Judul: Transformation of Red Mud from PT Indonesia Chemical Alumina into Coagulant for Water Treatment of Kapuas River
Abstrak: Red mud merupakan limbah industri aluminium yang dihasilkan dalam jumlah yang sangat besar oleh PT Indonesia Chemical Alumina. Penelitian ini bertujuan memanfaatkan senyawa oksida logam seperti besi oksida (Fe2O3) dan aluminium oksida (Al2O3) yang ada dalam limbah untuk memperoleh produk koagulan cair atau padat menggunakan media asam dan garam, menentukan konsentrasi pelarut asam sulfat yang optimum untuk mengekstraksi Fe dan Al, mengaplikasikan produk koagulan dalam pengolahan air sungai Kapuas, dan membandingkan kinerja produk koagulan dari material tersebut dan koagulan komersial (tawas). Proses ini melibatkan perlakuan sebanyak 40 g red mud, diekstraksi menggunakan 240 mL H2SO4 dan 18,75 g NaCl pada suhu 110 °C selama 4 jam. Hasil ekstraksi diperoleh 3,12% Fe dan 1,05% Al dengan menganalisis koagulan cair. Analisis difraksi sinar-X menunjukkan bahwa koagulan padat terdiri dari Na2S2O3.5H2O, AlClO4H6, Al2(SO4)3, Fe2(SO4)3, FeSO4, dan FeCl3. Koagulan padat yang dihasilkan dari red mud mampu mengurangi 42% nilai padatan terlarut total, 39% nilai padatan tersuspensi total, mengubah kadar logam besi (Fe), dan dapat memperbaiki pH air sungai Kapuas., Red mud is an industrial waste produced in large quantities by PT Indonesia Chemical Alumina. This study aims to use metal oxide such Fe2O3 and Al2O3 present in the waste to get liquid or solid coagulant products using acid and salt media, find the best concentration of sulfuric acid solvent to extract Fe and Al, apply coagulant products in Kapuas River water treatment, and compare the performance of coagulant products from these materials and commercial coagulants (alum). This process involved the treatment of 40 g of red mud, extracted using 240 mL of H2SO4 and 18.75 g of NaCl at 110 °C for 4 hours. As much as 3.12% Fe and 1.05% Al by analyzing liquid coagulant. X-ray diffraction analysis showed that the solid coagulant consisted of Na2S2O3.5H2O, AlClO4H6, Al2(SO4)3, Fe2(SO4)3, FeSO4, and FeCl3. The solid coagulant produced from red mud was able to cut 42% of the total dissolved solids value, 39% of the total suspended solids value, change the iron metal content (Fe), and may improve the pH of the Kapuas river.
Keyword: aluminum oxide, iron oxide, coagulant, aluminum industrial waste, red mud

Judul: Efektivitas Campuran Poli(Aluminium Klorida) (PAC) dan Aluminium Sulfat (Tawas) sebagai Koagulan dalam Pengolahan Air Bersih
Abstrak: Poly(aluminum chloride) (PAC) and aluminum sulfate (alum) are commonly used coagulants for water treatment. This study aimed to determine the effective coagulant dose of PAC and alum mixture Cisadane river water treatment. Coagulant mixture ratio used were 100:0, 75:25, 50:50, 25:75, and 0:100 with low and high levels of water turbidity. In addition to turbidity, effectiveness in decreasing the Fe, Mn, and organic substances contents were also studied. PAC was more effective in decreasing the levels of turbidity (88.29%), Fe (76.03%), Mn (75.57%), and organic substances contents (41.74%) compared to the other coagulant mixtures. In terms of cost, 75:25 ratio of PAC-alum coagulant mixture was more efficient under condition of high turbidity level.
Keyword: alum, aluminum sulfate, poly(aluminum chloride), PAC, turbidity

Judul: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
Keyword: