Cadmium Absorption With Mineralization In Paddy Crust And Its Response To Manganese

Rice fields in China are very polluted by external cadmium.Paddy field crust is the necessary passage for exogenous cadmium to enter the paddy field system.It is important to study the cadmium absorption and mineralization process in rice paddy.In this paper,the distribution characteristics of cadmium in rice crusts in manganese ore districts were analyzed,and the effects of manganese on cadmium uptake and mineralization in rice paddy were discussed.The details are as follows:1.Select the biological crust in the upper,middle and lower reaches of the manganese ore field,characterize its structure and element morphology,and analyze the bacterial community structure in the crust.The distribution and content of three heavy metals,manganese,cadmium and zinc in the biological crusts of the upper and lower reaches of the manganese ore district were analyzed.It was found that the contents of the three heavy metals in the biological crusts were decreased in the upper,middle and lower reaches,and the contents of manganese and zinc were mainly decreased.It is distributed in the non-EDTA exchangeable state in the crust,and the cadmium content is mainly distributed in the biosorption part.Comparing the content of manganese with cadmium,it was found that the content of cadmium in biological crust increased with the increase of manganese content.The presence of rhodochrosite in the crust was observed by scanning electron microscopy.It is speculated that the biomineralization of manganese promoted the adsorption of cadmium by biological crust.Since the manganese concentration in the manganese ore district is higher than that in other regions,the thick-walled bacteria,actinomycetes,and proteobacteria distributed with manganese oxidizing bacteria are the dominant species in the upstream,middle,and downstream of the manganese ore district.Because the downstream is relatively far from the mining area and less polluted,the most downstream biodiversity is the most abundant in the OUT,and the upstream and the middle and downstream are relatively poor.Long-term heavy metal pollution has significantly reduced the biodiversity and biomass of the manganese ore district.Because the bacterial community is very sensitive to heavy metals,the pollution of heavy metals changes the biodiversity and microbial biomass of the original area.Bacterial diversity decreases as the concentration of heavy metals increases,while lower concentrations of heavy metals increase microbial biomass and stimulate microbial growth.2.The biological crust that is prevalent in the southern paddy field environment is cultured under different manganese concentration environments and its cadmium removal efficiency in the manganese-containing environment is observed.After the completion of the culture,the biological crust is characterized and the biological knot is The product after cadmium removal was studied.We found that the higher the manganese concentration in the manganese-containing environment,the higher the adsorption efficiency of biological crust to cadmium.The removal efficiency of cadmium by biological crust can reach 95.75% under the condition of 20mg/L manganese salt.By characterizing the biological crust after adsorption,it is known that this is the main role of absorbing cadmium ions and embedding them into the lattice structure during the oxidation of manganese ions into birnessite.After extracting and identifying the bacteria in the biological crust,we found that there was a Bacillus(MH192379.1)capable of oxidizing Mn2+ to birnessite in the biological crust.This shows that Bacillus has played an important role in biomineralization in biological crusts.3.Separation of the collected M.aeruginosa in the collected biological crust,non-invasive micro-measurement and kinetic experiments,it was found that with the increase of surrounding manganese concentration,M.aeruginosa produced a large amount of hydrogen ions,and hydrogen ion production would It has an effect on the change of pH in the solution.Some studies have found that different types of manganese oxidizing bacteria have different optimum pH for growth and activity.Therefore,the production of hydrogen ions of A.sphaeroides has a certain effect on the biological mineralization of manganese oxidizing bacteria.In the process of adsorbing cadmium,biological crust does not only absorb the cadmium through the single biosorption of algae in the crust,but promotes the cadmium through the synergistic action of the whole.The manganese oxidizing bacteria promote the biomineralization of manganese,while the negatively charged manganese ore The capture of cadmium ions produces a stable mineral structure.