Ekstraksi dan Uji Pengaruh Waktu Ekuilibrasi terhadap Jerapan Fosfat pada Fraksi Nano dan Liat dari Tuf Volkan Gunung Salak, Bogor

Abstract

The use of natural nano material as a flocculant in the process of P-contaminated water purification was reported to be more effective, cheaper and environmentally friendly than synthetic chemicals (Yuan and Wu, 2007). Indonesia is rich in soils derived from volcanic tuff parent material containing natural nano materials (diameter [Φ] <100 nm), i.e. allophane and imogolith that pose pH-dependent charge properties (Sugiarti et al., 2010). Volcanic tuff in Java island from east to west direction change gradually from basaltic (calc-alkaline basaltic ash) to andesitic type (andesitic-tuffaceous ash) (Tan, 1964; van Ranst et al., 2004), so their nano fractions also change to those with dominant positive charge. From 12 volcanic tuff samples collected from Java island, the highest amount of positively-charged nano fraction could be extracted from that of M. Salak (Sherlie, 2010; Nursyirwan, 2010; Setiawan, 2010). One of the determining P-adsorption factors is equilibration-time. In the treatment of P-contaminated water, flocculant with fastest equilibration-time and highest P-adsorption is prefered. This study was aimed at to test the effects of equilibration-time on P-adsorption by nano and clay fractions extracted from volcanic tuff of M. Salak. This study was conducted at Lab. Soil Chemistry and Soil Fertility, Dep. Soil Science and Land Resource, IPB on February-July 2011. The nano and clay fractions were extracted according to Henmi and Wada (1976) procedure: volcanic tuff dispersion (Φ <2 mm) in a 1-L cylinder at pH-4.00 [HCl], ultrasonic [15 min], sedimentation [20 h], separation of the top 10 cm solution, flocculation [NaCl], flocculate redispersion [aquadest], 9 times separation by centrifugation [3500 rpm; 15 min] of nano fraction (which not settled, Φ <0.2 μm) from the clay (which settled, Φ <2 μm), reflocculation, washing the excess of NaCl [membrane dialysis], dilution [500 cc aquadest] and gravimetrically determination of the amount of the nano and clay fractions. The isothermal P-adsorption analisys was done by adding solutions containing 0, 5, 10, 20, 40, 80, 160 and 240 mg P/L in 1 mM CaCl2 into test tubes containing 10 cc of the suspension with equilibration time of 24, 72 and 144 hours (suspension was agitated 3x10 sec using magnetic stirrer at 08h and 16h, everyday). The equilibrium P content was determined with Murphy and Riley (1962) procedure using UV-Vis spectrophotometer [λ 660 nm]. From 1 g volcanic tuff of M. Salak, Bogor, it could be extracted 2.71 mg positively-charged nano and 3.88 mg clay fractions. The P-adsorption by both fractions increased with the increasing equilibration-time. The b values (maximum P-adsorption) after 24, 72 and 144 hours equilibration of the nano fraction [14.51, 25.13 and 32.79 mg/g] were higher than those of the clay ones [4.60, 20.37 and 25.13 mg/g]. The b value of the nano fraction of M. Salak [32.79 mg/g; 144 h] was around two and eight times higher than those respectively of China nanoclay [16.23 mg/g; 24 h; Yuan and Wu (2007)] and New Zealand imogolith [3.75 mg/g;16 h; Parfitt and Henmi (1980)].

Pemanfaatan material nano alami (nanoclay) sebagai flokulan dalam pengolahan air terkontaminasi P dilaporkan lebih efektif, murah dan ramah lingkungan daripada bahan kimia sintetik (Yuan dan Wu, 2007). Indonesia kaya tanah berbahan induk tuf volkan yang banyak mengandung material nano alami (diameter [Φ] <100 nm), yaitu alofan dan imogolit yang memiliki sifat muatan bergantung-pH (Sugiarti et al., 2010). Tuf volkan di Pulau Jawa dari arah timur ke barat berubah dari tipe basa (calc-alkaline basaltic ash) ke masam (andesitic-tuffaceous ash) (Tan, 1964; van Ranst et al., 2004), sehingga fraksi nanonya juga berubah ke dominan bermuatan positif. Dari 12 sampel tuf volkan di Pulau Jawa, fraksi nano bermuatan positif terbanyak dapat diekstraksi dari tuf volkan G. Salak, Bogor (Sherlie, 2010; Nursyirwan, 2010; Setiawan, 2010). Salah satu faktor penentu jerapan P adalah waktu ekuilibrasi. Dalam pengolahan air terkontaminasi P dipilih flokulan dengan waktu ekuilibrasi tercepat dan jerapan maksimum P tertinggi. Penelitian ini bertujuan menguji pengaruh waktu ekuilibrasi terhadap jerapan maksimum P pada fraksi nano dan liat yang diekstraksi dari tuf volkan G. Salak, Bogor. Penelitian ini dilakukan di Lab. Kimia dan Kesuburan Tanah, DITSL, IPB pada Februari-Juli 2011. Ekstraksi fraksi nano dan liat dilakukan dengan metode Henmi dan Wada (1976) sbb: dispersi tuf volkan (Φ <2 mm) dalam silinder 1-L pada pH-4.00 [HCl] dan diultrasonic [15 mnt], sedimentasi [20 jam], pemisahan 10 cm larutan teratas, flokulasi [NaCl], redispersi flokulat [aquadest], pemisahan dengan sentrifugasi 9 kali [3500 rpm; 15 mnt] fraksi nano (tidak mengendap, Φ <0.2 μm) dari liat (mengendap, Φ <2 μm), reflokulasi, pencucian kelebihan NaCl [membran dialisis], pelarutan [500 cc aquadest] dan uji gravimetrik penetapan kadar fraksi nano dan liat. Analisis jerapan isotermal P dilakukan dengan menambahkan 5 cc deret larutan 0, 5, 10, 20, 40, 80, 160 dan 240 mg P/L dalam 1 mM CaCl2 ke tabung reaksi berisi 10 cc suspensi dengan waktu ekuilibrasi 24, 72 dan 144 jam (setiap hari suspensi diagitasi 3x10 dtk menggunakan magnetic stirrer pada jam 08 dan 16). Kadar P-kesetimbangan diukur dengan metode Murphy dan Riley (1962) menggunakan UV-Vis spektrofotometer [λ 660 nm]. Dari setiap 1.00 g tuf volkan G. Salak dapat diekstraksi 2.71 mg fraksi nano dan 3.88 mg fraksi liat bermuatan positif. Jerapan P pada kedua fraksi tersebut meningkat dengan bertambahnya waktu ekuilibrasi. Nilai b (jerapan maksimum P) dengan waktu ekuilibrasi 24, 72 dan 144 jam pada fraksi nano [14.51, 25.13 dan 32.79 mg/g] lebih tinggi daripada fraksi liat [4.60, 20.37 dan 25.13 mg/g]. Nilai b fraksi nano G. Salak [32.79 mg/g; 144 jam] berturut-turut sekitar dua dan delapan kali lebih tinggi daripada nanoclay China [16.23 mg/g; 24 jam; Yuan dan Wu (2007)] dan imogolit New Zealand [3.75 mg/g;16 jam; Parfitt dan Henmi (1980)].