MERCURY (II) EQUILIBRIUM ADSORPTION STUDY ON IMMOBILIZED WATER HYACINTH (Eichornia crassipes) LEAF BIOMASS ON POLYSILICA MATRIX Himmatul Barroroh, Susi N.K., Diana C.D. Chemistry Department of Science and Technology Faculty of State Islamic University (UIN) Malang ABSTRACT Binding metal ion by biomass has a weakness that is easily degrade by microbe, therefore it was necessary to immobilize biomassa plant on a matrix. This research was focused to study mercury (II) equilibrium adsorption on immobilized water hyacinth leaf biomass at polysilica matrix and matrix interaction with biomass. The interaction of polysilica matrix with biomassa leaf of water hyacinth was determined by using FTIR. The determination of adsorption capacity, adsorption constant and energy of adsorption mercury (II) has done by interact of 25 ml Hg 2+ aquous solutions with concentration, 20, 30, 40, 50, 60, 70, 80, 90, 100 and 150 mg/L on optimum pH during 60 minute with biomass. The result of experiment data then was processed by using adsorption isothermic equation of Langmuir and Freundlich. The result of research shows that there were two possibilities interaction between polisilikat matrix with biomassa leaf of water hyacinth. First, that biomassa leaf of water hyacinth was trapped into polysilica matrix, this is the most dominant interaction, and second, that the interaction was happened between active site Si-OH with group of NH 2 and COOH. This is based on the loss of absorption spectra of Si-OH at wave number of 3601,82 cm -1 , 3503,45 cm -1 , 3410,68 cm -1 . Adsorption Isothermic of mercury (II) on biomassa leaf of water hyacinth (Eichhornia Crassipes) which diimmobilization at polysilica matrix followed isothermic equation of Langmuir with R 2 value = 0,982, but the active site of interaction is heterogenous, with adsorption capacities (X m ) of 4,649 x 10 -5 mol/g, adsorption constant of (K) 11334,796 mol/L and energy adsorption (E) equal to 23,28585 kJ/mol. Keywords: mercury (II), water hyacinth (Eichhornia crassipes), immobilization, polysilica matrix.