Judul: Karakteristik Mineralogi dan Potensi Pemanfaatan Batu Apung Indonesia sebagai Adsorben Timbal di Lingkungan Perairan
Abstrak: Pumice is an abundantly available pyroclastic rock in Indonesia. The geochemical characteristics of a pumice is site-specific and related to its magma characteristics and weathering state. For Indonesian pumices, the more to the East of the Sunda Arc, from the islands of Java, Bali, to Flores, the higher are their potassium levels and basaltic characteristic. In addition, pumice has a porous surface with a high specific surface area. This allows the alkaline activated pumice powder to be used as an adsorbent for cationic contaminants. The use of pumice as an adsorbent alternative material for cationic contaminants in water environment, such as heavy metal lead (Pb), is a kind of effort or application of the green remediation concept, which is considered as simple, but effective, efficient, and environmentally friendly. This study aimed to determine the differences in mineral composition and chemical characteristics between pumices sampled from Kalianda site, Lampung, and Kediri site, East Java, and to test the potential usage of both pumices, which were optimized by physical treatment of grain size refinement and chemical treatment of alkaline activation, as adsorbent for remediating heavy metal Pb contamination in water environment. This research was conducted from January to July 2021 at the Laboratory of the Department of Soil Science and Land Resources, Faculty of Agriculture, IPB University and several pumice samples were analyzed at LPPT UGM. Pumice samples were obtained from Way Urang Village, Kalianda District, South Lampung Regency, Lampung, and Wonorejo Trisulo Village, Plosoklaten District, Kediri Regency, East Java. The alkaline activation of pumice was carried out by mixing 5,0 g of 74 µm pumice powder with 50 mL 0,5 M NaOH, shaken at 175 rpm for 24 hours, and washed with distilled water until the pH of the washing water approached that of the distilled water. Then, the solid obtained was oven-dried at 105 oC for 24 hours. Pumice characterization to determine their mineral composition was carried out using polarization microscope and X-Ray Diffraction (XRD). Chemical properties of the pumice samples that were analyzed were cation exchange capacity (CEC) using N NH4OAc pH 7 method and chemical composition using X-Ray Fluorescense (XRF). The grain size distribution of the samples was analyzed by Pipette method. All analyzes were carried out on 200 mesh (± 74 µm) sieved samples, except for the mineral composition analysis that used sand fraction of 100- 120 mesh sieved samples. The morphology of the pumice adsorbent and its elemental content were analyzed using Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) and the application of FIJI Image-J software. The adsorption capacity and effectiveness test were carried out using adsorbent made from NaOH activated pumice powder of 74 µm grain size in batch experiments according to the Langmuir adsorption isothermal model. The isothermal adsorption test was carried out at laboratory temperature (±30 ℃). The experiment was started by making 14 series of Pb solutions with levels of 0, 5, 10, 15, 20, 30, 40, 50, 60, 100, 140, 180, 220, and 260 mg Pb L-1 using Pb(NO3)2. Then, 0,1 g of activated pumice adsorbent was mixed with 90 mL of each Pb
Keyword: Amorphous minerals, cationic contaminant, Kalianda pumice, Kediri pumice

Judul: Extraction of Nano Fraction from Volcanic Tuff of Mount Salak, West Java and Its Phosphate-adsorption Characterization
Abstrak: Nanoscience and nanotechnology is currently growing very rapidly. In 2003, Abidin (2003 in Sugiarti et al.,2010) discovered the chemical structure of nanoball allophane and nanotube imogolith so that these two clay minerals, previously considered to be amorphous, are now known as crystalline with nano dimension (<5 nm). Therefore, these pH-dependent charged allophane and imogolith pose high specific surface area and adsorption capacity of anions such as P and cations such as NH4. However, research publication on the potential use of allophane and imogolith from volcanic soils of Indonesia as natural nanomaterial in non-agricultural application is difficult to find. This study was aimed at to: (1) explore, select and extract nano fraction from volcanic tuff materials of Central Java and West Java, (2) know the phosphate adsorption characteristic of the selected nano fraction, and (3) study its usage prospects in phospahte contaminated (waste) water treatment process. Based on geology maps, exploration and sampling of the volcanic tuff material was carried out in 15 points that spread from Tawangmangu, Central Java to Bogor, West Java, in February 2010. The nano fraction sample preparation, extraction and phosphate-adsorption characterization were carried out in the Lab. Soil Chemistry and Soil Fertility, Dep. Soil Science and Land Resource, IPB in March-July 2010. Based on dispersion test, nano fraction containing volcanic tuffs were selected and extracted with the following steps: dispersion in a 1 L-cylinder at pH-4 or pH-10 placed in an ultrasonic apparatus [15 min], sedimentation [20 hours], separation of the top 10 cm solution [containing nano and clay fractions], flocculation with NaCl, redispersion, separation of the nano fraction (which did not settled, <0.2 μm) from the clay fraction (which settled, <2 μm) by mean of centrifugation [3500 rpm, 15 min], flocculation and washing the excess NaCl using dialysis membrane, dilution with distilled water [250 cc] and gravi-metrically determination of the amount of the nano and clay fractions. The Langmuir isothermal P-adsorption characterization was done by adding solutions containing 0, 0.5, 1, 2.5, 5, 10, 20, 30, 40 and 50 mg P/L. The P concentration at equilibrium was measured by UV-Vis spectrophotometer at λ 660 nm. From 1 g of volcanic tuff of M. Salak, Bogor, West Java, it could be extracted 0.71 mg positively charged nano fraction and 1.52 mg clay fraction only by applying the simple principle of dispersion at pH-4 and flocculation. The nano fraction was more effective than the clay one in adsorbing P with an average of 27-58% and 15-32%, respectively, of the initial P concentration with a range up to 15.63 mg P/L. The P adsorption effectiveness increased with the increasing ratio of fraction:solution or the weight of fraction used. The positively charged nano fraction extracted from volcanic tuff of M. Salak was found prospective to be used as a flocculant in P contaminated (waste) water treatment.
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Judul: Cycle Hamilton pada Graf Lengkap, Graf Regular, dan Graf 2-Connected 4-Regular Berorder Kurang dari Sepuluh.
Abstrak: Suatu graf disebut graf Hamilton apabila graf tersebut memuat cycle Hamilton, yaitu cycle yang melewati setiap vertex tepat satu kali. Menentukan keberadaan cycle Hamilton pada suatu graf dapat menggunakan syarat cukup yang berupa teorema-teorema yang telah diperkenalkan sejak tahun 1950-an. Beberapa syarat cukup yang dibahas dalam karya ilmiah ini adalah syarat cukup yang berhubungan dengan graf lengkap dan graf regular. ,,,
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular.