Abstract
To remove chromate from a wastewater, a porous permeable reactive barrier system (PRBS), using pyrite and biotite, was adapted. This study included bench‐scale column experiments to evaluate the efficiency of the PRBS and investigate the reaction process. The total chromium concentration of the effluent from the biotite and pyrite columns reached the influent concentration of 0·10 mM after passing through more than 150 pore volumes (PVs) and 27 PVs respectively, and remained constant thereafter. The Cr^VI^ concentration in the effluent from the biotite column became constant at about 0·08 mM, accounting for approximately 80% of the influent concentration, after passing through 200 PVs. Moreover, in the pyrite column, the Cr^VI^ concentration remained at about 0·01 mM, 10% of the input level, after passing through 116 PVs. This shows that both columns maintained their levels of chromate reduction once the Cr^VI^ breakthrough curves (BTCs) had reached the steady state, though the steady‐state output concentration of total chromium had reached the influent level. The variances of the iron concentration closely followed those of the chromium. The observed data for both columns were fitted to the predicted BTCs calculated by CXTFIT, a program for estimating the solute transport parameters from experimental data. The degradation coefficient µ of the total chromium BTCs for both columns was zero, suggesting the mechanisms for the removal of chromate limit the µ of the Cr^VI^ BTCs. The Cr^VI^ degradation of the pyrite column (6·60) was much greater than that of the biotite column (0·27). In addition, the Cr^VI^ retardation coefficient R of the pyrite column (253) was also larger than that of the biotite column (125). The R values for the total chromium BTCs from both columns were smaller than those of the Cr^VI^ BTC. Whereas the total chromium BTC for the pyrite column showed little retardation (1·5), the biotite column showed considerable retardation (80). The results for the 900 °C heat‐treated biotite column were analogous to those of the control column (quartz sand). This suggests that the heat‐treated biotite played no role in the retardation and removal of hexavalent chromium. The parameters of the heat‐treated biotite were calculated to an R of 1·2 and µ of 0·01, and these values confirmed quantitatively that the heated biotite had little effect on the transport of Cr^VI^. These solute transport parameters, calculated by CXTFIT from the data obtained from the column tests, can provide quantitative information for the evaluation of bench‐ or field‐scale columns as a removal technology for Cr^VI^ in wastewater or contaminated groundwater. Copyright © 2006 John Wiley & Sons, Ltd.