Karakteristik Mineralogi dan Potensi Pemanfaatan Batu Apung Indonesia sebagai Adsorben Timbal di Lingkungan Perairan

Abstract

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 serial solutions and 10 mL of 0,01 M CaCl2 as background electrolyte to obtain 0,03 ionic strength. The mixture was homogenized using a shaker at 150 rpm for 100 minutes and the equilibrium Pb levels were determined by Atomic Absorbtion Spectro photometer (AAS). The results showed that pumice from Kalianda was dominated by pumice fragments and volcanic glass as amorphous minerals. In contrast, the Kediri pumice sample was dominated by pumice fragments, volcanic glass, and plagioclase feldspar. Kalianda pumice has a finer grain size distribution than Kediri pumice, with CEC of 4,4 cmol(+) kg-1 for Kalianda pumice and 2,0 cmol(+) kg-1 for Kediri pumice, and a porosity of 46,48±5,95% for Kalianda pumice and 39,63±12,9% for Kediri pumice. The Pb adsorption maxima of Kalianda and Kediri pumice adsorbents were 37,31 and 28,49 mg g-1 , respectively, with Pb adsorption effective ness of 63,5% and 71,3%, respectively. This study showed that both pumices are differed in mineral and chemical composition and have a high potential usage as adsorbent for cationic contaminants in water environment.

Batu apung merupakan batuan piroklastik yang melimpah di Indonesia. Karakteristik geokimia batu apung bersifat spesifik lokasi yang berkaitan dengan karakteristik magma dan status pelapukannya. Untuk batu apung Indonesia, semakin ke arah Timur dari Busur Sunda, yaitu dari Pulau Jawa, Bali, hingga Flores semakin tinggi kadar Kalium dan sifat basaltiknya. Selain itu, batu apung memiliki permukaan berpori dengan luas permukaan spesifik yang tinggi. Hal tersebut memungkinkan serbuk batu apung yang diaktivasi alkalis dapat digunakan sebagai adsorben kontaminan kationik. Pemanfaatan batu apung sebagai adsorben alternatif kontaminan kationik di lingkungan perairan, salah satunya logam berat timbal (Pb), merupakan suatu upaya atau penerapan konsep remediasi hijau atau green remediation yang sederhana, namun efektif, efisien, dan ramah lingkungan. Penelitian ini bertujuan mengetahui perbedaan komposisi mineral dan sifat kimia batu apung yang berasal dari Kalianda, Lampung dan Kediri, Jawa Timur, serta menguji potensi penggunaannya sebagai adsorben yang dioptimalkan dengan perlakuan fisik penghalusan ukuran butir dan perlakuan kimiawi aktivasi alkalis untuk meremediasi kontaminasi logam berat Pb di lingkungan perairan. Penelitian ini dilakukan di Laboratorium Departemen Ilmu Tanah dan Sumberdaya Lahan, Fakultas Pertanian, IPB dan beberapa sampel batu apung dianalisis di LPPT UGM pada Januari sampai Juli 2021. Sampel batu apung diperoleh dari Desa Way Urang, Kecamatan Kalianda, Kabupaten Lampung Selatan, Lampung, dan Desa Wonorejo Trisulo, Kecamatan Plosoklaten, Kabupaten Kediri, Jawa Timur... dst..