SINTESIS SILIKA TERMODIFIKASI SULFONAT DARI ABU SEKAM PADI MELALUI PROSES SOL GEL SEBAGAI PENUKAR KATION LOGAM BERAT DALAM LARUTAN; SYNTHESIS OF SULFONATE MODIFIED SILICA FROM RICE HULL ASH THROUGH SOL GEL PROCESS AS THE HEAVY METALS CATION EXCHANGER

Sulastri, Siti, Nuryono

2015 | Tesis | FMIPA

Synthesis of sulfonate modified silica and their use as a cation exchanger of heavy metal ions have been done. The raw material silica source was rice husk ash without and with acid washing. The synthesis was conducted through sol-gel process of precursor with the addition of mercaptopropyltrimetoxysilane as the modifier to produce propylthiol modified silica, followed with oxidation process using H2O2 and HNO3. As a comparison purpose, synthesis of silica gel (non-modified silica) from the same raw materials was also carried out.The products from raw materials without acid-washing were silicagel (SG),-SH group modified silica (HMS),and sulfonate modified silica with oxidators of H2O2 (HSSP) and of HNO3 (HSSN). Whereas, notation of the relevant results from raw materials with acid wash were SGC, HMSC, HSSPC and HSSNC, respectively. The characterization of the results was carried out using some measurements; for functional groups, thermal properties, crystallinity, their composition and morphological structures, textural and cation exchange properties. The products were used as the adsorbents to study the properties of cation exchange. The results showed that the silica having properties of cation exchanger were HSSP, HSSPC, HSSN and HSSNC. The study showed that the products were resistant to high temperatures, had low crystallinity, different composition and morphological structures, and different textural properties.The adsorption properties of products toward Cr(III), Cd(II), Pb(II) andAg(I) metal ions in a solution were evaluated to SG, HMS, HSSP and HSSN. The experiments of adsorption properties included the effect of solution pH, adsorption contact time, and initial concentration of metal ions. The contact time data were analyzed by kinetic models as suggested by the Natarajan-Khalaf, Annadurai-Krishnan, Ho-Mc Kay, and Elovich. The appropriate model describing the kinetics of adsorption process was indicated by the values of r2 and s2. The analysis showed that the kinetics of adsorption system containing one ion and adsorbent was different from other systems. The mechanism of adsorption process was analyzed using both intraparticle diffusion and Boyd models from which the adsorption process occurred following external mass transfer mechanism or film diffusion. The equilibrium of adsorption was calculated from the data of various initial concentration of metal ion. Adsorption equilibrium data was evaluated by using isotherm models of Langmuir, Freundlich, Dubinin-Raduskevich and Temkin. The fit of the model was indicated by high value of r2 and small value of s2. The adsorption equilibriums which followed monolayer adsorption were systems containing Cd(II) on HMS, Cr(III) on each adsorbent, Ag(I) on each adsorbent, and Pb(II) on HSSN, and HMS. The Freundlich model adsorption was not favourable for the systems containing Cd(II) on HSSN, HSSP, and SG. Some systems of adsorptions was physisorption, e.g. Cd(II) on each adsorbent, Ag(I) on HMS and Pb(II) on HSSP. Adsorption of Cr(III) on each adsorbent was an ion exchange adsorption. The order of the metal ion affinity towards Lewis hard base HSSN, HSSP and SG was Cr(III) > Cd(II) > Pb > Ag(I), and the nature of the Lewis soft base HMS was in asequence of Cr(III) < Cd(II) < Pb (II) < Ag(I). This phenomenon has been in line with the rules of HSAB of Pearson, Misono softness, and ionic potential.

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