ADSORPTION OF PHOSPHATE FROM PAPER MILL EFFLUENT ONTO SEPIOLITE AND FLY ASH

Abstract

This study aimed to remove phosphate from paper mill industry (4500m(3)/h) wastewaters, which are discharged to the sea from a plant located in western Turkey. As adsorbents, fly ash, raw sepiolite and heat-activated sepiolite were used. The effect of factors such as, particle size, temperature, pH and initial of phosphate concentration on adsorption process was investigated. From kinetic studies, equilibrium time was found to be I h for fly ash and heat-activated sepiolite. The kinetic data supports pseudo-second order model (r(2) >= 0.99) but shows very poor fit for pseudo-first order model (0.81 >= r(2)). Intraparticle model also shows that there are two separate stages in sorption process, namely, external diffusion and pore diffusion. Adsorption isotherms for fly ash and activated sepiolite were obtained at three different temperatures. It was seen that Langmuir isotherm model is better than Freundlich for both sepiolit and fly ash (r(2)>0.98). From experiments carried out at different pH values, it was observed that pH plays an important role in the adsorption process in removal of phosphate, providing both ionizating the compounds and modifying sorbent surfaces. It was also observed that heat-activated sepiolite is more effective than raw sepiolite and fly ash to remove. Adsorption of phosphate compounds increases with decreasing particle size.