Remediation of Cr（VI）-Contaminated Soil by Reduction， Adsorption， and Solidification

Among the two major states of chromium， Cr（VI） is high mobile and carcinogenic whereas Cr（III） is less toxic. Remediation of chromium-contaminated soil usually involves reducing Cr（VI） to Cr（III） and subsequently immobilizing it. In this paper， a combined remediation technique including reduction， adsorption， and solidification was proposed. By employing an adsorbent， the remediation effectiveness was improved and the amount of reducing and curing agent was to some extent decreased. Synthetic precipitation leaching procedure （SPLP）， unconfined compressive strength （UCS）， and acid neutralization capacity （ANC） tests were carried out to evaluate the remediation effect of different agent combinations and different addition procedures. SPLP tests showed that the reduction-adsorption-solidification treatment significantly reduced the leached chromium. Using calcium polysulfide as the reducing agent was more effective than using ferrous sulfate. UCS tests showed that the strength of the solidified soil was reduced after employing the adsorbent， but the standards for strength could still be satisfied. ANC tests demonstrated that the combined remediation technology improved the capacity of the solidified system to resist acid erosion. The best combined dosage was calcium polysulfide， vermiculite， and cement. The researches on adding procedures showed that adding the reducing agent and adsorbent together and then adding the curing agent achieved similar effects to adding the three agents separately. This could facilitate the remediation process.