Research progress on remediation technologies of chromium-contaminated soil: a review

With the rapid economic development in China, more areas of industrial contaminated soil has been left unused because of industrial relocation or environmental protection. Considering the chromium (salt) industrial wasteland, the area of chromium-contaminated soil caused by the accumulation of chromium slag has reached 5 million square meters, and its direct utilization can result in health hazards to the public and threaten the environment. Therefore, it is of great practical significance to carry out research on economic, efficient, and clean methods for chromium-contaminated soil remediation. In this paper, the origin and occurrence of the chromium in soil, their extraction methods, and the research progress of chromium-contaminated soil in and outside China were reviewed. First, the occurrence of the chromium in soil was discussed. It is found that Cr exists predominantly in Cr(Ⅲ) and Cr(Ⅵ) oxidation states, whereby Cr(Ⅲ) is the more stable; under most prevailing environmental conditions Cr(Ⅵ) is rapidly reduced to Cr(Ⅲ). The methods of extracting chromium from soil were presented, including Tessier sequential extraction procedure and the European Community Bureau of Reference(BCR) three-step sequential extraction procedure, and then the two continuous extraction methods were compared and evaluated. Afterward, the remediation techniques of chromium-contaminated soil were systematically reviewed, including engineering physical repair methods, dilution methods, immobilization and stabilization, chemical reduction, electrokinetics repair, and bioremediation. The advantages and disadvantages of the various remediation techniques were compared, summarized, and evaluated. The developments of chromium-contaminated soil remediation technologies in the future were also explored, including the clean remediation technologies, combination of several remediation technologies, and novel nano-remediation materials. Accordingly, suggestions for the remediation of different chromium-contaminated soils were presented, which can provide references for clean and efficient remediation of chromium-contaminated soils.