EQUILIBRIUM, KINETIC AND MASS TRANSFER STUDIES AND COLUMN OPERATIONS FOR THE REMOVAL OF ARSENIC(Ⅲ) FROM AQUEOUS SOLUTIONS USING ACID TREATED SPENT BLEACHING EARTH

摘要

In the present study, a new adsorbent was produced from spent bleaching earth by H_2SO_4 impregnation method. The sorption of arsenic(Ⅲ) by acid treated spent bleaching earth was studied to examine the possibility of utilizing this material in water treatment systems. The effect of time, pH, initial concentration, temperature on the adsorption of arsenic(Ⅲ) was studied. Maximum adsorption was found to occur at pH 9.0. The adsorption process followed the first order Lagergren equation. Mass transfer coefficients and rate constants of intraparticle diffusion were calculated. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacity (Q_0) of the adsorbent and the value of Q_0 was found to be 0.46 mmol g~(-1). In order to understand the adsorption mechanism, Dubinin-Radushkevich (DR) isotherm was used. The magnitude of E calculated from DR equation was found to be 5.12 kJ mol~(-1). The heat of adsorption (ΔH~0= -30367 J mol~(-1)) implied that the adsorption was physical exothermic adsorption. The column studies were also carried out to simulate water treatment processes. The capacity values obtained in column studies were found to be greater than the capacity values obtained in batch studies. This result was explained by the difference between batch system and column system. The factors that affect the capacity values of column and batch systems were explained. The effect of other anions on the adsorption of arsenic(Ⅲ) in the presence of NO_3~-, SO_4~(2-), Cl~-, Br~- was studied. The presence of these anions did not affect the adsorption of arsenic(Ⅲ) significiantly.