Experimental Study On The Efficient Adsorption Of Low Concentration Uranium In Water By Biochar Loaded Polyphosphobacteria

Some microorganisms,like genera Pseudomonas and Bacillus,have been examined for their role immobilization of U(?)via direct precipitation of uranyl phosphate minerals which represents a possible complementary bioremediation technique to bioreduction.In this study,a highly efficient phosphate-accumulating bacterium was isolated and screened from the soil near a certain uranium deposit in Hengyang,and burdened on biochar as a high efficiency bio-adsorbent.The effects of pH value,contact time,adsorbent dosage,temperature and initial U(?)concentration on the removal of U(?)were investigated using the unburdened phosphorus-based biochar as control groups.Scanning electron microscopy(SEM),X-ray energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),and X-ray photoelectron spectroscopy(XPS)were used to analyze the mechanism of U(?)removal by biochar-accumulating phosphate-accumulating bacteria.The main findings are as follows:A high-efficiency dephosphorization bacteria with a phosphorus removal rate of 59% was isolated and screened from the soil near the uranium mine as the target strain of this experiment.Sequencing showed that the 16 S rDNA fragment of this strain was 1394 bp.The obtained sequence was compared with the data in the NCBI database.The sequence of the typical strain with high similarity in the Gen Bank database was searched forDNA sequence alignment in BLAST.The identification results showed that the target bacteria belonged to the genus R.sclerotiorum.The BET test showed that the specific surface areas of biochar,phosphorus-based biochar and biochar-accumulating phosphateaccumulating bacteria were 25.42m2/g,181.55m2/g and 1.44m2/g,respectively,and the total pore volume was 0.1793 cm3/g,0.2142 cm3/g and 0.0076 cm3/g,and the average pore diameters were 28.1972 nm,4.7145 nm,and 2.2463 nm,respectively.Combined with the SEM test,compared with the former two materials,the specific surface area,total pore volume,and average pore size of the phosphorus-accumulating bacteria biochar were reduced correspondingly due to the load of the bacteria.The removal rate of U(?)was 99.86% when the initial pH value was 3.5,the temperature was 30°C,the initial U(?)concentration was 10mg/L and the dosage 1g/L at the reaction time was 3h which is more effective than that of the control group.The adsorption kinetics study shows that the adsorption process conforms to the pseudo-second-order kinetics model,and the Freundlich adsorption isotherm model can better describe the adsorption behavior of the uranium by the adsorbent.FTIR analysis shows that the groups that act on U(?)are mainly hydroxyl,carboxyl,and phosphate groups.XPS analysis shows that the adsorbed uranium precipitate is a mixture of tetravalent uranium and hexavalent uranium,indicating that the removal mechanisms of U(?)by accumulating phosphate-accumulating bacteria biochar under an aerobic environment are more likely adsorbed through reductive tetravalent uranium and directly precipitation.