Extraction of Nano Fraction from Volcanic Tuff of Mount Lawu, Central Java and Its Ammonium-adsorption Characterization

Abstract

In the process of purification of water contaminated with nutrients causing eutrophication (P and NH4), the use of natural nano materials as a flocculant was reported to be more effective, cheaper and environmentally friendly than synthetic chemicals (Yuan and Wu, 2007). Indonesia is rich in volcanic soil material that contains allophane and imogolith that pose pH-dependent charge properties, high chemical reactivity, specific surface area and adsorption capacity of anions such as phosphate and cations such as amonium. Both clay minerals that were previously considered to be amorphous aluminosilicate has now been proved by Abidin (2003 in Sugiarti et al., 2010) as crystalline with nano dimension (<5 nm). This study was aimed at to: (1) explore, select and extract nano fraction of volcanic tuff materials from Central Java and West Java, (2) know the NH4-adsorption characteristics of the selected nano fraction, and (3) study the prospects of the selected nano fraction to be used as a natural flocculant in NH4-contaminated (waste) water treatment processes. Based on geological maps, in February 2010, exploration and sampling of the volcanic tuff materials were carried out in 15 points that spread from Tawangmangu, Central Java to Bogor, West Java. The nano fraction sample preparation, extraction and amonium-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 gravimetrically determination of the amount of the nano and clay fractions. The Langmuir isothermal NH4-adsorption characterization was done by adding solutions containing 0, 2.5, 5, 10, 20, 30, 40 and 50 mg NH4/L. Concentrations of NH4 at equilibrium state was measured by UV-Vis spectrophotometer at λ 630 nm. From 1 g volcanic tuff material of M. Lawu, Central Java, it could be extracted 1.19 mg of negatively-charged nano fraction and 1.95 mg of clay fraction only by applying a simple principle of dispersion at pH-10 and flocculation. The nano fraction was more effective than the clay one in NH4-adsorption with an average of 41-68% and 12-20%, respectively, of the initial NH4 concentration with a range up to 16.67 mg NH4/L. The NH4-adsorption effectiveness increased with the increasing ratio of fraction: solution or the weight of fraction used. The negatively-charged nano fraction derived from volcanic tuff of M. Lawu was prospective to be used as a natural flocculant in the process of NH4-contaminated water treatment.