Imobilisasi asam humat pada kitin dan aplikasinya untuk adsorpsi Ni(II)

KURNIAWAN, Agusta, Dr. Sri Juari Santosa, M.Eng

2004 | Tesis | S2 Ilmu Kimia

Telah dilakukan imobilisasi asam humat pada kitin dan aplikasinya untuk adsorpsi Ni(II). Sampel asam humat diisolasi dari tanah Rawa Pening menggunakan NaOH 0,1 M, sedangkan kitin diisolasi dengan cara deproteinasi cangkang kepiting air tawar dan air laut menggunakan NaOH 3,5 % dan dilanjutkan dengan penghilangan pengotor anorganik menggunakan larutan HCl 1 M. Parameter kajian yang diteliti meliputi: metode imobilisasi, stabilitas asam humat yang terimobilisasi, pengaruh keasaman pada adsorpsi, dan laju, kapasitas, energi dan mekanisme adsorpsi. Hasil karakterisasi menunjukkan bahwa asam humat mempunyai keasaman total 2309,5 mmol/kg yang terdistribusi ke dalam keasaman COOH sebesar 1687,5 mmol/kg dan OH fenolat sebesar 622,0 mmol/kg. Kitin 1 yang diperoleh dari cangkang kepiting air tawar dan kitin 2 yang diperoleh dari cangkang kepiting air laut mempunyai derajat asetilasi 69 dan 77 % dan keduanya mempunyai rasio N/C sebesar 0,69 %. Imobilisasi asam humat pada kitin berhasil dilakukan dengan mereaksikan larutan kitin dalam HCl 0,5 M dan asam humat dalam NaOH 0,5 M. Adsorben yang dibuat yaitu AH-kitin 1 dan AH-kitin 2, masing-masing mengandung asam humat sebesar 2,2 dan 1,9 % (b/b). Asam humat (AH) yang terdapat pada AH-kitin 1 maupun AH-kitin 2 stabil hingga pH 11. Adsorpsi Ni(II) pada adsorben maksimum pada pH 8, dengan konstanta laju adsorpsi sebesar 0,0101; 0,0078; 0,0161; 0,0119 menit-1 masing-masing untuk kitin 1, kitin 2, AH-kitin 1 dan AH-kitin 2. Kapasitas adsorpsi sesuai urutan AH-kitin 1 > AH-kitin 2 > kitin 1 > kitin 2, yang besarnya masing-masing adalah 4,563 x10-4; 5,458 x10-4; 6,368 x10-4; 6,575 x10-4 (mol/g). Energi adsorpsi Ni(II) pada kitin 1, kitin 2, AH-kitin 1 dan AH-kitin 2 masing-masing sebesar 23,86; 22,08; 23,56; 24,76 (kJ/mol). Ekstraksi sekuensial metode menunjukkan bahwa adsorpsi Ni(II) pada adsorben didominasi oleh adsorpsi kimia, dengan asam humat pada AH-kitin 1 maupun AH-kitin 2 jauh lebih berperan dalam adsorpsi Ni(II). Pada adsorben AH-kitin 1, Ni(II) teradsorp sebanyak 57,45 mg/g asam humat dan 3,56 mg/g kitin. Hasil serupa teramati untuk AHkitin 2, yaitu sebanyak 48,42 mg/g asam humat dan 3,14 mg/g kitin. Dengan menggunakan HCl 0,1 M, lebih dari 90 % Ni(II) teradsorp berhasil dilepaskan dari adsorben.

Immobilization of humic acid on chitin has been conducted and applied for the adsorption of Ni(II). The humic acid was isolated from Rawa Pening soil by using NaOH 0.1 M, while chitin was isolated by deproteination of freshwater- and marinecrab shells by using NaOH 3.5 % and followed by removing inorganic impurities using HCl 1 M. Parameters investigated in this study consist of: method of immobilization, stability of immobilized humic acid, effect of acidity on adsorption, and rate, capacity, energy and mechanism of adsorption. The result of characterization of humic acid showed that the total acidity of humic acid was 2309.5 mmol/kg, and it was distributed into the acidity of COOH 1687.5 mmol/kg and the phenolic-OH 622.0 mmol/kg. Chitin 1 which was obtained from freshwater crab shell and chitin 2 from marine crab shell possessed both with the N/C ratio of 0.69 %, while the degree of acetylation as high as 69 % and 77 %, respectively. The Immobilization of humic acid on chitin has been successfully done by reacting chitin solution in HCl 0.5 M and humic acid solution in NaOH 0.5 M. The obtained adsorbent i.e. AH-Chitin 1 and AH-Chitin 2, contained humic acid 2.2 and 1.9 % (w/w), respectively. Humic acid immobilized on both AH-Chitin 1 and AH-Chitin 2 was stabile up to pH=11. Adsorption of Ni(II) was maximum at pH 8, with rate constant of 0.0101; 0.0078; 0.0161; 0.0119 min-1 for chitin 1, chitin 2, AH-Chitin 1 and AH-Chitin 2, respectively. The Capacity of Adsorption was in the order of AH-Chitin 1 > AH-Chitin 2 > Chitin 1 > Chitin 2, i.e. 4.563 x10-4; 5.458 x10-4; 6.368 x10-4; 6.575 x10-4 mol/g, respectively. The Energy of adsorption of Ni(II) on Chitin 1, Chitin 2, AHChitin 1 and AH-Chitin 2 was 23.86; 22.08; 23.56; 24.76 (kJ/mol), respectively. Sequential extraction showed that the adsorption of Ni(II) was dominated by chemical adsorption with the role of humic acid on AH-Chitin 1 and AH-Chitin 2 was predominant in adsorbing Ni(II). On adsorbent AH-Chitin 1, the adsorbed Ni(II) was 57.45 mg/g humic acid and 3.56 mg/g chitin. The similar result was also observed for AH-Chitin 2, i.e. 48.42 mg/g humic acid and 3.14 mg/g chitin. By using HCl 0.1 M, more than 90 % of the adsorbed Ni(II) was able to be desorped from the adsorbents.

Kata Kunci : Adsorpsi Ni(II),Imobilisasi Asam Humat,Kitin