STUDI ADSORPSI-REDUKSI ION Au(III) PADA ASAM HUMAT, ASAM HUMAT TERESTERIFIKASI, DAN ASAM HUMAT TERETERIFIKASI

Dian Prasasti, Prof. Drs. Sri Juari Santosa, M.Eng., Ph.D.

2011 | Tesis | S2 Ilmu Kimia

Isolasi asam humat dan aplikasinya untuk adsorpsi reduksi ion Au(III) telah dilakukan. Asam humat diisolasi dari tanah gambut yang diambil dari Rawa Pening, Jawa Tengah. Isolasi asam humat dari tanah gambut didasarkan pada metode ekstraksi tradisional basa, yaitu dengan mengekstraksi asam humat dari tanah gambut dengan 0,1 M NaOH dan mengendapkan dengan 0,1 M HCl kemudian dilakukan pencucian dengan 0,1 M HCl/0,3 M HF 1/1. Dilakukan pula esterifikasi dan eterifikasi terhadap asam humat. Esterifikasi dilakukan dengan mereaksikan dengan etanol pada kondisi asam. Eterifikasi asam humat dilakukan dengan mereaksikan asam humat dengan dimethylsulfate dan pelarut methanol– air. Asam humat, asam humat teresterifikasi, dan asam humat tereterifikasi dikarakterisasi dengan spektroskopi Fourier-Transform Infrared (FTIR), X-Ray Diffraction (XRD), diukur kadar abu, keasaman total, kandungan –COOH, dan kandungan –OH, kemudian diaplikasikan untuk adsorpsi-reduksi ion Au(III). Pengaruh pH adsorpsi, kinetika adsorpsi, dan isoterm adsorpsi terhadap proses adsorpsi reduksi ion Au(III) juga telah dipelajari. Logam Au yang terbentuk dikonfirmasi dengan difraktogram XRD dan foto mikroskop optik. Asam humat hasil isolasi memiliki kadar abu 7,46 % dan setelah dimurnikan memiliki kadar abu 0,19 %. Asam humat murni hasil isolasi memiliki keasaman total 799 cmol/kg, kandungan gugus –COOH total 406 cmol/kg, dan kandungan gugus –OH total 393 cmol/kg. Asam humat hasil esterifikasi memiliki kadar abu 0,78 %, keasaman total 1022 cmol/kg, kandungan gugus –COOH total 217 cmol/kg, dan kandungan gugus –OH total 805 cmol/kg. Asam humat hasil eterifikasi memiliki kadar abu 0,89 %, keasaman total 699 cmol/kg, kandungan gugus –COOH 486 cmol/kg, dan kandungan gugus –OH 213 cmol/kg. Hasil perhitungan kapasitas adsorpsi dengan model isoterm Langmuir asam humat, asam humat teresterifikasi, dan asam humat tereterifikasi bertutut-turut adalah 192 mg/g, 625 mg/g, dan 158 mg/g. Hasil perhitungan konstanta laju adsorpsi (k) dengan model kinetika Ho untuk asam humat, asam humat teresterifikasi, dan asam humat tereterifikasi berturut-turut adalah 5,29.10-4 g/mg menit, 1,50.10-3 g/mg menit, dan 8,06.10-3 g/mg menit. Pembentukan logam Au ditunjukkan oleh munculnya puncak pada 2θ = 38, 44, dan 64 dalam difraktogram XRD.

Isolation of peat soil humic acid and its application for adsorption reduction of Au(III) have been conducted. Humic acid was isolated from peat soil that was collected from Rawa Pening, Central Java. Isolation of humic acid from peat soil was based on conventional alkaline extraction. Humic acid was extracted from peat soil with NaOH 0.1 M, then precipitated with 0.1 M HCl, and purified with 0.1 M HCl/0.3 M HF 1/1. Esterification and etherification of humic acid were also studied. Esterification was performed by reaction with ethanol in acidic conditions. Etherification of humic acid was performed by reacting humic acid with dimethylsulfate and methanol-water solvent. The isolated humic acid, esterified humic acid, and etherified humic acid was characterized by FTIR spectroscopy, XRD, ash content, total acidity, -COOH content, and –OH content, then applied for adsorption reduction of Au(III). The Effect of pH adsorption, adsorption kinetics, and adsorption isotherm on adsorption reduction process of Au (III) also were studied. The gold metal formed was confirmed by XRD diffractogram, and photo optical microscope. The isolated humic acid has 7.46 % ash content and after purification has 0.19% ash content. The isolated humic acid after purification has total acidity of 799 cmol/kg, -COOH content of 406 cmol/kg, and -OH content of 393 cmol/kg. Humic acid after esterification has 0.78% ash content, total acidity of 1022 cmol/kg, COOH content of 217 cmol/kg, and -OH content of 805 cmol/kg. Humic acid after etherification has 0.89% ash content, total acidity of 699 cmol/kg, - COOH content of 486 cmol/kg, and –OH content of 213 cmol/kg. The adsorption capacity with Langmuir isotherm model for humic acid, esterified humic acid, and etherified humic acid is 92 mg/g, 625 mg/g, and 158 mg/g, respectively. The adsorption rate constant (k) with Ho kinetic model for humic acid, esterified humic acid, and etherified humic acid are 5.29.10-4 g/mg min., 1.50.10-3 g/mg min., and 8.06.10-3 g/mg min., respectively. Peaks of gold particles in the difractogram are 2θ = 38, 44, and 64.

Kata Kunci : asam humat, Au(III), adsorpsi, reduksi, esterifikasi, eterifikasi