الفهرس 
1. INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The adsorption of herbicide (pendimethalin) onto natural clay has been investigated as a possible alternative method for its removal from aqueous solutions. Natural clay reached equilibrium with pendimethalin concentrations of 95.8, 172.6 mg/dm3 in contact time of less than 3 hours.
The effectiveness of natural clay for pendimethalin removal has been examined and compared with that of activated carbon.It was found that the natural clay has 54% pendimethalin removal efficiency in compared with that of activated carbon under similar conditions.
The influence of system variables, such as particle size (dp), pH and temperature on the removal efficiency have been studied. The removal efficiency has been_calculated for all variables. The maximum removal (54 %) was observed at 20°C and pH 3.44 with particle size range 80-125 pm.
The adsorption equilibrium has been studied at different system variables. The effect of pH on the adsorption capacity has been studied at pH value of 3.44, 8.19 and 9.62. The adsorption capacity was increased from 11.5 mg/g (13 %) to 30.8 mg/g (54.39 °A) as a pH decreased from 9.62 to 3.44.
Temperature also plays an interesting role in the adsorption of pendimethalin onto natural clay. As temperature raised from 20°C to 40°C, the adsorption capacity was decreased from 20.1mg/g (37.43 %) to 13.9 mg/g (18.76 %) this show the exothermic nature of the process. The heat of adsorption (AHad) has been evaluated and it has a value of (-29.36) KJ/g-mole.
The effect of particle size range of clay has also been studied with three ranges of 80125, 250-355 and 500-710 p.m. The adsorption capacity was increased from 18.2 mg/g (27.15 %) to 21 mg/g (45.11 %) as a particle size decreased from 500-710 pm to 80125 pm.
Equilibrium modelling has been carried out using the Langmuir, the Freundlich and the Redlich-Peterson models and constants have been calculated under different system variables. The Freundlich isotherm better fitted the experimental data since the average percent deviations were lower than with the Langmuir and the Redlich-Peterson models.
A series of contact-time experiments have been undertaken in an agitated batch adsorber to assess the effect of the design variables, namely, agitation speed, initial concentration, particle size, mass, and pH.
The external mass-transfer has been studied with five design variables. A simple kinetic model has been developed to determine the external mass-transfer coefficient (Ks)and correlated with the design variables. The Ks has been found to vary linearly with design variables according to the general equation:
KS = X (variable)Y
Intraparticle diffusion has also been studied and the macropore rate parameter (K1) has been determined and correlated with the design variables. The K1 has been found to vary linearly with design variables according to the general equation:
K1 = A (variable)B.
The kinetic studies strongly indicated that, the external mass-transfer is rate-limiting step in the early stages of the adsorption process, while the intraparticle diffusion is a major rate-limiting step in controlling pendimethalin removal from aqueous solutions.
The design procedures for agitated batch adsorber have been investigated and the design data are based on isotherm data and kinetic data.