show that the natural frequencies and frequency response function (FRF) are useful information to detect whether a metal bar is pure gold bar or containing other metals. Higher natural frequency orders are required when the volume of tungsten in the bar reduces as the gap of lower order natural frequencies of pure gold bar and the fake become small. Moreover, the excitation point at corner and central of area of gold bar are suggested to be chosen during purity testing
This study focuses on the biodesulfurization of lignite specifically the reduction of organic sulfur, namely aliphatic mercaptans/thiolsviabioprocess methods. The process was conducted by using multistage artificial biotreatment (A-Bmt) andPseudoclavibactersp.SKC/XLW-1 strains as biocatalysts. The aims are to improve the recovery of clean coal by reducing the organic sulfur both in nodules and globular forms on the maceral surface during the stage of coal biooxidation prior to column bioflotation stage, in which it is still possible to achieve higher recovery of fine coal grains without sulphide mineral. The results shows that the A-Bmt method carried out through biooxidation stage followed by column bioflotation stage has better performance compared to the method without biooxidation stage. The results of this study show that the content of organic sulfur are lower by 25%.
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