scholarly journals Studi Ekstraksi Bijih Thorit dengan Metode Digesti Asam dan Pemisahan Thorium dari Logam Tanah Jarang dengan Metode Oksidasi-Presipitasi Selektif

EKSPLORIUM ◽  
2017 ◽  
Vol 38 (2) ◽  
pp. 109
Author(s):  
Moch Iqbal Nur Said ◽  
Mutia Anggraini ◽  
Mohammad Zaki Mubarok ◽  
Kurnia Setiawan Widana
Keyword(s):  
Room Temperature ◽  
Ammonium Hydroxide ◽  
Chemical Precipitation ◽  
Lower Percentage ◽  
Radioactive Elements ◽  
Optimum Conditions ◽  
Acid Digestion ◽  
Digestion Method ◽  
Higher Temperature ◽  
Thorium Hydroxide

AbstrakThorium (Th) merupakan logam radioaktif yang dapat terbentuk bersama uranium dan logam tanah jarang (LTJ). Mineral-mineral yang mengandung unsur radioaktif diantaranya monasit ((Ce,La,Y,U/Th)PO4), thorianit ((Th,U)O2), dan thorit (ThSiO4). Daerah Mamuju, Sulawesi Barat diketahui mengandung mineral radioaktif, salah satunya adalah thorit. Untuk memisahkan LTJ dari unsur radioaktif dapat dilakukan dengan cara mengekstraksi thorium dari bijih thorit dengan metode digesti asam menggunakan asam sulfat (H2SO4), kemudian diikuti pelindian dalam air dan rekoveri thorium dalam bentuk thorium hidroksida dengan metode presipitasi kimia menggunakan ammonium hidroksida (NH4OH). Hasil percobaan menunjukkan bahwa kondisi optimum digesti asam yang memberikan persentase ekstraksi paling tinggi didapatkan pada rasio padat/cair 1:2 (g/mL) selama 60 menit dengan persentase ekstraksi Th, besi (Fe), dan LTJ masing-masing sebesar 82,47%, 80,08%, dan 83,31%. Persentase presipitasi Th tertinggi sebesar 95,47% diperoleh pada pH 4,5 dalam suhu ruangan (26±1°C). Pada temperatur yang lebih tinggi, (70°C), diperoleh persentase presipitasi thorium yang lebih rendah sebesar 83,69%. Pre-oksidasi dengan menggunakan larutan H2O2sebanyak dua kali stoikiometri selama 1,5 jam pada suhu kamar meningkatkan persentase presipitasi Fe dari 93,08% menjadi 99,93%. AbstractThorium (Th) is a radioactive metal that can be formed along with uranumand rare earth metals (REM). Minerals contain radioactive elements are monazite ((Ce,La,Y,U/Th)PO4), thorianite ((Th,U)O2), and thorite (ThSiO4). Mamuju Area is containing radioactive minerals, thorite is one of them. To separate REM from radioactive elements can be conducted by exctracting thorium from thorite ore by acid digestion method using sulphuric acid (H2SO4), followed by leaching and thorium recovery in the form of thorium hydroxide by chemical precipitation using ammonium hydroxide (NH4OH). The experimental results showed that the optimum conditions of acid digestion that give the highest Th extraction percentage on solid to liquid ratio are obtained at 1:2 (g/mL) in 60 minutes with extraction percentages of Th, iron (Fe) and REM are 82.47%, 80.08%, and 83.31% respectively. The highest thorium precipitation percentage, as much as 95.47% , was obtained at pH 4.5 on room temperature (26 ± 1°C). At higher temperature (70°C), a lower percentage of thorium precipitation is obtained, as much as 83.69%. Pre-oxidation by using H2O2 solution with two times stoichiometry for 1.5 hours at room temperature is increasing Fe precipitation percentage from 93.08% to 99.93%.

On the Chemistry of Tetrabenzyl Thiuram Disulfide and Tetramethyl Thiuram Disulfide with Bis (Triethoxysilylpropyl) Tetrasulfide in Silica Compounds

2003 ◽  
Vol 76 (4) ◽  
pp. 876-891 ◽  
Author(s):  
R. N. Datta ◽  
A. G. Talma ◽  
S. Datta ◽  
P. G. J. Nieuwenhuis ◽  
W. J. Nijenhuis ◽  
...  
Keyword(s):  
High Performance ◽  
Room Temperature ◽  
Succinic Anhydride ◽  
Dynamic Properties ◽  
The Other ◽  
Resonance Spectroscopy ◽  
Reaction Products ◽  
Negative Effect ◽  
Higher Temperature ◽  
Analytical Tools

Abstract The use of thiurams such as Tetramethyl thiuram disulfide (TMTD) or Tetrabenzyl thiuram disulfide (TBzTD) has been explored to achieve higher cure efficiency. The studies suggest that a clear difference exists between the effect of TMTD versus TBzTD. TMTD reacts with Bis (triethoxysilylpropyl) tetrasulfide (TESPT) and this reaction can take place even at room temperature. On the other hand, the reaction of TBzTD with TESPT is slow and takes place only at higher temperature. High Performance Liquid Chromatography (HPLC) with mass (MS) detection, Nuclear Magnetic Resonance Spectroscopy (NMR) and other analytical tools have been used to understand the differences between the reaction of TMTD and TESPT versus TBzTD and TESPT. The reaction products originating from these reactions are also identified. These studies indicate that unlike TMTD, TBzTD improves the cure efficiency allowing faster cure without significant effect on processing characteristics as well as dynamic properties. The loading of TESPT is reduced in a typical Green tire compound and the negative effect on viscosity is repaired by addition of anhydrides, such as succinic anhydride, maleic anhydride, etc.

Evaluation of heavy metals content in the canned/packed fruit juices from local and imported origin in Lahore, Pakistan

2021 ◽  
Author(s):  
Nazeefa Fatima ◽  
Munazza Khan ◽  
Muhammad Shuaib Kabeer
Keyword(s):  
Heavy Metals ◽  
Atomic Absorption ◽  
Fruit Juices ◽  
Human Consumption ◽  
Acid Digestion ◽  
Digestion Method ◽  
Mean Values ◽  
Nutritive Values ◽  
The Mean ◽  
Mean Concentration

This study was conducted to determine the mean concentration of heavy metals such as lead (Pb), copper (Cu), zinc (Zn), chromium (Cr), manganese (Mn), nickel (Ni), selenium (Se), magnesium (Mg), and iron (Fe) in canned/packed fruits juices, collected from various stores in Lahore in a period of three months. These juices were categorized into four groups; local packed and canned and also imported packed and canned products. Every group consisted of ten samples. By using the di-acid digestion method, the collected samples were digested and analyzed under Atomic Absorption Spectrophotometer (AAS). The results indicated that the mean values of 7 out of 9 tested heavy metals including Pb, Mg, Ni, Fe, Cr, Se and Mn were above permissible limits (set by WHO) in all four understudy groups. Therefore, it was concluded that commercially available fruit juices are not all safe according to their heavy metals content for the human consumption despite their nutritive values.

Thermal Resistance of Fly Ash Geopolymers with Alumina as Additive

2018 ◽  
Vol 281 ◽  
pp. 182-188
Author(s):  
Yong Sing Ng ◽  
Yun Ming Liew ◽  
Cheng Yong Heah ◽  
Mohd Mustafa Al Bakri Abdullah ◽  
Kamarudin Hussin
Keyword(s):  
Elevated Temperature ◽  
Fly Ash ◽  
Thermal Resistance ◽  
Sodium Hydroxide ◽  
Sodium Silicate ◽  
Room Temperature ◽  
Strength Degradation ◽  
Alumina Addition ◽  
Higher Temperature ◽  
Temperature Exposure

The present work investigates the effect of alumina addition on the thermal resistance of fly ash geopolymers. Fly ash geopolymers were synthesised by mixing fly ash with activator solution (A mixture of 12M sodium hydroxide and sodium silicate) at fly ash/activator ratio of 2.5 and sodium silicate/sodium hydroxide ratio of 2.5. The alumina (0, 2 and 4 wt %) was added as an additive. The geopolymers were cured at room temperature for 24 hours and 60°C for another 24 hours. After 28 days, the geopolymers was heated to elevated temperature (200 - 1000°C). For unexposed geopolymers, the addition of 2 wt % of alumina increased the compressive strength of fly ash geopolymers while the strength decreased when the content increased to 4 wt.%. The temperature-exposed geopolymers showed enhancement of strength at 200°C regardless of the alumina content. The strength reduced at higher temperature exposure (> 200°C). Despite the strength degradation at elevated temperature, the strength attained was relatively high in the range of 13 - 45 MPa up to 1000°C which adequately for application as structural materials.

Newly Developed Heat Resistant Magnesium Alloy by Thixomolding®

2005 ◽  
Vol 488-489 ◽  
pp. 287-290 ◽  
Author(s):  
Tadayoshi Tsukeda ◽  
Ken Saito ◽  
Mayumi Suzuki ◽  
Junichi Koike ◽  
Kouichi Maruyama
Keyword(s):  
Aluminum Alloy ◽  
Magnesium Alloy ◽  
Magnesium Alloys ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Die Casting ◽  
The Other ◽  
Heat Resistant ◽  
Higher Temperature ◽  
Better Than

We compared the newly developed heat resistant magnesium alloy with conventional ones by Thixomolding® and aluminum alloy by die casting. Tensile properties at elevated temperatures of AXEJ6310 were equal to those of ADC12. In particular, elongation tendency of AXEJ6310 at higher temperature was better than those of the other alloys. Creep resistance of AXEJ6310 was larger than that of AE42 by almost 3 orders and smaller than that of ADC12 by almost 2 orders of magnitude. Fatigue limits at room temperature and 423K of AXEJ6310 was superior among conventional magnesium alloys.

scholarly journals Influence of three alkalizing agents on some functional properties of cassava starch modified using epichlorohydrin

2015 ◽  
Vol 49 (2) ◽  
pp. 63-68
Author(s):  
B Daramola ◽  
EA Bamidele
Keyword(s):  
Functional Properties ◽  
Functional Property ◽  
Apparent Viscosity ◽  
Potassium Hydroxide ◽  
Room Temperature ◽  
Ammonium Hydroxide ◽  
Cassava Starch ◽  
Pasting Properties ◽  
Modified Starch ◽  
Cross Linkage

Influence of three alkalizing agents namely, potassium hydroxide (KOH) , ammonium hydroxide (NH4OH), and dimethyl sulphoxide (DMSO) during modification as modification facilitator on some functional properties of cassava starch modified using epichlorohydrin (EPI) at room temperature was studied. Assessment of the principal functional property; pasting properties and associated pasting indices of technological importance, notably peak viscosity and set back viscosity. The low peak viscosity (RVU) of the cassava EPI-modified starch ranged from 119.67-178.17; 128.50-161.17 for samples alkalized using KOH and DMSO respectively in comparison to the high peak viscosity (RVU) of the native starch. NH4OH was less effective alkalizing agent under the conditions used in this study. Cassava- EPI modified starch showed improved paste stability expressed in breakdown viscosity (RVU) values of 22.08-48.75 and 37.92-55.58 for KOH and DMSO alkalized samples respectively. Evaluation of other functional properties such as swelling power, apparent viscosity and paste clarity of the cassava-EPI modified starch showed alkaline-type dependent cross linkage activity of EPI. Assessment of all the functional properties of starch accomplished under the conditions employed in this study revealed that irrespective of concentration of EPI added, activity of alkalizing reagents is in the order: KOH>DMSO>NH4OH. DOI: http://dx.doi.org/10.3329/bjsir.v49i2.21997 Bangladesh J. Sci. Ind. Res. 49(2), 63-68, 2014

scholarly journals Lipase-catalyzed transesterification of rendering plant fat – Short Communication

2010 ◽  
Vol 56 (No. 3) ◽  
pp. 122-125 ◽  
Author(s):  
A. Prošková ◽  
Z. Kopicová ◽  
J. Kučera ◽  
L. Škarková
Keyword(s):  
Short Communication ◽  
Immobilized Enzyme ◽  
Immobilized Lipase ◽  
Covalent Bond ◽  
Novozym 435 ◽  
Optimum Temperature ◽  
Optimum Conditions ◽  
Soluble Lipase ◽  
Good Accordance ◽  
Higher Temperature

Soluble lipase (Lipozyme CALB L) was immobilized by covalent bond to chitosan pellets prepared from Aspergillus niger mycelium. This immobilized enzyme was compared with commercial immobilized lipase of the same origin (Novozym 435). Novozym 435 is also lipase CALB L commercially immobilized by sorption on poly-(methyl acrylate). Novozym 435 shows much higher conversion of rendering plant fat in methanol under optimum conditions, having, at the same time, lower optimum temperature and lower stability at higher temperature. Lipozyme CALB L immobilized on chitosan leads to a low conversion, regardless its higher thermal stability. Novozym 435 gives conversion of about 50% of theoretical value, which is in good accordance with basically catalyzed transesterification of rendering plant fat described elsewhere. Lipozyme CALB L immobilized on chitosan gives conversion of about 10% of theoretical value only. The use of Novozym 435 in two-step system (enzyme-acid) seems to be more convenient compared with traditional two-step system (base-acid)

scholarly journals Crystal Chemistry and Luminescence Properties of Eu-Doped Polycrystalline Hydroxyapatite Synthesized by Chemical Precipitation at Room Temperature

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 250 ◽  
Author(s):  
Francesco Baldassarre ◽  
Angela Altomare ◽  
Nicola Corriero ◽  
Ernesto Mesto ◽  
Maria Lacalamita ◽  
...  
Keyword(s):  
Fourier Transform ◽  
High Temperature ◽  
Inductively Coupled Plasma ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Chemical Precipitation ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Inductively Coupled

Europium-doped hydroxyapatite Ca10(PO4)6(OH)2 (3% mol) powders were synthesized by an optimized chemical precipitation method at 25 °C, followed by drying at 120 °C and calcination at 450 °C and 900 °C. The obtained nanosized crystallite samples were investigated by means of a combination of inductively coupled plasma (ICP) spectroscopy, powder X-ray diffraction (PXRD), Fourier Transform Infrared (FTIR), Raman and photoluminescence (PL) spectroscopies. The Rietveld refinement in the hexagonal P63/m space group showed europium ordered at the Ca2 site at high temperature (900 °C), and at the Ca1 site for lower temperatures (120 °C and 450 °C). FTIR and Raman spectra showed slight band shifts and minor modifications of the (PO4) bands with increasing annealing temperature. PL spectra and decay curves revealed significant luminescence emission for the phase obtained at 900 °C and highlighted the migration of Eu from the Ca1 to Ca2 site as a result of increasing calcinating temperature.

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