Immobilization Of Cadmium On Secondary Minerals Induced By Dissimilatory Iron Reduction And Its Effect On Cadmium Uptake By Rice

Cadmium（Cd）is a common heavy metal pollutant in the natural environment.It enters the food chain through plant enrichment and water migration,which seriously endangers human health.The process of microbial dissimilatory iron reduction exists widely in soil.It refers to the process of iron reducing bacteria using all kinds of organic matter as electron donor and Fe³⁺as electron acceptor to reduce Fe³⁺to Fe²⁺,which is considered to be the key factor affecting rice Cd accumulation.Dissimilatory iron reduction induced secondary mineral absorption of heavy metals,thus establishing a kind of microbial soil stabilization of heavy metals of iron transformation mediated repair technology,understanding the alienation of iron reduction process of iron oxide morphology transformation,Cd adsorption fixed form,and reveals its application in the inhibition of rice Cd accumulation is imminent,and offers a new technical means for environmental remediation of heavy metal pollution.The secondary iron mineralization directly influences the fate of heavy metals.Thus,it can provide new ideas and techniques for the bioremediation of heavy metal polluted areas.Shewanella oneidensis MR-1,a typical iron-reducing bacteria,and HY iron-reducing bacteria enriched in contaminated soil were used in the experiment.Under the condition of laboratory pure culture,a method of inducing the formation of secondary minerals by microorganisms dissimilatory iron reducing iron minerals,the immobilization of Cd²⁺by secondary minerals induced by dissimilatory iron reducing bacteria was studied.The results show that the iron minerals have better redox properties under the action of microbial reduction after the addition of iron reducing bacteria in the experimental system,and are reduced by microorganisms as electron acceptors to produce Fe²⁺.There was a significant negative correlation between the concentration of Fe²⁺from reduction and the concentration of Cd²⁺in the solution.The immobilization of cadmium on secondary minerals induced by the microorganisms was stronger than that the adsorption of iron minerals itself.Meanwhile,the secondary minerals were characterized by X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）analysis.The dissimilatory iron reduction process leads to the change of the crystal structure of iron minerals,which provides more Cd²⁺adsorption sites and enhances the immobilization of Cd²⁺.Based on the influence of various factors on dissimilatory iron reduction and secondary mineral formation,Different concentrations of fulvic acid were added exogenously,Preparation of biochar supported S.oneidensis MR-1 and setting different initial p H.The effects of fulvic acid,biochar and p H on the bioreduction of ferrihydrite and the immobilization of Cd were investigated.As a result,exogenous addition of fulvic acid as electron shuttle agent promoted iron minerasl reduction dissolution and the transformation of secondary minerals,thus enhanced the immobilization of cadmium.Scanning electron microscopy（SEM）imaging results showed that the biochar provides a place for microorganisms to colonize,because of the strong adsorption of metal ions by biochar,the Fe²⁺in solution reduced dissolution of iron mineral reduction was slowed down.However,it significantly improved the immobilization effect of Cd²⁺.According to the method of microbial dissimilated iron reduction to induce secondary minerals and its application in inhibiting rice Cd accumulation was tested.The results showed that the application of biochar and the process of dissimilatory iron reduction affected the change of soil p H.The addition of microbial agents increased the number of soil microorganisms and changed the micro-ecological environment of potted soil.The reduction of dissimilar iron in rice soil induced structural transformation of iron minerals,which increased the immobilization of Cd by iron oxides,thus reduced the accumulation of Cd in rice tissues.The combined application of anthocyanin had no effect on Cd accumulation in the rhizosphere,but significantly changed Cd transport in rice stems,leaves and grains.It could be applied in combination with iron transformation mediated by microorganism and immobilized heavy metal repair.