Reactive Barrier in the EK-PRB Process

2 DESIGN OF REACTIVE BARRIER IN THE EK-PRB PROCESS 23.2.1 Iron Fillings 

Depending on the contaminants in the soil, the fillings in the barrier will be different. Cr(VI)-contaminated sou is used as an example. To create a reactive zone for Cr(VI) reduction, the ZVI aggregate and silica sand can be used as filling material in the barrier. Commercial iron aggregate (Fig. 23.2), such as ConneUy-GPM Inc., 

In the design of the barrier, two key parameters ought to be considered the amount of ZVI in the barrier and thickness of the barrier. Depending upon the Cr(VI) species (Fig. 23.3) involved in the reaction, the amount of Fe in the PRB was determined based on Cr(VI) and ZVI reactions  

The chromate species are closely related to the pH and the total Cr(V) concentration. The dominant species in the solution are HCrOl and CrOl for low Cr(V) concentration, while Cr207 appears at an elevated Cr(VI) concentration (Fig. 23.3). For the EO solution having a high concentration of Cr(VI), each one of chromate ions, CrOl , HCrOl, and Cr207, needs to be accounted for for ZVI estimation. If the concentration of Cr(VI) in the EO flow is less than 50mg/l, then HCrOi and CrOl are the dominant species at all pHs. Based on Eqs. 23.1-23.3,1 molar concentration of ZVI can reduce 1 molar of Cr(VI). To ensure all chromate species are completely reduced to Cr(III), an excess amount of ZVI is needed. Thus, the minimum ZVI requirement (Wzvi in kilograms) in the barrier can be estimated as follows  

By accounting for only 90% of iron content in the ZVI aggregate sample with 10% impurities, the minimum requirement of ZVI in the barrier to treat 100 tons of soil with a Cr(VI) concentration of 2000 mg/kg was estimated as follows  

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