ConclusionsNowadays, heavy metals pollution in river/lake has gradually become a major concern worldwide. Most metals flowing into river would store in sediment and keep available to living organisms for a long period. The remediation of sediment is necessary.For different sediment contaminated by heavy metal, the adoption of remediation technology usually depends on some special characteristics of sediment, such as metal loads, size distributions of particles, metal species distribution. Generally, for the sediment contaminated severely, ex situ remediation technologies, such as sediment washing, flotation, ultrasound, electrochemical remediation should be considered priorly; for those contaminated slightly, in situ remediation technologies (e.g. phytoremediation, amendment and sand cap) usually are a perfect choice. If the sediment is mainly composed of larger particles (such as sand, grains and silt), washing and ultrasonic-assisted extraction should be given the priority; if the sediment is mainly composed by smaller particles (<63 μm), flotation, electrochemical remediation, immobilization and ultrasonic-assisted extraction should take the priority. Additionally, when metals in sediment are mainly composed of the mobile and the exchange fraction, such methods as amendment, ultrasound, electrochemical remediation, immobilization and washing can effectively lower the release of metal adsorbed; when the Mn-oxides fraction and the OM fraction take up a large proportion of sediment, such methods (e.g. ultrasound, electrochemical remediation, amendment, sand cap and chelating reagents washing) often present better remediation effects.In all environmental factors, the pH, ORP and OM are the most important factors affecting heavy metal distributions. The pH and OM can directly change metals distributions in sediment. However, mainly through oxidizing metal sulfide or changing pH values, ORP indirectly alter metal distribution.In situ remediation technologies, due to their easy operation, low costs and fast remediation effect, are applied widely. However, the immobilized metal still remains in sediment and may be released into water again under some special conditions. Therefore, for avoiding a possible pollution of the sediment remedied, the ex situ remediation should be advocated in future.
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