Comparison of Adsorption Models for Cd and Zn in the Berau Delta: Water–Sediment System (Perbandingan Model Penyerapan Cd dan Zn di Delta Berau: Sistem Perairan-Sedimen)

Abstract

Adsorpsi merupakan proses penting dalam mengontrol transfer logam dari larutan ke padatan. Cd dan Zn merupakan logam yang banyak digunakan manusia sehingga berpotensi banyak dibuang ke lingkungan. Penelitian ini membandingkan model adsorpsi Cd dan Zn dalam sistem air laut-sedimen di delta Berau, Kalimantan Timur. Sampel air dan sedimen didapat di 12 stasiun. Untuk mendapatkan konsentrasi Cd dan Zn, sampel air dianalisis menggunakan metode back extraction yang menggunakan bahan kimia organik (Amonium pirolidinditio karbamat dan metili sobutil keton) dan anorganik (asam nitrat). Sampel sedimen dianalisis menggunakan distruksi asam yang mengacu metode dari USEPA 3050b. Data yang didapat dikalkulasi berdasar model adsorpsi yaitu: Model partisi, Freundlich Model dan Langmuir Model. Dalam perhitungan di studi ini, Delta Berau dibagi menjadi dua bagian: bagian utara dan bagian selatan. Dari kedua bagian ini, Model isotermis langmuir merupakan model yang paling cocok untuk proses adsorpsi dalam sistem air sedimen. Di sungai bagian utara, hasil perhitungan linearitas memberikan angka R²=0.949 untuk Cd dan R²=0.838 untuk Zn, sedangkan, untuk sungai bagian selatan nilai R²=0.575 untuk Cd dan R²=0.944 untuk Zn. Kapasitas adsorpsi maksimum Cd adalah 0,5-0,6 mg.kg^-1 sedangkan kapasitas adsorpsi maksimum untuk Zn adalah 12-43 mg.kg^-1. Prediksi kapasitas maksimal sedimen menggambarkan total kapasitas sedimen sebagai Cd dan Zn deposit. Penambahan Cd dan Zn akan menyebabkan logam-logam tersebut tidak teradsorpsi dan berpotensi racun bagi organisme perairan.

Kata kunci: delta Berau, adsorpsi, air, sedimen, model isotermis langmuir

Adsorption is important process for controlling metals transfer from dissolved phase to solid phase. Cd and Zn become trace metal which generally used in human activity and the release of those trace metals into aquatic environment cannot be evaded.The purpose of this work was to compare adsorption models of Cd and Zn in water-sediment system in Berau Delta, East Kalimantan. Sediment and water sample were collected at 12 stations. Measuring Cd and Zn concentration, water sample analysis was conducted using organic chemicals (Ammonium Pyrrolidine Dithio Carbamate and Methyl Isobutyl Ketone) and inorganic chemicals (nitric acid) based on back extraction procedure. On the other hand, sediment analysis was conducted using acid destruction according to USEPA method 3050b. The data would be calculated in some different adsorption model: Partition model, Freundlich model and Langmuir model. In this study, Berau Delta was divided into two groups: North river stream (N) and South river stream (S). In both groups,Langmuir isotherm model was the most representative model for adsorption process in water-sediment system. In North stream, the linearity of data gave R²=0.949 for Cd and R²=0.838 for Zn, whereas, R²=0.575 for Cd and R²=0.944 for Zn calculated in the South stream. Maximum adsorption capacity of Cd was 0.5-0.6 mg.kg^-1 and maximum adsorption capacity of Zn was 12-43 mg. kg^-1. Those maximal adsorption capacities illustrated the total capability of sediment as Cd and Zn deposit. Another Cd and Zn input will not be adsorbed and probably become bioavailable for aquatic life.

Keywords: Berau delta, adsorption, water, sediment, langmuir isotherm model