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ItemRemediation technologies of heavy metal contaminated soilsAlaboudi, Khalid A. ( 2018)Environmental contamination with heavy metals has become a serious problem, worldwide. Several remediation technologies are available for treating heavy metal contaminated soils. However, each technology has some advantages and disadvantages. The main objective of the current study was to compare different remediation technologies of soil, which was artificially contaminated by Pb, Cd, Cr and Hg. To achieve these goals, several experiments were performed as follows: (1) phytoremediation by using sunflower plant for treating Pb and Cd contaminated soils, (2) soil washing of Pb, Cd and Cr contaminated soils by using FeCl3 and EDTA extracts, (3) stabilization of Pb, Cd and Cr metal ions by using biochar and (4) thermal treatment of Hg and Cd contaminated soils at 1000 °C. All experiments were performed at different concentrations of studied metals (200, 400 and 600 mg kg-1), and finally, concentrations and speciation of heavy metals were measured by using different extraction methods. In addition, the possible changes that might be occurring in the treated soils were also a matter of concern. The obtained results showed that the Helianthus annuus plant can accumulate Pb and Cd in its tissues. However, the uptake of Cd was more favourable for the plant compared to Pb. It could be recommended the use of plant growth promoters and/or biochar in combination, along with phytoremediation technology. The use of biochar enhanced the growth of maize plants, and stabilized Pb and Cd in soil. In addition, biochar positively improved soil fertility in terms of, nutrients contents and organic matter. Attention should be paid regarding the use of biochar in soil co-contaminated with Cr due to the release of Cr into the soil due to biochar addition. Therefore, biochar can be used effectively in combination with phytoremediation technology for enhancing the removal efficiency of heavy metals from contaminated soils. Soil washing technology has proven to be a suitable tool for removing heavy metals from contaminated soils. FeCl3 was more efficient and cheaper for washing Pb, Cd and Cr compared to EDTA salt. Considerable attention should be paid during soil washing technology to overcome the soil salinization and nutrients leaching problems. Thermal treatment application for 60 min. was not sufficient to remove Cd from contaminated soil, and the maximum removal capacity was 66.87%. However, more than 98% of Hg was removed by using thermal treatment. Thermal treatment has some disadvantages in terms of, increasing soil pH and decreasing nutrients availability. These findings contribute with helpful tools in environmental management of contaminated soil with heavy metals and the future of reclaiming contaminated soils for agricultural and other use is important factor for selecting the appropriate remediation technology with varying costs of the different technologies applied.