1,720,957 research outputs found
DEALCALIZATION OF SOUTHERN CIANJUR BENTONITE USING AMMONIUM HYDROXIDE AND CITRIC ACID
No full textDealcalization of southern Cianjur bentonite has been done to improve bentonite quality by reducing the alkali element (Na and Ca) content as impurities. The experiment used ammonium hydroxide and citric acid. The reaction parameters such as particle size, solution concentration, percent solid, time and contact temperature were optimized. Results of dealcalization using ammonium hydroxide ob- tained the optimum condition at particle size of -200+325 mesh, concentration of 4 N, percent solid of 10%, contact time of 36 hours and temperature of 100oC with recovery as much as 32.55% for Na and 29.14% for Ca. Meanwhile, dealcalization using citric acid, got optimum condition at particle size of - 325 mesh, concentration of 2N, percent solid of 10%, contact time of 24 hours, temperature of 100oC with recovery as much as 33.01% for Na and 30.07% for Ca. The results also showed that both solutions gave better recovery for Na rather than for Ca. In conclusion, experiment using citric acid was better than using ammonium hydroxide as demonstrated by its higher recovery of alkali elements. However, results of this work have not met the standards of bentonite for catalyst hydrocarbon crac- king
Pelarutan bijih bauksit dengan soda kaustik (NaOH) menjadi larutan sodium aluminat (NaAlO2) skala pilot
No full textSodium aluminat (NaAlO2) merupakan bahan kimia anorganik penting yang digunakan sebagai bahan baku untuk pembuatan berbagai macam produk kimia antara lain polialuminum chloride (PAC), alum, dan zeolit sintetik. Dalam penelitian ini, NaAlO2 dihasilkan melalui proses Bayer yaitu pelarutan (digestion) bauksit asal Tayan, Kalimantan Barat, dengan soda kaustik (NaOH) pada skala pilot berkapasitas 100 kg umpan/batch dengan menggunakan uap secara kontak langsung pada suhu sekitar 140oC dan tekanan 4 atm. Variabel yang diteliti meliputi : lama reaksi (1; 1,5; 2 jam), ukuran butir -0,177 mm (-80 mesh); -0,149 mm (-100 mesh); -0,0965 mm (-150 mesh), dan NaOH berlebih di atas kebutuhan stoikhiometrinya (1,37% sampai dengan 35,25%). Hasil penelitian menunjukkan bahwa waktu reaksi semakin lama, ukuran butir semakin halus, dan NaOH berlebih semakin tinggi sampai batas tertentu, memberikan perolehan alumina (Al2O3) yang semakin tinggi. Kondisi proses terbaik yang diperoleh adalah NaOH berlebih 28,83% , lama reaksi 2 jam dan ukuran butir -150 mesh (-0,105 mm) dengan perolehan alumina tertinggi 93,98%
PENGARUH PENAMBAHAN KALSIUM KLORIDA, KALSIUM HIDROKSIDA DAN KARBON AKTIF TERHADAP PENURUNAN SILIKA TERLARUT DALAM LARUTAN SODIUM ALUMINAT
No full textLarutan sodium aluminat adalah larutan hasil ekstraksi aluminium dari bijih bauksit melalui proses Bayer. Bijih bauksit Kalimantan Barat yang digunakan dalam percobaan ini mengandung mineral utama gibbsite, dan berasosiasi dengan mineral lain sebagai pengotor utama seperti silikat (kaolinit, halloysite) dan silika (kuarsa), serta oksida besi (goethite). Bijih bauksit kadar rendah mengandung pengotor yang tinggi dan berpengaruh terhadap kualitas larutan sodium aluminat yang dihasilkan dari proses Bayer. Pada percobaan ini, bijih bauksit memiliki komposisi oksida 50,98% Al2O3, 5,99% SiO2, 15,90% Fe2O3, 0,070% CaO, 0,0107% MgO, 1,35% TiO2 dan 25,3% LOI. Ekstraksi aluminium dengan proses Bayer menghasilkan larutan sodium aluminat dengan kandungan 60 g/L Al2O3, 17,5 g/L SiO2, 1,6 mg/L Fe2O3, 0,82 mg/L CaO dan 113 g/L Na2O. Pengotor utama SiO2 terlarut yang terkandung dalam larutan masih tinggi, lalu dimurnikan menggunakan reagen-reagen desilikasi CaCl2, Ca(OH)2 dan C-aktif. Masing-masing reagen desilikasi tersebut direaksikan dengan larutan sodium aluminat pada suhu 70oC. Percontoh larutan hasil desilikasi diambil pada menit ke 30, 90, 150, 210, 270 dan 300. Hasil percobaan terbaik diperoleh pada menit ke 180 menggunakan Ca(OH)2 yang mampu mengikat hampir semua silika dari larutan sodium aluminat.
Processing zirconia through zircon sand smelting with NaOH as a flux
No full textZirconia had been made through smelting the zircon sand along with NaOH as a flux. The zircon sand as the smelter feed was taken from CV. Kurnia Alam Sejati mine at Palangkaraya, Middle Kalimantan. Major content of the zircon sand was 28.04% ZrO2 and SiO2 51.22% with several minor oxides such as 0.54% HfO2, 2.53% Fe2O3, 10.53% TiO2, 3.27% Al2O3 and less than 1% of alkali, alkaline earth and rare earth elements. In order to economizing the process, zircon sand upgrading was conducted prior to zirconia production. The upgrading process was conducted using several comprehensive equipments, consist of shaking table, magnetic separator and high tension separator (HTS).The upgraded sand contained 65.35% of ZrO2+HfO2 with 73.25% recovery, which was then used for smelting process at 650C for 2 hours using NaOH as a flux. The product was then leached with water and sulphuric acid then crystallized to get precipitated zirconium hydroxide. The precipitated product was calcined at 900C for 1 hour to get the zirconia and analyzed for its content. The zirconia content was 97.27% of ZrO2+HfO2 with 65.13% recovery
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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