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Removal of polycyclic aromatic hydrocarbons from deionized water and landfill leachate by using modified clinoptilolites Hedayati, Monirehsadat

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are toxic, carcinogenic, and persistent in the environment. Clinoptilolite, a type of natural zeolite, was modified with cetylpridinium chloride (CPC), didodecyldimethylammonium bromide (DDAB), hexadecyltrimethylammonium bromide (HDTMA-Br), and tetramethylammonium chloride (TMA) separately as potential adsorbents for removal of PAHs. Leachability and thermal stability of modified clinoptilolites were investigated. Adsorption capacity, kinetics, sorbent dosage, pH, temperature, and competition effects were studied adopting batch adsorption tests using deionized water spiked with five PAHs (anthracene (50 µg/L), fluoranthene (100 µg/L), fluorene (100 µg/L), phenanthrene (100 µg/L), and pyrene (100 µg/L)). The leachability and thermal stability results indicated that CPC and DDAB modified clinoptilolites were less leachable and more stable compared to HDTMA modified clinoptilolites. The non-modified clinoptilolite, and TMA modified clinoptilolite exhibited 93 % of five PAHs after 24 hours at 1:100 solid: liquid ratio and met the local water quality criteria, except for fluorene on HDTMA modified clinoptilolite which retained >83%. For CPC and DDAB modified clinoptilolites, more than 80% of all PAHs were retained within 15 minutes and maximum adsorption was reached in < 2 hours. Three kinetic models were applied using pseudo-first, pseudo-second-order, and intra particle equations, and the results are well represented by the pseudo-second-order equation. With a 1:200 solid: liquid ratio, the removal of anthracene, fluoranthene, and pyrene were above 90, 80, and 70 % on CPC, DDAB, and HDTMA modified clinoptilolites, respectively. After performing 21 successive batch adsorption tests on CPC, DDAB, and HDTMA modified clinoptilolites, the PAHs had accumulated about 0.7 to 1.5 mg per gram of clinoptilolite. PAH leachabilities from these loaded PAHs were less than 5% after conducting a stability test. Different pH values and temperatures have insignificant effects on adsorption of PAHs, except for fluorene. Different pH values changed the adsorption of fluorene only slightly on HDTMA modified clinoptilolite. When temperature was increased, fluorene adsorption was decreased by 95%) from landfill leachate spiked with PAHs.

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