Status and prospect of in-situ remediation technologies applied in hexavalent chromium contaminated sites

Hexavalent chromium Cr(Ⅵ) is a typical heavy metal pollutant with a wide range of sources. Due to its diverse forms and valence states, the geo-chemical reaction process is extremely complicated. There are lots of Cr(Ⅵ) contaminated plots in China and the remediation of Cr(Ⅵ) contaminated sites is very challenging. In-situ remediation has gradually become the mainstream of remediation strategies for contaminated sites due to many advantages such as no excavation and less environmental interference. The latest research progress of different in-situ remediation technologies for Cr(Ⅵ) was reviewed. Based on a large number of in-situ remediation engineering cases at home and abroad, the application effects of in-situ biological, in-situ chemical and other remediation technologies and different injection methods were analyzed. The key parameters of different types of in-situ remediation technologies including applicable geological conditions, applicable concentration range, influence radius, remediation duration, remediation medium, agent type and dosage, and injection method were clarified. It played a key role to establish a precise contamination field concept model, and choose efficient chemicals and the best injection method or remediation process combinations for complex contaminated sites. The advantages and disadvantages of different in-situ remediation technologies of Cr(Ⅵ) were compared in examples, and their different applicable scenarios were explored. At the same time, the future development direction of technologies was prospected.