Abstract
Elevated hexavalent chromium (Cr(VI)) levels in pervious concrete may undermine its successful application in water treatment. Portland cement CEM I 52.5R (CEM I), coal fly ash (FA), natural zeolite and ground granulated blast-furnace slag (GGBS) were evaluated as adsorbents for removal of Cr(VI) from acid mine drainage (AMD). Adsorption experiments were conducted at dosages of 6, 10, 30 and 60 g of adsorbent in 200 mL of AMD, while the mixing contact time was varied from 15 to 300 min. It was found that the use of CEM1 and FA adsorbents strongly increased the Cr(VI) concentration in AMD. Conversely, zeolite and GGBS removed up to 76% and 100% of Cr(VI) from AMD, respectively, upon their use at dosages of at least 10 g of the adsorbent. Freundlich isotherm was found better fitted with a high correlation coefficient (R2 = 0.998 for zeolite and 0.973 for GGBS) than to the Langmuir model (R2 = 0.965 for zeolite and 0.955 for GGBS). Adsorption and ion exchange seem to be active mechanisms for the Cr(VI) removal. These results suggest that zeolite and GGBS can be considered as partial cement replacement materials for effective reduction or removal of Cr(VI) from the treated water.
Highlights
Chromium exists in various oxidation states ranging from Cr(II) to Cr(VI)
Adsorption and ion exchange seem to be active mechanisms for the Cr(VI) removal. These results suggest that zeolite and ground granulated blast-furnace slag (GGBS) can be considered as partial cement replacement materials for effective reduction or removal of
Adsorption tests were conducted on CEM I 52.5R (CEM I); Class F, fly ash (FA); natural zeolite and GGBS as adsorbents for Cr(VI) removal from acid mine drainage (AMD)
Summary
Chromium exists in various oxidation states ranging from Cr(II) to Cr(VI). Among these states, Cr(III) and Cr(VI) are the most common and most stable species [1,2]. Zeolites are low-cost ion exchangers that have been used as adsorbents for removal of heavy metals including chromium, etc., [15,16] from polluted water. The problems associated with use of physico-chemical methods for Cr(IV) removal include the high operating costs of the treatment, high energy consumption, excessive use of chemicals, generation of toxic sludge and air pollution resulting from the use of sulphur-based reducing agents [22,30]. Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), were used to investigate the physico-chemical properties of the adsorbents
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