Combined Treatment of Cr(VI)-Contaminated Soils by Reduction, Adsorption, and Solidification

Remediation of Cr(VI)-contaminated soil usually includes reducing Cr(VI) to Cr(III) with sub-sequent solidification. In this paper, a treatment technique that combines reduction, adsorption, and solidification was proposed. By introducing an adsorbent into the reduction process, the remediation effectiveness was improved and the amount of reducing and solidified agent was decreased. Synthetic precipitation leaching procedure (SPLP), unconfined compressive strength (UCS) test, and scanning electron microscope (SEM) analysis were carried out to evaluate the remediation effect under different agent combinations and different agent-adding procedures. The results of SPLP showed that the reduction/adsorption/solidification treatment significantly reduced the leachability of Cr. UCS increased with increasing dosage of cement and CaS 5 , and decreased with an increasing dosage of vermiculite. The best agent dosage was CaS 5 of 2 times molar stoichiometric ratio of Cr(VI), 15% of vermiculite, and 20% of cement. Orthogonal test showed that for soil with low Cr(VI) content, CaS 5 dosage was the most important factor that affected the leachability of Cr. Cement and vermiculite have greater impact in limiting the leachability of Cr when Cr(VI) content in soil increased.