Removal of Some Pollutants from Aqueous Solutions Using Ultrasonic Technique and Prepared Multi Walled Carbon Nanotubes

Abstract

Activated carbon is characterized as being of special importance for its large use in industry field and for purposes of the pollution control. Removal of the pollutants which are benzene, o-xylene and sulfide ion is a main goal of the present research. The present investigation included the use of: 1. Non-activated carbon, activated carbon and multi-walled carbon nanotubes (MWCNT) synthesized from fuel oil wastes. 2. Ultrasonic technique. In the first part the non-activated and activated carbons were prepared from the wastes of fuel oil through calcination and activation processes by using 20% of anhydrous zinc chloride. A novel MWCNT was synthesized from activated carbon by ultrasonic technique. Identification of MWCNT is achieved by using different techniques such as FE-SEM, TEM, AFM, XRD and FT-IR. Additional physical evaluations of the samples were also conducted such as the surface area, pH, density, moisture and ash content. The prepared carbon types were tested to remove benzene, o-xylene and sulfide ion from aqueous solutions with using normal equilibration for sulfide ion, while benzene and o-xylene by using a new circulating system. Evaluation and efficiency of MWCNT and of activated and non-activated carbon samples were concerned through adsorption of benzene, o-xylene and sulfide ion from aqueous solution. Adsorption process on carbon for benzene, o-xylene and sulfide ion solutions was investigated at concentrations of (50, 100, 150, 200, 250, 300) ppm at four different temperatures (283, 293, 313 and 333) K and at different periods of time. Equilibrium adsorption study was done by using a new circulating system and isothermal models which are Langmuir, Freundlich and Temkin. Kinetic and thermodynamic parameters were also calculated. Specific adsorption percentages of benzene and o-xylene were highly affected by the addition of activator and decreased with increasing temperature compatible to that of non-activated carbon. The adsorption rate was increased by increasing benzene and o-xylene concentrations. A complete removal of benzene and o-xylene concentrations were achieved for initial concentrations of (50,100) ppm by MWCNT at temperature of 283 K. As such, it is clearly proved that benzene and o-xylene adsorption by synthetic MWCNT suits fair enough with the adsorption models. It clarifies that benzene and o-xylene adsorption by synthetic activated carbon and non-activated carbon agrees fair enough with the Freundlich and Temkin adsorption models and it poorly fits with Langmuir isotherm model. The negative value of enthalpy (ΔHo ) indicates that the adsorption process is exothermic and physical in nature, while the negative values of (ΔSo ) are explained on the basis of decrease in order at adsorption system. The negative value of (ΔGo ) indicates that the adsorption process could occur spontaneously. Kinetic study of the considered compounds on carbon showed that the adsorption system fits the pseudo first order model. In the second part, degradation of benzene and o-xylene in an aqueous solution by ultrasonic has been done at different temperatures with initial concentrations of 100 and 200 ppm. Kinetic and thermodynamic degradation parameters of benzene and o-xylene were investigated, while, the mechanism of benzene and o-xylene sonolysis were proposed and discussed. The degradation rate of benzene and o-xylene increased with the increasing of electric power, sonication time and decreased with increasing liquid volume, temperature and initial concentration of benzene and o xylene. The beneficial effect of power on removal rates is believed to be due to increased cavitational activity occurring at higher levels of power. Thermodynamic parameters indicated that benzene and o-xylene degradation was spontaneous and exothermic in nature. Data obtained were fit with the pseudo-first order model.