Interactive relationship between cementitious materials and acid mine drainage : their effects on Chromium Cr(VI) removal.

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.