Abstract
The sorption behaviour of benzene, toluene, ethyl benzene, xylene and naphthalene using clay and sand sediments under ambient conditions is examined in this study. Experimental results showed that, the time taken to attain adsorption equilibrium for naphthalene, and BTEX were 28, 30, 30, 32, 28 hrs and 20, 22, 22, 24, 22 hrs while the desorption equilibrium time were 10, 13, 12, 15, 12 hrs and 9, 9, 9, 11, 10 hrs in clay and sand respectively. All of the naphthalene, and BTEX were adsorbed at the different equilibrium times, using clay while the amount of naphthalene and BTEX adsorbed by sand, at different equilibrium times were 117, 121, 127, 123 and 134 mg. Following the results of the adsorption/desorption experiments, quantitative measurements showed that sand exhibited higher affinity for the solute as retained more chemicals (as high as between 58% - 66%) within it pores while nearly all the chemicals adsorbed by the clay were released at the attainment of equilibrium. The implication of this is that occlusion within the sand particles may likely be the resultant effect of continued sand-chemicals contact. The amount of contaminant solute adsorbed and desorbed affirmed that clay has a better capacity to retain naphthalene and BTEX than sand and this may not be unrelated to its large surface area, high porosity and higher hydraulic conductivity for the solutes arising from its good binding sites (small pore sizes) that tend to hold the adsorbates to its particles.
Highlights
The major environmental concern in urban and industrial areas can be attributed to the increasing level of pollution by substances of organic origin
The amount of contaminant solute adsorbed and desorbed affirmed that clay has a better capacity to retain naphthalene and BTEX than sand and this may not be unrelated to its large surface area, high porosity and higher hydraulic conductivity for the solutes arising from its good binding sites that tend to hold the adsorbates to its particles
Adsorption-Desorption Kinetics Experiments The rates of adsorption by the sediments were determined from the uptake levels of polycyclic aromatic hydrocarbons (PAHs) and BTEX from aqueous solution in batch experiments before and after contact until adsorption equilibrium was attained in the clay and sand. 100 g of each of the sediments were mixed with 500 ml of aqueous solution of the adsorbates at room temperature following the procedure of Owabor et al [25]
Summary
The major environmental concern in urban and industrial areas can be attributed to the increasing level of pollution by substances of organic origin Various toxic chemicals such as polycyclic aromatic hydrocarbons (PAHs): naphthalene, anthracene, benzo(a)pyrene, phenanthrene, benzene, toluene, ethyl benzene and xylene (BTEX), heavy metals and dyes are continuously discharged into the environment as industrial waste, causing water, air and soil pollutions. The four and more condensed aromatic rings are considered to be more dangerous than the two and three rings PAHs [1,2,3] The presence of these compounds which are listed as priority pollutants [4,5,6,7] in the environment is of considerable public health and ecological concern due to their toxicity to a wide range of biological systems.
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