Removal Of Suspended Cadmium From Irrigation Water In Hunan Province

The cadmium polluted irrigation water was considered to be the main sources of paddy soil pollution in Hunan province. Suspended cadmium is the main forms of cadmium in natural water, suspended cadmium is generally too fine to settle by gravity and are usually negatively charged.Consequently, they would form a stable suspension and could not be removed without the introduction of a coagulant or other external factors. Therefore according to the feature of cadmium, the influence of physical-chemical properties, common fertilizer and common hydrophytes in south china on flocculation and sedimentation of suspended matter has been investigated systematically in this paper.The physical-chemical properties part:the influence of salt ionic> cations>pH and organic matter on the flocculation and sedimentation of suspended particles has been investigated. The results has revealed that salt ions has no obvious effect on the sedimentation of suspended matter. The sedimentation of suspended matter mainly controlled by pH and cation, it's because under acidic circumstance, the surface charge of suspended matter can be neutralization rapidly by large amounts of H+. The Fe3+ has stronger ability in neutralize suspended colloid surface charge than Ca2+, therefore, Fe3+ can promoting the sedimentation of suspended matter.The common fertilizer part:we sorted out K2HPO4 which have the prominent ability on suspended matter sedimentation through invistigated the sedimentation ability of potash fertilizer?phosphate fertilizer and organic fertilizer. The removal of suspended cadmium by K2HPO4 has been investigated,removal efficiency can reached to 80% after 12 hour processed. The analysis of ZETA potential revealed that K2HPO4 can reduce the surface charge of suspended matter, then aggregating of suspended particles occurs. Consequently, promoting the sedimentation rate of suspended colloid. The sedimentation of suspended matter is attributed to a fishing-net like structure formed by PO43-?OH- interaction with Ca2+ and Fe3+. But the structure was unstable, after 72h, the structure will be broken with cadmium and P released, then elevating the concentration of cadmium in water. Hence the sedimentation time must be controlled within 72 hours.The common hydrophytes part:we sorted out the Myriophyllum verticillatum and Eichhornia crassipes from four common aquatic plants in southern china(Myriophyllum verticillatum?Eichhornia crassipes^Canna indica and Spirodela polyrrhiza) both of them has prominent ability in sedimentation of suspended matter, both of them can accelerated the sedimentation of suspended cadmium. The results also showed that approximately81% cadmium was settled by plants, rest 19% are absorption by roots, indicating that root exudates is the main reason attributed to the sedimentation of cadmium. We also investigated the ability in removing dissolved cadmium by Myriophyllum verticillatum and Eichhornia crassipes, results showed that both of the two plants can absorption dissolved cadmium rapidly. Therefore, we choose Myriophyllum verticillatum and Eichhornia crassipes to removal of cadmium from irrigation water.